Lewis Acid Activated Olefin Metathesis Catalysts · Lewis Acid Activated Olefin Metathesis...
Transcript of Lewis Acid Activated Olefin Metathesis Catalysts · Lewis Acid Activated Olefin Metathesis...
Lewis Acid Activated Olefin Metathesis Catalysts
by
Adam Michael McKinty
A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy
Department of Chemistry University of Toronto
© Copyright by Adam Michael McKinty 2014
ii
Lewis Acid Activated Olefin Metathesis Catalysts
Adam Michael McKinty
Doctor of Philosophy
Department of Chemistry
University of Toronto
2014
Abstract
Since its discovery, catalytic olefin metathesis has been used as a powerful tool for the synthesis
of a variety of molecules. Over the last 20 years research in this area has received enormous
attention in the development of new catalysts and applications. The vast majority of the
ruthenium based catalysts developed have been modifications to the Grubbs Catalyst type
architecture. The research presented herein focuses on the development of new olefin metathesis
catalysts bearing tridentate, dianionic ligands and their activation with Lewis acids.
Complexes [(PPh3)2Ru(SCH2CH2)2O] and [(PPh3)2Ru(SC6H4)2O] were synthesized from
(PPh3)3RuCl2 and the corresponding dilithio-dithiolate salt or from (PPh3)4RuH2 and the
corresponding dithiol. These complexes were shown to react with BCl3 forming complexes
[(PPh3)2RuCl(Cl2B(SCH2CH2)2O)] and [(PPh3)2RuCl(Cl2B(SC6H4)2O)].
Complexes of the general structure [LRu(CHPh)(SC6H4)2O] and [LRu(CHPh)(XCH2CH2)2E]
where L = PCy3, SIMes, X = O, S, and E = O, S, PPh were prepared by ligand exchange with
Grubbs I and II. Alternatively, complexes [LRu(CHPh)(SC6H4)2O] and
[LRu(CHPh)(SCH2CH2)2E] where L = PCy3, SIMes and E = O, S were synthesized
independently of Grubbs Catalyst by the reaction of dithioacetals with Ru(0) sources. These
complexes proved to be inactive for catalytic olefin metathesis.
iii
The addition of BCl3 to these complexes resulted in the formation of new 6-coordinate ruthenium
alkylidene complexes of the general formula [LRuCl(CHPh)(Cl2B(SC6H4)2O)] and
[LRuCl(CHPh)(Cl2B(XCH2CH2)2E)] where L = PCy3, SIMes, X = O, S, and E = O, S, PPh.
These complexes also proved to be inactive for olefin metathesis. The addition of a second
equivalent of BCl3 results in the formation of 5-coordinate cationic ruthenium species of the
general formula [LRu(CHPh)(Cl2B(SC6H4)2O)][BCl4] and
[LRu(CHPh)(Cl2B(XCH2CH2)2E)][BCl4] where L = PCy3, SIMes, X = O, S, and E = O, PPh.
These cationic species proved to be active for a variety of olefin metathesis reactions including
ring closing metathesis (RCM), ring opening metathesis polymerization (ROMP) and cross
metathesis (CM).
iv
Acknowledgments
First and foremost I would like to thank Professor Doug Stephan for giving me the opportunity to
complete my degree in his group. His contagious enthusiasm, vast knowledge and continuous
support were invaluable in the completion and success of my degree. My grad school experience
has been nothing but a positive one. I am truly grateful for the experiences and opportunities
Doug gave me and I will always look back on my time in his group as a great chapter in my life.
I would also like to thank the Stephan group members, past and present, for their helpful
discussions, advice and friendship. I learned a lot from each one of them and they made a huge
contribution to my success. Outside of the lab I am thankful I could always count on them to
keep a healthy work-life balance.
I would like to thank my best friend and partner, Sanja for all her support and patience
throughout my degree. Her love and encouragement provided me with the strength and
determination to succeed and I could always count on her to provide support during difficult
times. Thank you so much.
Finally, I would like to thank my family for their unconditional support over the years.
Specifically I would like to thank my parents, Mike and Shirley McKinty. Without their
encouragement, support and love none of this would have been possible. I am extremely grateful
for the opportunities they've given me and the sacrifices they've made to enable me to pursue my
education.
v
Table of Contents
Acknowledgments .......................................................................................................................... iv
Table of Contents ............................................................................................................................ v
List of Tables ................................................................................................................................. ix
List of Schemes .............................................................................................................................. xi
List of Figures .............................................................................................................................. xiv
List of Abbreviations ................................................................................................................. xviii
Chapter 1 Introduction .................................................................................................................... 1
1.1 Catalysis .............................................................................................................................. 1
1.2 Catalytic Olefin Metathesis ................................................................................................. 1
1.2.1 Heterogenous Catalysis ........................................................................................... 1
1.2.2 Well-Defined Homogenous Catalysts ..................................................................... 2
1.2.3 Mechanism of Catalytic Olefin Metathesis ............................................................. 4
1.2.4 Variations of Grubbs Catalyst ................................................................................. 6
1.2.5 Z-selective Olefin Metathesis ................................................................................. 7
1.3 Lewis Acid Activation of Catalysts .................................................................................... 9
1.4 Nitrile Butadiene Rubber .................................................................................................... 9
1.5 Lanxess Project ................................................................................................................. 11
1.6 Scope of this Thesis .......................................................................................................... 11
Chapter 1 References .................................................................................................................... 14
Chapter 2 Coordination Chemistry of Tridentate, Dithiolate Ligands ......................................... 18
2.1 Introduction ....................................................................................................................... 18
2.1.1 Thiolate Ligands in Metal Complexes .................................................................. 18
2.2 Results and Discussion ..................................................................................................... 22
2.2.1 Synthesis of Ru Complexes .................................................................................. 22
vi
2.2.2 Reactivity of Complexes with BCl3 ...................................................................... 25
2.3 Conclusion ........................................................................................................................ 27
2.4 Experimental Section ........................................................................................................ 28
2.4.1 General Considerations ......................................................................................... 28
2.4.2 Synthetic Procedures ............................................................................................. 28
Chapter 2 References .................................................................................................................... 31
Chapter 3 Ruthenium Alkylidene Complexes with Tridentate, Dianionic Ligands ..................... 33
3.1 Introduction ....................................................................................................................... 33
3.1.1 Modifications to Grubbs Catalyst ......................................................................... 33
3.1.2 Halide Variations in Grubbs Catalyst ................................................................... 34
3.1.3 Pseudo-halides as Ligands on Ruthenium Metathesis Catalysts .......................... 35
3.1.4 Bidentate Monoanionic Ligands on Ruthenium Metathesis Catalysts ................. 36
3.1.5 Bidentate Dianionic Ligands on Ruthenium Metathesis Catalysts ....................... 37
3.1.6 Tridentate Ligands on Ruthenium Alkylidene Complexes ................................... 38
3.2 Results and Discussion ..................................................................................................... 38
3.2.1 Synthesis of Ruthenium Alkylidene Complexes .................................................. 38
3.3 Conclusions ....................................................................................................................... 48
3.4 Experimental Section ........................................................................................................ 49
3.4.1 General Considerations ......................................................................................... 49
3.4.2 Synthetic Procedures ............................................................................................. 49
3.4.3 X-ray Crystallography .......................................................................................... 54
Chapter 3 References .................................................................................................................... 57
Chapter 4 Synthesis of Ru Alkylidenes via Dithioacetals ............................................................ 59
4.1 Introduction ....................................................................................................................... 59
4.1.1 First Well Defined Olefin Metathesis Catalyst ..................................................... 59
4.1.2 Synthetic Routes to Ruthenium Alkylidenes ........................................................ 59
vii
4.2 Results and Discussion ..................................................................................................... 62
4.2.1 Attempted Synthesis Using Diazomethanes ......................................................... 62
4.2.2 Attempted Synthesis Using Propargyl Alcohol .................................................... 63
4.2.3 Synthesis of Ru Alkylidenes using Thioacetals .................................................... 63
4.3 Conclusion ........................................................................................................................ 67
4.4 Experimental Section ........................................................................................................ 68
4.4.1 General Considerations ......................................................................................... 68
4.4.2 Synthetic Procedures ............................................................................................. 68
4.4.3 X-ray Crystallography .......................................................................................... 72
Chapter 4 References .................................................................................................................... 75
Chapter 5 Lewis Acid Activation of Ruthenium Alkylidene Complexes ..................................... 77
5.1 Introduction ....................................................................................................................... 77
5.1.1 Lewis Acid Activation in Catalysis ...................................................................... 77
5.1.2 Lewis Acid Assisted Olefin Metathesis ................................................................ 77
5.1.3 Acid Activation of Olefin Metathesis Catalysts ................................................... 78
5.2 Results and Discussion ..................................................................................................... 81
5.2.1 Reactivity with One Equivalent of BCl3 ............................................................... 81
5.2.2 Reactivity with Two Equivalents of BCl3 ............................................................. 91
5.2.3 Reactivity with Bronsted Acid .............................................................................. 94
5.2.4 Reversibility of Lewis Acid Reactivity ................................................................. 96
5.3 Conclusion ........................................................................................................................ 96
5.4 Experimental Section ........................................................................................................ 97
5.4.1 General Considerations ......................................................................................... 97
5.4.2 Synthetic Procedures ............................................................................................. 97
5.4.3 X-ray Crystallography ........................................................................................ 103
Chapter 5 References .................................................................................................................. 107
viii
Chapter 6 Catalytic Olefin Metathesis ........................................................................................ 109
6.1 Introduction ..................................................................................................................... 109
6.1.1 Types of Olefin Metathesis Reactions ................................................................ 109
6.1.2 Catalyst Screening .............................................................................................. 110
6.1.3 Cross Metathesis of NBR and 1-Hexene ............................................................ 112
6.1.4 Hydrogenation of NBR ....................................................................................... 113
6.2 Results and Discussion ................................................................................................... 113
6.2.1 Comparing Catalytic Activity of BCl3 'Activated' and 'Non-Activated' Species 113
6.2.2 Catalytic Olefin Metathesis Activity of Catalyst Derivatives ............................. 117
6.2.3 Comparisons of Active Catalysts ........................................................................ 124
6.2.4 Cross Metathesis of NBR and 1-hexene ............................................................. 129
6.2.5 Hydrogenation of NBR ....................................................................................... 133
6.3 Conclusion ...................................................................................................................... 135
6.4 Experimental Section ...................................................................................................... 136
6.4.1 General Considerations ....................................................................................... 136
6.4.2 Synthetic Procedures ........................................................................................... 137
Chapter 6 References .................................................................................................................. 150
Chapter 7 Summary and Future Work ........................................................................................ 152
7.1 Summary ......................................................................................................................... 152
7.2 Future Work .................................................................................................................... 153
ix
List of Tables
Table 3.4.1. Select Crystallographic Data for 3-1, 3-2 and 3-3 .................................................... 55
Table 3.4.2. Select Crystallographic Data for 3-5, 3-6 and 3-9 .................................................... 56
Table 4.4.1. Select Crystallographic Data for 4-1 ........................................................................ 74
Table 5.4.1. Select Crystallographic Data for 5-2, 5-4 and 5-5 .................................................. 105
Table 5.4.2. Select Crystallographic Data for 5-11 and 5-12 ..................................................... 106
Table 6.1.1. Standard Olefin Metathesis Reactions Using Common Catalysts .......................... 112
Table 6.2.1. Ring Closing Metathesis of Diethyl Diallylmallonate Using 5-17 at a 5 mol%
Catalyst Loading .................................................................................................................... 121
Table 6.2.2. Hydrogenation of NBR with 3-5, 5-5 and 5-12 ...................................................... 134
Table 6.2.3. Hydrogenation of NBR using 3-9, 5-9 and 5-17 .................................................... 134
Table 6.4.1. RCM of Diethyl Diallylmallonate with 3-4, 5-4 and 5-10 ..................................... 138
Table 6.4.2. RCM of Diethyl Diallylmallonate with 3-5, 5-5 and 5-12 ..................................... 138
Table 6.4.3. ROMP of 1,5-cyclooctadiene with 3-5, 5-5 and 5-12 ............................................. 139
Table 6.4.4. CM of 5-hexenyl Acetate and Methyl Acrylate with 3-5, 5-5 and 5-12 ................. 140
Table 6.4.5. RCM of Diethyl Diallylmallonate with 5-14 .......................................................... 140
Table 6.4.6. RCM of Diethyl Diallylmallonate with 5-15 .......................................................... 141
Table 6.4.7. ROMP of 1,5-cyclooctadiene with 5-15 ................................................................. 142
Table 6.4.8. CM of 5-hexenyl Acetate and Methyl Acrylate with 5-15 ..................................... 142
Table 6.4.9. RCM of Diethyl Diallylmallonate with 5-16 .......................................................... 143
Table 6.4.10. RCM of Diethyl Diallylmallonate with 5-17 with 5 mol% Catalyst Loading ...... 144
Table 6.4.11. RCM of Diethyl Diallylmallonate with 5-17 with 1 mol% Catalyst Loading ...... 144
Table 6.4.12. ROMP of 1,5-cyclooctadiene with 5-17 ............................................................... 145
Table 6.4.13. CM of 5-hexenyl Acetate and Methyl Acrylate with 5-17 ................................... 145
Table 6.4.14. GPC Data for the Metathesis of NBR and 1-hexene using 0.007 phr Grubbs 2 .. 146
x
Table 6.4.15. GPC Data for the Metathesis of NBR and 1-hexene using 5-12 .......................... 147
Table 6.4.16. GPC Data for the Metathesis of NBR and 1-hexene using 5-15 .......................... 147
Table 6.4.17. GPC Data for the Metathesis of NBR and 1-hexene using 5-17 .......................... 148
Table 6.4.18. Hydrogenation of NBR using 3-5, 5-5, 5-12 ........................................................ 149
Table 6.4.19. Hydrogenation of NBR using 3-9, 5-9, 5-17 ........................................................ 149
xi
List of Schemes
Scheme 1.2.1. Depiction of Olefin Metathesis ............................................................................... 1
Scheme 1.2.2. Olefin Metathesis with Tebbe's Complex ............................................................... 2
Scheme 1.2.3. Isolation of a Metalocycllobutane with Tebbe's Complex ...................................... 2
Scheme 1.2.4. Synthesis of 1-2 ....................................................................................................... 3
Scheme 1.2.5. Synthesis of the First Well-Defined Ru Olefin Metathesis Catalyst ....................... 4
Scheme 1.2.6. Chauvin Mechanism of Olefin Metathesis .............................................................. 5
Scheme 1.2.7. Olefin Metathesis Mechanism with 1st Gen. Grubbs Catalyst ................................ 6
Scheme 1.2.8. Synthesis of a Ruthenium Phosphonium Alkylidene Complex .............................. 7
Scheme 1.3.1. Activation of an Ethylene Polymerization Catalyst with TMA .............................. 9
Scheme 2.1.1. Synthesis of a Bridged Titanium Thiolate Borane Complex ................................ 19
Scheme 2.1.2. Mechanism of BH3 Addition to a Ruthenium Thiolate Complex ......................... 22
Scheme 2.2.1. Synthesis of 2-1 From Ru(PPh3)3Cl2 ..................................................................... 23
Scheme 2.2.2. Synthesis of 2-1 From Ru(PPh3)4H2 ...................................................................... 23
Scheme 2.2.3. Attempted Synthesis of a Thioether Dithiolate Ru Complex ................................ 23
Scheme 2.2.4. Synthesis of Phosphine Containing Ligand 2-2 .................................................... 24
Scheme 2.2.5. Attempted Synthesis of a Phosphino Dithiolate Ru Complex .............................. 24
Scheme 2.2.6. Synthesis of Dithiol Proligand 2-3 ........................................................................ 25
Scheme 2.2.7. Synthesis of 2-4 ..................................................................................................... 25
Scheme 2.2.8. Synthesis of 2-5 ..................................................................................................... 26
Scheme 2.2.9. Synthesis of 2-6 ..................................................................................................... 27
Scheme 3.2.1. Synthesis of 3-1 and 3-2 ........................................................................................ 39
Scheme 3.2.2. Synthesis of 3-3 ..................................................................................................... 42
Scheme 3.2.3. Synthesis of 3-4 and 3-5 ........................................................................................ 43
Scheme 3.2.4. Synthesis of 3-6 and 3-7 ........................................................................................ 45
xii
Scheme 3.2.5. Synthesis of 3-8 and 3-9 ........................................................................................ 47
Scheme 4.1.1. Synthesis of the First Isolated Transition Metal Alkylidene ................................. 59
Scheme 4.1.2. Synthesis of the First Ruthenium Alkylidene ....................................................... 59
Scheme 4.1.3. Synthesis of Grubbs Catalyst Using Phenyldiazomethane ................................... 60
Scheme 4.1.4. Synthesis of Grubbs Catalyst Using a Sulfur Ylide .............................................. 60
Scheme 4.1.5. Synthesis of a Vinylalkylidene Using Propargyl Chloride ................................... 60
Scheme 4.1.6. Synthesis of Ru Alkylidenes from Phenyl Vinylsulfide ....................................... 61
Scheme 4.1.7. Synthesis of Grubbs Catalyst via Indenylidene Intermediate ............................... 61
Scheme 4.1.8. Synthesis of Grubbs Catalyst from Ru(0) Species ................................................ 62
Scheme 4.2.1. Failed Preparation of Ruthenium Alkylidene From Diazomethanes and 2-1 ....... 62
Scheme 4.2.2. Failed Preparation of Ruthenium Alkylidene From Diazomethanes and 2-3 ....... 63
Scheme 4.2.3. Failed Preparation of Ruthenium Indenylidene From Propargyl Alcohol and
2-3 ............................................................................................................................................ 63
Scheme 4.2.4. Synthesis of 4-1 and 4-2 ........................................................................................ 64
Scheme 4.2.5. Synthesis of 4-3 ..................................................................................................... 65
Scheme 4.2.6. Synthesis of 3-4 From Dithioacetal 4-1 and Ru(cod)(cot) .................................... 65
Scheme 4.2.7. Synthesis of 3-4, 3-1 and 3-6 From Dithioacetals and Ru(PPh3)4(H)2 ................. 66
Scheme 4.2.8. Synthesis of 3-5, 3-2 and 3-7 From Dithioacetals and Ru(PPh3)4(H)2 .................. 66
Scheme 4.2.9. Ruthenium Alkylidene Formation From Dithioacetals ......................................... 67
Scheme 4.2.10. Synthesis of Grubbs II From 3-5 ......................................................................... 67
Scheme 5.1.1. Lewis Acid Catalyst Activation by Electronic Influence ...................................... 79
Scheme 5.1.2. Catalyst Activation by CuCl Ligand Abstraction ................................................. 80
Scheme 5.1.3. Synthesis of a Four-Coordinate Olefin Metathesis Catalyst by Halide
Abstraction ............................................................................................................................... 81
Scheme 5.2.1. Synthesis of 5-1 ..................................................................................................... 82
Scheme 5.2.2. Synthesis 5-2 ......................................................................................................... 83
Scheme 5.2.3. Synthesis of 5-3a and 5-3b .................................................................................... 86
xiii
Scheme 5.2.4. Synthesis of 5-4 and 5-5 ........................................................................................ 88
Scheme 5.2.5. Synthesis of 5-6 and 5-7 ........................................................................................ 90
Scheme 5.2.6. Synthesis of 5-8 and 5-9 ........................................................................................ 90
Scheme 5.2.7. Synthesis of 5-10 - 5-13 ........................................................................................ 92
Scheme 5.2.8. Synthesis of 5-18 ................................................................................................... 95
Scheme 5.2.9. Reversibility of Lewis Acid Reactivity ................................................................. 96
Scheme 6.1.2. Standard Test Reaction for RCM ........................................................................ 111
Scheme 6.1.3. Standard Test Reaction for ROMP ...................................................................... 111
Scheme 6.1.4. Standard Test Reaction for CM ........................................................................... 111
xiv
List of Figures
Figure 1.2.1. Generalized Structure of a Schrock-type Catalyst ..................................................... 3
Figure 1.2.2. 1st and 2
nd Generation Grubbs Catalysts .................................................................... 4
Figure 1.2.3. Hoveyda-Grubbs Catalyst ......................................................................................... 7
Figure 1.2.4. Examples of Schrock Catalyst Based Z-Selective Olefin Metathesis Catalysts ........ 8
Figure 1.2.5. Ru-based Z-Selective Olefin Metathesis Catalyst ..................................................... 8
Figure 1.4.1. Depiction of Functional Groups Found in Nitrile Butadiene Rubber ..................... 10
Figure 1.4.2. Depiction of Hydrogenated Nitrile Butadiene Rubber with Functional Groups
Highlighted ............................................................................................................................... 10
Figure 2.1.1. The Active Sites of Hydrogenase Enzymes Containing Metal Thiolate
Structures.................................................................................................................................. 18
Figure 2.1.2. Titanium Thiolate Complexes ................................................................................. 19
Figure 2.1.3. Multimetallic Titanium Thiolate Complexes .......................................................... 19
Figure 2.1.4. Thiolate Bridged Bimetallic Complexes for Propargylic Alcohol Catalysis .......... 20
Figure 2.1.5. Tethered Ruthenium Thiolate Complex .................................................................. 20
Figure 2.1.6. Thiolate Complexes with Bridging BH2 Fragments ................................................ 21
Figure 2.1.7. Thiolate Bridged Ruthenium BH3 Complex ............................................................ 21
Figure 2.2.1. 31
P{1H} NMR Spectrum (top) and Ligand Backbone Region of
1H NMR
Spectrum (bottom) of 2-5 ......................................................................................................... 26
Figure 3.1.1. Generalized Structure of a Ruthenium Alkylidene Complex used for Catalytic
Olefin Metathesis ..................................................................................................................... 33
Figure 3.1.2. Generalized structures of NHCs Used as Ligands for Ruthenium Olefin
Metathesis Catalysts ................................................................................................................. 34
Figure 3.1.3. Electron Deficient Aryloxides as Ligands on Olefin Metathesis Catalysts ............ 35
Figure 3.1.4. Z-selective Olefin Metathesis Catalyst with a Thiolate Ligand .............................. 35
Figure 3.1.5. Ruthenium Olefin Metathesis Catalysts with Bidentate Monoanionic Ligands ..... 36
Figure 3.1.6. Ruthenium Metathesis Catalysts With Bidentate, Dianionic Ligands .................... 37
xv
Figure 3.1.7. Ruthenium Olefin Metathesis Catalysts with Tridentate, Dianionic Ligands ......... 38
Figure 3.2.1. POV-ray depiction of 3-1; C: black, P: orange, S: yellow, Ru: teal ........................ 40
Figure 3.2.2. POV-ray depiction of 3-2; C: black, N: blue-green, S: yellow, Ru: teal ................. 41
Figure 3.2.3. POV-ray depiction of 3-3; C: black, P: orange, S: yellow, Ru: teal ........................ 42
Figure 3.2.4. POV-ray depiction of 3-5; C: black, N: blue-green, O: red, S: yellow, Ru: teal ..... 44
Figure 3.2.5. POV-ray depiction of 3-6; C: black, O: red, P: orange, S: yellow, Ru: teal ........... 45
Figure 3.2.6. POV-ray depiction of 3-8; C: black, O: red, P: orange, Ru: teal. Insufficient data
for full solution ......................................................................................................................... 46
Figure 3.2.7. POV-ray depiction of 3-9; C: black, O: red, N: blue-green, Ru: teal ...................... 48
Figure 4.2.1. POV-ray depiction of 4-1; C: black, O: red, S: yellow, H: black ............................ 64
Figure 5.1.1. Latent Olefin Metathesis Catalysts which can be Activated by Bronsted or
Lewis Acids .............................................................................................................................. 79
Figure 5.1.2. Highly Active Bimetallic Olefin Metathesis Catalyst ............................................. 80
Figure 5.2.1. POV-ray depiction of 5-2a; B: pink, C: black, N: blue-green, S: yellow, Cl:
green, Ru: teal .......................................................................................................................... 83
Figure 5.2.2. (a) 31
P{1H} NMR spectrum and (b) alkylidene region of
1H NMR spectrum of
5-3 in CD2Cl2 ........................................................................................................................... 85
Figure 5.2.3. (a) 1H NMR Spectrum of 5-4. (b) Expansion of Ligand Backbone Region of
1H
NMR Spectrum of 5-4 .............................................................................................................. 87
Figure 5.2.4. POV-ray depiction of 5-4; B: pink, C: black, O: red, P: orange, S: yellow, Cl:
green, Ru: teal .......................................................................................................................... 88
Figure 5.2.5. POV-ray depiction of 5-5; B: pink, C: black, N: blue-green O: red, S: yellow,
Cl: green, Ru: teal .................................................................................................................... 89
Figure 5.2.6. POV-ray depiction of 5-11; B: pink, C: black, N: blue-green, O: red, P: orange,
S: yellow, Cl: green, Ru: teal ................................................................................................... 92
Figure 5.2.7. POV-ray depiction of 5-13; B: pink, C: black, N: blue-green, O: red, S: yellow,
Cl: green, Ru: teal. Anion omitted for clarity .......................................................................... 93
Figure 5.2.8. Complexes 5-14 - 5-17 ............................................................................................ 94
Figure 5.2.9. 1H NMR spectra of 3-4 (Top) and 5-18 (Bottom) ................................................... 95
Figure 6.1.1. Common Olefin Metathesis Reactions .................................................................. 110
xvi
Figure 6.2.1. Compounds used to Compare BCl3 Activation Effects on Catalysis .................... 113
Figure 6.2.2. Ring Closing Metathesis of Diethyl Diallylmalonate using Complexes 3-4
(Green Triangles), 5-4 (Red Squares), and 5-10 (Blue Diamonds) with 5 mol% Catalyst
Loadings at 25 ºC in CD2Cl2 .................................................................................................. 114
Figure 6.2.3. Ring Closing Metathesis of Diethyl Diallylmalonate With Complexes 3-5
(Green Triangles), 5-5 (Red Squares), and 5-12 (Blue Diamonds) with 5 mol% Catalyst
Loadings at 25 ºC in CD2Cl2 .................................................................................................. 115
Figure 6.2.4. Ring Opening Metathesis Polymerization of 1,5-Cyclooctadiene With
Complexes 3-5 (Green Triangles), 5-5 (Red Squares), and 5-12 (Blue Diamonds) with
0.1 mol% Catalyst Loadings at 25 ºC in CD2Cl2 ................................................................... 116
Figure 6.2.5. Cross Metathesis of 5-Hexenyl Acetate And Methyl Acrylate With Complexes
3-5 (Green Triangles), 5-5 (Red Squares), and 5-12 (Blue Diamonds) with 5 mol%
Catalyst Loadings at 25 ºC in CD2Cl2 .................................................................................... 117
Figure 6.2.6. Compounds 5-14 and 5-15 .................................................................................... 118
Figure 6.2.7. Ring Closing Metathesis of Diethyl Diallylmalonate with 5-14 and 5-15 at a
5 mol% Catalyst Loadings at 25 ºC in CD2Cl2 ...................................................................... 118
Figure 6.2.8. Ring Opening Metathesis Polymerization of 1,5-Cyclooctadiene with 5-15 at a
0.1 mol% Catalyst Loading at 25 ºC in CD2Cl2 ..................................................................... 119
Figure 6.2.9. Cross Metathesis of 5-Hexenyl Acetate and Methyl Acrylate With 5-15 at a
5 mol% Catalyst Loading at 25 ºC in CD2Cl2 ........................................................................ 119
Figure 6.2.10. Complexes 5-16 and 5-17 .................................................................................... 120
Figure 6.2.11. Ring Closing Metathesis of Diethyl Diallylmalonate Using 5-16 at a 5 mol%
Catalyst Loading at 25 ºC in CD2Cl2 ..................................................................................... 121
Figure 6.2.12. Ring Closing Metathesis of Diethyl Diallylmalonate Using 5-17 at a at a
1 mol% Catalyst Loading at 25 ºC in CD2Cl2 ........................................................................ 122
Figure 6.2.13. Ring Opening Metathesis Polymerization of 1,5-Cyclooctadiene with 5-17 at a
5 mol% Catalyst Loading at 25 ºC in CD2Cl2 ........................................................................ 123
Figure 6.2.14. Cross Metathesis of 5-Hexenyl Acetate and Methyl Acrylate With 5-17 at a
5 mol% Catalyst Loading at 25 ºC in CD2Cl2 ........................................................................ 123
Figure 6.2.15. Comparing the Activity of SIMes containing 5-12 and PCy3 Containing 5-10
for RCM of Diethyl Diallylmalonate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2 ....... 124
Figure 6.2.16. Comparing the Activity of SIMes containing 5-15 and PCy3 Containing 5-14
for RCM of Diethyl Diallylmalonate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2 ....... 125
xvii
Figure 6.2.17. Comparing the Activity of PCy3 Containing 5-16 and SIMes Containing 5-17
for RCM of Diethyl Diallylmalonate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2 ....... 126
Figure 6.2.18. Comparing the Activity of 5-10, 5-14 and 5-16 for RCM of Diethyl
Diallylmalonate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2 ........................................ 126
Figure 6.2.19. Comparing the Activity of 5-12, 5-15 and 5-17 for RCM of Diethyl
Diallylmalonate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2 ........................................ 127
Figure 6.2.20. Comparing Activities of 5-12, 5-15 and 5-17 for ROMP of 1,5-Cyclooctadiene
at 0.1 mol% Catalyst Loadings at 25 ºC in CD2Cl2 ............................................................... 128
Figure 6.2.21. Comparing Activities of 5-12, 5-15 and 5-17 for CM of 5-hexenyl Acetate and
Methyl Acrylate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2 ....................................... 129
Figure 6.2.22. Mw (Blue Diamonds) and Mn (Red Squares) Over Time of NBR Cross
Metathesis with 1-hexene Using 2nd
Gen. Grubbs Catalyst at a 0.007 phr Catalyst Loading
at 25 ºC in Chlorobenzene ...................................................................................................... 130
Figure 6.2.23. Mw Over Time of NBR Cross Metathesis With 1-Hexene at Various Catalyst
Loadings of 5-12 at 25 ºC in Chlorobenzene ......................................................................... 131
Figure 6.2.24. Mw Over Time of NBR Cross Metathesis With 1-Hexene at Various Catalyst
Loadings of 5-15 at 25 ºC in Chlorobenzene ......................................................................... 132
Figure 6.2.25. Mw Over Time of NBR Cross Metathesis With 1-Hexene at Various Catalyst
Loadings of 5-17 at 25 ºC in Chlorobenzene ......................................................................... 133
Figure 6.2.26. FTIR Spectrum of NBR (top) and Hydrogenated NBR (bottom) ....................... 135
xviii
List of Abbreviations
°C degrees Celsius
Å angstrom, 10-10
m
abs absorption
Ac Acetate
appt Apparent triplet
atm atmosphere
Ar Aryl
br broad
CD2Cl2 deuterated dichloromethane
calc calculated
cat. catalyst
CCD charge coupled device
CM cross metathesis
cm centimeter
coeff coefficient
Cp cyclopentadienyl
Cp* pentamethylcyclopentadienyl
Cy cyclohexyl
d doublet
dd doublet of doublets
DCM dichloromethane
deg degree
Dipp 2,6-diisopropylphenyl
equiv. equivalent
Et ethyl
Et2O diethyl ether
FTIR Fourier transform infrared
g gram
GOF goodness of fit
h hour
xix
H2 dihydrogen
Hz Hertz
I nuclear spin
Ind indenyl
iPr iso-propyl
m meta
m multiplet
Me methyl
Mes mesityl, 2,4,6-trimethylphenyl
min minute
mL milliliter
mm millimeter
mmol millimole
NHC N-heterocyclic carbene
nJxy n-bond scalar coupling constant between X and Y atoms
NMR nuclear magnetic resonance
o ortho
p para
Ph phenyl
phr parts per hundred
POV-Ray Persistence of Vision Raytracer
ppm parts per million, 10-6
py pyridine
q quartet
RCM ring closing metathesis
ROMP ring opening metathesis polymerization
r.t. room temperature
SIMes 1,3-Bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene
t triplet
tol toluene
thf tetrahydrofuran
TMS trimethylsilyl
1
Chapter 1 Introduction
1.1 Catalysis
A catalyst can be defined as a compound that lowers the activation energy for a given chemical
reaction.1 During the course of the reaction the catalyst is not consumed and therefore is only
required in a small amount. Enzymes are catalysts acting in our bodies everyday performing
tasks which are essential for our survival.2 Catalysis is used ubiquitously throughout industry
from the production of plastics such as polyethylene3-4
, to the synthesis of pharmaceuticals5, and
fine chemicals.6
1.2 Catalytic Olefin Metathesis
In chemistry, metathesis is described as a bimolecular reaction in which the products contain the
same groups as the reactants only redistributed over new bonds.7 This requires the breaking of
two bonds followed by the formation of two new bonds. Therefore, olefin metathesis can be
described as the redistribution of alkene groups by scission, redistribution and bond formation,
over two molecules containing an alkene fragment.8-9
A general scheme for olefin metathesis can
be seen in Scheme 1.2.1.10
Scheme 1.2.1. Depiction of Olefin Metathesis.
1.2.1 Heterogeneous Catalysis
The discovery by Karl Ziegler and Giulio Natta that combinations of Ti and alkylaluminum
species can catalyze the polymerization of olefins revolutionized industrial chemistry and the
way we live today.11
Modern polymerization of ethylene and propylene is done heterogeneously
on a silica support.4 Researchers at Dupont were investigating the polymerization of norbornene
with Ti-based Ziegler-Natta type catalysts. They were expecting the typical Ziegler addition
2
polymer as seen with ethylene and propylene but instead obtained a polymer that was highly
unsaturated.12
Following this discovery, early olefin metathesis catalysts were based on Ziegler-
Natta type systems involving early metal, high oxidation state species.13-14
1.2.2 Well-Defined Homogenous Catalysts
1.2.2.1 Tebbe's Complex
Initial studies of the mechanism of olefin metathesis suggested a pathway involving a metal
alkylidene and a metallocycle.15-17
In order to prove this hypothesis, well-defined species and
intermediates needed to be isolated. Fred Tebbe at DuPont discovered a reaction which
demonstrated the mechanism of olefin metathesis.18-19
Tebbe's Complex, 1-1 was shown to react
in a catalytic fashion with terminal olefins (Scheme 1.2.2).
Scheme 1.2.2. Olefin Metathesis with Tebbe's Complex
Subsequently, Grubbs and coworkers were able to trap a metallocyclobutane from a catalytic
metathesis reaction involving Tebbe's Complex (Scheme 1.2.3).20
The addition of a strong base
such as dimethylaminopyridine (DMAP) to the reaction mixture sequestered the Lewis acidic
allane and drove the equilibrium towards the metallocyclobutane.
Scheme 1.2.3. Isolation of a Metallocyclobutane with Tebbe's Complex
3
1.2.2.2 Schrock's Catalyst
In 1973, Schrock and coworkers were investigating alkyl complexes of tantalum. In an attempt to
synthesize Ta(CH2tBu)5, two equivalents of LiCH2
tBu were added to Ta(CH2
tBu)3Cl2.
21
However, tantalum alkylidene 1-2 was isolated which was formed by -hydrogen elimination
(Scheme 1.2.4).22
They went on to synthesize the first well defined Ta carbene species that was
active for catalytic olefin metathesis.23
Scheme 1.2.4. Synthesis of 1-2
Schrock and others went on to synthesize a number of other early transition metal alkylidene
complexes.24-25
Most notably are the W and Mo imido, alkylidene complexes. The Mo species
being commercially available as "Schrock's Catalyst" (Figure 1.2.1).26
These early metal
alkylidene species are extremely active for olefin metathesis but suffer from being extremely
reactive and functional group intolerant.
Figure 1.2.1. Generalized Structure of a Schrock-type Catalyst
1.2.2.3 Grubbs Catalyst
Due to the lengthy and laborious preparation of Schrock's W and Mo metathesis catalysts along
with their extreme sensitivity and functional group reactivity, new well-defined catalysts with
more tolerant metals were sought out. Based on earlier reports that Ru species could perform ring
opening metathesis polymerization (ROMP), the synthesis of Ru based catalysts was investigated
by the Grubbs group. The first well-defined Ru based catalyst to be isolated was from the ring
opening of a cyclopropene by Ru(PPh3)3Cl2 to give the alkylidene species 1-3 (Scheme 1.2.5).27
4
This complex was found to be active for ROMP and replacement of the PPh3 ligands with PCy3
resulted in a complex that was active for cross metathesis.28
Scheme 1.2.5. Synthesis of the First Well-Defined Ru Olefin Metathesis Catalyst
This opened up a new field of research in catalytic olefin metathesis chemistry. Although these
new Ru based systems were less active for olefin metathesis than the previous Mo and W based
systems, they were stable in the presence of water, acid, and many other functional groups. As
new methods were developed to prepare Ru alkylidenes (discussed in 5.1), a library of Ru based
catalysts began to become available.29
Of major significance to this field was the report of
(PCy3)2Ru(CHPh)Cl2 and (SIMes)(PCy3)Ru(CHPh)Cl2 known as 1st Generation and 2
nd
Generation Grubbs Catalyst respectively (Figure 1.2.2).28, 30
The substitution of a phosphine with
the N-heterocyclic carbene (NHC) in 2nd
Generation Grubbs increased the activity of the catalyst
dramatically. These catalysts are used in a variety of commercial applications.31-32
Figure 1.2.2. 1st and 2
nd Generation Grubbs Catalysts
1.2.3 Mechanism of Catalytic Olefin Metathesis
Initial speculation into the mechanism of olefin metathesis involved a number of hypotheses.9
Calderon proposed the formation of a cyclobutane in the coordination sphere of the metal
centre.33
An alternative mechanism by Grubbs involved a metallocyclopentane intermediate.15
Pettit proposed an intermediate in which four carbon atoms form sigma bonds with the metal
5
centre.34
In 1971, Chauvin proposed a mechanism for catalytic olefin metathesis which involved
a metal alkylidene species undergoing a 2+2 cycloaddition with an olefin to afford a
metallocyclobutane which could undergo constructive or non-constructive olefin and alkylidene
formation (Scheme 1.2.6).35
As the field of olefin metathesis grew, a number of other
mechanisms were proposed. Through labeling experiments and analyzing the distribution of
metathesis products the Chauvin mechanism gained support and is now the accepted mechanism
for olefin metathesis.16-17
Scheme 1.2.6. Chauvin Mechanism of Olefin Metathesis
More specifically, with a Grubbs type catalyst there are additional considerations that play a role
in the catalytic cycle. Based on kinetic data, it was determined that the five-coordinate ruthenium
species must undergo phosphine dissociation to give a four-coordinate active species (Scheme
1.2.7).36-38
This information was used in the rational design of 2nd
Generation Grubbs as well as a
number of other derivatives, some of which are discussed in 1.2.4. This four-coordinate species
could proceed in the mechanism by two different routes. One possibility is the incoming olefin
could coordinate trans to the phosphine. The second possibility is a ligand rearrangement around
the ruthenium centre and coordination cis to the phosphine. This coordination mode would
influence how the metallocyclobutane forms on the metal. In the case of Grubbs Catalyst it has
been determined that coordination trans to the phosphine is the favored pathway.39
An example
of when this distinction becomes important will be discussed in 1.2.5.
6
Scheme 1.2.7. Olefin Metathesis Mechanism with 1st Gen. Grubbs Catalyst
1.2.4 Variations of Grubbs Catalyst
The field of Ru based olefin metathesis catalysts has exploded since the report of Grubbs
catalyst. A number of variations have been made on these systems in an attempt to increase
activity and tailor them for specific applications.8-9, 31
This topic will be discussed in more detail
in 3.1 however, some systems are of significant importance and will be highlighted here. Based
on the accepted mechanism of olefin metathesis by a Grubbs type complex, the Hoveyda group
developed a catalyst which takes advantage of the initiation step and eliminates the phosphine
coordination-dissociation equilibrium that influences the amount of four-coordinate, active
species in the reaction mixture.40-41
The PCy3 present in 2nd
Generation Grubbs Catalyst is
replaced with a chelating ether group bound to the alkylidene fragment (Figure 1.2.3). After one
turn-over of the catalytic cycle, a new four-coordinate alkylidene complex is formed without this
chelate and this active species can enter the catalytic cycle again and an olefin can coordinate
without competitive coordination from a phosphine. Removing this competition creates an
increase in catalytic activity as seen by the ability for this Hoveyda-Grubbs Catalyst to perform
olefin metathesis on tetrasubstituted olefins.
7
Figure 1.2.3. Hoveyda-Grubbs Catalyst
A unique and more recent example of modification to the Grubbs framework came from the
Piers group in 2004.42
They found that protonation of the Ru carbide 1-4 with Jutzi's acid led to
the formation of the phosphonium alkylidene 1-5 (Scheme 1.2.8). These 14e- phosphonium
alkylidene complexes were found to be rapidly initiating olefin metathesis catalysts.43
Scheme 1.2.8. Synthesis of a Ruthenium Phosphonium Alkylidene Complex
1.2.5 Z-selective Olefin Metathesis
The product olefin from catalytic olefin metathesis can have one of two configurations. The E
isomer is the thermodynamically preferred product since the E configuration is more stable than
the Z configuration. A number of natural products and target pharmaceutical compounds contain
Z alkenes and therefore a catalyst that favors this configuration over the E would be desirable.
The use of bulky enantiopure ligands on transition metal catalysts to influence the selectivity of
catalysis has been exploited in a variety of transformations.44
This is the strategy employed by
the collaborative efforts of the Hoveyda and Schrock groups in olefin metathesis. By
incorporating large aryloxy ligands to the Schrock catalyst framework (Figure 1.2.4), they have
been able to produce catalysts with high Z-selectivities with up to 98% of the product being the Z
isomer.45-46
These monoaryloxide-pyrrolide (MAP) catalysts have been used in the total
synthesis of natural products.47
8
Figure 1.2.4. Examples of Schrock Catalyst Based Z-selective Olefin Metathesis Catalysts
Recently, there have also been reports of Z-selective Ru based olefin metathesis catalysts from
the Grubbs group.48-50
Their strategy uses a chelating NHC and a chelating anion. One of the
substituents on the NHC has been C-H activated and the anionic carbon is bound to Ru. The
other anionic ligands used are either a carboxylate or nitrate anion (Fig. 1.2.5). The Z-selectivity
comes from the chelating anion occupying the coordination site trans to the NHC carbon during
the catalytic cycle. This forces the incoming olefin to bind cis to the NHC which is itself also
locked in place by the chelate. The metallocyclobutane intermediate is formed in a side on
fashion which allows the Mes group on the NHC to influence the configuration. The substituents
on the metallocyclobutane are forced to point away from the Mes group and the resulting olefin
that is produced adopts a Z configuration.51
Figure 1.2.5. Ru-based Z-Selective Olefin Metathesis Catalyst
9
1.3 Lewis Acid Activation of Catalysts
The activation of transition metal catalysts with a Lewis acid has been exploited extensively in
the field of olefin polymerization.4 Specifically with metallocene catalysts for ethylene
polymerization, Lewis acids such as trimethylaluminum (TMA) are used to alkylate the complex
and abstract an anionic ligand to open up a coordination site and form a cationic metal complex
with a vacant coordination site where an olefin can bind and insert to start the polymerization
process (Scheme 1.3.1).
Scheme 1.3.1. Activation of an Ethylene Polymerization Catalyst with TMA.
Alternatively the alkylation and activation can be performed in discrete steps. This allows control
over the Lewis acid used for the alkyl-abstraction and therefore control over the resulting anion.
In many cases the Lewis acid used for the activation has a dramatic effect on the catalytic
activity of the system.52-53
1.4 Nitrile Butadiene Rubber
A specific industrial use of catalytic olefin metathesis is for the modification of nitrile butadiene
rubber (NBR). NBR is a co-polymer of butadiene and acrylonitrile. It is polymerized on an
industrial scale by anionic, emulsion polymerization.54
The resulting polymer contains cis- and
trans- alkene functionalities, vinyl groups, and nitrile groups (Figure 1.4.1). It's these nitrile
groups which give NBR many of its useful properties. NBR is stable in oils, fats and fuels, has
low permeability and high temperature resistance.55
It is used in a number of machine parts and
belts, for automotive tubing, and in the soles of running shoes.
10
Figure 1.4.1 Depiction of Functional Groups Found in Nitrile Butadiene Rubber
Modifications to crude NBR can give polymers with properties tailored for specific applications.
Such modifications include performing cross metathesis with 1-hexene and the C=C double
bonds of NBR.56-57
This decreases the molecular weight and narrows the polydispersity.
Following this olefin metathesis step, hydrogenation of the residual double bonds can be carried
out creating HNBR (Figure 1.4.2).55, 58
The resulting polymer is still extremely resistant to oils
and fuels, has better thermal stability than NBR, and is resistant to ozone and oxidative aging.
This high strength polymer has numerous oilfield and automotive applications.
Figure 1.4.1 Depiction of Hydrogenated Nitrile Butadiene Rubber with Functional Groups
Highlighted
11
1.5 Lanxess Project
Lanxess is a multinational specialty chemicals and polymers company. At the date of this thesis,
they are the world's largest manufacturer of NBR and HNBR. To accomplish the modifications
to NBR described in 1.4, 2nd
Generation Grubbs Catalyst is used for cross metathesis and
Wilkinson's Catalyst is used for hydrogenation. Both processes have considerable costs
associated with them. Wilkinson's catalyst is based on the precious metal Rh which is very
expensive. A system using a cheaper technology would be advantageous and economically
beneficial to Lanxess. The use of Grubbs Catalyst requires the licensing of this technology. This
also adds cost to the process. Ideally Lanxess would like their own technology to perform olefin
metathesis of NBR.
The work presented herein was sponsored by Lanxess. The goals of the project are twofold.
1) The development of new hydrogenation catalysts based on less expensive metals that are
effective for the hydrogenation of NBR; and 2) the development of new olefin metathesis
catalysts that are novel from any current patent literature and effective at performing cross
metathesis of 1-hexene and NBR. The majority of this thesis will focus on the development of
novel olefin metathesis catalysts. The current patent literature is extensive and covers a broad
range of catalysts. There is however, a large gap when it comes to complexes with tridentate
ligands.
1.6 Scope of this Thesis
The goal of this thesis was to develop proprietary olefin metathesis catalysts that could affect the
cross metathesis of NBR and 1-hexene. Recognizing the gap in the patent literature covering
tridentate ligands for olefin metathesis catalysts, an effort was made to explore their use for the
development of novel catalysts. In Chapter 2, the coordination chemistry of tridentate dithiolate
ligands on ruthenium is explored. In some cases the coordination chemistry of these types of
ligands proves to be more difficult than originally thought. The reactivity of the successfully
prepared compounds with BCl3 is also explored in an effort to determine if Lewis acid activation
of olefin metathesis catalysts with these ligands is a viable option.
In Chapter 3, the coordination chemistry of tridentate dianionic ligands on ruthenium alkylidene
species is described. The motivation was to easily prepare new ruthenium alkylidene species
12
from Grubbs catalyst as a convenient route to probe the reactivity and catalytic activity of these
species. This proved to be more successful than the coordination chemistry in Chapter 2. A
library of complexes was prepared with tridentate ligand variations to the anionic donors, central
neutral donor and the ligand backbone.
Chapter 4 describes the synthesis of ruthenium alkylidenes from Ru(0) sources and dithioacetals.
This newly developed method provides a synthetic route to some of the complexes described in
Chapter 3, however, this synthetic strategy is independent of any prior patent literature. An
independent route to these species was required in order to patent these new complexes and
provide Lanxess with the freedom to use these catalysts in their industrial processes.
The reactivity and activation of the ruthenium alkylidene species described in Chapters 3 and 4
with the Lewis acid BCl3 is explored in Chapter 5. The addition of one equivalent of BCl3
resulted in a ligand rearrangement and the formation of a 6-coordinate Ru centre. A second
equivalent of BCl3 resulted in the formation of a 5-coordinate, cationic Ru species via halide
abstraction.
Finally, in Chapter 6 the complexes synthesized in the previous chapters were tested for catalytic
olefin metathesis. They were tested for a variety of reactions including ring closing metathesis
(RCM), ring opening metathesis polymerization (ROMP), cross metathesis (CM) and the
metathesis of NBR and 1-hexene which was the ultimate goal of this thesis.
The work described herein was completed solely by the author with the exception of elemental
analysis which was completed in house by departmental staff.
Portions of each chapter that are published at the time of writing:
Chapter 3: McKinty, A. M., Lund, C., Stephan, D. W., "A Tridentate-Dithiolate Ruthenium
Alkylidene Complex: An Olefin Metathesis Catalyst Activated by BCl3" Organometallics, 2013,
32, 4730-4732.
Chapter 4: McKinty, A. M., Stephan, D. W., "A Facile Route to Ru-Alkylidenes" Dalton
Transactions, 2014, 43, 2710-2712.
13
Chapter 5: McKinty, A. M., Lund, C., Stephan, D. W., "A Tridentate-Dithiolate Ruthenium
Alkylidene Complex: An Olefin Metathesis Catalyst Activated by BCl3" Organometallics, 2013,
32, 4730-4732.
Chapter 6: McKinty, A. M., Lund, C., Stephan, D. W., "A Tridentate-Dithiolate Ruthenium
Alkylidene Complex: An Olefin Metathesis Catalyst Activated by BCl3" Organometallics, 2013,
32, 4730-4732.
14
Chapter 1 References
1. Crabtree, R. H., The Organometallic Chemistry of the Transition Metals. Wiley-VCH:
Hoboken, New Jersey, 2009.
2. Cox, D. L. N. a. M. M., Principles of Biochemistry 3rd Ed. Worth Publishing: New York,
2000.
3. Alt, H. G.; Köppl, A., Chemical Reviews 2000, 100 (4), 1205-1222.
4. Malpass, D. B., Introduction to Industrial Polyethylene: Properties, Catalysts, and
Processes. Scrivener Publishing LLC: 2010.
5. Busacca, C. A.; Fandrick, D. R.; Song, J. J.; Senanayake, C. H., Advanced Synthesis &
Catalysis 2011, 353 (11-12), 1825-1864.
6. Stan M Roberts, G. P., Catalysts for Fine Chemical Synthesis, Volume 1: Hydrolysis,
Oxidation and Reduction. John Wiley & Sons: 2002.
7. Wilkinson, C. b. A. D. M. a. A., IUPAC. Compendium of Chemical Terminology, 2nd ed.
(the "Gold Book"). Blackwell Scientific Publications: Oxford, 1997.
8. (Ed.), R. H. G., Handbook of Metathesis. Wiley-VCH: Weinheim, 2003.
9. Astruc, D., New Journal of Chemistry 2005, 29 (1), 42-56.
10. Grubbs, R. H.; Chang, S., Tetrahedron 1998, 54 (18), 4413-4450.
11. Ziegler, K.; Holzkamp, E.; Breil, H.; Martin, H., Angewandte Chemie 1955, 67 (16), 426-
426.
12. Truett, W. L.; Johnson, D. R.; Robinson, I. M.; Montague, B. A., Journal of the American
Chemical Society 1960, 82 (9), 2337-2340.
13. Calderon, N.; Ofstead, E. A.; Ward, J. P.; Judy, W. A.; Scott, K. W., Journal of the
American Chemical Society 1968, 90 (15), 4133-4140.
14. Natta, G.; Dall'Asta, G.; Mazzanti, G., Angewandte Chemie International Edition 1964, 3
(11), 723-729.
15. Grubbs, R. H.; Brunck, T. K., Journal of the American Chemical Society 1972, 94 (7),
2538-2540.
16. Grubbs, R. H.; Burk, P. L.; Carr, D. D., Journal of the American Chemical Society 1975,
97 (11), 3265-3267.
17. Grubbs, R. H.; Carr, D. D.; Hoppin, C.; Burk, P. L., Journal of the American Chemical
Society 1976, 98 (12), 3478-3483.
15
18. Tebbe, F. N.; Parshall, G. W.; Ovenall, D. W., Journal of the American Chemical Society
1979, 101 (17), 5074-5075.
19. Tebbe, F. N.; Parshall, G. W.; Reddy, G. S., Journal of the American Chemical Society
1978, 100 (11), 3611-3613.
20. Howard, T. R.; Lee, J. B.; Grubbs, R. H., Journal of the American Chemical Society
1980, 102 (22), 6876-6878.
21. Schrock, R. R.; Meakin, P., Journal of the American Chemical Society 1974, 96 (16),
5288-5290.
22. Schrock, R. R., Journal of Organometallic Chemistry 1976, 122 (2), 209-225.
23. Rupprecht, G. A.; Messerle, L. W.; Fellmann, J. D.; Schrock, R. R., Journal of the
American Chemical Society 1980, 102 (20), 6236-6244.
24. Oskam, J. H.; Fox, H. H.; Yap, K. B.; McConville, D. H.; O`Dell, R.; Lichtenstein, B. J.;
Schrock, R. R., Journal of Organometallic Chemistry 1993, 459 (1–2), 185-198.
25. Schrock, R. R.; Murdzek, J. S.; Bazan, G. C.; Robbins, J.; DiMare, M.; O'Regan, M.,
Journal of the American Chemical Society 1990, 112 (10), 3875-3886.
26. Schrock, R. R., Accounts of Chemical Research 1986, 19 (11), 342-348.
27. Nguyen, S. T.; Johnson, L. K.; Grubbs, R. H.; Ziller, J. W., Journal of the American
Chemical Society 1992, 114 (10), 3974-3975.
28. Schwab, P.; France, M. B.; Ziller, J. W.; Grubbs, R. H., Angewandte Chemie
International Edition 1995, 34 (18), 2039-2041.
29. Trnka, T. M.; Grubbs, R. H., Accounts of Chemical Research 2000, 34 (1), 18-29.
30. Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H., Organic Letters 1999, 1 (6), 953-956.
31. Vougioukalakis, G. C.; Grubbs, R. H., Chemical Reviews 2009, 110 (3), 1746-1787.
32. Pederson, R. L.; Fellows, I. M.; Ung, T. A.; Ishihara, H.; Hajela, S. P., Advanced
Synthesis & Catalysis 2002, 344 (6-7), 728-735.
33. Calderon, N.; Chen, H. Y.; Scott, K. W., Tetrahedron Letters 1967, 8 (34), 3327-3329.
34. S. Lewandos, G.; Pettit, R., Tetrahedron Letters 1971, 12 (11), 789-793.
35. Jean-Louis Hérisson, P.; Chauvin, Y., Die Makromolekulare Chemie 1971, 141 (1), 161-
176.
36. Hinderling, C.; Adlhart, C.; Chen, P., Angewandte Chemie International Edition 1998, 37
(19), 2685-2689.
16
37. Sanford, M. S.; Love, J. A.; Grubbs, R. H., Journal of the American Chemical Society
2001, 123 (27), 6543-6554.
38. Sanford, M. S.; Ulman, M.; Grubbs, R. H., Journal of the American Chemical Society
2001, 123 (4), 749-750.
39. Tallarico, J. A.; Bonitatebus, P. J.; Snapper, M. L., Journal of the American Chemical
Society 1997, 119 (30), 7157-7158.
40. Garber, S. B.; Kingsbury, J. S.; Gray, B. L.; Hoveyda, A. H., Journal of the American
Chemical Society 2000, 122 (34), 8168-8179.
41. Gessler, S.; Randl, S.; Blechert, S., Tetrahedron Letters 2000, 41 (51), 9973-9976.
42. Romero, P. E.; Piers, W. E.; McDonald, R., Angewandte Chemie International Edition
2004, 43 (45), 6161-6165.
43. Romero, P. E.; Piers, W. E., Journal of the American Chemical Society 2005, 127 (14),
5032-5033.
44. Zhou, Q.-L., Privileged Chiral Ligands and Catalysts. Wiley-VCH: Verlag GmbH & Co.
KGaA, 2011.
45. Flook, M. M.; Jiang, A. J.; Schrock, R. R.; Müller, P.; Hoveyda, A. H., Journal of the
American Chemical Society 2009, 131 (23), 7962-7963.
46. Jiang, A. J.; Zhao, Y.; Schrock, R. R.; Hoveyda, A. H., Journal of the American
Chemical Society 2009, 131 (46), 16630-16631.
47. Meek, S. J.; O'Brien, R. V.; Llaveria, J.; Schrock, R. R.; Hoveyda, A. H., Nature 2011,
471 (7339), 461-6.
48. Endo, K.; Grubbs, R. H., Journal of the American Chemical Society 2011, 133 (22),
8525-8527.
49. Keitz, B. K.; Endo, K.; Herbert, M. B.; Grubbs, R. H., Journal of the American Chemical
Society 2011, 133 (25), 9686-9688.
50. Keitz, B. K.; Endo, K.; Patel, P. R.; Herbert, M. B.; Grubbs, R. H., Journal of the
American Chemical Society 2011, 134 (1), 693-699.
51. Liu, P.; Xu, X.; Dong, X.; Keitz, B. K.; Herbert, M. B.; Grubbs, R. H.; Houk, K. N.,
Journal of the American Chemical Society 2012, 134 (3), 1464-1467.
52. Chen, E. Y.-X.; Marks, T. J., Chemical Reviews 2000, 100 (4), 1391-1434.
53. Li, L.; Metz, M. V.; Li, H.; Chen, M.-C.; Marks, T. J.; Liable-Sands, L.; Rheingold, A.
L., Journal of the American Chemical Society 2002, 124 (43), 12725-12741.
17
54. Kaiser, A.; Brandau, S.; Klimpel, M.; Barner-Kowollik, C., Macromolecular rapid
communications 2010, 31 (18), 1616-21.
55. Schulz, D. N.; Turner, S. R.; Golub, M. A., Rubber Chemistry and Technology 1982, 55
(3), 809-859.
56. Ong, C.; Mueller, J. M. Process for the preparation of low molecular weight
hydrogenated nitrile rubber. WO2011023788A1, 2011.
57. Ong, C.; Mueller, J. M.; Soddemann, M.; Koenig, T. Metathesis of nitrile rubbers in the
presence of transition metal catalysts. WO2011023763A1, 2011.
58. Xie, H.-Q.; Li, X.-D.; Guo, J.-S., Journal of Applied Polymer Science 2003, 90 (4), 1026-
1031.
18
Chapter 2 Coordination Chemistry of Tridentate, Dithiolate Ligands
2.1 Introduction
2.1.1 Thiolate Ligands in Metal Complexes
Sulfur containing compounds are typically thought to be catalyst poisons which inhibit catalysis
and either slow it down or stop it completely.1-5
However, nature utilizes sulfur as a ligand in the
transition metal containing hydrogenase enzymes (Figure 2.1.1).6-9
These enzymes perform the
reversible oxidation of H2 in microorganisms.
Figure 2.1.1. The Active Sites of Hydrogenase Enzymes Containing Metal Thiolate
Structures
Thiolates have been used as ligands on transition metals across the periodic table for making
interesting complexes and to develop catalysts. In the 1990's the Stephan group explored their
chemistry on group 4 metals for the synthesis of piano stool complexes.10-12
They examined
bidentate, tridentate and tetradentate dithiolate ligands and their coordination chemistry around
Ti.13-14
They observed a number of monomeric and dimeric structures (Figure 2.1.2). They also
found that the coordinated thiolates were able to form bridged structures with other transition
metals (Figure 2.1.3). They exploited the bridging capabilities of the thiolate ligands to form
titanium hydride complexes with a B-S-Ti moiety when these complexes were reacted with
NaBH4 (Scheme 2.1.1).15
19
Figure 2.1.2. Titanium Thiolate Complexes
Figure 2.1.3. Multimetallic Titanium Thiolate Complexes
Scheme 2.1.1. Synthesis of a Bridged Titanium Thiolate Borane Complex
The examples of nature's hydrogenase enzymes and the work by Stephan and co-workers
demonstrates that thiolate ligands often form bimetallic species or bridged species with other
Lewis acids. Indeed, this is the case with a variety of examples from the literature. Nishibashi
and co-workers have developed a library of thiolate bridged bimetallic species that are
catalytically active for alkylation16-18
, cycloaddition19
, substitution20-21
and reduction22-23
of
20
propargylic alcohols (Figure 2.1.4). These catalytically active complexes are bimetallic
ruthenium and iron species bridged through two thiolate ligands.
Figure 2.1.4. Thiolate Bridged Bimetallic Complexes for Propargylic Alcohol Catalysis
When monometallic thiolate complexes can be synthesized, the thiolate ligand can act in a
non-innocent fashion where the thiolate functionality participates in bond activation with the
metal centre. Oestreich and co-workers have exploited this capability to catalytically activate C-
F bonds24
, generate borenium species25
, perform dehydrogenative C-H - silane coupling26-27
and
hydrosilyation.28
They used a tethered ruthenium thiolate species developed by Tatsumi and co-
workers who used this complex for dihydrogen activation (Figure 2.1.5).29
The activation of the
substrate occurs between the metal centre and the coordinated thiolate. The XH bond is cleaved
as H binds to the metal centre and X binds to the thiolate.
Figure 2.1.5. Tethered Ruthenium Thiolate Complex
Complexes of the first row transition metals with thiolate ligands bridging the metal centre and a
BH2 fragment were prepared in 1990.30
The proposed structures for Fe(III) and Cr(III) have three
21
bidentate borate ligands in the coordination sphere (Figure 2.1.6). Each ligand has two sulfur
donors bridged between a BH2 fragment. The Cu(II) complex is square planer with two bidentate
ligands coordinated. In these examples the bidentate borate ligands were prepared prior to
coordination to the metal centre.
Figure 2.1.6. Thiolate Complexes with Bridging BH2 Fragments
In 2004 Hille and co-workers reported two ruthenium complexes bearing tetradentate dithiolate
ligands.31
These complexes were shown to bind N2, H2 and BH3. Binding of N2 and H2 occur
exclusively at the metal centre. However, when BH3 was added to the complex the thiolate
ligand behaved non-innocently (Figure 2.1.7). The thiolate coordinated to boron and a hydride on
BH3 coordinated the ruthenium. They propose the coordination of the hydride to ruthenium
occurs first followed by the thiolate coordinating to boron to create the bridged species
(Scheme 2.1.2).
Figure 2.1.7. Thiolate Bridged Ruthenium BH3 Complex
22
Scheme 2.1.2. Mechanism of BH3 Addition to a Ruthenium Thiolate Complex
2.2 Results and Discussion
2.2.1 Synthesis of Ru Complexes
The deprotonation of the commercially available dithiols (HSCH2CH2)2O and (HSCH2CH2)2S
with two equivalents of n-BuLi provided the corresponding dilithiated dithiolate salts. These
salts were used to accomplish salt metathesis reactions with transition metals to provide a
convenient, straight forward method for the synthesis of new complexes bearing tridentate,
dithiolate ligands.
Mixing (LiSCH2CH2)2O with Ru(PPh3)3Cl2 in THF overnight at room temperature resulted in a
brown solution. After removing the solvent, the brown residue was dissolved in toluene and
filtered to remove the LiCl. Washing the isolated brown product with hexanes to remove PPh3
led to the isolation of 2-1 as a brown solid (Scheme 2.2.1). The 31
P{1H} NMR spectrum displays
a new chemical shift at 71.9 ppm. The 1H NMR spectrum has two triplets at 3.61 and 2.07 ppm
(3JHH = 5.54 Hz) suggesting symmetry of the ligand backbone. The only other signals in the
1H NMR spectrum are from the PPh3 protons which have a relative integration of 30:4:4 to the
ligand signals. Based on this and the one signal in the 31
P{1H} NMR there must be two
equivalent PPh3. Alternatively, mixing the dithiol (HSCH2CH2)2O with Ru(PPh3)4H2 in benzene
resulted in the formation of bubbles and a red-brown precipitate (Scheme 2.2.2). The spectral
parameters of this product match those of 2-1 demonstrating an alternative less laborious route to
these types of compounds.
23
Scheme 2.2.1. Synthesis of 2-1 From Ru(PPh3)3Cl2
Scheme 2.2.2. Synthesis of 2-1 From Ru(PPh3)4H2
Following similar procedures to the synthesis of 2-1, mixing the dithiol (HSCH2CH2)2S with
Ru(PPh3)4H2 resulted in H2 bubbling out of solution as a brown precipitate formed. A brown
solid was also collected from the reaction of (LiSCH2CH2)2S with Ru(PPh3)3Cl2 however in both
cases the collected solid was an intractable mixture of products which could not be identified by
NMR studies (Scheme 2.2.3).
Scheme 2.2.3. Attempted Synthesis of a Thioether Dithiolate Ru Complex
The influence of the central donor was further investigated by synthesizing a dithiolate ligand
with a central phosphine donor. The synthesis of (LiSCH2CH2)PPh was accomplished following
24
the procedure described by Escriche and co-workers.32
The nucleophilic ring opening of ethylene
sulfide by lithiated H2PPh provided half the ligand framework as LiSCH2CH2PHPh. Subsequent
lithiation followed by ring opening of a second equivalent of ethylene sulfide gave the dithiolate
ligand as a white solid (Scheme 2.2.4).
Scheme 2.2.4. Synthesis of Phosphine Containing Ligand 2-2
In an analogous fashion to the preparation of 2-1 the dithiolate ligand 2-3 was reacted with
Ru(PPh3)3Cl2 in THF overnight. Similar to the reaction with (LiSCH2CH2)2S the reaction of 2-2
with Ru(PPh3)3Cl2 results in the formation of an intractable mixture of unidentifiable products
(Scheme 2.2.5).
Scheme 2.2.5. Attempted Synthesis of a Phosphino Dithiolate Ru Complex
To investigate the influence of a more rigid and electron withdrawing ligand backbone, the aryl
analogue of diethylene glycol dithiol was prepared. (HSC6H4)2O (2-5) was prepared following
literature procedures (Scheme 2.2.5).33
Starting from diphenylether, dilithiation was
accomplished with n-BuLi in the presence of TMEDA. Elemental sulfur was added to the
dilithiated salt followed by the addition of LiAlH4 and refluxed. An acidic work up with HCl
resulted in formation of the dithiol as a pale yellow oil.
25
Scheme 2.2.6. Synthesis of Dithiol Proligand 2-3
Following an analogous procedure used to prepare 2-1, from Ru(PPh3)4H2 in benzene, when 2-3
was mixed with Ru(PPh3)4H2 bubbles evolved as 2-4 was formed. The 31
P{1H} NMR spectrum
displays a single shift at 72.1 ppm suggesting molecular symmetry and the 1H and
13C{
1H} NMR
spectra support the formulation of 2-4 as Ru(PPh3)2[(SC6H4)2O] (Scheme 2.2.6).
Scheme 2.2.7. Synthesis of 2-4
2.2.2 Reactivity of Complexes with BCl3
Interestingly, when 1 equivalent of BCl3 was added to a CH2Cl2 solution of 2-1, a color change
from brown to dark green was observed as 2-5 was formed (Scheme 2.2.8). The 31
P{1H} NMR
spectrum of the crude reaction mixture showed complete conversion to a single product with 2
unique phosphorus environments displaying doublets at 47.8 and 31.1 ppm (Figure 2.2.1). The
pair of doublets have a coupling constant of 37.3 Hz indicative of a cis phosphine geometry. The
11B NMR spectrum displays a sharp singlet at 12.0 ppm which suggests the presence of a
4-coordinate boron centre. The ligand backbone protons in the 1H NMR spectrum appear as 8
multiplets suggesting the loss of symmetry (Figure 2.2.1). The remaining signals in the aromatic
region are attributed to the phenyl rings of the two PPh3 ligands. These data support the
formulation of 2-5 as (PPh3)2RuCl[O(CH2CH2S)2BCl2] where a chloride has been transferred
from boron to ruthenium and the remaining BCl2 fragment is bridging the thiolate ligands. It is
26
this bridging of the thiolates and the 6-coordinate ruthenium centre which forces the PPh3 to
adopt a cis geometry. Similar reactivity with related compounds and structural evidence is
discussed in Section 5.2.1.
Scheme 2.2.8. Synthesis of 2-5
Figure 2.2.1. 31
P{1H} NMR Spectrum (top) and Ligand Backbone Region of
1H NMR
Spectrum (bottom) of 2-5
27
In an analogous fashion, when BCl3 was added to a solution of 2-4 the CH2Cl2 mixture
instantaneously changed from brown to dark green as 2-6 was formed (Scheme 2.2.9). The
31P{
1H} NMR spectrum is similar to that of 2-5 displaying two doublets. Compared to 2-5 the
peaks in the 31
P{1H} NMR spectrum are shifted slightly downfield and resonate at 52.5 and
33.2 ppm with a coupling constant of 36.1 Hz indicative of cis phosphines. The 11
B NMR
spectrum displays a sharp singlet at 12.9 ppm suggesting a four-coordinate boron centre. The 1H
NMR spectrum displays multiplets in the aromatic region assigned to the ligand backbone
protons and the PPh3 ligands. This data supports the formulation of 2-6 as
(PPh3)2RuCl[O(C6H4S)2BCl2] which is analogous to 2-5.
Scheme 2.2.9. Synthesis of 2-6
2.3 Conclusion
Two ruthenium complexes bearing tridentate dithiolate-ether ligands were prepared by two
different methods. Attempts to synthesize the analogous thioether and phosphino complexes
were unsuccessful. Based on NMR spectroscopy, the successfully prepared complexes contained
equivalent phosphines and a plane of symmetry. Upon the addition of BCl3 to these complexes
the thiolate ligands became bridged between the ruthenium centre and boron. A chloride was
transferred from the BCl3 to ruthenium and the BCl2 fragment bridged the two thiolates. The
NMR data of these 6-coordinate species suggests a loss in symmetry with two inequivalent
cis-phosphines and inequivalent ligand backbone protons. This reactivity with boranes and the
complexes obtained are similar to the examples presented in the introduction.
28
2.4 Experimental Section
2.4.1 General Considerations
All manipulations were carried out under an atmosphere of dry, O2-free N2 employing a Vac
Atmospheres glove box and a Schlenk vacuum-line. Solvents were purified with a Grubbs-type
column system manufactured by Innovative Technology and dispensed into thick-walled Schlenk
glass flasks equipped with Teflon-valve stopcocks. All solvents were thoroughly degassed after
purification (repeated freeze-pump-thaw cycles). CD2Cl2 was dried over CaH2 and vacuum
transferred into a Schlenk flask equipped with a Teflon-valve stopcock. 1H,
13C, and
31P NMR
spectra were recorded at 25 °C on Varian 300 and 400 MHz and Bruker 400 MHz spectrometers.
Chemical shifts are given relative to SiMe4 and referenced to the residual solvent signal (1H,
13C)
or relative to an external standard (31
P: 85% H3PO4). Chemical shifts are reported in ppm and
coupling constants as scalar values in Hz. Combustion analyses were performed in house
employing a Perkin-Elmer CHN Analyzer. All chemicals were obtained from Aldrich and used
as received unless stated. Pro-ligands were synthesized by the addition of two equivalents of
n-BuLi or KOtBu to the corresponding dithiol. (LiSCH2CH2)2PPh and (HSC6H4)O were prepared
according to literature procedures.32-33
2.4.2 Synthetic Procedures
Synthesis of 2-1: Ru(PPh3)3Cl2 (0.200 g, 0.209 mmol) was dissolved in 5 mL of THF. To this, a
THF solution (10 mL) of (LiSCH2CH2)O (37.6 mg, 0.250 mmol) was added. The solution was
stirred at room temperature overnight. The solvent was removed in vacuo and the resulting
brown solid was dissolved in CH2Cl2 (5 mL) and quickly filtered through celite. Pentane (15 mL)
was added to the solution to precipitate the brown product which was isolated by vacuum
filtration and washed with pentane (2 x 5 mL). 2-1 was isolated in 89% yield (0.142 g,
0.186 mmol).
Alternative synthesis of 2-1: Ru(PPh3)4H2 (0.200 g, 0.225 mmol) was dissolved in 10 mL of
benzene. (HSCH2CH2)2O (31 µL, 0.247 mmol) was added dropwise as bubbles of H2 evolved.
After the full addition of the dithiol, the reaction was stirred for 30 min. Pentane (10 mL) was
added to the mixture to fully precipitate the product which was collected by vacuum filtration
and washed with pentane (2 x 5 mL). The product was isolated as a brown solid in 93% yield
29
(0.159 g, 0.209 mmol). 1H NMR (CD2Cl2): 7.22 (br, 12H, PPh), 7.16 (t, 6H, PPh), 7.01 (t, 12H,
PPh), 3.61 (t, 4H, CH2), 2.08 (t, 4H, CH2). 13
C{1H} NMR (CD2Cl2): 134.2 (t, PPh), 133.6 (d,
PPh), 128.9 (s, PPh), 128.7 (s, PPh), 128.4 (d, PPh), 128.3 (s, PPh), 127.0 (t, PPh), 81.3 (s, CH2),
31.6 (s, CH2). 31
P{1H} NMR (CD2Cl2): 71.9. Analysis calculated for C40H38OP2RuS2: C, 63.06;
H, 5.03. Found: C, 62.63; H, 4.88.
Synthesis of 2-4: Ru(PPh3)4H2 (0.200 g, 0.225 mmol) was dissolved in 10 mL of benzene. 2-3
(58 mg, 0.247 mmol) was added dropwise as bubbles of H2 evolved. After the full addition of the
dithiol, the reaction was stirred for 30 min. Pentane (10 mL) was added to the mixture to fully
precipitate the product which was collected by vacuum filtration and washed with pentane (2 x 5
mL). The product was isolated as a light green solid in 88% yield (170 g, 0.198 mmol). 1H NMR
(CD2Cl2): 7.68, (m, 1H, (-SC6H4)2O), 7.59, (m, 1H, (
-SC6H4)2O), 7.51 (m, 1H, (
-SC6H4)2O), 7.37
(br, 6H, PPh), 7.25 (t, 12H, PPh), 7.10 (br, 12H, PPh), 6.87 (m, 1H, (-SC6H4)2O), 6.83 (m, 1H,
(-SC6H4)2O), 6.77 (m, 1H, (
-SC6H4)2O), 6.68 (m, 1H, (
-SC6H4)2O), 5.57 (m, 1H, (
-SC6H4)2O).
13C{
1H} NMR (CD2Cl2): 154.9 (Ph), 152.1 (Ph), 149.3 (Ph), 141.2 (Ph), 134.1 (PPh3), 133.7
(PPh3), 131.9 (PPh3), 131.8 (PPh3), 130.2 (PPh3), 129.4 (PPh3), 128.5 (PPh3), 127.5 (PPh3),
127.4 (PPh3), 126.6 (PPh3), 124.4 (PPh3), 124.2 (Ph), 123.5 (Ph), 123.1 (Ph), 120.6 (Ph), 119.2
(Ph), 118.5 (Ph), 118.4 (Ph), 115.2 (Ph). 31
P{1H} NMR (CD2Cl2): 72.1. Analysis calculated for
C40H38BCl3OP2RuS2: C, 54.65; H, 4.36. Found: C, 54.16; H, 3.98.
Synthesis of 2-5: To a CH2Cl2 solution of 2-1 (50 mg, 0.066 mmol) was added a hexanes
solution of BCl3 (1M, 66 µL, 0.066 mmol). The reaction mixture immediately turned from
brown to dark green. The solvent was removed in vacuo and the resulting green solid was
washed with 5 mL of hexanes and dried in vacuo to give 2-5 as a dark green solid in 94% yield
(54 mg, 0.061 mmol). 1H NMR (CD2Cl2): 7.59 (m, 6H, PPh), 7.45 (m, 7H, PPh), 7.34 (m, 4H,
PPh), 7.26 (m, 3H, PPh), 7.19 (m, 5H, PPh), 7.12 (m, 5H, PPh), 5.26 (m, 1H, CH2), 3.51 (m, 1H,
CH2), 3.27 (m, 1H, CH2), 2.94 (m, 1H, CH2), 2.61 (m, 1H, CH2), 2.57 (m, 1H, CH2), 2.26 (m,
1H, CH2). 13
C{1H} NMR (CD2Cl2): 136.8 (d,
1JPC = 48.1 Hz, PPh3), 135.3 (d,
1JPC = 38.5 Hz,
PPh3), 135.0 (d, 3JPC = 9.5 Hz, PPh3), 134.6 (d,
3JPC = 9.0 Hz, PPh3), 129.3 (d,
4JPC = 2.2 Hz,
PPh3), 128.8 (d, 4JPC = 1.9 Hz, PPh3), 127.4 (d,
2JPC = 9.1 Hz, PPh3), 126.8 (d,
2JPC = 10.1 Hz,
PPh3), 71.6 (CH2), 69.3 (CH2), 34.5 (CH2), 28.2 (CH2). 31
P{1H} NMR (CD2Cl2): 47.8 (d,
2JPP =
30
37.3 Hz, PPh3) 31.1 (d, 2JPP = 37.3 Hz, PPh3).
11B NMR (CD2Cl2): 12.0. Analysis calculated for
C48H38OP2RuS2: C, 67.20; H, 4.46. Found: C, 66.77; H, 4.31.
Synthesis of 2-6: To a CH2Cl2 solution of 2-4 (50 mg, 0.058 mmol) was added a hexanes
solution of BCl3 (1M, 58 µL, 0.058 mmol). The reaction mixture immediately turned from
brown to dark green. The solvent was removed in vacuo and the resulting green solid was
washed with 5 mL of hexanes and dried in vacuo to give 2-6 as a dark green solid in 90% yield
(51 mg, 0.052 mmol). 1H NMR (CD2Cl2): 7.84 (m, 1H, Ph), 7.60 (m, 6H, PPh3), 7.53 (m, 2H,
Ph), 7.41 (m, 2H, Ph), 7.24 (m, 12H, PPh3), 7.15 (m, 6H, PPh3), 7.06 (m, 6H, PPh3), 6.84 (m,
2H, Ph), 6.63 (m, 1H, Ph). 13
C{1H} NMR (CD2Cl2): 162.8 (Ph), 162.6 (Ph), 135.8 (d,
1JPC = 48.9
Hz, PPh3), 135.0 (d, 3JPC = 9.3 Hz, PPh3), 134.5 (Ph), 134.2 (d,
3JPC = 9.2 Hz, PPh3), 134.1 (Ph),
133.6 (Ph), 133.5 (Ph), 132.8 (Ph), 129.8 (Ph), 128.7 (Ph), 129.3 (Ph), 129.2 (d, 4JPC = 2.3 Hz,
PPh3), 129.0 (d, 4JPC = 2.3 Hz, PPh3), 127.3 (d,
2JPC = 9.2 Hz, PPh3), 127.0 (d,
2JPC = 9.9 Hz,
PPh3), 126.6 (Ph), 125.9 (Ph). 31
P{1H} NMR (CD2Cl2): 52.5 (d,
2JPP = 36.2 Hz, PPh3) 33.2 (d,
2JPP = 36.1 Hz, PPh3).
11B NMR (CD2Cl2): 12.9. Analysis calculated for C48H38BCl3OP2RuS2: C,
59.12; H, 3.93. Found: C, 58.43; H, 3.76.
31
Chapter 2 References
1. Oudar, J., Catalysis Reviews 1980, 22 (2), 171-195.
2. Yu, T.-C.; Shaw, H., Applied Catalysis B: Environmental 1998, 18 (1–2), 105-114.
3. Maurel, R.; Leclercq, G.; Barbier, J., Journal of Catalysis 1975, 37 (2), 324-331.
4. Bartholomew, C.; Agrawal, P.; Katzer, J., Advances in Catalysis 1982, 31, 135-242.
5. Chang, J. R.; Chang, S. L.; Lin, T. B., Journal of Catalysis 1997, 169 (1), 338-346.
6. Volbeda, A.; Garcin, E.; Piras, C.; de Lacey, A. L.; Fernandez, V. M.; Hatchikian, E. C.;
Frey, M.; Fontecilla-Camps, J. C., Journal of the American Chemical Society 1996, 118 (51),
12989-12996.
7. Peters, J. W.; Lanzilotta, W. N.; Lemon, B. J.; Seefeldt, L. C., Science 1998, 282 (5395),
1853-1858.
8. Volbeda, A.; Charon, M. H.; Piras, C.; Hatchikian, E. C.; Frey, M.; Fontecilla-Camps, J.
C., Nature 1995, 373 (6515), 580-7.
9. Cammack, R., Nature 1999, 397 (6716), 214-5.
10. Stephan, D. W.; Timothy Nadasdi, T., Coordination Chemistry Reviews 1996, 147 (0),
147-208.
11. White, G. S.; Stephan, D. W., Inorganic Chemistry 1985, 24 (10), 1499-1503.
12. Wark, T. A.; Stephan, D. W., Inorganic Chemistry 1990, 29 (9), 1731-1736.
13. Huang, Y.; Drake, R. J.; Stephan, D. W., Inorganic Chemistry 1993, 32 (14), 3022-3028.
14. Nadasdi, T. T.; Stephan, D. W., Inorganic Chemistry 1993, 32 (26), 5933-5938.
15. Huang, Y.; Stephan, D. W., Organometallics 1995, 14 (6), 2835-2842.
16. Nishibayashi, Y.; Onodera, G.; Inada, Y.; Hidai, M.; Uemura, S., Organometallics 2003,
22 (4), 873-876.
17. Nishibayashi, Y.; Wakiji, I.; Ishii, Y.; Uemura, S.; Hidai, M., Journal of the American
Chemical Society 2001, 123 (14), 3393-3394.
18. Nishibayashi, Y.; Imajima, H.; Onodera, G.; Inada, Y.; Hidai, M.; Uemura, S.,
Organometallics 2004, 23 (21), 5100-5103.
19. Nishibayashi, Y.; Yoshikawa, M.; Inada, Y.; Hidai, M.; Uemura, S., The Journal of
Organic Chemistry 2004, 69 (10), 3408-3412.
32
20. Inada, Y.; Nishibayashi, Y.; Hidai, M.; Uemura, S., Journal of the American Chemical
Society 2002, 124 (51), 15172-15173.
21. Nishibayashi, Y.; Wakiji, I.; Hidai, M., Journal of the American Chemical Society 2000,
122 (44), 11019-11020.
22. Nishibayashi, Y.; Shinoda, A.; Miyake, Y.; Matsuzawa, H.; Sato, M., Angewandte
Chemie International Edition 2006, 45 (29), 4835-4839.
23. Yuki, M.; Miyake, Y.; Nishibayashi, Y., Organometallics 2010, 29 (22), 5994-6001.
24. Stahl, T.; Klare, H. F. T.; Oestreich, M., Journal of the American Chemical Society 2013,
135 (4), 1248-1251.
25. Stahl, T.; Müther, K.; Ohki, Y.; Tatsumi, K.; Oestreich, M., Journal of the American
Chemical Society 2013, 135 (30), 10978-10981.
26. Königs, C. D. F.; Klare, H. F. T.; Ohki, Y.; Tatsumi, K.; Oestreich, M., Organic Letters
2012, 14 (11), 2842-2845.
27. Klare, H. F. T.; Oestreich, M.; Ito, J.-i.; Nishiyama, H.; Ohki, Y.; Tatsumi, K., Journal of
the American Chemical Society 2011, 133 (10), 3312-3315.
28. Königs, C. D. F.; Klare, H. F. T.; Oestreich, M., Angewandte Chemie International
Edition 2013, 52 (38), 10076-10079.
29. Ohki, Y.; Takikawa, Y.; Sadohara, H.; Kesenheimer, C.; Engendahl, B.; Kapatina, E.;
Tatsumi, K., Chemistry – An Asian Journal 2008, 3 (8-9), 1625-1635.
30. Zaidi, S. A. A.; Zahoor, M. A.; Siddiqi, K. S., Transition Met Chem 1990, 15 (3), 231-
235.
31. Sellmann, D.; Hille, A.; Heinemann, F. W.; Moll, M.; Reiher, M.; Hess, B. A.; Bauer,
W., Chemistry – A European Journal 2004, 10 (17), 4214-4224.
32. Antonio Muñoz, J.; Escriche, L.; Casabó, J.; Pérez-Jiménez, C.; Kivekäs, R.; Sillanpää,
R., Inorganica Chimica Acta 1997, 257 (1), 99-104.
33. Alvarado-Rodríguez, José G.; Andrade-López, N.; González-Montiel, S.; Merino, G.;
Vela, A., European Journal of Inorganic Chemistry 2003, 2003 (19), 3554-3562.
33
Chapter 3 Ruthenium Alkylidene Complexes with Tridentate, Dianionic
Ligands
3.1 Introduction
3.1.1 Modifications to Grubbs Catalyst
The discovery of well-defined ruthenium alkylidene complexes, specifically Grubbs catalyst, and
their ability to catalyze olefin metathesis has led to the development of a number of variations to
the Grubbs architecture being investigated.1 Based on the accepted mechanism of ruthenium
catalyzed olefin metathesis, the only essential ligand on the metal center is the alkylidene.2-4
This
leaves all other ligands including the anionic ligands (X), both neutral ligands (L) and even the
substituents on the alkylidene open for modification to adjust steric and electronic properties in
an attempt to increase catalyst activity, lifetime, stability and selectivity (Figure. 3.1.1). There's
also the possibility of introducing a sixth ligand to the coordination sphere and/or using chelating
ligands. A small sample of modified catalysts was discussed in 1.2.4. The replacement of PCy3
in 1st Generation Grubbs catalyst with SIMes in 2
nd Generation Grubbs catalyst led to increased
activity and stability.5 In an attempt to further increase these features, over 400 complexes
containing different NHC ligands have been prepared.6 A summary of generalized structures is
depicted in Figure 3.1.2.
Figure 3.1.1. Generalized Structure of a Ruthenium Alkylidene Complex used for Catalytic
Olefin Metathesis
34
Figure 3.1.2. Generalized structures of NHCs Used as Ligands for Ruthenium Olefin
Metathesis Catalysts
The modifications to the NHC have led to the synthesis of catalysts with increased activity for
specific applications and specific catalyst properties such as aqueous7-8
and asymmetric9-11
catalysis. However, the 2nd
Generation Grubbs Catalyst or Hoveyda-Grubbs Catalyst provide
reasonable activity and stability for most olefin metathesis applications and thus remain the most
popular catalysts in the ruthenium based family.5-6, 12
Modifications to the NHC in Grubbs
Catalyst has received an enormous amount of attention and by comparison the modification to
the anions of the complex has received very little.
3.1.2 Halide Variations in Grubbs Catalyst
To investigate the effect of exchanging the chloride ligands in Grubbs Catalysts for other halides
on catalytic activity, Grubbs and coworkers prepared [(PCy3)2RuX2(CHPh)] and
[SIMes(PCy3)RuX2(CHPh)] where X=Cl, Br, I.2 When X=I, initiation of catalysis occurs much
faster followed by X=Br and X=Cl. This is due to steric effects with the size of the halide
influencing the dissociation of the phosphine ligand. However, the activity of the catalysts
decreases in the order Cl>Br>I. This is due again to the size of the halide preventing the
coordination of the incoming olefin.
35
3.1.3 Pseudo-halides as Ligands on Ruthenium Metathesis Catalysts
Halides are not the only anionic ligands which have been used on ruthenium-based olefin
metathesis catalysts. A number of other X-type ligands have been investigated such as
alkoxides,13
aryloxides,14-18
carboxylates,19-21
and more recently, thiolates22-23
and nitrates.24
Grubbs and coworkers have prepared [(PCy3)Ru(OtBu)2(CHPh)] by simple salt metathesis with
KOtBu and [(PCy3)2RuCl2(CHPh)].
13 This compound is four-coordinate due to the ability of the
alkoxides to act as XL-type ligands and donate three electrons to the ruthenium centre. Even
though these complexes are 4-coordinate, they display low activity for olefin metathesis even at
elevated temperatures. Fogg and coworkers have successfully overcome this deleterious effect
using electron deficient, perfluorinated aryloxides as ligands (Figure 3.1.3).14-15
These catalysts
were showed to be active for ring closing metathesis.
Figure 3.1.3. Electron Deficient Aryloxides as Ligands on Olefin Metathesis Catalysts
More recently, Jensen and coworkers have prepared an olefin metathesis catalyst with a bulky
arylthiolate ligand (Figure 3.1.4).23
The large aryl group on the thiolate induces Z-selectivity on
the product olefin with up to 96% selectivity.
Figure 3.1.4. Z-selective Olefin Metathesis Catalyst with a Thiolate Ligand
36
3.1.4 Bidentate Monoanionic Ligands on Ruthenium Metathesis Catalysts
In the current literature there are a number of examples of bidentate, monoanionic ligands on
ruthenium alkylidene complexes. Grubbs et al. have reported a class of these compounds with
ligands containing a carboxylate donor and a neutral phosphine, ether or amine donor
(Figure 3.1.5).20
These catalysts proved to be active for ring closing metathesis of diethyl
diallymalonate at elevated temperatures. Interestingly, the activity of the catalysts was improved
with the addition of CuCl.
A related ruthenium alkylidene species with a phosphino-carboxylate ligand was reported by He
et al.19
This complex was active for olefin metathesis but again, elevated temperatures were
required. Verpoort has reported the use of an imino-aryloxide ligand on a ruthenium olefin
metathesis catalyst.25
This catalyst displayed high activity for ring opening metathesis
polymerization at 70 ºC. Herrmann et al. have reported a related pyridino-alkoxide ligand on a
ruthenium alkylidene complex.26
This catalyst displays low activity at room temperature but at
elevated temperatures it becomes a moderately active catalyst for ring opening metathesis
polymerization.
Figure 3.1.5. Ruthenium Olefin Metathesis Catalysts with Bidentate Monoanionic Ligands
37
3.1.5 Bidentate Dianionic Ligands on Ruthenium Metathesis Catalysts
Fogg and coworkers have also developed metathesis catalysts containing bidentate aryloxy
ligands.17-18
One variation which has a bidentate, dianionic sulfonato-aryloxide ligand exists as
two isomers (Figure 3.1.6). The mixture of these isomers is active for a limited number of
standard ring closing metathesis tests at elevated temperatures. The elevated temperatures are
required to labilize the pyridine ligand. A related catalyst bearing a catecholate ligand is active
for a wider variety of ring closing metathesis reactions at elevated temperatures.
Figure 3.1.6. Ruthenium Metathesis Catalysts With Bidentate, Dianionic Ligands
More recently, Hoveyda et al. have developed a class of olefin metathesis catalysts with
bidentate, dithiolate ligands.22
The bidentate nature of these catalysts forces monomer
coordination cis to the NHC ligand. This results in high Z-selectivity in ring opening metathesis
polymerization and ring opening cross metathesis reactions.
38
3.1.6 Tridentate Ligands on Ruthenium Alkylidene Complexes
Currently there is a limited number of examples of tridentate ligands on ruthenium alkylidene
complexes. Recently Stephan et al. have reported a ruthenium-O(CH2CH2PCy2)2 alkylidene
complex.27
This coordinatively saturated species is inactive for olefin metathesis. Attempted
activation of this species by halide abstraction with a Lewis acid resulted in the formation of a
ruthenium alkylidyne-hydride complex. Erker et al. have reported a dianionic pincer-type ligand
with amido donors on a ruthenium alkylidene complex (Figure 3.1.7).28
This species is active for
ring closing metathesis of 1,7-octadiene at 80 ºC. Jensen et al. have reported an ONO dianionic
ruthenium alkylidene complex.29
This complex displayed low catalytic activity for ring closing
metathesis at room temperature. At elevated temperatures or with the addition of a proton source
catalytic activity increased.
Figure 3.1.7. Ruthenium Olefin Metathesis Catalysts with Tridentate, Dianionic Ligands
3.2 Results and Discussion
3.2.1 Synthesis of Ruthenium Alkylidene Complexes
To investigate the potential of dianionic, tridentate ligands in olefin metathesis, the complexes
were first prepared from the commercially available 1st and 2
nd Generation Grubbs Catalysts. A
general strategy involves performing a salt metathesis reaction with the dilithiated ligand of
interest to eliminate two equivalents of LiCl and replace a phosphine. This route provided the
target compounds in exceptional yields.
39
The stoichiometric reaction of dithiolate (LiSCH2CH2)2S and (PCy3)2RuCl2(CHPh) gave rise to a
dark brown solution from which a dark brown solid 3-1 was isolated in 99% yield
(Scheme 3.2.1). The 1H NMR spectrum displays a doublet at 13.48 ppm with a
3JPH of 19.3 Hz
attributed to the proton on the alkylidene fragment. The ethylene backbone gives rise to four
signals between 3.41 and 1.93 ppm appearing as multiplets suggesting a plane of symmetry. All
other signals in the 1H NMR spectrum can be assigned to the PCy3 ligand and the phenyl
substituent of the alkylidene. The 13
C{1H} NMR resonance of the alkylidene carbon can be
observed at 235.2 ppm as a doublet with a 2JPC of 14.8 Hz. A resonance in the
31P{
1H} NMR
from the remaining PCy3 can be observed at 41.7 ppm. This data is consistent with the
formulation of 3-1 as (PCy3)Ru(CHPh)(SCH2CH2)2S. This was confirmed via an X-ray
crystallographic study (Figure 3.2.1). The geometry around Ru is best described as a distorted
trigonal bipyramidal. The phosphine and thioether ligands occupy the axial positions of the
distorted trigonal bipyramid. The Ru-P and Ru-S distances are 2.3720(3) and 2.3711(3) Å,
respectively, forming a S-Ru-P angle of 176.285(10)º. The Ru-S(thiolate) distances were found
to be 2.2916(3) and 2.2981(3) Å and the Ru-C bond length was determined to be 1.8639(11) Å.
The S-Ru-C angles are 110.51(3) and 110.97(3)º and the S-Ru-S' angle is 138.172(13)º.
Scheme 3.2.1. Synthesis of 3-1 and 3-2
40
Figure 3.2.1. POV-ray depiction of 3-1; C: black, P: orange, S: yellow, Ru: teal
A similar reaction was performed with (SIMes)(PCy3)RuCl2(CHPh) to give the analogous
complex 3-2 in a 97% yield. The 1H NMR spectrum has a resonance for the alkylidene at
14.41 ppm. All other signals are consistent with the NHC and ligand backbone. The resonance
for the alkylidene carbon appears at 211.18 ppm in the 13
C{1H} NMR. These data along with a
crystallographic study are consistent with a formulation of 3-2 as
(SIMes)Ru(CHPh)(SCH2CH2)2S. The geometry in the molecular structure is similar to that of
3-1 with a distorted trigonal bipyramidal Ru centre (Figure 3.2.2). The thioether and NHC
occupy the axial positions with bonds to ruthenium being 2.380(1) and 2.084(5) Å in length
respectively. The S-Ru-C(NHC) angle was found to be 173.54(13)º. The thiolates and alkylidene
fragments complete the trigonal plane with the Ru-S distances being 2.3126(13) and
2.3356(13) Å and the Ru-C distance being 1.860(5) Å. The S-Ru-C(alkylidene) angles were
found to be 108.91(16) and 111.43(16)º and the S-Ru-S' angle is 138.67(5)º.
41
Figure 3.2.2. POV-ray depiction of 3-2; C: black, N: blue-green, S: yellow, Ru: teal
In an attempt to investigate the effect of the central donor on the reactivity of the complexes,
variants were prepared. Stirring the dithiolate salt (LiSCH2CH2)2PPh in THF with
(PCy3)2RuCl2(CHPh) produced a dark brown solution. The 31
P{1H} NMR of the isolated brown
solid shows two doublets at 114.7 and 28.9 ppm with a 2JPP of 332 Hz suggesting trans-
phosphines. The alkylidene signal in the 1H NMR shifts upfield to 13.3 ppm and appears as a
doublet of doublets due to coupling to both phosphines. The alkylidene carbon gives rise to an
apparent triplet at 239.5 ppm in the 13
C{1H} NMR spectrum with a two bond coupling constant
of 12.57 Hz. All other signals account for the formation of 3-3 as
(PCy3)Ru(CHPh)(SCH2CH2)2PPh (Scheme 3.2.2). The formulation was confirmed via an X-ray
crystallographic study (Figure 3.2.3). The Ru-C distance is 1.873(2) Å. The Ru-PCy3 and
Ru-PPh distances are 2.4462(6) and 2.2869(7) Å respectively in length. The Ru-S bonds are
2.3004(7) and 2.2876(6) Å in length. The P-Ru-P angle is 172.47(2)º and the S-Ru-S angle is
130.94(3)º. The C-Ru-S angles are 119.12(8) and 109.73(8)º. Attempted coordination of this
ligand to (SIMes)(PCy3)RuCl2(CHPh) resulted in an intractable mixture of products with loss of
the alkylidene signal. This decomposition could be due to the extremely electron rich Ru centre
that would arise from coordination of this ligand facilitating undesired reactivity.
42
Scheme 3.2.2. Synthesis of 3-3
Figure 3.2.3. POV-ray depiction of 3-3; C: black, P: orange, S: yellow, Ru: teal.
In a similar fashion, compounds 3-4 and 3-5 were prepared from (LiSCH2CH2)2O and
(PCy3)2RuCl2(CHPh) and (SIMes)(PCy3)RuCl2(CHPh) respectively (Scheme 3.2.3). 3-4 was
isolated as a dark brown solid which displays a doublet in the alkylidene region of the 1H NMR
at 13.68 ppm, similar to that of 3-1. The 31
P{1H} NMR of the crude reaction shows free PCy3
and a resonance which had shifted significantly downfield from the starting material at 65.6 ppm.
The 13
C{1H} NMR spectrum shows an alkylidene signal at 207.95 ppm. The similarities between
this data and the chemical shifts of 3-1 led to the conclusion that the formulation of 3-4 is
(PCy3)Ru(CHPh)(SCH2CH2)2O.
43
The 1H NMR spectrum of red 3-5 is characterized by a singlet at 14.85 ppm attributable to the
proton of an alkylidene fragment. The remaining signals in the 1H NMR spectrum are assigned to
the presence of the dithiolate and NHC ligands and the phenyl substituent on the alkylidene. The
13C{
1H} NMR resonance of the alkylidene is observed at 209.98 ppm. Collectively these data
were consistent with the formulation of 3-5 as (SIMes)Ru(CHPh)(SCH2CH2)2O. This was
confirmed via a crystallographic study (Figure 3.2.4). The geometry about the Ru center in 3-5 is
best described as distorted trigonal bipyramidal with the NHC ligand and the central O atom of
the dithiolate ligand occupying the axial positions and the two S atoms and the alkylidene
completing the trigonal plane. The Ru-O and Ru-C(NHC) distances were found to be 2.218(2)
and 2.009(3) Å respectively with a O-Ru-C angle of 168.97(10)º. The alkylidene fragment gives
rise to a Ru-C distance of 1.853(3) Å, while the Ru-S distances were found to be 2.3017(9) and
2.3454(9) Å. The C-Ru-S angles are 110.61(11)º and 98.93(11)º while the S-Ru-S' angle was
determined to be 147.35(4)º. The remaining angles between the axial ligands and those in the
equatorial plane varied from 82.34(6)º to 101.88(9)º. These metric parameters reveal the marked
distortion of trigonal bipyramidal geometry.
Scheme 3.2.3. Synthesis of 3-4 and 3-5
44
Figure 3.2.4. POV-ray depiction of 3-5; C: black, N: blue-green, O: red, S: yellow, Ru: teal
In an effort to see the influence of the basicity of the thiolates and the rigidity of the backbone,
(LiSC6H4)2O was used as a ligand on Ru alkylidene complexes. After stirring with
(PCy3)2RuCl2(CHPh) in THF the isolated red solid displays a resonance at 14.7 ppm in the 1H
NMR spectrum from the alkylidene proton. The signal from the PCy3 ligand in the 31
P{1H}
NMR spectrum is shifted downfield from the starting material and appears at 68.6 ppm. In the
13C{
1H} NMR spectrum a resonance from the alkylidene carbon is observed at 192.2 ppm. The
structure of 3-6 was unambiguously determined by X-ray crystallography (Figure 3.2.5). The
geometry around the ruthenium centre is best described as distorted trigonal bipyramidal. The
axial phosphorus and oxygen atoms are located 2.2754(7) and 2.1931(19) Å away from
ruthenium respectively. The P-Ru-O angle is 175.32(6)°. The Ru-S distances in the trigonal
plane are 2.2870(8) and 2.3080(8) Å and the Ru-C distance is 1.848(3) Å. The S-Ru-S' angle is
138.96(3)° and the S-Ru-C angles are 107.70(9) and 110.34(9)°. All other angles range from
80.73(6) to 98.83(3)°.
45
Figure 3.2.5. POV-ray depiction of 3-6; C: black, O: red, P: orange, S: yellow, Ru: teal
The analogous compound 3-7 where PCy3 has been replaced with an NHC was prepared by
using (SIMes)(PCy3)RuCl2(CHPh) as a starting material (Scheme 3.2.4). The isolated red solid
gives rise to an alkylidene signal in the 1H NMR spectrum at 15.6 ppm. The
31P{
1H} NMR
spectrum of the crude reaction mixture shows only the presence of free PCy3. In the 13
C{1H}
NMR spectrum the signal at 209.1 ppm is due to the alkylidene carbon. All other signals can be
attributed to the formulation of 3-7 as (SIMes)Ru(CHPh)(SC6H4)2O.
Scheme 3.2.4. Synthesis of 3-6 and 3-7
46
The effect of the anionic donors in these tridentate systems was investigated by substituting the
thiolates for alkoxides. Stirring the related pro-ligand (KOCH2CH2)2O with
(PCy3)2RuCl2(CHPh) resulted in the isolation of the red compound 3-8 in 90% yield. A doublet
which can be assigned to the alkylidene proton is observed in the 1H NMR at 15.72 ppm with a
3JPH of 14.8 Hz. Four multiplets from 4.19 to 2.96 ppm arise from the ethylene linkers in the
backbone of the tridentate ligand. A singlet at 64.8 ppm is observed in the 31
P{1H} NMR and
signal at 192.2 ppm in the 13
C{1H} NMR spectrum is attributed to the carbon of the alkylidene.
From these data, along with an X-ray crystallographic study, the formulation of 3-8 was
determined to be (PCy3)Ru(CHPh)(OCH2CH2)2O. Although a molecular structure was obtained
from the X-ray study, the data was insufficient for a full solution therefore a discussion of metric
parameters is unavailable (Figure 3.2.6).
Figure 3.2.6. POV-ray depiction of 3-8; C: black, O: red, P: orange, Ru: teal. Insufficient
data for full solution
47
As with the previous ligands, the all oxygen tridentate ligand was reacted with
(SIMes)(PCy3)RuCl2(CHPh) to give 3-9 (Scheme 3.2.5). The alkylidene proton of the resulting
compound displays the characteristic chemical shift in the 1H NMR at 16.23 ppm. An X-ray
crystallographic study confirmed the formulation and structure of 3-9 as
(SIMes)Ru(CHPh)(OCH2CH2)2O (Figure 3.2.7). In the solid state, one of the alkoxy arms is
disordered over two positions. The alkylidene fragment gives rise to a Ru-C bond length of
1.830(3) Å. The Ru-O(ether) and Ru-C(carbene) bond lengths are 2.194(1) and 1.983(2) Å
respectively giving rise to a O-Ru-C angle of 165.18(2)°. The Ru-O(alkoxy) bond lengths range
from 1.944(3) to 2.020(4) Å. These parameters describe the distorted trigonal bipyramidal
geometry.
Scheme 3.2.5. Synthesis of 3-8 and 3-9
48
Figure 3.2.7. POV-ray depiction of 3-9; C: black, O: red, N: blue-green, Ru: teal.
3.3 Conclusions
A library of ruthenium complexes containing an alkylidene and a tridentate, dianionic ligand
along with either PCy3 or SIMes have been prepared. These compounds were easily prepared in
high yields from inexpensive, commercially available ligands and Grubbs Catalyst as a
convenient method to obtain the desired species for further investigation. Ligand variants include
dithiolates with a central thioether, ether, and phosphine donor. Ligands with both an alkyl and
an aryl backbone have been prepared and a dialkoxy ligand with a central ether donor has been
introduced. The obtained molecular structures display similar geometries which can be best
described as distorted trigonal bipyramidal with the central donor of the tridentate ligand trans to
the PCy3 or NHC. The alkylidene and the anionic donors complete the trigonal plane.
49
3.4 Experimental Section
3.4.1 General Considerations
All manipulations were carried out under an atmosphere of dry, O2-free N2 employing a Vac
Atmospheres glove box and a Schlenk vacuum-line. Solvents were purified with a Grubbs-type
column system manufactured by Innovative Technology and dispensed into thick-walled Schlenk
glass flasks equipped with Teflon-valve stopcocks. All solvents were thoroughly degassed after
purification (repeated freeze-pump-thaw cycles). CD2Cl2 was dried over CaH2 and vacuum
transferred into a Schlenk flask equipped with a Teflon-valve stopcock. 1H,
13C, and
31P NMR
spectra were recorded at 25 °C on Varian 300 and 400 MHz and Bruker 400 MHz spectrometers.
Chemical shifts are given relative to SiMe4 and referenced to the residual solvent signal (1H,
13C)
or relative to an external standard (31
P: 85% H3PO4). Chemical shifts are reported in ppm and
coupling constants as scalar values in Hz. Combustion analyses were performed in house
employing a Perkin-Elmer CHN Analyzer. All chemicals were obtained from Aldrich and used
as received unless stated. Pro-ligands were synthesized by the addition of two equivalents of n-
BuLi or KOtBu to the corresponding dithiol or diol. (LiSCH2CH2)2PPh and (HSC6H4)2O were
prepared according to literature procedures.30-31
3.4.2 Synthetic Procedures
Synthesis of 3-1: A THF solution (5 mL) of (LiSCH2CH2)2S.2THF (0.020
g, 0.123 mmol) was added to a THF solution (5 mL) of Grubbs 1 (0.092
g, 0.112 mmol) and stirred overnight. All volatiles were removed from
the dark brown solution. The dark brown solid was taken up in CH2Cl2 (5
mL) and filtered through a celite packed pipette. Upon concentration to
dryness, the resulting dark brown solid was washed with hexane (2 20 mL) and dried to yield a
dark red solid (0.068 g, 97%). X-ray quality crystals were grown from a CH2Cl2/CH3CN
solution. 1H NMR (CD2Cl2): 13.48 (d,
3JPH = 19.3 Hz, 1H, Ru=CH), 7.12 (m, 3H, Ph), 6.93 (m,
2H, Ph), 3.41 (m, 2H, CH2), 3.24 (m, 2H, CH2), 2.45 (m, 2H, CH2), 1.93 (m, 2H, CH2), 2.28,
2.04, 1.73, 1.57, 1.19 (all m, P(C6H11)3). 13
C{1H} NMR (CD2Cl2): 235.16 (d,
2JPC = 14.78 Hz,
Ru=CH), 157.02 (ipso-C, Ph), 127.51 (2 CH, Ph), 125.84 (2 CH, Ph),125.40 (CH, Ph), 45.17
(2 CH2), 36.28 (2 CH2), 35.19 (d, 1JPC = 19.78 Hz, ipso-C of P(C6H11)3), 29.98 (m-C of
P(C6H11)3), 28.37 (d, 2JPC = 10.25 Hz, o-C of P(C6H11)3), 26.93 (p-C of P(C6H11)3).
31P{
1H}
50
NMR (CD2Cl2): 41.71. Analysis calculated for C29H47PRuS3: C, 55.83; H, 7.59. Found: C,
55.71; H,7.33.
Synthesis of 3-2: A THF solution (5 mL) of (LiSCH2CH2)2S.2THF
(0.020 g, 0.123 mmol) was added to a THF solution (5 mL) of
Grubbs 2 (0.095 g, 0.112 mmol) and stirred overnight. All volatiles
were removed from the dark brown solution. The dark brown solid
was taken up in CH2Cl2 (5 mL) and filtered through a celite packed
pipette. Upon concentration to dryness, the resulting dark brown
solid was washed with hexane (2 20 mL) and dried to yield a dark red solid (0.071 g, 98%). X-
ray quality crystals were grown from a CH2Cl2/CH3CN solution. 1H NMR (CD2Cl2): 14.41 (s,
1H, Ru=CH), 7.19 (t, 1H, p-H, Ph), 7.07 (t, 2H, m-H, Ph), 6.88 (d, 2H, o-H, Ph), 6.80 (s, 4H, 4
CH, Mes), 3.99 (s, 4H, 2 CH2, Im), 3.22 (m, 2H, CH2), 3.00 (m, 2H, CH2), 2.52 (s, 12H, 4
CH3, Mes), 2.24 (m, 2H, CH2), 2.19 (s, 6H, 2 CH3, Mes), 1.73 (m, 2H, CH2). 13
C{1H} NMR
(CD2Cl2): 211.18 (Ru=CH), 138.08 (ipso-C, Ph), 137.79 (ipso-C, NCN), 137.73 (ipso-C, Mes),
129.18 (4 CH, Mes), 127.25.18 (2 CH, Ph), 127.11 (2 CH, Ph), 125.14 (CH, p-C, Ph),
52.43 (2 CH2), 44.56 (2 CH2, Im), 34.77 (2 CH2), 20.98 (2 CH3, Mes), 19.68 (4 CH3,
Mes). Analysis calculated for C32H40N2RuS3+CH2Cl2 (In crystal lattice) : C, 53.94; H, 5.76; N,
3.81. Found: C, 55.69; H, 5.96; N, 3.81.
Synthesis of 3-3: A THF solution (5 mL) of (LiSCH2CH2)2PPh (0.032 g,
0.134 mmol) was added to a THF solution (5 mL) of Grubbs 1 (0.100 g,
0.122 mmol) and stirred overnight. All volatiles were removed from the
dark brown solution. The dark brown solid was taken up in CH2Cl2 (5
mL) and filtered through a celite packed pipette. Upon concentration to
dryness, the resulting dark brown solid was washed with hexane (2 20 mL) and dried to yield a
dark red solid (0.076 g, 89%). 1H NMR (CD2Cl2): 13.31 (dd,
3JPH = 23.2 Hz,
3JPH = 1.8 Hz, 1H,
Ru=CH), 7.04 (m, 5H, PPh), 6.94 (d, 2H, Ph), 6.71 (m, 3H, Ph), 3.07 (m, 2H, CH2), 2.93 (m, 2H,
CH2), 2.47 (m, 5H, CH2, P(C6H11)3), 2.15 (m, 2H, CH2), 2.20, 1.86, 1.72, 1.33 (all m, P(C6H11)3.
13C{
1H} NMR (CD2Cl2): 235.90 (appt,
2JPC = 12.57 Hz, Ru=CH), 155.7 (dd,
3JPC = 10.50 Hz,
3.85 Hz, ipso-C, Ph), 130.74 (d, 2JPC = 9.27 Hz, 2 CH, PPh), 128.56 (CH, PPh), 128.55 (d,
1JPC
= 267.1 Hz, CH, PPh), 127.65 (d, 3JPC = 9.25 Hz, 2 CH, PPh), 127.09 (2 CH, Ph), 126.03 (2
51
CH, Ph),124.99 (CH, Ph), 34.16 (m, 2 CH2), 31.49 (m, 2 CH2), 29.53 (m-C of P(C6H11)3),
28.04 (d, 1JPC = 9.02 Hz, ipso-C of P(C6H11)3), 27.70 (d,
2JPC = 9.02 Hz, o-C of P(C6H11)3), 26.56
(p-C of P(C6H11)3). 31
P{1H} NMR (CD2Cl2): 114.7 (d,
2JPP = 330.6 Hz), 28.9 (d,
2JPP = 331.8
Hz). Analysis calculated for C35H52P2RuS2: C, 60.06; H, 7.49. Found: C, 59.58; H, 7.32.
Synthesis of 3-4: A THF solution (5 mL) of (LiSCH2CH2)2O.2THF
(0.020 g, 0.137 mmol) was added to a THF solution (5 mL) of Grubbs 1
(0.100 g, 0.126 mmol) and stirred overnight. All volatiles were removed
from the dark brown solution. The dark brown solid was taken up in
CH2Cl2 (5 mL) and filtered through a celite packed pipette. Upon
concentration to dryness, the resulting dark brown solid was washed with hexane (2 20 mL)
and dried to yield a dark red solid (0.075 g, 98%). 1H NMR (CD2Cl2): 13.68 (d,
3JPH = 11.8 Hz,
1H, Ru=CH), 7.27 (m, 2H, Ph), 7.14 (m, 3H, Ph), 3.84 (m, 2H, CH2), 3.21 (m, 2H, CH2), 2.74
(m, 4H, 2 CH2), 2.11, 1.98, 1.74, 1.61, 1.50, 1.19 (all m, P(C6H11)3. 13
C{1H} NMR (CD2Cl2):
207.95 (Ru=CH), 153.25 (ipso-C, Ph), 128.15 (2 CH, Ph), 125.58 (CH, Ph), 125.39 (2 CH,
Ph), 77.96 (2 CH2), 35.91 (d, 1JPC = 24.17 Hz, ipso-C of P(C6H11)3), 32.42 (2 CH2), 29.97
(m-C of P(C6H11)3), 28.31 (d, 2JPC = 10.25 Hz, o-C of P(C6H11)3), 26.93 (p-C of P(C6H11)3).
31P{
1H} NMR (CD2Cl2): 65.60. Analysis calculated for C29H47OPRuS2: C, 57.30; H, 7.79.
Found: C, 56.92; H, 7.55.
Synthesis of 3-5: Grubbs 2 (0.326 g, 0.384 mmol) in MeCN (5 mL)
was added to (LiSCH2CH2)2O.2THF (0.144 g, 0.489 mmol) in MeCN
(5 mL) and toluene (10 mL) and stirred for 16 h. All volatiles were
removed from the dark brown solution. CH2Cl2 (5mL) was added to
give a dark brown solution which was filtered through celite. Upon
concentration to dryness, the resulting dark brown solid was washed
with hexane (2 20 mL) and dried to yield a black-red solid. X-ray quality crystals were grown
from a CH2Cl2/CH3CN solution. (0.243 g, 99%). 1H NMR (CD2Cl2): 14.85 (s, 1H, Ru=CH), 7.14
(t, 1H, p-H, Ph), 6.97-7.05 (m, 4H, Ph), 6.86 (s, 4H, 4 CH, Mes), 3.92 (s, 4H, 2 CH2, Im),
3.65 (m, 2H, CH2), 2.82 (m, 2H, CH2), 2.45 (s, 12 H, 4 CH3, Mes), 2.32-2.41 (m, 4H, 2
CH2), 2.23 (s, 6H, 2 CH3, Mes). 13
C{1H} NMR (CD2Cl2): 209.98 (Ru=CH), 153.68 (ipso-C,
Ph), 137.89 (ipso-C, NCN), 137.38 (ipso-C, Mes), 137.31 (ipso-C, Mes), 127.27 (2 CH, Ph),
52
128.81 (4 CH, Mes), 125.02 (2 CH, Ph), 124.65 (CH, p-C, Ph), 77.56 (2 CH2), 51.84 (2
CH2, Im), 31.59 (2 CH2), 20.59 (2 CH3, Mes), 19.12 (4 CH3, Mes). Analysis calculated for
C32H40N2ORuS2: C, 60.63; H, 6.36; N, 4.42. Found: C, 60.19; H, 5.97; N, 4.30.
Synthesis of 3-6: A THF solution (5 mL) of (LiSC6H4)2O (0.033 g,
0.134 mmol) was added to a THF solution (5 mL) of Grubbs 1 (0.100
g, 0.122 mmol) and stirred overnight. All volatiles were removed from
the dark brown solution. The dark brown solid was taken up in CH2Cl2
(5 mL) and filtered through a celite packed pipette. Upon concentration
to dryness, the resulting dark brown solid was washed with hexane (2
20 mL) and dried to yield a red solid (0.068 g, 97%). X-ray quality crystals were grown from a
CH2Cl2 solution. 1H NMR (CD2Cl2): 14.69 (d,
3JPH = 14.7 Hz, 1H, Ru=CH), 7.48 (d,
3JHH = 7.6
Hz, 2H, Ph), 7.48 (m, 3H, Ph), 6.90 (m, 4H, Ph), 6.82 (t, 3JHH = 7.3 Hz, 2H, Ph), 6.72 (m, 2H,
Ph), 2.15, 2.02, 1.77, 1.55, 1.19 (all m, P(C6H11)3. 13
C{1H} NMR (CD2Cl2): 192.20 (Ru=CH),
154.03 (2 ipso-C, Ph), 152.23 (ipso-C, Ph), 139.08 (2 ipso-C, Ph), 132.14 (2 CH, Ph),
130.14 (2 CH, Ph), 127.94 (2 CH, Ph), 126.31 (CH, Ph), 125.27 (2 CH, Ph), 123.97 (2
CH, Ph), 122.70 (2 CH, Ph), 115.86 (2 CH, Ph), 35.95 (d, 1JPC = 25.05 Hz, ipso-C of
P(C6H11)3), 31.62 (m-C of P(C6H11)3), 30.09 (p-C of P(C6H11)3), 28.19 (d, 2JPC = 10.24 Hz, o-C
of P(C6H11)3). 31
P{1H} NMR (CD2Cl2): 68.60. Analysis calculated for C37H47OPRuS2: C, 63.13;
H, 6.73. Found: C, 62.52; H, 6.30.
Synthesis of 3-7: A THF solution (5 mL) of (LiSC6H4)2O (0.038 g,
0.153 mmol) was added to a THF solution (5 mL) of Grubbs 2 (0.100
g, 0.118 mmol) and stirred overnight. All volatiles were removed from
the dark brown solution. The dark brown solid was taken up in CH2Cl2
(5 mL) and filtered through a celite packed pipette. Upon concentration
to dryness, the resulting dark brown solid was washed with hexane (2
20 mL) and dried to yield a red solid (0.074 g, 86%). 1H NMR (CD2Cl2): 15.60 (s, 1H, Ru=CH),
7.41 (d, 2H, Ph), 6.91 (m, 8H, Ph, Mes), 6.79 (m, 5H, Ph), 6.64 (m, 2H, Ph), 4.08 (s, 4H, 2
CH2, Im), 2.51 (s, 12 H, 4 CH3, Mes), 2.22 (s, 6H, 2 CH3, Mes). 13
C{1H} NMR (CD2Cl2):
209.13 (Ru=CH), 153.13 (ipso-C, Ph), 151.45 (ipso-C, Ph) 139.53 (ipso-C, NCN), 137.97 (ipso-
C, Mes), 137.17 (ipso-C, Mes), 131.26 (2 CH, Ph), 129.18 (2 CH, Ph), 128.90 (2 CH, Ph),
53
128.14 (2 CH, Ph), 126.10 (4 CH, Mes), 127.42 (2 CH, Ph), 125.22 (CH, p-C, Ph), 122.90
(CH, Ph), 121.54 (2 CH, Ph), 114.78 (2 CH, Ph), 51.84 (2 CH2, Im), 20.71 (2 CH3,
Mes), 18.99 (4 CH3, Mes). Analysis calculated for C40H40N2ORuS2+CH2Cl2 : C, 60.43; H,
5.19; N, 3.44. Found: C, 61.08; H, 5.78; N, 2.88.
Synthesis of 3-8: A THF solution (5 mL) of (KOCH2CH2)2O (0.025 g,
0.137 mmol) was added to a THF solution (5 mL) of Grubbs 1 (0.100 g,
0.126 mmol) and stirred overnight. All volatiles were removed from the
dark brown solution. The dark brown solid was taken up in toluene (5
mL) and filtered through a celite packed pipette. Upon concentration to
dryness, the resulting red solid was washed with hexane (2 20 mL) and dried to yield a red
solid (0.068 g, 90%). 1H NMR (CD2Cl2): 15.72 (d,
3JPH = 14.8 Hz, 1H, Ru=CH), 7.91 (d,
3JHH =
8.02 Hz 2H, Ph), 7.31 (m, 3H, Ph), 4.19 (m, 2H, CH2), 3.96 (m, 2H, CH2), 3.39 (m, 2H, CH2),
2.96 (m, 2H, CH2), 2.44, 2.22, 1.87, 1.67, 1.65 (all m, P(C6H11)3. 13
C{1H} NMR (CD2Cl2):
207.95 (Ru=CH), 128.6 (Ph), 128.2 (Ph), 126.4 (Ph), 124.7 (Ph), 79.5 (2 CH2), 72.1 (2 CH2),
33.2 (d, 1JPC = 26.1 Hz, ipso-C of P(C6H11)3), 28.8 (m-C of P(C6H11)3), 27.7 (d,
2JPC = 10.4 Hz,
o-C of P(C6H11)3), 26.5 (p-C of P(C6H11)3). 31
P{1H} NMR (CD2Cl2): 64.76. Analysis calculated
for C29H47O3PRu: C, 60.50; H, 8.23. Found: C, 59.94 H, 7.83.
Synthesis of 3-9: Grubbs 2 (0.100 g, 0.118 mmol) in THF (5 mL) was
added to (KOCH2CH2)2O (0.028 g, 0.153 mmol) in THF (10 mL) and
stirred for 16 h. All volatiles were removed from the dark brown
solution. Toluene (5mL) was added to give a dark brown solution
which was filtered through celite. Upon concentration to dryness, the
resulting dark brown solid was washed with hexane (2 20 mL) and dried to yield a dark red
solid. (0.63 g, 90%). 1H NMR (CD2Cl2): 16.23 (s, 1H, Ru=CH), 7.58 (d, 2H, Ph), 7.18 (m, 3H,
Ph), 6.87 (s, 4H, 4 CH, Mes), 3.78 (m, 4H, 2 CH2), 3.44 (s, 4H, 2 CH2, Im), 3.18 (m, 4H, 2
CH2), 2.57 (s, 12 H, 4 CH3, Mes), 2.19 (s, 6H, 2 CH3, Mes). 13
C{1H} NMR (CD2Cl2):
212.4 (Ru=CH), 153.3 (ipso-C, Ph), 138.7 (ipso-C, NCN), 137.5 (ipso-C, Mes), 137.4 (ipso-C,
Mes), 128.5 (2 CH, Ph), 128.2 (4 CH, Mes), 124.6 (2 CH, Ph), 123.6 (CH, p-C, Ph), 79.4
(2 CH2), 70.7 (2 CH2), 51.4 (2 CH2, Im), 20.7 (2 CH3, Mes), 18.4 (4 CH3, Mes).
54
Analysis calculated for C32H40N2O3Ru: C, 63.87; H, 6.70; N, 4.66. Found: C, 63.30 H, 6.43 N,
4.25.
3.4.3 X-ray Crystallography
3.4.3.1 X-ray Data Collection and Reduction
Crystals were coated in Paratone-N oil in the glove-box, mounted on a MiTegen Micromount
and placed under an N2 stream, thus maintaining a dry, O2-free environment for each crystal. The
data were collected on a Bruker Apex II diffractometer employing Mo Kα radiation (λ = 0.71073
Å). Data collection strategies were determined using Bruker Apex software and optimized to
provide >99.5% complete data to a 2θ value of at least 55°. The data were collected at 150(±2) K
for all crystals. The frames were integrated with the Bruker SAINT software package using a
narrow-frame algorithm. Data were corrected for absorption effects using the empirical multi-
scan method (SADABS).32
3.4.3.2 X-ray Data Solution and Refinement
Non-hydrogen atomic scattering factors were taken from the literature tabulations.33
The heavy
atom positions were determined using direct methods employing the SHELXTL direct methods
routine. The remaining non-hydrogen atoms were located from successive difference Fourier
map calculations. The refinements were carried out by using full-matrix least squares techniques
on F, minimizing the function (Fo–Fc)2 where the weight is defined as 4Fo2/2 (Fo
2) and Fo
and Fc are the observed and calculated structure factor amplitudes, respectively. In the final
cycles of each refinement, all non-hydrogen atoms were assigned anisotropic temperature factors
in the absence of disorder or insufficient data. In the latter cases atoms were treated isotropically.
C-H atom positions were calculated and allowed to ride on the carbon to which they are bonded
assuming a C-H bond length of 0.95 Å. H-atom temperature factors were fixed at 1.20 times the
isotropic temperature factor of the C-atom to which they are bonded. The H-atom contributions
were calculated, but not refined. The locations of the largest peaks in the final difference Fourier
map calculation as well as the magnitude of the residual electron densities in each case were of
no chemical significance.
55
Table 3.4.1. Select Crystallographic Data for 3-1, 3-2 and 3-3.
(3-1) (3-2) (3-3)
Formula C29H47PRuS3 C32H40N2RuS3
(CH2Cl2)
C35H52P2RuS2
Formula weight 623.92 734.87 699.92
Crystal System Triclinic Monoclinic Monoclinic
Space group P-1 P21/c P21/n
a(Å) 8.4357(4) 11.0572(10) 8.3215(10)
b(Å) 10.0451(4) 26.702(2) 17.7887(19)
c(Å) 17.6088(7) 12.1075(11) 22.489(3)
α(deg) 88.602(2) 90 90
β(deg) 80.783(2) 114.176(3) 96.735(5)
γ(deg) 86.310(2) 90 90
V(Å3) 1469.66(11) 3261.2(5) 3306.0(7)
Z 2 4 4
d(calc)gcm-3
1.410 1.497 1.406
R(int) 0.0290 0.0458 0.0731
Abs coeff,μ,mm-1
0.819 0.863 0.721
Data collected 11193 7483 7577
>2(FO2) 10137 6329 5988
Variables 331 370 406
R(>2) 0.0216 0.0616 0.0338
Rw 0.0538 0.1571 0.0795
GOF 1.022 1.123 1.039
56
Table 3.4.2. Select Crystallographic Data for 3-5, 3-6 and 3-9.
(3-5) (3-6) (3-9)
Formula C32H40N2ORuS2
(CH3CN)
C37H47OPRuS C32H40N2O3Ru
Formula weight 674.92 703.93 601.73
Crystal System Monoclinic Monoclinic Monoclinic
Space group P21/n P21/c P21/n
a(Å) 14.1830(6) 10.4646(7) 9.6299(6)
b(Å) 10.3197(4) 18.4403(12) 14.408(1)
c(Å) 22.6405(11) 17.6740(11) 21.2995(14)
α(deg) 90 90 90
β(deg) 101.407(2) 94.848(2) 95.679(4)
γ(deg) 90 90 90
V(Å3) 3248.3(2) 3398.4(4) 2940.8(3)
Z 4 4 4
d(calc)gcm-3
1.380 1.376 1.359
R(int) 0.0349 0.0480 0.0313
Abs coeff,μ,mm-1
0.642 0.659 0.567
Data collected 8016 8032 8753
>2(FO2) 6375 6258 7309
Variables 375 379 371
R(>2) 0.0352 0.0398 0.0362
Rw 0.0817 0.0958 0.0904
GOF 0.975 0.983 1.026
57
Chapter 3 References
1. Nguyen, S. T.; Johnson, L. K.; Grubbs, R. H.; Ziller, J. W., Journal of the American
Chemical Society 1992, 114 (10), 3974-3975.
2. Dias, E. L.; Nguyen, S. T.; Grubbs, R. H., Journal of the American Chemical Society
1997, 119 (17), 3887-3897.
3. Sanford, M. S.; Love, J. A.; Grubbs, R. H., Journal of the American Chemical Society
2001, 123 (27), 6543-6554.
4. Sanford, M. S.; Ulman, M.; Grubbs, R. H., Journal of the American Chemical Society
2001, 123 (4), 749-750.
5. Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H., Organic Letters 1999, 1 (6), 953-956.
6. Vougioukalakis, G. C.; Grubbs, R. H., Chem Rev 2010, 110 (3), 1746-87.
7. Lynn, D. M.; Mohr, B.; Grubbs, R. H.; Henling, L. M.; Day, M. W., Journal of the
American Chemical Society 2000, 122 (28), 6601-6609.
8. Rolle, T.; Grubbs, R. H., Chemical Communications 2002, (10), 1070-1071.
9. Seiders, T. J.; Ward, D. W.; Grubbs, R. H., Organic Letters 2001, 3 (20), 3225-3228.
10. Funk, T. W.; Berlin, J. M.; Grubbs, R. H., Journal of the American Chemical Society
2006, 128 (6), 1840-1846.
11. Berlin, J. M.; Goldberg, S. D.; Grubbs, R. H., Angewandte Chemie International Edition
2006, 45 (45), 7591-7595.
12. Garber, S. B.; Kingsbury, J. S.; Gray, B. L.; Hoveyda, A. H., Journal of the American
Chemical Society 2000, 122 (34), 8168-8179.
13. Sanford, M. S.; Henling, L. M.; Day, M. W.; Grubbs, R. H., Angewandte Chemie
International Edition 2000, 39 (19), 3451-3453.
14. Conrad, J. C.; Amoroso, D.; Czechura, P.; Yap, G. P. A.; Fogg, D. E., Organometallics
2003, 22 (18), 3634-3636.
15. Conrad, J. C.; Parnas, H. H.; Snelgrove, J. L.; Fogg, D. E., Journal of the American
Chemical Society 2005, 127 (34), 11882-3.
16. Conrad, J. C.; Camm, K. D.; Fogg, D. E., Inorganica Chimica Acta 2006, 359 (6), 1967-
1973.
17. Conrad, J. C.; Snelgrove, J. L.; Eeelman, M. D.; Hall, S.; Fogg, D. E., Journal of
Molecular Catalysis A: Chemical 2006, 254 (1–2), 105-110.
58
18. Monfette, S.; Fogg, D. E., Organometallics 2006, 25 (8), 1940-1944.
19. Zhang, W.; Liu, P.; Jin, K.; He, R., Journal of Molecular Catalysis A: Chemical 2007,
275 (1–2), 194-199.
20. Samec, J. S. M.; Grubbs, R. H., Chemistry – A European Journal 2008, 14 (9), 2686-
2692.
21. Endo, K.; Grubbs, R. H., Journal of the American Chemical Society 2011, 133 (22),
8525-8527.
22. Khan, R. K. M.; Torker, S.; Hoveyda, A. H., Journal of the American Chemical Society
2013, 135 (28), 10258-10261.
23. Occhipinti, G.; Hansen, F. R.; Törnroos, K. W.; Jensen, V. R., Journal of the American
Chemical Society 2013, 135 (9), 3331-3334.
24. Cannon, J. S.; Grubbs, R. H., Angewandte Chemie International Edition 2013, 52 (34),
9001-9004.
25. De Clercq, B.; Verpoort, F., Tetrahedron Letters 2002, 43 (50), 9101-9104.
26. Denk, K.; Fridgen, J.; Herrmann, W. A., Advanced Synthesis & Catalysis 2002, 344 (6-
7), 666.
27. Boone, M. P.; Brown, C. C.; Ancelet, T. A.; Stephan, D. W., Organometallics 2010, 29
(19), 4369-4374.
28. Wasilke, J.-C.; Wu, G.; Bu, X.; Kehr, G.; Erker, G., Organometallics 2005, 24 (17),
4289-4297.
29. Occhipinti, G.; Bjørsvik, H.-R.; Törnroos, K. W.; Jensen, V. R., Organometallics 2007,
26 (24), 5803-5814.
30. Antonio Muñoz, J.; Escriche, L.; Casabó, J.; Pérez-Jiménez, C.; Kivekäs, R.; Sillanpää,
R., Inorganica Chimica Acta 1997, 257 (1), 99-104.
31. Alvarado-Rodríguez, José G.; Andrade-López, N.; González-Montiel, S.; Merino, G.;
Vela, A., European Journal of Inorganic Chemistry 2003, 2003 (19), 3554-3562.
32. Apex 2 Software Package;, Bruker AXS Inc. : 2013.
33. D. T. Cromer, J. T. W., Int. Tables X-Ray Crystallography. 1974; Vol. 4.
59
Chapter 4 Synthesis of Ru Alkylidenes via Dithioacetals
4.1 Introduction
4.1.1 First Well Defined Olefin Metathesis Catalyst
The synthesis of alkylidenes has been done a number of ways. The first isolated transition metal
alkylidene complex was reported by Schrock and co-workers in 1974.1 It was formed by the
attempted formation of a homoleptic, pentaneopentyl Ta species (Scheme 4.1.1).2-3
This opened
up the field of well defined olefin metathesis catalysts.
Scheme 4.1.1. Synthesis of the First Isolated Transition Metal Alkylidene
4.1.2 Synthetic Routes to Ruthenium Alkylidenes
The first well-defined ruthenium based olefin metathesis catalyst was reported by Grubbs and
co-workers.4-5
It was synthesized by the ring opening of 2,2-diphenylcyclopropene with
Ru(PPh3)3Cl2 to give the vinylalkylidene (Scheme 4.1.2). Drawbacks of this method include the
laborious synthesis of the cyclopropene and the synthesis of the vinylalkylidene which initiates
slower than the typical benzylidene.6-7
Scheme 4.1.2. Synthesis of the First Ruthenium Alkylidene
Following this discovery, a number of new synthetic methods to prepare ruthenium alkylidenes
were discovered including direct routes to the faster initiating benzylidene present in
commercially available Grubbs Catalysts. These methods include the use of diazomethanes as
alkylidene transfer reagents (Scheme 4.1.3).4 This route is high yielding and provides a direct
60
pathway to the ruthenium benzylidene, however, diazomethanes are shock sensitive and
explosive and thus must be handled with extreme caution.
Scheme 4.1.3. Synthesis of Grubbs Catalyst Using Phenyldiazomethane
Milstein and co-workers developed a method using a sulfur ylide as an alkylidene transfer
reagent.8 This provides a safer starting material than using diazomethanes and a direct route to
the ruthenium benzylidene, however, there is a stoichiometric amount of thioether waste
generated (Scheme 4.1.4). This method is also patent protected and would require a licensing
agreement in order to use it commercially.
Scheme 4.1.4. Synthesis of Grubbs Catalyst Using a Sulfur Ylide
Starting from ruthenium hydrides, there are a variety of methods to convert these species to an
alkylidene. Reacting Ru(PPh3)3HCl with 3-chloro-3-methyl-1-butyne followed by phosphine
exchange affords the Ru vinylalkylidene in greater than 70% yield (Scheme 4.1.5).9 This
synthetic route has similar drawback to the cyclopropene route which also gives a
vinylalkylidene which have slower initiation rates compared to the benzylidene derivatives.
Scheme 4.1.5. Synthesis of a Vinylalkylidene Using Propargyl Chloride
61
Starting from [Ru(PiPr3)2HCl]2, this synthon can be converted to an alkylidene via the addition of
vinyl chloroformate.10
This results in the liberation of CO2 and transfer of the chloride to the Ru
centre as the ethylidene is formed. Similarly, reacting (Im(OMe)2)Ru(SIMes)(PPh3)HCl with
phenyl vinylsulfide results in the formation of the ruthenium thiolate alkylidene complex
(Scheme 4.1.6).11
Even though these compounds are active for catalytic olefin metathesis they
also suffer from forming an alkylidene which is slower initiating than a benzylidene.
Scheme 4.1.6. Synthesis of Ru Alkylidenes from Phenyl Vinylsulfide
By reacting Ru(PPh3)3Cl2 with 1,1-diphenyl-2-propyn-1-ol in THF with the loss of H2O,
followed by addition of PCy3 a ruthenium indenylidene can be isolated (Scheme 4.1.7).12
This
reaction is thought to be catalyzed by HCl and go through a ruthenium carbyne intermediate.
This ruthenium indenylidene complex is active for olefin metathesis but is slower initiating than
1st Generation Grubbs Catalyst. This species can be converted to Grubbs Catalyst by the
addition of 60 equivalents of styrene over 3 h.
Scheme 4.1.7. Synthesis of Grubbs Catalyst via Indenylidene Intermediate
Grubbs and coworkers have developed a method for preparing Grubbs Catalyst starting from a
Ru(0) species and dichloroalkanes.13
For example, heating Ru(cod)(cot) in the presence of PCy3
and Cl2CHPh results in the formation of 1st Generation Grubbs Catalyst in 50% yield
(Scheme 4.1.8). In a similar fashion, mixing RuH2(H2)2(PCy3)2 with cyclohexene results in the
62
formation of a Ru(0) species which reacts with Cl2CHPh to also give 1st Generation Grubbs
Catalyst in a 70% yield.
Scheme 4.1.8. Synthesis of Grubbs Catalyst from Ru(0) Species
4.2 Results and Discussion
4.2.1 Attempted Synthesis Using Diazomethanes
Reacting 2-1 with a diazomethane compound could lead to the synthesis of a ruthenium
alkylidene similar to 3-4 with a PPh3 in place of the PCy3 ligand (Scheme 4.2.1). This reaction is
conceptually related to the synthesis of Grubbs catalyst from Ru(PPh3)3Cl2 and a diazomethane.
To probe the potential of this synthetic strategy, commercially available, and less hazardous
TMSCHN2 was initially used as the diazomethane. Mixing 2-1 and TMSCHN2 in CD2Cl2 at
room temperature resulted in no observable change to the solution. NMR data showed no
evidence of a reaction taking place. In an optimistic attempt, PhCHN2 was prepared and mixed
with a CH2Cl2 solution of 2-1. A red solid was isolated from the reaction mixture. Multiple
alkylidene peaks were observed in the 1H NMR spectrum however they were very minor and
multiple attempts to increase the conversion proved unsuccessful and inconsistent.
Scheme 4.2.1. Failed Preparation of Ruthenium Alkylidene From Diazomethanes and 2-1
63
Replacing a phosphine with an alkylidene in 2-3 using a diazomethane reagent would lead to a
complex similar to 5-4 (Scheme 4.2.2). To see if this ruthenium starting material was more
reactive with diazomethanes it was mixed with either TMSCHN2 or PhCHN2 in CH2Cl2. In both
cases no reactivity was observed.
Scheme 4.2.2. Failed Preparation of Ruthenium Alkylidene From Diazomethanes and 2-3
4.2.2 Attempted Synthesis Using Propargyl Alcohol
In an attempt to prepare a ruthenium alkylidene using the propargyl alcohol route to an
indinylidene, 2-1 and 1,1-diphenylprop-2-yn-1-ol were refluxed in THF for 5 h in the presence of
a catalytic amount of acyl chloride (Scheme 4.2.3). This resulted in no observable reaction.
Scheme 4.2.3. Failed Preparation of Ruthenium Indenylidene From Propargyl Alcohol and
2-3
4.2.3 Synthesis of Ru Alkylidenes using Thioacetals
With unsuccessful attempts in synthesizing these ruthenium alkylidene complexes via
diazomethanes and propargyl alcohols, a more creative approach was developed. Based on the
work by Grubbs and co-workers using dihaloalkanes with Ru(0) sources to form
dihalo-ruthenium alkylidenes a related strategy using dithioacetals and Ru(0) sources to form
dithiolate-ruthenium alkylidene complexes was developed.
64
4.2.3.1 Synthesis of Thioacetals
The cyclic thioacetals were prepared employing a modification of the literature procedure
described by Hu and co-workers.14
Thus, to a solution of p-toluenesulfonic acid in MeOH heated
to 55 °C, was added a mixture of 2-mercaptoethyl ether and benzaldehyde in a slow drop-wise
fashion in order to selectively obtain the monomer. Following stirring overnight at 55 °C,
subsequent work-up afforded the cyclic thioacetal O(CH2CH2S)2CHPh 4-1 in 95% isolated yield
(Scheme 4.2.4). 1H NMR data for 4-1 confirmed the cyclic formation with the presence of the
S2CHPh proton resonating as a singlet at 5.80 ppm, the backbone protons resonating at 3.50,
2.90, 2.50 and 2.05 ppm as multiplets and the phenyl protons at 7.22, 6.84 and 6.75 ppm.
Scheme 4.2.4. Synthesis of 4-1 and 4-2
An X-ray crystallographic study confirmed the monomer formation (Figure 4.2.1). The eight
membered ring generated by the dithioacetal formation adopts a boat-chair conformation. This
reaction proved amenable to variation and was adapted to give the species S(CH2CH2S)2CHPh
4-2 and O(C6H4S)2CHPh 4-3 each isolated in greater than 90% yield (Scheme 4.2.5).
Figure 4.2.1. POV-ray depiction of 4-1; C: black, O: red, S: yellow, H: black
65
Scheme 4.2.5. Synthesis of 4-3
4.2.3.2 Synthesis of Ru Complexes
The dithioacetal 4-1 was reacted with Ru(cod)(cot)15
in the presence of 1.1 equiv of PCy3 in
C6H6 at 50 ºC for 2 h. Cooling the solution afforded a red solid in 73% yield. The 31
P{1H} NMR
of the red solid exhibits a single signal at 65.6 ppm and the 1H NMR spectrum is consistent with
the presence of the dithiolate ligand and PCy3 in a 1:1 ratio. In addition, a doublet resonance at
13.68 ppm with P-H coupling constant of 11.3 Hz is consistent with the presence of a ruthenium
alkylidene. This is further supported by the observation of the corresponding 13
C{1H} resonance
at 208.0 ppm. These NMR data is consistent with the formation of 3-4 (Scheme 4.2.6).
Scheme 4.2.6. Synthesis of 3-4 From Dithioacetal 4-1 and Ru(cod)(cot)
Due to the low yielding and tedious preparation of Ru(cod)(cot) a more convenient and higher
yielding Ru synthon was desired. Based on the success of Grubbs and co-workers using a
ruthenium dihydride as a Ru(0) source,13
Ru(PPh3)4(H)216
was reacted with dithioacetal 4-1 in
the presence of PCy3. During heating to 50 ºC for 4 h, the yellow solution became dark red with
the evolution of gas. Subsequent work-up afforded 3-4 in 89% isolated yield. Following a
similar process, the dithioacetals 4-2 and 4-3 were treated in a similar fashion with
Ru(PPh3)4(H)2 in the presence of PCy3 to give 3-1 and 3-6 in yields of 87, and 84%, respectively
(Scheme 4.2.7).
66
Scheme 4.2.7. Synthesis of 3-4, 3-1 and 3-6 From Dithioacetals and Ru(PPh3)4(H)2.
Replacement of PCy3 with SIMes in the reaction mixture with dithioacetal 4-1 lead to the
formation of a ruthenium alkylidene with a resonance at 14.85 ppm in the 1H NMR spectrum
indicating the formation of 3-5. However, the formation of a new hydride resonance at -26.5 ppm
as a doublet of doublets indicated the formation of a byproduct determined to be the C-H
activated SIMesRuH(PPh3)2.17
To prevent the formation of this byproduct, the dithioacetal was
reacted with Ru(PPh3)4(H)2 in the absence of SIMes to form the ruthenium alkylidene. After 4 h,
SIMes was added to the reaction mixture and heated for an addition 30 min. This led to an
increased yield of 86% of 3-5 (Scheme 4.2.8). This methodology was be applied with
dithioacetals 4-2 and 4-3 to give compounds 3-2 and 3-7 in 84 and 88 % yield, respectively.
Scheme 4.2.8. Synthesis of 3-5, 3-2 and 3-7 From Dithioacetals and Ru(PPh3)4(H)2
This synthetic route to Ru-alkylidene is thought to proceed by oxidative addition of the S-C
bonds to Ru followed by -thiolate transfer (Scheme 4.2.9). In these reactions Ru(PPh3)4(H)2
reacts as a Ru(0) source, presumably with loss of H2. This latter supposition is consistent with
the observation of gas evolution upon addition of the dithioacetal to the Ru-synthon. This
reaction is conceptually related to the oxidative addition of dihalomethanes to Ru(0), although
the present strategy affords the simultaneous delivery of a tridentate ligand and an alkylidene to
Ru, affording access to a family of new compounds.13
67
Scheme 4.2.9. Ruthenium Alkylidene Formation From Dithioacetals
These ruthenium alkylidene compounds can act as synthons for the preparation of Grubbs
Catalyst. Reacting 3-5 with 2 equivalents of PhC(O)Cl and 1 equivalent of PCy3 in CH2Cl2
cleanly liberated the dithioester (PhC(O)SCH2CH2)2O and 2nd
Generation Grubbs Catalyst
(Scheme 4.2.10). Thus this synthetic strategy offers a unique and facile, safe and high yielding
route to this catalyst.
Scheme 4.3.10. Synthesis of Grubbs II From 3-5.
4.3 Conclusion
In conclusion, a new method of preparing ruthenium alkylidenes from Ru(0) starting materials
and dithioacetals has been developed. This new method is amiable, high yielding, safe, and uses
inexpensive starting materials. This provides an alternative route to the ruthenium alkylidene
complexes with tridentate, dithiolate ligands presented in Chapter 3 avoiding the use of Grubbs
Catalysts. This method conveniently installs the alkylidene fragment as well as the tridentate
68
dithiolate ligand in one simple step. These complexes can be used as synthons to prepare Grubbs
catalyst.
4.4 Experimental Section
4.4.1 General Considerations
All synthetic manipulations were carried out under an atmosphere of dry, O2-free N2 employing
a VAC Atmospheres glove box and a Schlenk vacuum-line. Hexanes, pentane and
dichloromethane were purified with a Grubbs-type column system manufactured by Innovative
Technology and dispensed into thick-walled glass Schlenk bombs equipped with Young-type
Teflon valve stopcocks. Acetonitrile was dried over CaH2 and distilled. Dichloromethane-d2 was
dried over CaH2 and benzene-d6 was dried over Na metal and vacuum-transferred into a Young
bomb. All solvents were thoroughly degassed after purification (three freeze-pump-thaw cycles).
1H,
13C, and
31P NMR spectra were recorded at 25 °C on Varian 300 and 400 MHz and Bruker
400 MHz spectrometers. Commercially available substrates were obtained from Sigma-Aldrich
and used without further purification. SIMes18
, Ru(cod)(cot)15
, Ru(PPh3)4(H)216
and thioacetal
4-219
were prepared according to literature procedures. Chemical shifts are given relative to
SiMe4 and referenced to the residual solvent signal (1H,
13C) or relative to an external standard
(31
P: 85% H3PO4). In some instances, signal and/or coupling assignment was derived from two-
dimensional NMR experiments. Chemical shifts are reported in ppm and coupling constants as
scalar values in Hz. Combustion analyses were performed in house employing a Perkin-Elmer
CHN Analyzer.
4.4.2 Synthetic Procedures
A general procedure for the synthesis of thioacetals is as follows. A solution of p-toluenesulfonic
acid (5 mg) in 200 mL of MeOH was heated to 55 oC in a 3-neck round bottom flask fitted with a
condenser, addition funnel and septum. A solution of 2-Mercaptoethyl ether (1.065 g, 7.7 mmol)
and benzaldehyde (0.817 g, 7.7 mmol) in 150 mL MeOH was added drop wise from the addition
funnel over 4 hours. The mixture was left at 55oC overnight. The reaction mixture was cooled
and filtered through a plug of alumina to remove the acid. All volatiles were removed and the
white solid was dissolved in 10 mL of toluene. The solution was passed through an alumina plug
to remove any oligomers that may have formed and all volatiles were removed from the filtrate.
69
Thioacetal 4-1 was crystallized from CH2Cl2 and obtained as colorless needles (1.65 g, 95%). X-
ray quality crystals were obtained from a CH2Cl2 solution at -35 o
C. 1H NMR (C6D6): 7.22 (s,
2H, Ph), 6.84 (t, 2H, Ph), 6.75 (t, 1H, Ph), 5.80 (s, 1H, CH), 3.50 (m, 2H, CH2), 2.90 (m, 2H,
CH2), 2.50 (m, 2H, CH2), 2.05 (m, 2H, CH2). 13
C{1H} NMR (C6D6): 143.2 (ipso-Ph), 128.7 (Ph),
128.0 (Ph), 127.8 (Ph), 127.6 (Ph), 72.7 (CH2), 59.2 (S2CHPh), 33.2 (CH2). Analysis calculated
for C11H14OS2: C, 58.37; H, 6.23. Found: C, 57.94; H, 6.38.
Thioacetal 4-3 was crystallized from CH2Cl2 and obtained as colorless needles. (2.26 g, 91%).
1H NMR (C6D6): 7.61 (m, 2H, Ph), 7.01 (m, 2H, Ph), 6.93 (m, 3H, Ph), 6.84 (m, 2H, Ph), 6.64
(m, 4H, Ph), 5.84 (s, 1H, S2CHPh). 13
C{1H} NMR (C6D6): 155.4, 140.4, 132.3, 130.3, 129.9,
128.8, 128.1, 127.8, 124.6, 123.0, 119.1 (all Ph), 61.3 (S2CH). Analysis calculated for
C19H14OS2: C, 70.77; H, 4.38. Found: C, 70.46; H, 4.11.
General procedures for synthesis of Ru alkylidene complexes
Procedure 1: Ru(cod)(cot) (20 mg, 0.063 mmol), PCy3 (20 g, 0.070 mmol) and thioacetal 4-1 (14
g, 0.063 mmol) were mixed and heated in C6H6 at 50oC for 4 h. The solution was cooled to room
temperature and the solvent was removed in vacuo. The resulting solid was washed with hexanes
and recrystallized from CH2Cl2 and pentane to give 3-4 as a red solid.
Procedure 2: To a C6H6 (1 mL) solution of Ru(PPh3)4(H)2 (20 mg, 0.022 mmol) was added PCy3
(9 mg, 0.033 mmol) and the thioacetal 4-1 (6 mg, 0.026 mmol). The mixture was heated at 50oC
in an oil bath for 4 h and the yellow solution turned dark red as bubbles evolved. Pentane was
added to the solution to crash out the red product, 3-4 which was washed with pentane. The
product was recrystallized from CH2Cl2 and pentane.
Procedure 3: To a C6H6 (1 mL) solution of Ru(PPh3)4(H)2 (20 mg, 0.022 mmol) was added
thioacetal 4-1 (6 mg, 0.026 mmol). The mixture was heated at 50oC in an oil bath for 4 h and the
yellow solution turned dark red as bubbles evolved. A solution of SIMes (10 mg, 0.033 mmol) in
C6H6 was added and the reaction was heated for another 30 min. Pentane was added to the
solution to crash out the red product 3-5 which was washed with pentane. The product was
recrystallized from CH2Cl2 and pentane.
70
Synthesis of 3-4: Isolated as a red solid in 73% yield (28 mg, 0.046 mmol) by
procedure 1 and 89% yield (12 mg, 0.020 mmol) by procedure 2 as a red
solid. 1
H NMR (CD2Cl2): 13.68 (d, 3JPH = 11.8 Hz, 1H, Ru=CH), 7.27
(m, 2H, Ph), 7.14 (m, 3H, Ph), 3.84 (m, 2H, CH2), 3.21 (m, 2H, CH2), 2.74
(m, 4H, 2 CH2), 2.11, 1.98, 1.74, 1.61, 1.50, 1.19 (all m, P(C6H11)3.
13C{
1H} NMR (CD2Cl2): 207.95 (Ru=CH), 153.25 (ipso-C, Ph), 128.15 (2 CH, Ph), 125.58
(CH, Ph), 125.39 (2 CH, Ph), 77.96 (2 CH2), 35.91 (d, 1JPC = 24.17 Hz, ipso-C of P(C6H11)3),
32.42 (2 CH2), 29.97 (m-C of P(C6H11)3), 28.31 (d, 2JPC = 10.25 Hz, o-C of P(C6H11)3), 26.93
(p-C of P(C6H11)3). 31
P{1H} NMR (CD2Cl2): 65.60. Analysis calculated for C29H47OPRuS2:
C, 57.30; H, 7.79. Found: C, 56.92; H, 7.55.
Synthesis of 3-1: Isolated in 87% yield (12 mg, 0.019 mmol) following
procedure 2 with thioacetal 4-2 as a dark red solid. X-ray quality crystals
were grown from a CH2Cl2/CH3CN solution. 1H NMR (CD2Cl2): 13.48
(d, 3JPH = 19.3 Hz, 1H, Ru=CH), 7.12 (m, 3H, Ph), 6.93 (m, 2H, Ph), 3.41
(m, 2H, CH2), 3.24 (m, 2H, CH2), 2.45 (m, 2H, CH2), 1.93 (m, 2H, CH2), 2.28, 2.04, 1.73, 1.57,
1.19 (all m, P(C6H11)3. 13
C{1H} NMR (CD2Cl2): 235.16 (d,
2JPC = 14.78 Hz, Ru=CH), 157.02
(ipso-C, Ph), 127.51 (2 CH, Ph), 125.84 (2 CH, Ph),125.40 (CH, Ph), 45.17 (2 CH2), 36.28
(2 CH2), 35.19 (d, 1JPC = 19.78 Hz, ipso-C of P(C6H11)3), 29.98 (m-C of P(C6H11)3), 28.37
(d, 2JPC = 10.25 Hz, o-C of P(C6H11)3), 26.93 (p-C of P(C6H11)3).
31P{
1H} NMR (CD2Cl2): 41.71.
Analysis calculated for C29H47PRuS3: C, 55.83; H, 7.59. Found: C, 55.71; H,7.33.
Synthesis of 3-6: Isolated in 84% (13 mg, 0.018 mmol) yield following
procedure 2 with thioacetal 3 as a red solid. X-ray quality crystals were
grown from a CH2Cl2 solution. 1H NMR (CD2Cl2): 14.69
(d, 3JPH = 14.7 Hz, 1H, Ru=CH), 7.48 (d,
3JHH = 7.6 Hz, 2H, Ph), 7.48
(m, 3H, Ph), 6.90 (m, 4H, Ph), 6.82 (t, 3JHH = 7.3 Hz, 2H, Ph), 6.72
(m, 2H, Ph), 2.15, 2.02, 1.77, 1.55, 1.19 (all m, P(C6H11)3. 13
C{1H} NMR (CD2Cl2): 192.20
(Ru=CH), 154.03 (2 ipso-C, Ph), 152.23 (ipso-C, Ph), 139.08 (2 ipso-C, Ph), 132.14
(2 CH, Ph), 130.14 (2 CH, Ph), 127.94 (2 CH, Ph), 126.31 (CH, Ph), 125.27 (2 CH, Ph),
123.97 (2 CH, Ph), 122.70 (2 CH, Ph), 115.86 (2 CH, Ph), 35.95 (d, 1JPC = 25.05 Hz,
ipso-C of P(C6H11)3), 31.62 (m-C of P(C6H11)3), 30.09 (p-C of P(C6H11)3), 28.19
71
(d, 2JPC = 10.24 Hz, o-C of P(C6H11)3).
31P{
1H} NMR (CD2Cl2): 68.60. Analysis calculated for
C37H47OPRuS2: C, 63.13; H, 6.73. Found: C, 62.52; H, 6.30.
Synthesis of 3-5: Isolated in 86% yield (12 mg, 0.019 mmol) following
procedure 3 as a red solid. 1H NMR (CD2Cl2): 14.85 (s, 1H, Ru=CH),
7.14 (t, 1H, p-H, Ph), 6.97-7.05 (m, 4H, Ph), 6.86 (s, 4H, 4 CH,
Mes), 3.92 (s, 4H, 2 CH2, Im), 3.65 (m, 2H, CH2), 2.82 (m, 2H,
CH2), 2.45 (s, 12 H, 4 CH3, Mes), 2.32-2.41 (m, 4H, 2 CH2), 2.23
(s, 6H, 2 CH3, Mes). 13
C{1H} NMR (CD2Cl2): 209.98 (Ru=CH), 153.68 (ipso-C, Ph), 137.89
(ipso-C, NCN), 137.38 (ipso-C, Mes), 137.31 (ipso-C, Mes), 127.27 (2 CH, Ph), 128.81
(4 CH, Mes), 125.02 (2 CH, Ph), 124.65 (CH, p-C, Ph), 77.56 (2 CH2), 51.84
(2 CH2, Im), 31.59 (2 CH2), 20.59 (2 CH3, Mes), 19.12 (4 CH3, Mes). Analysis
calculated for C32H40N2ORuS2: C, 60.63; H, 6.36; N, 4.42. Found: C, 60.19; H, 5.97; N, 4.30.
Synthesis of 3-2: Isolated in 84% yield (12 mg, 0.018 mmol) following
procedure 3 using thioacetal 2 as a dark brown solid. X-ray quality
crystals were grown from a CH2Cl2/CH3CN solution. 1H NMR
(CD2Cl2): 14.41 (s, 1H, Ru=CH), 7.19 (t, 1H, p-H, Ph), 7.07
(t, 2H, m-H, Ph), 6.88 (d, 2H, o-H, Ph), 6.80 (s, 4H, 4 CH, Mes), 3.99
(s, 4H, 2 CH2, Im), 3.22 (m, 2H, CH2), 3.00 (m, 2H, CH2), 2.52 (s, 12H, 4 CH3, Mes), 2.24
(m, 2H, CH2), 2.19 (s, 6H, 2 CH3, Mes), 1.73 (m, 2H, CH2). 13
C{1H} NMR (CD2Cl2): 211.18
(Ru=CH), 138.08 (ipso-C, Ph), 137.79 (ipso-C, NCN), 137.73 (ipso-C, Mes), 129.18
(4 CH, Mes), 127.25.18 (2 CH, Ph), 127.11 (2 CH, Ph), 125.14 (CH, p-C, Ph), 52.43
(2 CH2), 44.56 (2 CH2, Im), 34.77 (2 CH2), 20.98 (2 CH3, Mes), 19.68 (4 CH3, Mes).
Analysis calculated for C32H40N2RuS3+CH2Cl2 (In crystal lattice) : C, 53.94; H, 5.76; N, 3.81.
Found: C, 55.69; H, 5.96; N, 3.81.
Synthesis of 3-7: Isolated in 88% yield (14 mg, 0.019 mmol) following
procedure 3 using thioacetal 3 as a red solid. 1
H NMR (CD2Cl2): 15.60
(s, 1H, Ru=CH), 7.41 (d, 2H, Ph), 6.91 (m, 8H, Ph, Mes), 6.79 (m, 5H,
Ph), 6.64 (m, 2H, Ph), 4.08 (s, 4H, 2 CH2, Im), 2.51 (s, 12 H, 4 CH3,
Mes), 2.22 (s, 6H, 2 CH3, Mes). 13
C{1H} NMR (CD2Cl2): 209.13
72
(Ru=CH), 153.13 (ipso-C, Ph), 151.45 (ipso-C, Ph) 139.53 (ipso-C, NCN), 137.97
(ipso-C, Mes), 137.17 (ipso-C, Mes), 131.26 (2 CH, Ph), 129.18 (2 CH, Ph), 128.90
(2 CH, Ph), 128.14 (2 CH, Ph), 126.10 (4 CH, Mes), 127.42 (2 CH, Ph), 125.22
(CH, p-C, Ph), 122.90 (CH, Ph), 121.54 (2 CH, Ph), 114.78 (2 CH, Ph), 51.84
(2 CH2, Im), 20.71 (2 CH3, Mes), 18.99 (4 CH3, Mes). Analysis calculated for
C40H40N2ORuS2+CH2Cl2: C, 60.43; H, 5.19; N, 3.44. Found: C, 61.08; H, 5.78; N, 2.88.
Synthesis of 2nd Gen. Grubbs Catalyst from 3-5
To a CH2Cl2 solution of 3-5 (20 mg, 0.032 mmol) was added PCy3 (10 mg, 0.035 mmol) and
PhC(O)Cl (7.7 L, 0.066 mmol). The solution was stirred for 30 min and a color change from
red to purple was observed. Hexanes was added to precipitate the product which was collected
and washed with hexanes to give a purple solid in 93% yield (25 mg, 0.029 mmol). Spectral data
was identical to previous reports of 2nd
Gen. Grubbs.6
4.4.3 X-ray Crystallography
4.4.3.1 X-ray Data Collection and Reduction
Crystals were coated in Paratone-N oil in the glove-box, mounted on a MiTegen Micromount
and placed under an N2 stream, thus maintaining a dry, O2-free environment for each crystal. The
data were collected on a Bruker Apex II diffractometer employing Mo Kα radiation (λ = 0.71073
Å). Data collection strategies were determined using Bruker Apex software and optimized to
provide >99.5% complete data to a 2θ value of at least 55°. The data were collected at 150(±2) K
for all crystals. The frames were integrated with the Bruker SAINT software package using a
narrow-frame algorithm. Data were corrected for absorption effects using the empirical multi-
scan method (SADABS).20
4.4.3.2 X-ray Data Solution and Refinement
Non-hydrogen atomic scattering factors were taken from the literature tabulations.21
The heavy
atom positions were determined using direct methods employing the SHELXTL direct methods
routine. The remaining non-hydrogen atoms were located from successive difference Fourier
map calculations. The refinements were carried out by using full-matrix least squares techniques
on F, minimizing the function (Fo–Fc)2 where the weight is defined as 4Fo2/2 (Fo
2) and Fo
73
and Fc are the observed and calculated structure factor amplitudes, respectively. In the final
cycles of each refinement, all non-hydrogen atoms were assigned anisotropic temperature factors
in the absence of disorder or insufficient data. In the latter cases atoms were treated isotropically.
C-H atom positions were calculated and allowed to ride on the carbon to which they are bonded
assuming a C-H bond length of 0.95 Å. H-atom temperature factors were fixed at 1.20 times the
isotropic temperature factor of the C-atom to which they are bonded. The H-atom contributions
were calculated, but not refined. The locations of the largest peaks in the final difference Fourier
map calculation as well as the magnitude of the residual electron densities in each case were of
no chemical significance.
74
Table 4.4.1. Select Crystallographic Data for 4-1.
(4-1)
Formula C11H14OS2
Formula weight 226.36
Crystal System Monoclinic
Space group P21
a(Å) 5.74600
b(Å) 28.43100
c(Å) 13.44600
α(deg) 90
β(deg) 92.8400
γ(deg) 90
V(Å3) 2193.902
Z 8
d(calc)gcm-3
1.371
R(int) 0.0308
Abs coeff,μ,mm-1
0.449
Data collected 16225
>2(FO2) 14045
Variables 505
R(>2) 0.0474
Rw 0.1192
GOF 1.043
75
Chapter 4 References
1. Schrock, R. R.; Meakin, P., Journal of the American Chemical Society 1974, 96 (16),
5288-5290.
2. Rupprecht, G. A.; Messerle, L. W.; Fellmann, J. D.; Schrock, R. R., Journal of the
American Chemical Society 1980, 102 (20), 6236-6244.
3. Schrock, R. R., Journal of Organometallic Chemistry 1976, 122 (2), 209-225.
4. Nguyen, S. T.; Johnson, L. K.; Grubbs, R. H.; Ziller, J. W., Journal of the American
Chemical Society 1992, 114 (10), 3974-3975.
5. Schwab, P.; France, M. B.; Ziller, J. W.; Grubbs, R. H., Angewandte Chemie
International Edition 1995, 34 (18), 2039-2041.
6. Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H., Organic Letters 1999, 1 (6), 953-956.
7. Trnka, T. M.; Grubbs, R. H., Accounts of Chemical Research 2000, 34 (1), 18-29.
8. Gandelman, M.; Rybtchinski, B.; Ashkenazi, N.; Gauvin, R. M.; Milstein, D., Journal of
the American Chemical Society 2001, 123 (22), 5372-3.
9. Wilhelm, T. E.; Belderrain, T. R.; Brown, S. N.; Grubbs, R. H., Organometallics 1997,
16, 3867-3869.
10. Ferrando, G.; Coalter, I. I. I. J. N.; Gerard, H.; Huang, D.; Eisenstein, O.; Caulton, K. G.,
New Journal of Chemistry 2003, 27 (10), 1451-1462.
11. Dahcheh, F.; Stephan, D. W., Organometallics 2013, 32 (19), 5253-5255.
12. Dorta, R.; Kelly, A., III; Nolan, S. P., Advanced Synthesis & Catalysis 2004, 346, 917-
920.
13. Belderrain, T. R.; Grubbs, R. H., Organometallics 1997, 16, 4001-4003.
14. Xianming, H.; Kellogg, R. M.; Bolhuisb, F. v., J. Chem. Soc. Perkins Trans. 1994, 707-
714.
15. Frosin, K.-M.; Dahlenburg, L., Inorg. Chim. Acta 1990, 167, 83-89.
16. Nolan, S. P.; Belderrain, T. R.; Grubbs, R. H., Organometallics 1997, 16 (25), 5569-
5571.
17. Abdur-Rashid, K.; Fedorkiw, T.; Lough, A. J.; Morris, R. H., Organometallics 2003, 23
(1), 86-94.
18. Kuhn, K. M.; Grubbs, R. H., Organic Letters 2008, 10 (10), 2075-2077.
76
19. Xianming, H.; Kellogg, R. M.; van Bolhuis, F., Journal of the Chemical Society, Perkin
Transactions 1 1994, (6), 707.
20. Apex 2 Software Package;, Bruker AXS Inc. : 2013.
21. D. T. Cromer, J. T. W., Int. Tables X-Ray Crystallography. 1974; Vol. 4.
77
Chapter 5 Lewis Acid Activation of Ruthenium Alkylidene Complexes
5.1 Introduction
5.1.1 Lewis Acid Activation in Catalysis
There are many examples of catalysts requiring activation from a Lewis acid co-catalyst. The
classic example employing this strategy is in the field of olefin polymerization with early
transition metals.1 The addition of a Lewis acid to a group 4 metallocene results in the
abstraction of an anionic ligand from the metal centre creating a metal-alkyl cation which is the
active species in olefin polymerization. The field of Lewis acid co-catalysts has been explored
extensively and a variety of Lewis acids have been used such as MAO2, boranes
3 and
carbocations4-5
to name a few. The choice of Lewis acid co-catalyst can result in a dramatic
effect on the structure of the resulting polymer, influencing the degree of branching, the
molecular weight, the PDI and the overall catalyst activity.6-7
Although Lewis acid activation of
catalysts has been explored extensively in the olefin polymerization field, the use of Lewis acid
co-catalysts has been relatively unexplored in olefin metathesis.
5.1.2 Lewis Acid Assisted Olefin Metathesis
The addition of Lewis acids to specific olefin metathesis reactions has proved to increase yields
when the substrates have a reactive or Lewis basic functional group. For example, the yield of
the cross metathesis product of various substrates and acrylonitrile is increased as much as
two-fold when Ti(OiPr)4 is added to the reaction catalyzed by Grubbs Catalyst.
8-9 Olefin
metathesis of acrylonitrile is difficult and often low yielding due to the nitrile functionality
poisoning the catalyst. When a Lewis acid is added to the reaction mixture, it quenches the
Lewis basicity of the nitrile group. This prevents the nitrile from binding to the ruthenium centre
and shutting down catalysis resulting in higher yields of metathesis product. With a similar
approach, the yield of the ring closed product of diallylamines can be dramatically increased by
the addition of Ti(OiPr)4
to the metathesis reaction mixture.
10 While useful for increasing yields
of specific reactions, this use of Lewis acids in olefin metathesis reactions is fundamentally
different from the direct activation of catalysts by Lewis acids.
78
5.1.3 Acid Activation of Olefin Metathesis Catalysts
There are a few examples of activation of olefin metathesis catalyst by Bronsted or Lewis acids
in the literature. The mechanism of activation can be by protonation of a ligand, abstraction of a
ligand via coordination to the Lewis acid or via halide abstraction. Similar to olefin
polymerization catalysts, the acid activation of olefin metathesis catalysts creates a vacant
coordination site. This results in a more Lewis acidic, coordinatively unsaturated metal centre
with a site for substrate to coordinate to the catalyst.
The activation of ruthenium alkylidene complexes bearing monoanionic, bidentate ligands with
Lewis or Bronsted acids for catalytic olefin metathesis has been explored in some detail
(Figure 5.1.1).11-15
In 2013, Pietraszuk reported a ruthenium alkylidene complex with a chelating
aryloxide ligand attached to the alkylidine.15
This complex is inactive for olefin metathesis on its
own but upon the addition of HCl the catalyst becomes active for ring opening metathesis
polymerization and cross metathesis. Activation is believed to occur by protonation of the
aryloxy ligand and coordination of the chloride to the metal centre to generate a
Hoveyda-Grubbs type species which is active for olefin metathesis. This catalyst can also be
activated by the Lewis acid CuCl, although the resulting catalyst is less active than when
activated with HCl. Hahn and co-workers reported a bispicolinate alkylidene complex which is
inactive for olefin metathesis.11
This catalyst also becomes activate for ring closing metathesis
upon the addition of HCl and in 2010 Grubbs and co-workers demonstrated its activity for cross
metathesis and ring opening metathesis polymerization.14
They also investigated the mechanism
of activation which was determined to be protonation of the picolinate ligands releasing two
equivalents of picolinic acid and generating a 14-electron ruthenium alkylidene species which is
active for olefin metathesis. In 2006, Verpoort et al. reported a Schiff base aryloxy ruthenium
alkylidene complex.12
Similar to the examples above, this catalyst is inactive for olefin
metathesis at room temperature but upon the addition of HCl or a Lewis acid such as CuCl,
AlCl3, silane, or BF3 the catalyst becomes active for ring opening metathesis polymerization.
Activation is believed to occur through protonation or coordination of the imine to the Lewis
acid.
79
Figure 5.1.1. Latent Olefin Metathesis Catalysts which can be Activated by Bronsted or
Lewis Acids
Grela and co-workers have published an example of acid activation of the catalyst periphery and
not on the metal centre resulting in an electronic influence.16
The protonation of an amine
functionality on the phenyl ring of a Hoveyda-Grubbs type catalyst creates an electronic effect
that results in greater lability of the ether ligand creating a more active catalyst for olefin
metathesis. They also describe a related compound that is activated by a Lewis acid following
the same principles (Scheme 5.1.1). The abstraction of a hydroxyl group from a quaternary
carbon attached to the phenyl ring of a Hoveyda-Grubbs type catalyst creates a tertiary
carbocation. This cationic charge results in an electronic effect labilizing the ether ligand and as
a result initiating catalysis more rapidly.
Scheme 5.1.1. Lewis Acid Catalyst Activation by Electronic Influence
A similar example where a Lewis acid creates an electronic effect labilizing a ligand was
published by Butenschön and co-workers (Figure 5.1.2).17
The coordination of chromium to the
phenyl ring of Hoveyda-Grubbs catalyst results in increased catalyst activity for ring closing
metathesis, ene-yne metathesis and cross metathesis reactions. Although in this example, the
80
Lewis acid is incorporated in the catalyst structure during the synthesis of the ruthenium
alkylidene and not by in situ addition, it still demonstrates activation of a olefin metathesis
catalyst by a Lewis acid.
Figure 5.1.2. Highly Active Bimetallic Olefin Metathesis Catalyst
Grubbs and co-workers have published an example of an olefin metathesis catalyst which can be
activated by a Lewis acid (Scheme 5.1.2).18
The pre-catalyst has an amino-carboxylate ligand
and upon the addition of CuCl the ligand coordinates to the copper metal centre creating a
bimetallic species bridged through the carboxylate. In order for this to happen the amine
disconnects from the ruthenium centre creating a four-coordinate ruthenium species with a
vacant site which can enter a catalytic cycle.
Scheme 5.1.2. Catalyst Activation by CuCl Ligand Abstraction
More recently, Cazin and co-workers reported a four-coordinate cationic olefin metathesis
catalyst.19
This catalyst is formed as a result of halide abstraction from a five coordinate Grubbs
type complex (Scheme 5.1.3). Both the parent neutral species and the cationic species are active
for ring closing metathesis and cross metathesis at 140 oC. Interestingly, even though the cationic
81
species is more active for olefin metathesis than the parent neutral complex, it is slower
initiating.
Scheme 5.1.3. Synthesis of a Four-Coordinate Olefin Metathesis Catalyst by Halide
Abstraction
In 2013, Wagener and co-workers published results demonstrating the effects of boron based
Lewis acids on olefin metathesis and isomerization tendency.20
They found that for Grubbs 1 and
Grubbs 2 Catalysts, the addition of triphenylborane, pinacol phenyl borane or boric acid resulted
in an increased yield of the cross metathesis product of 1-hexene. However, the addition of these
boranes to Hoveyda-Grubbs Catalysts resulted in a decreased yield of the cross metathesis
product. They speculate that the Lewis acid acts as a phosphine sponge for the Grubbs type
catalysts whereas with the Hoveyda-Grubbs type catalysts it causes catalyst decomposition.
5.2 Results and Discussion
5.2.1 Reactivity with One Equivalent of BCl3
In the mechanism for a Grubbs type olefin metathesis reaction, the active species is a four
coordinate Ru alkylidene complex. In an effort to increase the activity of the previously reported
five coordinate, Ru alkylidene species bearing tridentate ligands, an investigation into the
reactivity of these species with Lewis acids was pursued. The motivation was based on previous
reports of Lewis acid activation and the potential for working against the chelate effect in
creating a four coordinate complex.
As a starting point, BCl3 was used as the Lewis acid due to its cost and commercial availability.
Thus, when a 1 M BCl3 solution in hexanes was added to a CD2Cl2 solution of 3-1, a color
change from red to green immediately occurred as 5-1 was formed (Scheme 5.2.1). A downfield
shift of the alkylidene proton signal is observed in the 1H NMR spectrum from 13.48 to
82
17.96 ppm. Ligand backbone signals which appear as four multiplets in 3-1 now display eight
multiplets suggesting loss of symmetry. The signal for the alkylidene carbon also shifts
downfield from 235.2 to 275.3 ppm in the 13
C NMR. The 31
P{1H} NMR has a new resonance at
34.9 ppm with complete disappearance of the signal from 3-1. In the 11
B NMR a resonance at 9.9
ppm as a sharp singlet is observed suggesting four-coordinate boron.
Scheme 5.2.1. Synthesis of 5-1
Similar chemistry was observed in the reaction of 3-2 with BCl3, and similar NMR changes were
seen. However, the presence of two isomers was observed based on spectroscopic data. The
isolated green solid displays two downfield shifted resonances for the alkylidene protons in the
1H NMR at 17.20 and 16.30 ppm. There are two sharp singlets at 12.0 and 9.9 ppm in the
11B NMR suggesting the presence of two four-coordinate boron environments. X-ray quality
crystals of one of the isomers of 5-2 were grown and an X-ray crystallographic study confirmed
its formulation as (SIMes)Ru(CHPh)Cl[S(CH2CH2S)2BCl2] (Figure. 5.2.1). The dithiolates
which are trans in 3-2 are now cis in 5-2 and bridge between the Ru and B centers. The Ru-S
thiolate bond lengths are 2.3557(5) and 2.5027(5) Å with a S-Ru-S angle of 78.21(2)º. The B-S
bond lengths are 1.950(2) and 1.960(2) Å with as S-B-S angle of 103.28(11)º. A chloride from
the BCl3 has been transferred to Ru making it six coordinate with a geometry best described as
distorted octahedral. The Ru-Cl bond length is 2.4350(5) Å and the two Cl remaining on the B
are 1.844(3) and 1.850(2) Å from B. The tridentate ligand has flipped and the thioether which
was trans to the NHC in 3-2 is now trans to the alkylidene and has a Ru-S bond distance of
2.4919(5) Å. The Ru-C(alkylidene) and Ru-C(NHC) distances are 1.909(2) and 2.081(2) Å
respectively. All other angles around Ru range from 81.42(2)º to 94.54(2)º giving the distorted
octahedral geometry. The reason for this ligand rearrangement can be explained by the trans
effect. The BCl2 fragment which bridges the two thiolates forces them to be cis and the transfer
83
of a chloride to Ru creates a six coordinate species. In a distorted octahedral geometry there must
be a ligand trans to the strongly donating alkylidene ligand. Although similar, the thioether has a
slightly weaker trans effect than the boron-ruthenium bridged thiolate in 5-2. The two carbene
ligands (NHC and alkylidene) also have similar trans effects however the alkylidene is slightly
stronger. This difference in trans effects results in the weaker thioether donor being trans to the
stronger alkylidene donor as observed in the molecular structure. However, since the trans
effects are so similar, both isomers with and without ligand rearrangement are formed.
(Scheme 5.2.2).
Scheme 5.2.2. Synthesis 5-2
Figure 5.2.1. POV-ray depiction of 5-2a; B: pink, C: black, N: blue-green, S: yellow, Cl:
green, Ru: teal
84
Analogous to the reaction of 3-2 with BCl3, an isomeric mixture was obtained from the reaction
of 3-3 with BCl3 (Scheme 5.2.3). The presence of two phosphine NMR handles provides more
evidence to support the identity of the isomeric structures. The 31
P{1H} NMR shows two sets of
two doublets (Figure 5.2.2a). One set occurs at 81.5 and 26.9 ppm with a coupling constant of
226 Hz suggesting trans-phosphines. The other set occurs at 75.8 and 29.6 ppm with a coupling
constant of 26 Hz which is indicative of cis-phosphines. The alkylidene region of the 1H NMR
spectrum also displays two signals (Figure 5.2.2b). One signal is at 18.2 ppm and appears as a
doublet with a coupling constant of 6.8 Hz and the other is at 17.4 ppm and is a doublet of
doublets with coupling constants of 17.4 and 10.6 Hz. The 11
B NMR shows a sharp singlet at
10.7 ppm. This data suggests the formation of two isomers in a ratio of 9:1 with the formulation
(PCy3)RuCl(CHPh)[Cl2B(SCH2CH2)2PPh]. 5-3a is the product of the analogous rearrangement
seen for 5-1 where the tridentate ligand has rearranged to have the central phosphine donor trans
to the alkylidene. In the second isomer, 5-3b, the ligand has not rearranged on the ruthenium
centre and the central phosphine donor remains trans to the PCy3.
85
(a)
(b)
Figure 5.2.2. (a) 31
P{1H} NMR spectrum and (b) alkylidene region of
1H NMR spectrum of
5-3 in CD2Cl2
86
In 5-3 the central PPh is a much stronger donor than the central thioether in 5-1. The stronger
donating ability and trans effect of the central phosphine results in an isomeric mixture in which
one isomer has the PPh trans to the strongly donating alkylidene ligand and the other has the PPh
trans to the PCy3. Attempting to force the reaction towards one of the isomers with heating or
cooling was unsuccessful.
Scheme 5.2.3. Synthesis of 5-3a and 5-3b
3-4 and 3-5 reacted with BCl3 in an analogous fashion (Scheme 5.2.4). The red CH2Cl2 solution
of 3-4 turned green with the addition of BCl3 to give 5-4. The doublet for the alkylidene proton
shifts downfield from 13.68 in 3-4 to 18.93 in 5-4. There is an obvious loss in symmetry based
on the eight multiplets present in the alkyl region (Figure 5.2.3). The alkylidene carbon resonates
at 277.4 ppm in the 13
C{1H} NMR spectrum and the PCy3 signal in the
31P{
1H} NMR spectrum
has shifted upfield to 35.5 ppm. Four coordinate boron can be observed in the 11
B NMR
spectrum at 11.1 ppm as a sharp singlet.
87
(a)
(b)
Figure 5.2.3. (a) 1H NMR Spectrum of 5-4. (b) Expansion of Ligand Backbone Region of
1H NMR Spectrum of 5-4
Based on these data and a X-ray crystallographic study 5-4 was determined to be
(PCy3)Ru(CHPh)Cl[O(CH2CH2S)2BCl2] (Figure 5.2.4). 5-4 adopts a disordered octahedral
geometry about Ru. A chloride has been transferred from BCl3 to Ru and has a Ru-Cl distance of
2.3982(4) Å. The remaining BCl2 fragment (B-Cl distances 1.8304(18) and 1.8367(17) Å)
bridges the two thiolates arising to B-S distances of 1.8228(14) and 1.9472(17) Å. The S-B-S
88
angle is 104.04(8)º. The Ru-S distances for the axial and equatorial S are 2.4622(4) and
2.3702(4) Å respectively and produce a S-Ru-S angle of 78.889(13)º. The central ether of the
tridentate ligand is trans to the alkylidene with a Ru-O bond distance of 2.3554(9) Å. The Ru-C
and Ru-P distances are 1.8679(13) and 2.3666(4) Å, respectively. All remaining angles around
Ru range from 75.90(3)º to 98.82(4)º which are consistent with the distorted octahedral
geometry.
Scheme 5.2.4. Synthesis of 5-4 and 5-5
Figure 5.2.4. POV-ray depiction of 5-4; B: pink, C: black, O: red, P: orange, S: yellow, Cl:
green, Ru: teal
The NMR data for the reaction of 3-5 with one equivalent of BCl3 displays the characteristic
shifts seen for the identical reaction of 3-1 through 3-4 leading to 5-5 in 92% yield. The signal
89
attributed to the proton of the alkylidene shifts downfield to 17.68 ppm. The 13
C spectrum has a
resonance at 308.9 ppm from the alkylidene carbon and a sharp singlet is observed in the
11B NMR at 11.5 ppm. An X-ray crystallographic study confirmed the formulation of 5-5 as
(SIMes)Ru(CHPh)Cl[O(CH2CH2S)2BCl2] (Figure 5.2.5). Similar to the crystallographically
studied isomer of 5-2, this complex adopts a geometry in which the NHC ligand is trans to S,
alkylidene is trans to the ether O atom and the remaining S atom is trans to a Cl which was
transferred from BCl3 to Ru. The trans C(NHC)-Ru-S, CCHPh-Ru-O, S-Ru-Cl angles in 5-5 of
175.64(9)º, 161.79(9)º and 167.22(3)º are consistent with a distorted octahedral geometry. The
Ru-C(NHC), Ru-CCHPh, Ru-O and the two Ru-S distances in 5-5 were determined to be 2.056(3),
1.864(3), 2.300(2), 2.3444(7) and 2.4105(7) Å, respectively, all slightly longer than those seen in
3-5. Bridging the two S atoms is a BCl2 fragment with S-B distances of 1.951(3) and 1.929(3) Å
and B-Cl bond lengths of 1.831(3) and 1.845(3) Å. The S-Ru-S and S-B-S angles were found to
be 79.07(2)º and 104.62(15)º, respectively.
Figure 5.2.5. POV-ray depiction of 5-5; B: pink, C: black, N: blue-green O: red, S: yellow,
Cl: green, Ru: teal
90
Compounds 3-6 and 3-7 displayed identical reactivity to that previously discussed giving only
one isomer (Scheme 5.2.5). Compound 3-6 reacted to give (PCy3)RuCl(CHPh)[Cl2B(SC6H4)2O],
5-6 which displays a downfield shifted alkylidene signal in the 1H NMR at 18.9 ppm
(d, 3JPH = 11.6 Hz) and an upfield phosphorus shift at 36.5 ppm. 3-7 gives the analogous product
(SIMes)RuCl(CHPh)[Cl2B(SC6H4)2O], 5-7 which is characterized by its downfield alkylidene
signal at 17.75 ppm in the 1H NMR. The characteristic
11B shift can be observed for 5-6 and 5-7
at 12.1 and 14.7 ppm, respectively.
Scheme 5.2.5. Synthesis of 5-6 and 5-7
Complexes 3-8 and 3-9 reacted with one equivalent of BCl3 to give 5-8 and 5-9, respectively
(Scheme 5.2.6). These complexes proved difficult to isolate cleanly but the evidence for their
formation could be observed in situ via NMR spectroscopy. In the 1H NMR, the characteristic
downfield shift of the alkylidene can be seen for 5-8 and 5-9 to 20.13 and 16.83 ppm,
respectively. The PCy3 signal in the 31
P NMR spectra shifts from 64.76 ppm in 3-8 to 28.8 ppm
in 5-8. Four coordinate boron can be seen at 23.4 and 18.2 for 5-8 and 5-9 respectively in the
11B NMR. Based on these data 5-8 and 5-9 are formulated as
(PCy3)Ru(CHPh)Cl[O(CH2CH2O)2BCl2] and (SIMes)Ru(CHPh)Cl[O(CH2CH2O)2BCl2]
respectively.
Scheme 5.2.6. Synthesis of 5-8 and 5-9
91
5.2.2 Reactivity with Two Equivalents of BCl3
The addition of one equivalent of BCl3 to the Ru alkylidene complexes 3-1 through 3-9 results in
the formation of a 6-coordinate complex. Although this reaction is interesting, the formation of a
6-coordinate species from a catalytic point of view is undesirable. As discussed in Section 1.2.3
the active species in the mechanism of Grubbs Catalyst is a four-coordinate species. There have
been reports of 5-coordinate complexes being catalytically active, but it is very unlikely that a
coordinatively saturated Ru alkylidene would be active for olefin metathesis. In an effort to form
a coordinatively unsaturated species, the effect of an additional equivalent of BCl3 on 5-1
through 5-9 was investigated.
Although the addition of a second equivalent of BCl3 to 5-1 and 5-2 showed no reaction, an
obvious reaction occurred with the addition of BCl3 to 5-4 and 5-5 (Scheme 5.3.7). When a
second equivalent of BCl3 was added to a CH2Cl2 solution of 5-4 the reaction mixture became
darker green. Preliminary 11
B NMR data suggested the formation of the BCl4- anion presumably
via halide abstraction and generation of salt 5-10. In the 1H NMR a broadening of the peaks
occurs. In an attempt to isolate this salt, a small excess of CH3CN was added which resulted in
an immediate color change to red as 5-11 formed. Ultimately a red solid was isolated in 87%
yield. The resonance attributed to the alkylidene proton in the 1H NMR shifts from 18.93 ppm
for 5-4 to 18.66 ppm for 5-11. A small shift in the 31
P NMR is observed with a new signal at
36.14 ppm. There are two peaks in the 11
B NMR at 11.8 and 7.0 ppm with the later attributed to
the BCl4- anion. An X-ray crystallographic study confirmed the structure of 5-11 as
[(PCy3)Ru(CHPh)CH3CN(O(CH2CH2S)2BCl2)][BCl4] (Figure 5.2.6). The geometry remains a
distorted octahedral about Ru, similar to 5-4. The Ru-P bond lengthens slightly from 2.3666(4)
in 5-4 to 2.4080(9) Å in 5-11. The Ru-S bonds shorten from 2.4622(4) and 2.3702(4) Å to
2.4405(10) and 2.3596(9) Å with a S-Ru-S angle of 79.55(3)º. The Ru-O and Ru-C bonds are
2.292(2) and 1.874(3) Å respectively. The Ru-N bond length is 2.053(3) Å and the N-Ru-C and
N-Ru-O angles are 98.18(14) and 89.66(10)º, respectively. The B-S bond lengths are 1.967(5)
and 1.950(4) Å and the S-B-S angle is 103.3(2)º. The B-Cl bond length of the coordinated borate
are 1.841(4) and 1.811(5) Å with a Cl-B-Cl angle of 112.0(2)º.
92
Scheme 5.2.7. Synthesis of 5-10 - 5-13
Figure 5.2.6. POV-ray depiction of 5-11; B: pink, C: black, N: blue-green, O: red, P:
orange, S: yellow, Cl: green, Ru: teal
The addition of a second equivalent of BCl3 to 5-5 also resulted in the green solution darkening
as 5-12 formed. Assuming salt formation by halide abstraction, an excess of CH3CN was added
to trap it. The solution immediately turned red and the red compound, 5-13 was isolated. The
11B NMR shows the presence of a BCl4
- anion with a resonance at 6.92 ppm with the coordinated
93
borate giving a signal at 11.39 ppm. The proton resonance from the alkylidene shifts from 17.68
in 5-5 to 17.26 ppm in 5-13. The remaining 1H NMR data were consistent with the NHC,
dithiolate and CH3CN ligands. An X-ray crystallographic study confirmed the formation of the
salt [(SIMes)Ru(CHPh)CH3CN(O(CH2CH2S)2BCl2)][BCl4] 5-13 (Figure 5.2.7). The cation of
5-13 adopts a pseudo-octahedral geometry similar to that of 5-5. The Ru-C(NHC) bond length has
lengthened from 2.056(3) Å in 5-5 to 2.099(2) Å. The Ru-C(CHPh) distance has also slightly
lengthened from 1.864(3) to 1.872(2) Å. The Ru-O, and Ru-S bonds have remained very similar
in length with bonding distances of 2.2960(15), 2.3607(5) and 2.4475(5) Å respectively. The
new Ru-N bond is 2.0407(18) Å which is similar to 5-11. The trans C(NHC)-Ru-S, C(CHPh)-Ru-O
and S-Ru-N angles are 167.50(6), 166.21(7) and 169.81(5)º respectively, displaying the pseudo-
octahedral geometry. The B-S bond distances are 1.948(3) and 1.943(3) Å and form a S-B-S
angle of 105.20(11)º. The B-Cl lengths of the coordinated borate are 1.828(3) and 1.854(3) Å
with a Cl-B-Cl angle of 111.42(13)º.
Figure 5.2.7. POV-ray depiction of 5-13; B: pink, C: black, N: blue-green, O: red, S:
yellow, Cl: green, Ru: teal. Anion omitted for clarity
94
Complexes 5-6 - 5-9 display analogous reactivity with a second equivalent of BCl3 to give
complexes 5-14 - 5-17 (Figure 5.2.8). The formation of the BCl4- anion can be observed in the
11B NMR spectrum and a small shift and broadening of the signals in the
1H and
31P{
1H} NMR
spectrums occurs. While the formation of the analogous 5-coordinate cationic ruthenium species
is observed via halide abstraction, attempts to trap these species with a Lewis base failed.
Figure 5.2.8. Complexes 5-14 - 5-17
5.2.3 Reactivity with Bronsted Acid
Since Lewis acids react with these Ru alkylidene complexes, the reactivity with Bronsted acid
was investigated. Potentially, the acid could protonate a coordinated thiolate ligand causing it to
be more labile and possibly activate the catalyst. In order to prevent coordinatively saturating the
metal centre, a non-coordinating anion must be used which would create a formally cationic Ru
species. This motivated the use of [Et2O•H][BF4] which when combined with 3-4 in CH2Cl2
resulted in a lightening of the brown solution as 5-18 formed. Preliminary 1H NMR data shows
the loss of the alkylidene signal and the appearance of a new singlet at 4.20 ppm that integrates
to two protons (Figure 5.2.9). All other peaks can be assigned to the PCy3, the tridentate ligand
backbone, and the phenyl group. The presence of the BF4 anion can be observed in the 11
B and
19F NMR spectra of the product with resonance at -1.2 and -151.8 ppm respectively. A new
resonance in the 31
P{1H} NMR is observed at 53.2 ppm, which is shifted upfield from the
starting material 3-4 (65.6 ppm). Based on this data, 5-18 is formulated to be
[(PCy3)Ru(CH2Ph)(SCH2CH2)2O][BF4] where protonation of the alkylidene carbon has occurred
with the formation of a formally cationic Ru(IV) species (Scheme 5.2.8). To test this conclusion,
PtBu3 was added to 5-18 which resulted in the precipitation of a white solid which was identified
as [HPtBu3][BF4]. All the NMR data of the resulting compound matched that of 3-4. This type of
95
reactivity has been seen for earlier transition metal alkylidene complexes but is rare for Ru
alkylidenes.21-22
Reacting 3-5 with [Et2O•H][BF4] resulted in the observation of the analogous
compound. However, it quickly decomposed as the formation of protonated SIMes is observed.
Figure 5.2.9. 1H NMR spectra of 3-4 (Top) and 5-18 (Bottom)
Scheme 5.2.8. Synthesis of 5-18
96
5.2.4 Reversibility of Lewis Acid Reactivity
Due to the reversibility of the Bronsted acid reactivity, the reversibility of the Lewis acid
reactivity was probed. The addition of PtBu3 to 5-4 in CH2Cl2 resulted in the green solution
becoming red. A white precipitate formed and preliminary 31
P and 11
B NMR data showed the
presence of the tBu3PBCl3 adduct. The
31P{
1H} NMR displays a singlet at 65.60 ppm suggesting
the recovery of 3-4 (Scheme 5.2.9). The 1H NMR spectrum confirms the formation of 3-4 with
the reappearance of the alkylidene resonance at 13.68 ppm and all other peaks corresponding to
3-4. This reversibility where PtBu3 abstracts the BCl3 moiety from the complex resulting in the
reformation of the parent Ru alkylidene complex is observed for complexes 5-1 through 5-9.
Compounds 5-10 and 5-12 also display reversible BCl3 reactivity. Addition of 1 equivalent of
PtBu3 to these complexes resulted in the recovery of 5-4 and 5-5, respectively with the
elimination of the tBu3PBCl3 adduct.
Scheme 5.2.9. Reversibility of Lewis Acid Reactivity
5.3 Conclusion
The Ru alkylidene complexes with tridentate, dianionic ligands were shown to react sequentially
with 2 equivalents of BCl3. The first equivalent results in a chloride being transferred to the
metal centre and the remaining BCl2 fragment bridges the two anionic donors. Due to the trans
effect this causes a rearrangement of the tridentate ligand on the metal centre. However, in some
cases due to similarities in donor strength two isomers are formed. One isomer with the
rearranged ligand and the other isomer has the original ligand binding mode. The second
equivalent of BCl3 abstracts the chloride from the metal centre resulting in a cationic ruthenium
species. In some cases this cation can be trapped with the addition of a small donor such as
CH3CN. This step-wise reactivity is reversed in a step-wise manner with the sequential addition
97
of 2 equivalents of PtBu3 with the elimination of the Lewis acid-base adduct
tBu3PBCl3. By
contrast, these Ru complexes react with Bronsted acids via protonation of the alkylidene carbon.
This creates a cationic Ru benzyl species. This reactivity is also reversible and with the addition
of PtBu3 the benzyl carbon is deprotonated resulting in the formation of the original starting
material.
5.4 Experimental Section
5.4.1 General Considerations
All synthetic manipulations were carried out under an atmosphere of dry, O2-free N2 employing
a VAC Atmospheres glove box and a Schlenk vacuum-line. Hexanes, pentane and
dichloromethane were purified with a Grubbs-type column system manufactured by Innovative
Technology and dispensed into thick-walled glass Schlenk bombs equipped with Young-type
Teflon valve stopcocks. Acetonitrile was dried over CaH2 and distilled. Dichloromethane-d2 was
dried over CaH2 and benzene-d6 was dried over Na metal and vacuum-transferred into a Young
bomb. All solvents were thoroughly degassed after purification (three freeze-pump-thaw cycles).
1H,
13C, and
31P NMR spectra were recorded at 25 °C on Varian 300 and 400 MHz and Bruker
400 MHz spectrometers. Commercially available substrates were obtained from Sigma-Aldrich
and used without further purification. Chemical shifts are given relative to SiMe4 and referenced
to the residual solvent signal (1H,
13C) or relative to an external standard (
31P: 85% H3PO4). In
some instances, signal and/or coupling assignment was derived from two-dimensional NMR
experiments. Chemical shifts are reported in ppm and coupling constants as scalar values in Hz.
Combustion analyses were performed in house employing a Perkin-Elmer CHN Analyzer.
5.4.2 Synthetic Procedures
Synthesis of 5-1: To a CH2Cl2 solution (1 mL) of 3-1 (0.020 g, 0.032
mmol) was added BCl3 in hexanes (1 M, 32 µL, 0.032 mmol). The red
solution immediately turned green. All volatiles were removed, and the
resulting dark solid was washed with CH3CN (2 mL) and dried to yield a
green solid. (0.022 g, 93%). 1H NMR (CD2Cl2): 17.96 (d,
3JPH = 15.1 Hz,
1H, Ru=CH), 8.34 (d, 3JHH = 8.81 Hz, 2H, o-H of C6H5), 7.65 (t,
3JHH =
7.73 Hz, 1H, p-H of C6H5), 7.40 (t, 3JHH = 7.83Hz, 2H, m-H of C6H5), 3.66, 3.13, 2.95 (all m,
1H, CH2), 2.55 (m, 5H, 5 CH2), 2.05, 1.88, 1.75-1.45, and 1.18 (all m, P(C6H11)3). 11
B NMR
98
(CD2Cl2): 9.94 (s). 13
C{1H} NMR (CD2Cl2): 275.25 (Ru=CH), 154.83 (ipso-C, Ph), 132.15 (CH,
Ph), 131.84 (2 CH, Ph), 128.77 (2 CH, Ph), 39.32, 38.98 (2 CH2), 36.73 (d, 1JPC = 19.32
Hz, ipso-C of P(C6H11)3), 30.24, 30.03 (2 CH2), 27.79 (m-C of P(C6H11)3), 27.55 (o-C of
P(C6H11)3), 26.56 (p-C of P(C6H11)3). 31
P{1H} NMR (CD2Cl2): 34.92. Analysis calculated for
C29H47BCl3PRuS3: C, 47.00; H, 6.39. Found: C, 46.89 H, 6.46.
Synthesis of 5-2: To a CH2Cl2 solution (1 mL) of
3-2 (0.020 g, 0.031 mmol) was added BCl3 in
hexanes (1 M, 31 µL, 0.031 mmol). The brown
solution immediately turned dark green. All
volatiles were removed, and the resulting dark
solid was washed with CH3CN (2 mL) and dried
to yield a blue-green solid. (0.022 g, 93%). X-Ray quality crystals were grown from a
CH2Cl2/CH3CN solution.1H NMR (CD2Cl2): 17.20 (Ru=CH, 5-2a), 16.30 (Ru=CH, 5-2b), 7.61
(m, 2H, o-H of C6H5) 7.43 (m, 1H, p-H, Ph), 7.34 (m, 2H, m-H of C6H5), 7.12 (s, 2H, 2 CH,
Mes), 7.04 (s, 1H, CH, Mes) 6.58 (s, 1H, CH, Mes), 3.90 (m, 2H, CH2, Im), 3.77 (m, 2H, CH2,
Im), 3.51, 3.31, 3.20 (all m, 1H, CH2), 2.97 (m, 2H, CH2) 2.65, 2.60, 2.49, 2.40, 2.33, 2.28 (all s,
3 H, 6 CH3, Mes), 2.06 (m, 1H, CH2), 1,85 (m, 2H, CH2). 13
C{1H} NMR (CD2Cl2): 152.7,
150.4, 138.7, 138.6, 137.7,137.3, 131.7, 131.2, 129.6,129.5, 128.3 (all Ph, Mes), 65.6 (2 CH2,
Im), 52.1, 51.9, 42.2, 40.5, 39.4, 35.4, 31.5, 31.2, 28.5, 26.8, 25.5 (all CH2), 20.8, 20.6, 19.3,
19.0, 18.8, 18.7 (CH3, Mes). 11
B NMR (CD2Cl2): 11.95, 9.89. Analysis calculated for
C32H40BCl3N2RuS3: C, 50.10; H, 5.26; N, 3.65. Found: C, 49.46 H, 5.14; N, 3.39.
Synthesis of isomeric 5-3: To a CH2Cl2
solution (1 mL) of 3-3 (0.020 g, 0.029 mmol)
was added BCl3 in hexanes (1 M, 29 µL,
0.029 mmol). The brown solution
immediately turned dark green. All volatiles
were removed, and the resulting dark solid
was washed with CH3CN (2 mL) and dried to
yield a dark green solid. (0.022 g, 93%). The compound exists as a mixture of isomers (12a,
12b). With the addition of one more equivalent of BCl3 the compound becomes an active olefin
metathesis catalyst. 1H NMR (CD2Cl2): 18.06 (d,
3JPH = 6.78 Hz, Ru=CH, 5-5b), 17.32 (dd,
3JPH
99
= 17.4 Hz, 3JPH = 10.6 Hz, Ru=CH, 5-5a), 7.80 (m, Ph), 7.76 (m, Ph), 7.64 (m, Ph), 7.59 (m, Ph),
7.55 (m, Ph), 7.43 (m, Ph), 7.35 (m, Ph), 7.26 (m, Ph), 7.17 (m, Ph), 7.11 (m, Ph), 6.99 (m, Ph),
4.63 (m, CH2, 5-3a), 4.39 (m, CH2, 5-3a), 4.19 (m, CH2, 5-3a), 4.05 (m, CH2, 5-3a), 3.61 (m,
CH2, 5-3b), 3.17 (m, CH2, 5-3b), 2.89 (m, CH2, 5-3b), 2.82 (m, CH2, 5-3b), 2.49 (m, PCy3), 2.16
(m, PCy3), 1.87 (m, PCy3), 1.68 (m, PCy3), 1.32 (m, PCy3). 13
C{1H} NMR (CD2Cl2): 153.3 (Ph),
151.1 (Ph), 137.3 (Ph), 134.9 (Ph), 133.3 (Ph), 131.9 (Ph), 131.5 (Ph), 130.6 (Ph), 130.2 (Ph),
129.7 (Ph), 129.2 (Ph), 128.8 (Ph), 128.6 (Ph), 128.4 (Ph), 128.1 (Ph), 128.0 (Ph), 127.9 (Ph),
127.6 (Ph), 127.1 (Ph), 126.4 (Ph), 37.6 (CH2), 35.8 (CH2), 35.7 (CH2), 34.1 (CH2), 31.3 (d, 1JPC
= 29.9 Hz, PCy3), 30.9 (CH2), 30.6 (CH2), 30.1 (CH2), 29.7 (CH2), 29.5 (CH2), 27.7 (d, 3JPP = 4.2
Hz, PCy3), 27.2 (d, 2JPP = 10.5 Hz, PCy3), 26.5 (CH2), 25.7(CH2).
11B NMR (CD2Cl2): 10.67.
31P{
1H} NMR (CD2Cl2): 81.54 (d,
2JPP = 255.2 Hz, PPh, 5-5b), 75.76 (d,
2JPP = 25.8 Hz, PPh, 5-
5a), 29.64 (d, 2JPP = 25.9 Hz, PCy3, 5-5a), 26.87 (d,
2JPP = 256.6 Hz, PCy3, 5-5b).
Synthesis of 5-4: To a CH2Cl2 solution (1 mL) of 3-4 (0.020 g, 0.033 mmol)
was added BCl3 in hexanes (1 M, 33 µL, 0.033 mmol). The red solution
immediately turned green. All volatiles were removed, and the resulting
dark solid was washed with CH3CN (2 mL) and dried to yield a green solid.
(0.021 g, 89%). X-Ray quality crystals were grown from a CH2Cl2/CH3CN
solution. 1H NMR (CD2Cl2): 18.93 (d,
3JPH = 11.7 Hz, 1H, Ru=CH), 8.87
(d, 3JHH = 8.27 Hz, 2H, o-H of C6H5), 7.74 (t,
3JHH = 7.98 Hz, 1H, p-H of C6H5), 7.51 (t,
3JHH =
8.17 Hz, 2H, m-H of C6H5), 5.05, 4.56, 4.19, 3.82, 3.13, 3.00, 2.89, 2.78 (all m, 1H, CH2), 2.12,
1.88, 1.82-1.64, 1.52, and 1.21-1.13 (all m, P(C6H11)3). 11
B NMR (CD2Cl2): 11.08 (s). 13
C{1H}
NMR (CD2Cl2): 277.37 (Ru=CH), 153.05 (ipso-C, Ph), 132.67 (2 CH, Ph), 131.81 (CH, Ph),
128.36 (2 CH, Ph), 71.15, 68.58 (2 CH2), 36.20 (d, 1JPC = 19.21 Hz, ipso-C of P(C6H11)3),
33.24, 30.57 (2 CH2), 29.54 (m-C of P(C6H11)3), 27.93 (o-C of P(C6H11)3), 26.43 (p-C of
P(C6H11)3). 31
P{1H} NMR (CD2Cl2): 35.54. Analysis calculated for C29H47BCl3OPRuS2: C,
48.04; H, 6.53. Found: C, 47.83 H, 6.62.
100
Synthesis of 5-5: To a CH2Cl2 solution (1 mL) of 3-5 (0.020 g, 0.032
mmol) was added BCl3 in hexanes (1 M, 32 µL, 0.032 mmol). The
brown solution immediately turned dark green. All volatiles were
removed, and the resulting dark solid was washed with CH3CN (2 mL)
and dried to yield a blue-green solid. (0.022 g, 92%). X-Ray quality
crystals were grown from a CH2Cl2/CH3CN solution.1H NMR (CD2Cl2):
17.68 (s, 1H, Ru=CH), 8.09 (br, 2H, o-H of C6H5) 7.56 (t, 3JHH = 7.54
Hz, 1H, p-H, Ph), 7.24 (t, 3JHH = 7.54 Hz, 2H, m-H of C6H5), 7.03 (s, 2H, 2 CH, Mes), 6.56 (s,
2H, 2 CH, Mes), 4.84 (m, 1H, CH2), 3.84 (m, 2H, CH2, Im), 3.74 (m, 1H, CH2), 3.64 (m, 2H,
CH2, Im), 3.01, 2.80, 2.62 (all m, 1H, CH2), 2.52 (s, 6 H, 2 CH3, Mes), 2.34 (m, 2H, CH2), 2.25
(s, 6 H, 2 CH3, Mes), 2.20 (s, 6 H, 2 CH3, Mes), 2.17 (m, 1H, CH2). 13
C{1H} NMR
(CD2Cl2): 308.91 (Ru=CH), 214.62 (ipso-C, Ph), 152.04 (ipso-C, NCN), 138.54 (CMe, Mes),
137.59 (ipso-C, Mes), 137.39 (ipso-C, Mes), 132.65 (2 o-CH, Ph), 130.65 (p-CH, Ph), 129.64,
129.25 (4 CH, Mes), 126.96 (2 m-CH, Ph), 70.30, 68.12 (2 CH2), 52.16, 53.83 (2 CH2,
Im), 30.56, 26.53 (2 CH2), 20.70 (2 CH3, Mes), 19.05 (2 CH3, Mes), 18.73 (2 CH3, Mes).
11B NMR (CD2Cl2): 11.46. Analysis calculated for C32H40BCl3N2ORuS2•CH2Cl2: C, 47.41; H,
5.06; N, 3.35. Found: C, 48.05 H, 5.36; N, 3.78.
Synthesis of 5-6: To a CH2Cl2 solution (1 mL) of 3-6 (0.020 g, 0.028
mmol) was added BCl3 in hexanes (1 M, 28 µL, 0.028 mmol). The red
solution immediately turned green and a blue-green precipitate began to
form. All volatiles were removed, and the resulting dark solid was
washed with CH3CN (2 mL) and dried to yield a blue-green solid. (0.020
g, 87%). 1H NMR (CD2Cl2): 18.85 (d,
3JPH = 11.6 Hz, 1H, Ru=CH), 8.54 (d,
3JHH = 7.9 Hz, 2H,
Ph), 7.74 (m, 3H, Ph), 7.57-7.37 (m, 6H, Ph), 7.20 (m, 2H, Ph), 2.40, 2.07, 1.80, 1.62, 1.43 (all
m, P(C6H11)3. 13
C{1H} NMR (Partial) (CD2Cl2): 154.6, 131.9, 131.2, 130.9, 128.7, 126.7, 123.1,
122.2, 121.2, 118.1, 116.3, 35.3, 31.6, 29.7, 29.1, 27.8, 27.7, 27.5 27.2 26.9, 26.3. 31
P{1H} NMR
(CD2Cl2): 36.51. 11
B NMR (CD2Cl2): 12.11. Analysis calculated for C37H47BCl3OPRuS2: C,
54.12; H, 5.77. Found: C, 53.94 H, 5.62.
101
Synthesis of 5-7: To a CH2Cl2 solution (1 mL) of 3-7 (0.020 g, 0.027
mmol) was added BCl3 in hexanes (1 M, 27 µL, 0.027 mmol). The red
solution immediately turned green and a blue-green precipitate began
to form. All volatiles were removed, and the resulting dark solid was
washed with CH3CN (2 mL) and dried to yield a green solid. (0.019 g,
83%). 1H NMR (CD2Cl2): 17.75 (s, 1H, Ru=CH), 7.60 (t, 1H, Ph), 7.40
(m, 5H, Ph), 7.31 (m, 2H, Ph), 7.13 (m, 3H, Ph), 7.06 (m, 3H, Ph, Mes), 6.82 (m, 1H, Ph), 6.04
(s, 2H, Mes), 3.83 (m, 1H, CH2, Im), 3.68 (m, 1H, CH2, Im), 3.48 (m, 2H, CH2, Im), 2.59 (s, 6 H,
2 CH3, Mes), 2.18 (s, 6H, 2 CH3, Mes), 2.05 (s, 6H, 2 CH3, Mes).13
C{1H} NMR (CD2Cl2):
289.9 (Ru=CH), 212.4, 183.7, 161.4, 160.4, 151.3, 138.6, 137.6, 137.3, 136.6, 134.1, 131.3,
130.2, 129.6, 129.4, 129.1, 128.5, 128.3, 126.8, 126.1, 125.7, 125.0, 123.0, 120.2, 52.2 (2 CH2,
Im), 20.8 (2 CH3, Mes), 19.0 (2 CH3, Mes), 18.5 (2 CH3, Mes). 11
B NMR (CD2Cl2): 14.7.
In situ synthesis of 5-8: To a CH2Cl2 solution (1 mL) of 3-8 (0.020 g, 0.035
mmol) was added BCl3 in hexanes (1 M, 35 µL, 0.035 mmol). The red solution
immediately turned green.
In situ synthesis of 5-9: To a CH2Cl2 solution (1 mL) of 3-9 (0.020 g,
0.033 mmol) was added BCl3 in hexanes (1 M, 33 µL, 0.033 mmol). The
brown solution immediately turned dark green.
102
Synthesis of 5-11: To a CH2Cl2 solution (1 mL) of 5-3 (0.050 g,
0.069 mmol) was added BCl3 in hexanes (1 M, 69 µL, 0.069
mmol). The green solution immediately turned darker green. To
this, CH3CN (0.30 mL) was added and the solution turned dark
red. All volatiles were removed and the dark red solid was
dissolved in CH2Cl2 (1 mL) and filtered. Pentane (5 mL) was
added and a dark red precipitate formed. The solid was collected, washed with pentane
(2 x 2 mL) and dried in vacuo to yield a dark red solid. (0.053 g, 87%). X-Ray quality crystals
were grown from a CH2Cl2 solution layered with pentane. 1H NMR (CD2Cl2): 18.66
(d, 3JPH = 9.3 Hz, 1H, Ru=CH), 8.36 (d,
3JHH = 7.9 Hz, 2H, o-H of C6H5), 7.91 (t,
3JHH = 7.4 Hz,
1H, p-H of C6H5), 7.71 (t, 3JHH = 7.6 Hz, 2H, m-H of C6H5), 4.66 (m, 2H, CH2), 4.50 (m. 1H,
CH2), 4.37 (m, 2H, CH2), 4.25 (m, 1H, CH2), 3.95 (m, 2H, CH2), 2.65 (s, 3H CH3CN) 2.09, 1.95,
1.89-1.77, and 1.26-1.15 (all m, P(C6H11)3). 11
B NMR (CD2Cl2): 11.74 (s, S2BCl2), 6.98 (s,
BCl4). 13
C{1H} NMR (CD2Cl2): 152.0 (ipso-C, Ph), 134.7 (2 CH, Ph), 131.9 (CH, Ph), 129. 6
(2 CH, Ph), 75.2, 70.5 (2 CH2), 36.7 (d, 1JPC = 18.9 Hz, ipso-C of P(C6H11)3), 33.4, 31.6
(2 CH2), 29.5 (m-C of P(C6H11)3), 27.7 (o-C of P(C6H11)3), 26.0 (p-C of P(C6H11)3), 13.9
(CH3, CH3CN). 31
P{1H} NMR (CD2Cl2): 36.12. Analysis calculated for C31H50B2Cl6NOPRuS2:
C, 42.15; H, 5.71; N, 1.59. Found: C, 42.28 H, 5.51; N, 1.10.
Synthesis of 5-13: To a CH2Cl2 solution (1 mL) of 4 (0.030 g,
0.040 mmol) was added BCl3 in hexanes (1 M, 40 µL, 0.040
mmol). The green-blue solution immediately turned darker
green. To this, CH3CN (0.100 mL) was added and the solution
turned red. All volatiles were removed and the red solid was
dissolved in CH2Cl2 (1 mL) and filtered. Pentane (5 mL) was
added and a red precipitate formed. The solid was collected,
washed with pentane (2 x 2 mL) and dried in vacuo to yield a red solid. (0.034 g, 94%). X-Ray
quality crystals were grown from a CH2Cl2 solution layered with pentane.1H NMR (CD2Cl2):
17.26 (s, 1H, Ru=CH), 7.64 (m, 3H, o-H and p-H of C6H5) 7.38 (t, 3JHH = 7.99 Hz, 2H, m-H of
C6H5), 7.00 (s, 2H, 2 CH, Mes), 6.77 (s, 2H, 2 CH, Mes), 4.02 (m, 1H, CH2), 3.83 (br, 5H,
1H, CH2 and 2 CH2, Im), 3.46 (m, 2H, CH2, Im), 3.21 (m, 1H, CH2), 2.66 (m, 3H, 3 CH,
103
CH2), 2.53 (s, 6 H, 2 CH3, Mes), 2.47 (s, 3H, CH3CN), 2.27 (s, 6 H, 2 CH3, Mes), 2.25 (s, 6
H, 2 CH3, Mes). 13
C{1H} NMR (CD2Cl2): 208.50 (ipso-C, Ph), 151.65 (ipso-C, NCN), 140.05
(CMe, Mes), 137.53 (ipso-C, Mes), 136.85 (Mes), 136.43 (Mes), 134.08 (2 o-CH, Ph), 131.79
(p-CH, Ph) 130.33, 129.92 (4 CH, Mes), 129.06 (2 m-CH, Ph), 70.35, 69.45 (2 CH2),
54.10, 53.14 (2 CH2, Im), 34.52, 33.92 (2 CH2), 22.76 (2 CH3, Mes), 19.03 (2 CH3,
Mes), 18.79 (2 CH3, Mes), 14.20 (CH3, CH3CN). 11
B NMR (CD2Cl2): 11.39 (BS2Cl2), 6.92
(BCl4). Analysis calculated for C34H43B2Cl6N3ORuS2: C, 44.91; H, 4.77; N, 4.62. Found: C,
44.52 H, 4.60; N, 4.27.
Synthesis of 5-18: To a CH2Cl2 solution of 3-4 (0.050 g,
0.082 mmol) was added [Et2O•H][BF4] (0.011 mL, 0.082 mmol).
The solution immediately became lighter. The solvent was
removed under vacuum and the resulting brown solid was washed
with hexanes (5 mL) and dried in vacuo. (0.052 g, 91 %). 1H
NMR (CD2Cl2): 7.40 (t, 3JHH = 7.7 Hz, 1H, p-H of C6H5), 7.32 (t,
3JHH = 7.7 Hz, 2H, m-H of
C6H5), 7.20 (d, 3JHH = 7.7 Hz, 2H, m-H of C6H5), 4.23 (s, 2H, CH2Ph), 4.64 (m, 2H, CH2), 4.49
(m. 2H, CH2), 4.43 (m, 2H, CH2), 2.74 (m, 2H, CH2), 2.40, 2.11, 1.94, 1.81, 1.68 and 1.44-1.23
(all m, P(C6H11)3). 11
B NMR (CD2Cl2): -1.2. 19
F NMR (CD2Cl2): -151.8. 13
C{1H} NMR
(CD2Cl2): 142.7 (ipso-C, Ph), 130.4 (2 CH, Ph), 129.0 (2 CH, Ph), 127.7 (CH, Ph), 71.2
(2 CH2), 52.1 (CH2Ph), 39.3 (2 CH2), 36.4 (d, 1JPC = 23.9 Hz, ipso-C of P(C6H11)3), 29.4
(m-C of P(C6H11)3), 27.5 (d, 2JPC = 11.3 Hz, o-C of P(C6H11)3), 25.9 (p-C of P(C6H11)3).
31P{
1H}
NMR (CD2Cl2): 53.2. Analysis calculated for C29H48BF4OPRuS2: C, 50.07; H, 6.95. Found:
C, 50.21 H, 6.85.
5.4.3 X-ray Crystallography
5.4.3.1 X-ray Data Collection and Reduction
Crystals were coated in Paratone-N oil in the glove-box, mounted on a MiTegen Micromount
and placed under an N2 stream, thus maintaining a dry, O2-free environment for each crystal. The
data were collected on a Bruker Apex II diffractometer employing Mo Kα radiation (λ = 0.71073
Å). Data collection strategies were determined using Bruker Apex software and optimized to
provide >99.5% complete data to a 2θ value of at least 55°. The data were collected at 150(±2) K
104
for all crystals. The frames were integrated with the Bruker SAINT software package using a
narrow-frame algorithm. Data were corrected for absorption effects using the empirical multi-
scan method (SADABS).23
5.4.3.2 X-ray Data Solution and Refinement
Non-hydrogen atomic scattering factors were taken from the literature tabulations.24
The heavy
atom positions were determined using direct methods employing the SHELXTL direct methods
routine. The remaining non-hydrogen atoms were located from successive difference Fourier
map calculations. The refinements were carried out by using full-matrix least squares techniques
on F, minimizing the function (Fo–Fc)2 where the weight is defined as 4Fo2/2 (Fo
2) and Fo
and Fc are the observed and calculated structure factor amplitudes, respectively. In the final
cycles of each refinement, all non-hydrogen atoms were assigned anisotropic temperature factors
in the absence of disorder or insufficient data. In the latter cases atoms were treated isotropically.
C-H atom positions were calculated and allowed to ride on the carbon to which they are bonded
assuming a C-H bond length of 0.95 Å. H-atom temperature factors were fixed at 1.20 times the
isotropic temperature factor of the C-atom to which they are bonded. The H-atom contributions
were calculated, but not refined. The locations of the largest peaks in the final difference Fourier
map calculation as well as the magnitude of the residual electron densities in each case were of
no chemical significance.
105
Table 5.4.1. Select Crystallographic Data for 5-2, 5-4 and 5-5.
(5-2) (5-4) (5-5)
Formula 2(C32H40BCl3N2RuS3)
CH2Cl2
C29H47BCl3OPRuS2 2(C32H40BCl3N2ORuS2)
CH2Cl2
Formula weight 1619.13 725.01 1586.99
Crystal System Monoclinic Monoclinic Monoclinic
Space group C2/c P21/n C2/c
a(Å) 34.498 17.7135(6) 34.706(4)
b(Å) 10.716 10.0800(3) 10.5082(13)
c(Å) 23.057 19.4358(7) 28.072(4)
α(deg) 90 90 90
β(deg) 124.73 109.048(2) 138.090(9)
γ(deg) 90 90 90
V(Å3) 7005.187 3280.29(19) 6838.5(19)
Z 4 4 4
d(calc)gcm-3
1.535 1.468 1.541
R(int) 0.0440 0.0413
Abs coeff,μ,mm-1
0.959 0.921 0.923
Data collected 12148 12965 7972
>2(FO2) 9427 10021 5575
Variables 406 343 412
R(>2) 0.0369 0.0318 0.0389
Rw 0.0962 0.0524 0.0623
GOF 1.023 1.370 1.249
106
Table 5.4.2. Select Crystallographic Data for 5-11 and 5-13.
(5-11) (5-13)
Formula C31H50B2Cl6NOPRuS2 C34H40B2Cl6N3ORuS2
CH2Cl2
Formula weight 883.22 991.15
Crystal System Monoclinic Monoclinic
Space group P21/n P21/n
a(Å) 10.5984(5) 11.8055(2)
b(Å) 13.8097(7) 21.9531(3)
c(Å) 27.2535(15) 17.1265(2)
α(deg) 90 90
β(deg) 100.467(3) 96.030(1)
γ(deg) 90 90
V(Å3) 3922.5(3) 4414.07(11)
Z 4 4
d(calc)gcm-3
1.496 1.492
R(int) 0.0778 0.0337
Abs coeff,μ,mm-1
0.983 0.966
Data collected 9330 13981
>2(FO2) 6104 11002
Variables 411 469
R(>2) 0.0454 0.0367
Rw 0.1022 0.0935
GOF 1.006 0.967
107
Chapter 5 References
1. Malpass, D. B., Introduction to Industrial Polyethylene: Properties, Catalysts, and
Processes. Scrivener Publishing LLC: 2010.
2. Yoshida, Y.; Matsui, S.; Fujita, T., Journal of Organometallic Chemistry 2005, 690 (20),
4382-4397.
3. Yang, X.; Stern, C. L.; Marks, T. J., Journal of the American Chemical Society 1991, 113
(9), 3623-3625.
4. Brintzinger, H. H.; Fischer, D.; Mülhaupt, R.; Rieger, B.; Waymouth, R. M., Angewandte
Chemie International Edition 1995, 34 (11), 1143-1170.
5. Williams, V. C.; Irvine, G. J.; Piers, W. E.; Li, Z.; Collins, S.; Clegg, W.; Elsegood, M.
R. J.; Marder, T. B., Organometallics 2000, 19 (9), 1619-1621.
6. Chen, E. Y.-X.; Marks, T. J., Chemical Reviews 2000, 100 (4), 1391-1434.
7. Li, L.; Metz, M. V.; Li, H.; Chen, M.-C.; Marks, T. J.; Liable-Sands, L.; Rheingold, A.
L., Journal of the American Chemical Society 2002, 124 (43), 12725-12741.
8. Bai, C. X.; Lu, X. B.; He, R.; Zhang, W. Z.; Feng, X. J., Organic & biomolecular
chemistry 2005, 3 (22), 4139-42.
9. Love, J. A.; Morgan, J. P.; Trnka, T. M.; Grubbs, R. H., Angewandte Chemie
International Edition 2002, 41 (21), 4035-4037.
10. Yang, Q.; Xiao, W.-J.; Yu, Z., Organic Letters 2005, 7 (5), 871-874.
11. Hahn, F. E.; Paas, M.; Fröhlich, R., Journal of Organometallic Chemistry 2005, 690 (24-
25), 5816-5821.
12. Ledoux, N.; Drozdzak, R.; Allaert, B.; Linden, A.; Van Der Voort, P.; Verpoort, F.,
Dalton transactions 2007, (44), 5201-10.
13. Monsaert, S.; Lozano Vila, A.; Drozdzak, R.; Van Der Voort, P.; Verpoort, F., Chemical
Society reviews 2009, 38 (12), 3360-72.
14. Samec, J. S. M.; Keitz, B. K.; Grubbs, R. H., Journal of Organometallic Chemistry 2010,
695 (14), 1831-1837.
15. Żak, P.; Rogalski, S.; Kubicki, M.; Przybylski, P.; Pietraszuk, C., European Journal of
Inorganic Chemistry 2014, 2014 (7), 1131-1136.
16. Gułajski, Ł.; Michrowska, A.; Bujok, R.; Grela, K., Journal of Molecular Catalysis A:
Chemical 2006, 254 (1-2), 118-123.
108
17. Vinokurov, N.; Garabatos-Perera, J. R.; Zhao-Karger, Z.; Wiebcke, M.; Butenschön, H.,
Organometallics 2008, 27 (8), 1878-1886.
18. Samec, J. S.; Grubbs, R. H., Chemistry 2008, 14 (9), 2686-92.
19. Songis, O.; Slawin, A. M.; Cazin, C. S., Chem Commun 2012, 48 (9), 1266-8.
20. Simocko, C.; Wagener, K. B., Organometallics 2013, 32 (9), 2513-2516.
21. Schrock, R. R., Journal of Organometallic Chemistry 1976, 122 (2), 209-225.
22. Schrock, R. R.; Meakin, P., Journal of the American Chemical Society 1974, 96 (16),
5288-5290.
23. Apex 2 Software Package;, Bruker AXS Inc. : 2013.
24. D. T. Cromer, J. T. W., Int. Tables X-Ray Crystallography. 1974; Vol. 4.
109
Chapter 6 Catalytic Olefin Metathesis
6.1 Introduction
6.1.1 Types of Olefin Metathesis Reactions
The power of carbon-carbon bond redistribution offered by catalytic olefin metathesis has been
harnessed in a variety of ways and used for a number of applications.1-7
The most common
reactions are categorized into a few specific types (Figure 6.1.1). This includes ring closing
metathesis (RCM) where two olefinic functionalities are contained within the same molecule and
the catalytic transformation links these olefins together creating a cyclic product with the
liberation of ethylene or another byproduct.8 This can be used to form heterocycles, bicycles and
cycloalkenes.9-11
The equilibrium of this reaction can be driven to the cyclic product by the
removal of ethylene from the system. The reverse reaction can be accomplished by pressurizing
the system with ethylene driving the equilibrium to the ring opened product in a process called
ring opening metathesis (ROM).
Olefin metathesis can be used to synthesize polymers by ring opening metathesis polymerization
(ROMP).12-14
This is accomplished by the continuous opening of cyclic olefinic monomers
resulting in a growing polymer attached to the metal centre. The driving force for this reaction is
typically from the relief of ring strain in the monomer. This can be used to synthesize a number
of interesting polymers including polydicyclopentadiene15
and polynorbornene16-17
which are
used for body panels of vehicles and anti-vibration, anti-impact and grip improvement
respectively.
By combining two olefinic substrates in the presence of an olefin metathesis catalyst, cross
metathesis (CM) of the two substrates can occur resulting in a coupled product with the
liberation of ethylene or another byproduct.18-20
Similar to RCM, this equilibrium is driven to the
coupled product by the liberation of ethylene. CM is synthetically equivalent to, and has
replaced, performing ozonolysis on an olefinic substrates to give a carbonyl functionality
followed by a reaction with a Wittig reagent. The reverse reaction can be accomplished by
applying an ethylene pressure resulting in ethenolysis and cleavage of the carbon-carbon double
110
bond resulting in two terminal olefinic products.21-22
This process is used for the production of
biodiesel from unsaturated fatty acids.23
Figure 6.1.1. Common Olefin Metathesis Reactions
6.1.2 Catalyst Screening
6.1.2.1 Standard Test Reactions
Due to the lack of a set of standard reaction conditions and substrates, the process of screening
new olefin metathesis catalysts and being able to compare their activities to existing catalysts
was highly inconsistent. This was the motivation for Grubbs and coworkers to develop a series of
standard transformations to serve as a useful and easily applicable platform for catalyst
comparison.24
These standard tests and conditions give researchers the ability to easily and
accurately assess the impact of structural changes made to catalyst frameworks thus leading to
more effective rational catalyst design. The three standard tests provide insight into a catalysts
ability to perform the three common reactions described above (RCM, ROMP and CM).
The standard test for RCM is the ring closing of diethyl diallylmalonate (Scheme. 6.1.1). The
reaction takes place at 30 ºC in CD2Cl2 at a concentration of 0.1 M with 1 mol% of metathesis
catalyst.
111
Scheme 6.1.1. Standard Test Reaction for RCM
To investigate the effectiveness of a catalyst to accomplish ROMP, 1,5-cyclooctadiene is
polymerized using 0.1 mol% catalyst loading (Scheme 6.1.2). This is done with a 0.5 M solution
of 1,5-cyclooctadiene at 30 ºC in CD2Cl2.
Scheme 6.1.2. Standard Test Reaction for ROMP
The standard metathesis test for CM involves the coupling of 5-hexenyl acetate and methyl
acrylate with the test reaction taking place at a concentration of 0.4 M and 2.5 mol % catalyst at
room temperature in CD2Cl2 (Scheme 6.1.3). This reaction can give the desired heterocoupled
product as shown in Scheme 6.1.3 and also the homocoupled 5-hexenyl acetate product.
Scheme 6.1.3. Standard Test Reaction for CM
6.1.2.2 Activity of Common Catalysts
As a comparison for the results discussed in this chapter, the activity of some common olefin
metathesis catalysts are presented in Table 6.1.1.24
1st Generation Grubbs Catalyst (Grubbs 1)
can convert diethyl diallylmalonate to the ring closed product in 66 % yield after 30 min. 2nd
Generation Grubbs Catalyst (Grubbs 2), 1st Generation Hoveyda-Grubbs Catalyst (HG 1), and
2nd
Generation Hoveyda-Grubbs Catalyst (HG 2) can accomplish RCM of diethyl
diallylmalonate to over 90% in 30 min with HG 2 being the most active. For ROMP, Grubbs 2
and HG 2 are the most active achieving 99% conversion in 6 and 5 min respectively. After
112
90 min Grubbs 1 achieves 40% conversion and after 100 min HG 1 achieves 4% conversion. For
CM Grubbs 2 and HG 2 achieve 90% conversion after 70 min with 97 and 99% consumption of
5-hexenyl acetate respectively. Grubbs 1 achieves 8% conversion to the heterocoupled product
with 87% consumption of 5-hexenyl acetate and HG 1 achieves 3% conversion with 73%
consumption of 5-hexenyl acetate. The consumption of 5-hexenyl acetate in these reactions is
due to both the formation of the heterocoupled product and the homocoupled 5-hexenyl acetate
product.
Table 6.1.1. Standard Olefin Metathesis Reactions Using Common Catalysts.
Catalyst RCM1 ROMP
2 CM
3
Grubbs 1 66% 40% (90 min) 8% (87 %)
Grubbs 2 96% 99% (6 min) 90% (97%)
HG 1 90% 4% (100 min) 3% (73 %)
HG 2 99.5% 99% (5 min) 90% (99 %)
1Conversions at 30 min reaction time under standard conditions.
2Max conversions at the respective reaction times.
3Conversion to heterocoupled product at 70 min. In brackets, consumption of 5-hexenylacetate.
6.1.3 Cross Metathesis of NBR and 1-Hexene
As previously mentioned in Section 1.4, NBR can be processed by performing cross metathesis
with 1-hexene to give a polymer with a lower molecular weight.6, 25
This process is conceptually
related to ethenolysis where the internal olefins in the polymer structure are undergoing cross
metathesis with a small olefinic substrate (1-hexene) to essentially cut the polymer into shorter
chains. Industrially this is accomplished by employing 2nd
Generation Grubbs Catalyst.
Depending on the catalyst loading and reaction times, polymers of varying molecular weights
and viscosities can be obtained. The crude NBR obtained from Lanxess has an initial Mn and Mw
of 95 000 and 270 000 Da respectively resulting in a PDI of 2.8.
113
6.1.4 Hydrogenation of NBR
To reduce the susceptibility of the polymer to oxidative aging and to alter its properties to be
more oil and hydrocarbon resistant NBR is hydrogenated.26-27
This is done by Lanxess using the
rhodium based Wilkinson's Catalyst. It is important that the catalyst is selective for the
hydrogenation of the olefins and unreactive towards the nitrile functionalities present in NBR.
When the nitrile groups are reduced, the resulting amines react with olefins in the polymer
creating a cross linked structure. Reduction of the nitrile groups also alters the polymers
properties resulting in undesirable products.
6.2 Results and Discussion
With a library of ruthenium alkylidene species prepared, their activity for catalytic olefin
metathesis was probed. To do this, the standard system of characterization for olefin metathesis
catalysts was followed using the three specific reactions outlined above. From this, active
catalysts were then screened for activity in the cross metathesis of NBR with 1-hexene.
6.2.1 Comparing Catalytic Activity of BCl3 'Activated' and 'Non-Activated' Species
With each ligand set, there are three ruthenium alkylidene compounds related by the number of
equivalents of BCl3 reacted with the parent tridentate complex. Therefore, it was of interest to
compare the activities of these related species. To do this, the series of compounds 3-4, 5-4, and
5-10 and the series 3-5, 5-5, and 5-12 were tested for the three standard metathesis reactions
(Figure 6.2.1). The first standard test which was investigated was the ring closing metathesis of
diethyl diallylmalonate with 5 mol% catalyst loading (Scheme 6.1.1).
.
Figure 6.2.1. Compounds used to Compare BCl3 Activation Effects on Catalysis
114
Comparing the series containing PCy3 (3-4, 5-4, 5-10) for RCM activity, it is clear to see that
reacting the parent complex, 3-4, with 2 equivalents of BCl3 to generate cationic 5-10 gives the
most conversion to the ring closed product (Figure 6.2.2). Not surprisingly, the parent complex
3-4 shows no catalytic activity. This is similar to the related species bearing tridentate dianionic
ligands reported by Jensen and Erker.28-29
Considering the accepted mechanism of ruthenium
based olefin metathesis, the inactivity of this system can be easily explained. In order for the
olefinic substrate to coordinate to the metal centre, one of the phosphines in 1st Generation
Grubbs Catalyst must dissociate to create a 4-coordinte species.30-31
In the case of 3-4 the PCy3 is
bound too strong to dissociate. The central ether donor on the tridentate ligand could potentially
dissociate to form a 4-coordinate species but the chelate effect drives the equilibrium towards the
5-coordinate species preventing any coordination of olefin and subsequent catalysis. Complex
5-4 also shows no catalytic activity for RCM of diethyl diallylmalonate. This is also of no
surprise as there is no open coordination site for the incoming olefin to bind to the metal. 5-10
displays moderate activity achieving 42% conversion to the ring closed product in 40 min.
Figure 6.2.2. Ring Closing Metathesis of Diethyl Diallylmalonate using Complexes 3-4
(Green Triangles), 5-4 (Red Squares), and 5-10 (Blue Diamonds) with 5 mol% Catalyst
Loadings at 25 ºC in CD2Cl2
115
A similar trend is observed with the SIMes series of ruthenium alkylidene complexes (3-5, 5-5,
5-12) (Figure 6.2.3). Both 3-5 and 5-5 show no catalytic activity for the RCM of diethyl
diallylmalonate. However, cationic 5-12 which is formed from the reaction of 5-5 with one
equivalent of BCl3 gives 98% conversion to the ring closed product after just 40 min.
Figure 6.2.3. Ring Closing Metathesis of Diethyl Diallylmalonate With Complexes 3-5
(Green Triangles), 5-5 (Red Squares), and 5-12 (Blue Diamonds) with 5 mol% Catalyst
Loadings at 25 ºC in CD2Cl2
When tested for ROMP of COD, complexes 3-4, 5-4, and 5-10 all displayed no activity. Even
though the cationic 5-10 was active for RCM of diethyl diallylmalonate, at 0.1 mol% catalyst
loading it did not convert any COD to polymer. This is consistent with previous reports from
Dixneuf and co-workers who demonstrated that their cationic ruthenium allenylidene species
were only active for RCM.32
Examining the SIMes, series (3-5, 5-5, 5-12) for ROMP of COD gave results which follow the
trend seen previously with these compounds. The cationic species, 5-12 is the most active,
achieving 53% conversion to polymer after 44 min. However, unlike the previous results, the
parent complex 3-5 and the complex formed by the addition of one equivalent of BCl3, 5-5
116
display some catalytic activity. 3-5 and 5-5 achieve 26% and 4.8% conversion, respectively after
44 min (Figure 6.2.4). Not surprisingly, 5-coordinate 3-5 is more active for ROMP of
1,5-cyclooctadiene than 6-coordinate 5-5.
Figure 6.2.4. Ring Opening Metathesis Polymerization of 1,5-Cyclooctadiene With
Complexes 3-5 (Green Triangles), 5-5 (Red Squares), and 5-12 (Blue Diamonds) with
0.1 mol% Catalyst Loadings at 25 ºC in CD2Cl2
The test reaction which is most applicable to our ultimate goal of cross metathesis of NBR with
1-hexene was the CM of 5-hexenyl acetate with methyl acrylate. Similar to the ROMP of COD,
complexes 3-4, 5-4, and 5-10 were all inactive for the standard CM test. However, for the series
of compounds containing SIMes (3-5, 5-5, 5-12), a similar trend to the previous test reactions is
observed with the cationic species being most active. 3-5 and 5-5 are inactive for the CM
reaction. However, complex 5-12 is active for CM giving the heterocoupled CM product in 62%
yield 160 min (Figure 6.2.5).
117
Figure 6.2.5. Cross Metathesis of 5-Hexenyl Acetate And Methyl Acrylate With Complexes
3-5 (Green Triangles), 5-5 (Red Squares), and 5-12 (Blue Diamonds) with 5 mol% Catalyst
Loadings at 25 ºC in CD2Cl2
Based on these experiments, it is clear that the cationic species generated upon the reaction of the
parent five-coordinate species with 2 equivalents of BCl3 is the most active. In most cases the
parent species 3-4 and 3-5 are completely inactive for olefin metathesis. Similarly, the
complexes generated by reacting these parent species with 1 equivalent of BCl3 (5-4, 5-5) are
inactive for olefin metathesis.
6.2.2 Catalytic Olefin Metathesis Activity of Catalyst Derivatives
The previously mention trends (Section 6.2.1) demonstrated that the cationic alkylidene species
were the most active catalysts, with both types of neutral species displaying very limited to no
conversion. Therefore, in subsequent investigations into the influence of the dianionic, tridentate
ligand structure, only the activated cationic species will be discussed.
To determine the influence of backbone rigidity and the basicity of the thiolate ligands
complexes 5-14 and 5-15 were screened for olefin metathesis activity (Figure 6.2.6). Compounds
5-6 and 5-7 were activated with another equivalent of BCl3 to form the 5-coordinate cationic
species, and screened for RCM, ROMP and CM in an identical fashion as the compounds tested
118
above. For RCM, 5-14 reaches 38.8 % in 40 min and 5-15 is slightly less active reaching 35.9 %
in 40 min (Figure 6.2.7).
Figure 6.2.6. Compounds 5-14 and 5-15
Figure 6.2.7. Ring Closing Metathesis of Diethyl Diallylmalonate with 5-14 and 5-15 with
5 mol% Catalyst Loadings at 25 ºC in CD2Cl2
Compound 5-14 is inactive for ROMP of COD. This is expected based on the result of the
related species 5-10. However, 5-15 is active for ROMP of COD resulting in 86% conversion of
the monomer to polymer (Figure 6.2.8).
119
Figure 6.2.8. Ring Opening Metathesis Polymerization of 1,5-Cyclooctadiene with 5-15 at a
0.1 mol% Catalyst Loading at 25 ºC in CD2Cl2
The CM of 5-hexenyl acetate and methyl acrylate with 5-14 at 5 mol% is inactive similar to the
alkyl backbone analogue 5-10. 5-15 achieves 74% conversion after 180 min (Figure 6.2.9).
Figure 6.2.9. Cross Metathesis of 5-Hexenyl Acetate and Methyl Acrylate With 5-15 at a
5 mol% Catalyst Loading at 25 ºC in CD2Cl2
120
When another equivalent of BCl3 is added to a solution of compounds 5-1 and 5-2 the resulting
mixtures are inactive for all of the standard olefin metathesis tests. This is because the second
equivalent of BCl3 is unable to abstract a chloride form the ruthenium centre. It is unclear why
this is the case. It is presumably a result of the central thioether donor since all other related
compounds with a different central donor undergo this type of reactivity. This includes
compound 5-3 with the central phosphine donor. However the resulting complex is only slightly
active for RCM of diethyl diallylmalonate achieving only 3% conversion after 40 min. Similar to
the previously discussed compounds containing a PCy3 ligand, it is also inactive for the standard
ROMP and CM tests.
The final complexes that were tested were the ones containing the all oxygen ligands where the
tridentate dianionic ligand consist of two alkoxy ligands and a central ether donor. Since the
intermediate complexes with the addition of one equivalent of BCl3 were difficult to isolate, for
these catalytic tests complexes 3-8 and 3-9 were activated with two equivalents of BCl3 in situ to
give 5-16 and 5-17 respectively. These solutions were used for the catalytic tests (Figure 6.2.10).
Figure 6.2.10. Complexes 5-16 and 5-17
When 5-16 was screened for catalytic activity in RCM of diethyl diallylmalonate at a 5 mol%
catalyst loading, 99% conversion to the ring closed product was achieved after 30 min
(Figure 6.2.11).
121
Figure 6.2.11. Ring Closing Metathesis of Diethyl Diallylmalonate Using 5-16 at a 5 mol%
Catalyst Loading at 25 ºC in CD2Cl2
When 5-17 was used for RCM of diethyl diallylmalonte at a 5 mol% catalyst loading conversion
to the ring closed product was 93% complete after 6 min and essentially complete after 8 min
(Table 6.2.1). When the catalyst loading was dropped to 1 mol% the catalyst was able to achieve
56% conversion to the ring closed product after 40 min (Figure 6.2.12).
Table 6.2.1. Ring Closing Metathesis of Diethyl Diallylmalonate Using 5-17 at a 5 mol%
Catalyst Loading at 25 ºC in CD2Cl2
Time (min) Conv (%)
2 24
4 67
6 93
8 >99
122
Figure 6.2.12. Ring Closing Metathesis of Diethyl Diallylmalonate Using 5-17 at a at a
1 mol% Catalyst Loading at 25 ºC in CD2Cl2
Complex 5-17 was able to accomplish ROMP of COD achieving 96% conversion of monomer to
polymer after 30 min (Figure 6.2.13). Although 5-17 was more active than the previously
reported catalysts in this section for RCM and ROMP, it only achieved 31% conversion to the
heterocoupled product for the standard CM test reaction (Figure 6.2.14). However, in the
1H NMR spectrum it is evident that the 5-hexenyl acetate has been fully consumed and converted
to the homocoupled product. This has been observed with other olefin metathesis catalysts
including Grubbs 1. Grubbs and coworkers have provided an explanation for this observation.18
They categorized all olefins into 4 classes: Type 1 undergoes fast homodimerization; Type 2
undergoes slow homodimerization; Type 3 undergoes no homodimerization; and Type 4 are
spectators to olefin metathesis. 5-hexenyl acetate is considered a Type 1 olefin which rapidly
undergoes homodimerization with the release of ethylene as a byproduct. The homodimer can
then undergo secondary olefin metathesis and react with methyl acrylate resulting in the
heterocoupled CM product. The amount of secondary olefin metathesis which occurs resulting in
the heterocoupled product is dependent on catalyst used. For example, it can be seen in
Table 6.1.1. that Grubbs 1 results in only 8% conversion to the heterocoupled CM product.
123
However, 87% of the 5-hexenyl acetate is consumed. Using Grubbs 2 as the catalyst results in
90% conversion to the heterocoupled product with 97% of the 5-hexenyl acetate being
consumed.
Figure 6.2.13. Ring Opening Metathesis Polymerization of 1,5-Cyclooctadiene with 5-17 at
a 5 mol% Catalyst Loading at 25 ºC in CD2Cl2
Figure 6.2.14. Cross Metathesis of 5-Hexenyl Acetate and Methyl Acrylate With 5-17 at a
5 mol% Catalyst Loading at 25 ºC in CD2Cl2
124
6.2.3 Comparisons of Active Catalysts
In general, the SIMes versions of the catalysts are more active than the PCy3 containing
catalysts. This is especially evident for ROMP and CM test reaction since the PCy3 containing
catalysts are inactive for these reactions. For RCM of diethyl diallylmalonate, it is obvious that
the SIMes analogue 5-12 is more active than the PCy3 analogue 5-10 (Figure 6.2.15). 5-12
reached 98% completion after 40 min whereas 5-10 only achieved 42% conversion after 40 min.
Figure 6.2.15. Comparing the Activity of SIMes containing 5-12 and PCy3 Containing 5-10
for RCM of Diethyl Diallylmalonate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2
Interestingly, when 5-14 and 5-15 are compared for RCM activity, the PCy3 containing catalyst
is slightly more active than the SIMes containing catalyst (Figure 6.2.16). Complex 5-14
achieved 39% conversion to the ring closed product after 40 min. The SIMes derivative, 5-15
accomplished slightly less conversion reaching 36% after 40 min.
125
Figure 6.2.16. Comparing the Activity of SIMes containing 5-15 and PCy3 Containing 5-14
for RCM of Diethyl Diallylmalonate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2
The trend of the catalyst containing the SIMes ligand being more active than the PCy3 analogues
was observed again when looking at complexes 5-16 and 5-17. At 5 mol% both 5-16 and 5-17
accomplish 100 % conversion to the ring closed product of diethyl diallylmalonate. However, the
reaction was complete after 30 min using 5-16 while it took 5-17 only 8 min (Figure 6.2.17).
This demonstrates once again that keeping everything else about the catalyst structure constant
and changing PCy3 to SIMes results in increased activity.
126
Figure 6.2.17. Comparing the Activity of PCy3 Containing 5-16 and SIMes Containing 5-17
for RCM of Diethyl Diallylmalonate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2
Of the three catalysts containing a PCy3 ligand, the catalyst with the dialkoxy ether ligand (5-16)
is the most active for RCM of diethyl diallylmalonate (Figure 6.2.18). After 30 min this catalyst
accomplished nearly 100% conversion to the ring closed product. After 40 min, complexes 5-10
and 5-14 accomplished nearly the same conversion reaching 41 and 39% completion,
respectively.
Figure 6.2.18. Comparing the Activity of 5-10, 5-14 and 5-16 for RCM of Diethyl
Diallylmalonate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2
127
When comparing the activities of the SIMes derivatives of the catalysts for the RCM of diethyl
diallylmalonate it is evident that complex 5-17 with the all oxygen ligand was the most active
accomplishing complete conversion after 8 min. The alkyl backbone derivative (5-12) of the
dithiolate complexes was second best achieving near complete conversion after 34 min. While
5-15 which achieved only 36 % conversion to the ring closed product after 40 min was the worst
(Figure 6.2.19).
Figure 6.2.19. Comparing the Activity of 5-12, 5-15 and 5-17 for RCM of Diethyl
Diallylmalonate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2
Similar to the trend observed for the standard RCM test, complex 5-17 was more active than
5-15 and 5-12 for ROMP of 1,5-cyclooctadiene (Figure 6.2.20). After 30 min 5-17 achieved 96%
conversion to the polymer. Catalyst 5-15 was second best achieving 86% conversion after 40
min and 5-12 was the least effective catalyst achieving 53% conversion.
128
Figure 6.2.20. Comparing Activities of 5-12, 5-15 and 5-17 for ROMP of 1,5-Cyclooctadiene
at 0.1 mol% Catalyst Loadings at 25 ºC in CD2Cl2
The trend of catalyst 5-17 being most active was not observed for the standard CM test
(Figure 6.2.21). Catalyst 5-15 was the most active accomplishing 74% conversion to the
heterocoupled product in 180 min. 5-12 was second best achieving 62% conversion and the
alkoxide containing catalyst, 5-17 was the least effective achieving only 32% conversion to the
heterocoupled product. However, when the consumption of 5-hexenyl acetate was tracked by
1H NMR catalyst 5-17 showed nearly complete consumption of the starting material. As
discussed, this is due to the formation of the homocoupled product. When considering activity to
produce the heterocoupled product, 5-17 was the worst of the three catalysts tested. However in
terms of overall metathesis, 5-17 was the most active catalyst.
129
Figure 6.2.21. Comparing Activities of 5-12, 5-15 and 5-17 for CM of 5-hexenyl Acetate and
Methyl Acrylate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2
6.2.4 Cross Metathesis of NBR and 1-hexene
The ultimate goal of this thesis was to develop olefin metathesis catalyst which were active for
the cross metathesis of NBR and 1-hexene to achieve a decreased molecular weight and PDI of
the polymer. The NBR had an initial Mw of 270 000 Da and a Mn of 95 000 Da with a PDI of
2.8. For comparison purposes, a benchmark was set using 2nd
Generation Grubbs Catalyst at the
currently industrially used loading of 0.007 phr with 5 phr of 1-hexene. In polymer science phr
stands for parts per hundred. This is used as a measurement of the amount of additives in a
mixture per one hundred parts polymer. In this example, this equates to 5 mg of catalyst and 4 g
of 1-hexene for 75 g of NBR in 425 g of chlorobenzene. After 1 h the Mw and Mn were slightly
reduced to 208 000 and 79 000 Da respectively. After 24 h the Mw and Mn were reduced to
164 000 and 69 000 Da respectively (Figure 6.2.22). This results in a PDI of 2.4.
130
Figure 6.2.22. Mw (Blue Diamonds) and Mn (Red Squares) Over Time of NBR Cross
Metathesis with 1-hexene Using 2nd
Gen. Grubbs Catalyst at a 0.007 phr Catalyst Loading
at 25 ºC in Chlorobenzene
Only catalysts which displayed activity for CM of 5-hexenyl acetate and methyl acrylate were
tested for CM of NBR and 1-hexene. Using 5-12 at the same loading as Grubbs catalyst resulted
in an initial decrease in Mw and Mn after 1 h but after 24 h the NBR was essentially at the initial
molecular weight (Figure 6.2.23). The catalyst was then tested at loadings of 0.014, 0.028, 0.05
and 0.10 phr. It was found that to achieve the same degree of CM as Grubbs Catalyst, 0.05 phr of
5-12 was required. After 24 h the Mw and Mn of the NBR were 155 000 and 67 000 Da
respectively. At a catalyst loading of 0.10 phr 5-12 reduces the Mw and Mn to 97 000 and
48 000 Da respectively.
131
Figure 6.2.23. Mw Over Time of NBR Cross Metathesis With 1-Hexene at Various Catalyst
Loadings of 5-12 at 25 ºC in Chlorobenzene
Catalyst 5-15 was also not as active as Grubbs catalyst for the cross metathesis of NBR and
1-hexene. It was also less active than 5-12. At 0.007, 0.014 and 0.028 phr catalyst loading it
essentially accomplished no metathesis (Figure 6.2.24). At the higher loading of 0.050 phr after
24 h it had reduced the Mw and Mn slightly to 240 000 and 60 000 respectively.
132
Figure 6.2.24. Mw Over Time of NBR Cross Metathesis With 1-Hexene at Various Catalyst
Loadings of 5-15 at 25 ºC in Chlorobenzene
Complex 5-17 was the most active for the standard metathesis tests. Similar to the metathesis of
NBR and 1-hexene using catalyst 5-12, this species required higher catalyst loadings to achieve
the same conversion as Grubbs Catalyst. However, the metathesis occurs much faster than with
Grubbs Catalyst (Figure 6.2.25). After 15 min at a catalyst loading of 0.05 phr the Mw and Mn of
the NBR were reduced to 157 000 and 64 000 Da respectively. After 24 h the Mw increased
slightly to 160 000 Da while the Mn stayed the same. This result was similar to using Grubbs
Catalyst at a loading of 0.007 phr.
133
Figure 6.2.25. Mw Over Time of NBR Cross Metathesis With 1-Hexene at Various Catalyst
Loadings of 5-17 at 25 ºC in Chlorobenzene
6.2.5 Hydrogenation of NBR
The second goal of the Lanxess funded project was to develop new hydrogenation catalysts for
the hydrogenation of NBR. There are a number of examples of ruthenium based complexes
being active olefin hydrogenation catalysts including ruthenium alkylidene complexes. This was
the motivation for testing these complexes for hydrogenation of NBR. The series of compounds
3-5, 5-5 and 5-12 were therefore also tested for catalytic hydrogenation of NBR. Using 10 µmol
of catalyst for 2 mL of a 5 wt% NBR solution in chlorobenzene at 50 bar hydrogen pressure and
80 ºC for 20 h, compound 3-5 was able to achieve 82% hydrogenation (Table 6.2.2). The degree
of hydrogenation was determined from the FTIR spectrum of the polymer (Figure 6.2.26). The
olefinic stretch at 973 cm-1
disappears upon hydrogenation. However, the reaction became more
viscous indicating that cross linking had occurred. This occurs when the catalyst is not selective
for the hydrogenation of the olefin and also hydrogenates the nitrile groups within the polymer.
These amines can then react with olefins within the polymer creating a cross linked structure. In
an attempt to prevent this the catalyst loading was reduced to 5 µmol for 2 mL of a 5 wt% NBR
solution. The pressure was increased to 82 bar in an attempt to push the hydrogenation to
134
completion. This resulted in 71% hydrogenation of the olefins in the NBR but still with some
minor cross linking. At both pressures compounds 5-5 and 5-12 are inactive for hydrogenation of
NBR.
Table 6.2.2. Hydrogenation of NBR with 3-5, 5-5 and 5-12
Compound
Catalyst
Loading
(µmol)
Pressure
(bar)
Degree of
Hydrogenation
3-5 10 50 82%1
5 82 71%1
5-5 10 50 0%
10 82 0%
5-12 10 50 0%
10 82 0% Conditions: 80 ºC for 20 h. 2 mL of a 5 wt% NBR solution in chlorobenzene
1Minor cross linking observed
Compound 3-9 was screened for hydrogenation of NBR by itself and with the addition of 1 and 2
equivalents of BCl3 to generate 5-9 and 5-17, respectively. They were all found to be active for
hydrogenation with 3-9 resulting in such a cross linked polymer that the 2 mL, 5 wt% NBR
solution became a solid (Table 6.2.3). This occurred at a lower catalyst loading as well.
Complexes 5-9 and 5-17 were able to accomplished 74 and 36% hydrogenation respectively at
50 bar hydrogen pressure. Increasing the hydrogen pressure to 82 bar resulted in 99 and 96%
hydrogenation for 5-9 and 5-17 respectively.
Table 6.2.3. Hydrogenation of NBR using 3-9, 5-9 and 5-17
Compound
Catalyst
Loading
(µmol)
Pressure
(bar)
Degree of
Hydrogenation
3-9 10 50 Major Cross Linking
5 82 Major Cross Linking
5-9 10 50 74%
10 82 99%
5-18 10 50 36%
10 82 96% Conditions: 80 ºC for 20 h. 2 mL of a 5 wt% NBR solution in chlorobenzene
135
Figure 6.2.26. FTIR Spectrum of NBR (top) and Hydrogenated NBR (bottom)
6.3 Conclusion
Ruthenium alkylidene complexes bearing tridentate dianionic ligands 3-1 - 3-9 were inactive for
RCM, ROMP and CM. The complexes generated by the addition of one equivalent of BCl3
136
(5-1 - 5-9) were also inactive for RCM, ROMP and CM. Conversely, the cationic complexes
generated by the addition of a second equivalent of BCl3 (5-10, 5-12, 5-14 - 5-17) were active for
RCM, ROMP and CM achieving near complete conversion for certain cases. The complexes
containing the (SCH2CH2)2PPh and (SCH2CH2)2S ligands (3-1 - 3-3) were inactive for catalytic
olefin metathesis even with the addition of 2 equivalents of BCl3. In general the catalysts which
contain a SIMes ligand were more active than the catalysts containing a PCy3 ligand. The
catalysts with the (OCH2CH2)2O ligand (5-16 and 5-17) are most active compared to the
catalysts with the same L (SIMes or PCy3) ligand. The catalysts with the aryl backbone dithiolate
ligand (5-14 and 5-15) are the second best and the alkyl dithiolate complexes (5-10, 5-12) are the
least active. These complexes were shown to be active for cross metathesis of NBR and 1-
hexene. However, higher catalyst loadings were required to achieve the similar conversions as
Grubbs 2 Catalyst. Complexes 3-5, 3-9¸ 5-9 and 5-17 are active for hydrogenation of NBR.
However, catalyst 3-5 and 3-9 both resulted in crosslinking of the polymer.
6.4 Experimental Section
6.4.1 General Considerations
All synthetic manipulations were carried out under an atmosphere of dry, O2-free N2 employing
a VAC Atmospheres glove box and a Schlenk vacuum-line. Hexanes, pentane and
dichloromethane were purified with a Grubbs-type column system manufactured by Innovative
Technology and dispensed into thick-walled glass Schlenk bombs equipped with Young-type
Teflon valve stopcocks. Dichloromethane-d2 was dried over CaH2 and benzene-d6 was dried over
Na metal and vacuum-transferred into a Young bomb. All solvents were thoroughly degassed
after purification (three freeze-pump-thaw cycles). 1H,
13C, and
31P NMR spectra were recorded
at 25 °C on Varian 300 and 400 MHz and Bruker 400 MHz spectrometers. Commercially
available substrates were obtained from Sigma-Aldrich and used without further purification.
NBR was obtained from Lanxess and stored at -40 ºC. Chemical shifts are given relative to
SiMe4 and referenced to the residual solvent signal (1H,
13C) or relative to an external standard
(31
P: 85% H3PO4). In some instances, signal and/or coupling assignment was derived from two-
dimensional NMR experiments. Chemical shifts are reported in ppm and coupling constants as
scalar values in Hz. FTIR spectrum were collected on a Perkin Elmer Spectrum One
spectrometer. GPC data was collected using Styragel HR 5E-THF columns at 45 ºC using a
137
Waters 2414 RI Detector. Data was processed using Empower Pro software and Mw and Mn data
were determined against a polystyrene calibration curve.
6.4.2 Synthetic Procedures
6.4.2.1 Standard Metathesis Reaction Tests
All standard metathesis reaction tests were performed employing a modified procedure of
Grubbs et al.24
A standard procedure for the ring closing metathesis of diethyl diallylmalonate is as follows. The
required amount of catalyst (5 or 1 mol%) was weighed out and dissolved in CD2Cl2.
Compounds 5-10, 5-12, 5-14 and 5-15 were generated by the addition of 1 equiv. of a 1 M BCl3
in hexanes solution to solutions of 5-4, 5-5, 5-6 and 5-7 respectively. For compounds 5-16 and
5-17, 2 equiv. of a 1 M BCl3 in hexanes solution were added to solutions of 3-8 and 3-9
respectively. The solutions were placed in an NMR tube equipped with a septa. Diethyl
diallylmalonate (40 μL, 0.165 mmol) was added via the septum and solution was mixed.
Reaction progress was monitored by 1H NMR every 2 min. Reaction progress was determined by
integration of the olefinic peaks of the starting material versus the product.
A standard procedure for the ring opening polymerization of 1,5-cyclooctadiene is as follows.
Standard solutions in CD2Cl2 were prepared and the appropriate volumes (0.1 mol%) were
diluted for the tests. Compounds 5-10, 5-12, 5-14 and 5-15 were generated by the addition of
1 equiv. of a 1 M BCl3 in hexanes solution to solutions of 5-4, 5-5, 5-6 and 5-7 respectively. For
compounds 5-16 and 5-17, 2 equiv. of a 1 M BCl3 in hexanes solution were added to solutions of
3-8 and 3-9 respectively. The solutions were placed in an NMR tube equipped with a septa.
1,5-cyclooctadiene (50 μL, 0.40 mmol) was added via the septum and solution was mixed.
Reaction progress was monitored by 1H NMR every 2 min. Reaction progress was determined by
integration of the peaks of the starting material versus the product.
A standard procedure for cross metathesis of 5-hexenyl acetate and methyl acrylate is as follows.
The required amount of catalyst (5 mol%) was weighed out and dissolved in CD2Cl2.
Compounds 5-10, 5-12, 5-14 and 5-15 were generated by the addition of 1 equiv. of a 1 M BCl3
in hexanes solution to solutions of 5-4, 5-5, 5-6 and 5-7 respectively. For compounds 5-16 and
5-17, 2 equiv. of a 1 M BCl3 in hexanes solution were added to solutions of 3-8 and 3-9
138
respectively. The solutions were placed in an NMR tube equipped with a septa. A mixture of
5-hexenyl acetate (20 μL, 0.12 mmol) and methyl acrylate (10 μL, 0.11 mmol) was added via the
septum and solution was mixed. Reaction progress was monitored by 1H NMR every 2 min.
Reaction progress was determined by integration of the olefinic peaks of the starting material
versus the product.
Table 6.4.1. RCM of Diethyl Diallylmalonate with 3-4, 5-4 and 5-10
3-4 5-3 5-10
Time (min) Conv (%) Time (min) Conv (%) Time (min) Conv (%)
1 2 0 1 2 0 1 2 1.6
2 4 0 2 4 0 2 4 3.7
3 6 0 3 6 0 3 6 5.4
4 8 0 4 8 0 4 8 7.3
5 10 0.1 5 10 0 5 10 9.1
6 12 0.1 6 12 0 6 12 10.7
7 14 0.1 7 14 0 7 14 13.0
8 16 0.1 8 16 0 8 16 14.5
9 18 0.1 9 18 0 9 18 16.7
10 20 0.2 10 20 0 10 20 18.0
11 22 0.2 11 22 0 11 22 20.6
12 24 0.2 12 24 0 12 24 22.5
13 26 0.2 13 26 0 13 26 23.7
14 28 0.2 14 28 0 14 28 26.5
15 30 0.3 15 30 0 15 30 28.6
16 32 0.3 16 32 0 16 32 31.0
17 34 0.3 17 34 0 17 34 33.3
18 36 0.3 18 36 0 18 36 35.9
19 38 0.3 19 38 0 19 38 38.7
20 40 0.4 20 40 0 20 40 41.5
Table 6.4.2. RCM of Diethyl Diallylmalonate with 3-5, 5-5 and 5-12
3-5 5-5 5-12
Time (min) Conv (%) Time (min)
(min(min) Conv (%) Time (min) Conv (%)
1 5 0 1 5 0 1 5 55.8
2 7 0 2 7 0 2 7 67.5
3 9 0 3 9 0 3 9 75.4
4 11 0.1 4 11 0 4 11 81.1
5 13 0.1 5 13 0.3 5 13 85.1
6 15 0.1 6 15 0.4 6 15 88.2
139
7 17 0.2 7 17 0.5 7 17 90.7
8 19 0.2 8 19 0.6 8 19 92.4
9 21 0.2 9 21 0.6 9 21 93.7
10 23 0.3 10 23 0.7 10 23 94.8
11 25 0.3 11 25 0.7 11 25 95.9
12 27 0.3 12 27 0.8 12 27 96.4
13 29 0.4 13 29 0.9 13 29 97
14 31 0.4 14 31 0.9 14 31 97.4
15 33 0.4 15 33 1 15 33 97.8
16 35 0.5 16 35 1.1 16 35 98.1
17 37 0.5 17 37 1.2 17 37 98.2
18 39 0.6 18 39 1.3 18 39 98.4
19 41 0.7 19 41 1.4 19 41 98.6
20 43 0.7 20 43 1.4 20 43 98.6
Table 6.4.3. ROMP of 1,5-cyclooctadiene with 3-5, 5-5 and 5-12
3-5 5-5 5-12
Time (min) Conv (%) Time (min) Conv (%) Time (min) Conv (%)
1 2 1.1 1 2 1.1 1 2 17.3
2 4 2.4 2 4 1.6 2 4 30.9
3 6 3.5 3 6 2 3 6 36.5
4 8 4.6 4 8 2.3 4 8 39.8
5 10 5.7 5 10 2.5 5 10 41.7
6 12 6.8 6 12 2.7 6 12 43.4
7 14 7.9 7 14 2.9 7 14 44.7
8 16 8.9 8 16 3.1 8 16 45.7
9 18 10 9 18 3.2 9 18 46.7
10 20 11.4 10 20 3.3 10 20 47.4
11 22 12.4 11 22 3.6 11 22 48.2
12 24 13.6 12 24 3.8 12 24 48.9
13 26 14.8 13 26 3.8 13 26 49.4
14 28 16.1 14 28 3.9 14 28 49.9
15 30 17.3 15 30 4.1 15 30 50.4
16 32 18.5 16 32 4.2 16 32 50.8
17 34 19.7 17 34 4.4 17 34 51.1
18 36 21 18 36 4.5 18 36 51.5
19 38 22.1 19 38 4.6 19 38 52
20 40 23.5 20 40 4.7 20 40 52.3
21 42 24.7 21 42 4.8 21 42 52.8
22 44 25.9 22 44 4.8 22 44 53.1
140
Table 6.4.4. CM of 5-hexenyl Acetate and Methyl Acrylate with 3-5, 5-5 and 5-12
3-5 5-5 5-12
Time (min) Conv (%) Time (min) Conv (%) Time (min) Conv (%)
1 2 0 1 2 0 1 2 30.9
2 4 0 2 4 0 2 4 40.4
3 6 0 3 6 0 3 6 45.6
4 8 0 4 8 0 4 8 48.2
5 10 0 5 10 0 5 10 50.2
6 12 0 6 12 0 6 12 51.9
7 14 0 7 14 0 7 14 52.4
8 16 0 8 16 0 8 16 53.7
9 18 0 9 18 0 9 18 53.7
10 20 0 10 20 0 10 20 54.2
11 22 0 11 22 0 11 22 54.9
12 24 0 12 24 0 12 24 55.2
13 26 0 13 26 0 13 26 55.6
14 28 0 14 28 0 14 28 56.7
15 30 0 15 30 0 15 30 56.8
16 32 0 16 32 0 16 32 57.4
17 34 0 17 34 0 17 34 57.5
18 36 0 18 36 0 18 36 57.8
19 38 0 19 38 0 19 38 57.9
20 40 0 20 40 0 20 40 58.1
30 60 0 30 60 0 30 60 59.2
40 80 0 40 80 0 40 80 60.4
50 100 0 50 100 0 50 100 60.7
60 120 0 60 120 0 60 120 60.9
70 140 0 70 140 0 70 140 61.7
80 160 0 80 160 0 80 160 62
90 180 0 90 180 0 90 180 62.3
Table 6.4.5. RCM of Diethyl Diallylmalonate with 5-14
5-14
Time (min) Conv (%)
1 2 3.8
2 4 14
3 6 19.4
4 8 23.1
5 10 25.4
6 12 27.5
141
7 14 29.1
8 16 30.1
9 18 31.5
10 20 32
11 22 33.3
12 24 33.8
13 26 34.6
14 28 35.9
15 30 36.5
16 32 37.5
17 34 38.3
18 36 38.4
19 38 38.7
20 40 38.8
Table 6.4.6. RCM of Diethyl Diallylmalonate with 5-15
5-15
Time (min) Conv (%)
1 2 5.7
2 4 12.6
3 6 15.3
4 8 17.5
5 10 19.7
6 12 21.2
7 14 23.4
8 16 25.3
9 18 26.7
10 20 27.5
11 22 29.3
12 24 30.4
13 26 31.3
14 28 32.2
15 30 32.8
16 32 33.6
17 34 33.8
18 36 34.6
19 38 35.2
20 40 35.9
142
Table 6.4.7. ROMP of 1,5-cyclooctadiene with 5-15
5-15
Time (min) Conv (%)
1 2 52.2
2 4 66.6
3 6 71.3
4 8 74.4
5 10 77.7
6 12 78.4
7 14 79.2
8 16 80.3
9 18 81.1
10 20 81.7
11 22 82.1
12 24 82.4
13 26 82.5
14 28 83.2
15 30 83.8
16 32 84.1
17 34 84.9
18 36 85.4
19 38 85.7
20 40 86.3
Table 6.4.8. CM of 5-hexenyl Acetate and Methyl Acrylate with 5-15
5-15
Time (min) Conv (%)
1 2 9.0
2 4 13.0
3 6 18.0
4 8 23.1
5 10 25.4
6 12 30.1
7 14 33.3
8 16 36.7
9 18 39.8
10 20 42.9
11 22 45.1
12 24 46.8
13 26 49.5
143
14 28 52.8
15 30 53.9
16 32 54.8
17 34 57.1
18 36 58.3
19 38 60.2
20 40 60.6
30 60 68.2
40 80 70.8
50 100 71.7
60 120 72.6
70 140 73.1
80 160 73.7
90 180 74.4
Table 6.4.9. RCM of Diethyl Diallylmalonate with 5-16
5-16
Time (min) Conv (%)
1 2 8.7
2 4 23.1
3 6 35.9
4 8 47.9
5 10 58.3
6 12 66.7
7 14 74.4
8 16 80.8
9 18 85.3
10 20 89.5
11 22 92.2
12 24 94.5
13 26 96.6
14 28 98.5
15 30 99.6
16 32 99.6
17 34 99.6
18 36 99.6
19 38 99.6
20 40 99.6
144
Table 6.4.10. RCM of Diethyl Diallylmalonate with 5-17 with 5 mol% Catalyst Loading
5-17, 5 mol%
Time (min) Conv (%)
1 2 24
2 4 67
3 6 93
4 8 100
5 10 100
Table 6.4.11. RCM of Diethyl Diallylmalonate with 5-17 with 1 mol% Catalyst Loading
5-17, 1 mol%
Time (min) Conv (%)
1 2 3.7
2 4 10.3
3 6 15.7
4 8 20.3
5 10 24.1
6 12 28.0
7 14 31.2
8 16 34.1
9 18 36.8
10 20 39.4
11 22 41.8
12 24 43.8
13 26 45.7
14 28 47.4
15 30 49.1
16 32 50.5
17 34 52.2
18 36 53.5
19 38 55.0
20 40 55.9
145
Table 6.4.12. ROMP of 1,5-cyclooctadiene with 5-17
5-17
Time (min) Conv (%)
1 2 11.5
2 4 56.5
3 6 74.3
4 8 82.1
5 10 86.2
6 12 87.6
7 14 88.9
8 16 90.5
9 18 91.1
10 20 92.9
11 22 93.5
12 24 94.1
13 26 94.9
14 28 95.3
15 30 95.6
16 32 95.8
Table 6.4.13. CM of 5-hexenyl Acetate and Methyl Acrylate with 5-17
5-17
Time (min) Conv (%)
5 10 19.2
10 20 22.2
15 30 26.1
20 40 27.4
30 60 28.6
40 80 29.4
50 100 30.5
60 120 30.8
70 140 31.0
80 160 31.3
90 180 31.5
6.4.2.2 Cross Metathesis of NBR and 1-hexene
A standard procedure for the cross metathesis of nitrile butadiene rubber (NBR) and 1-hexene is
as follows. 75 g of NBR was placed in 325 g of chlorobenzene and placed on a shaker for 48 hr
146
to give a 15 wt% NBR solution. 1-hexene (4 g) was added to the solution and shaken for 1 hr.
The catalysts were prepared by dissolving the required mass of precatalyst in CH2Cl2 (5 mL) in a
glove box and 1 or 2 equivalents of BCl3 was added. The solutions were stirred for 5 min before
being taken out of the glove box and added to the NBR solutions. Samples were taken at 1, 2, 3,
4, and 24 hr. The catalysts were poisoned with ethyl vinyl ether (0.5 mL) to stop the metathesis.
All volatiles were removed from the samples. GPC samples were made by preparing a 1 mg/mL
THF solution of the resulting NBR. The samples were passed through a microporous filter and
the Mn, Mw, and PDI were determined by GPC using a polystyrene calibration curve.
Table 6.4.14. GPC Data for the Metathesis of NBR and 1-hexene using 0.007 phr Grubbs 2
Time (h)
1 Mw (Da) 208500
Mn (Da) 78750
PDI 2.65
2 Mw (Da) 180000
Mn (Da) 74500
PDI 2.42
3 Mw (Da) 174000
Mn (Da) 71300
PDI 2.44
24 Mw (Da) 164000
Mn (Da) 69200
PDI 2.37
147
Table 6.4.15. GPC Data for the Metathesis of NBR and 1-hexene using 5-12
Catalyst loading (phr)
Time (h)
0.007 0.014 0.028 0.05 0.10
1 Mw (Da) 230000 235000 232500 174000 123500
Mn (Da) 83750 84950 82500 71800 57400
PDI 2.75 2.77 2.82 2.42 2.15
2 Mw (Da) 266000 246500 246500 178000 122500
Mn (Da) 91500 86850 86900 71400 56450
PDI 2.91 2.84 2.84 2.49 2.17
3 Mw (Da) 257000 251000 238500 181500 127000
Mn (Da) 91800 87600 89600 73900 59000
PDI 2.80 2.87 2.66 2.46 2.15
4 Mw (Da) 263000 253500 246500 NA NA
Mn (Da) 94750 88750 86800
PDI 2.78 2.86 2.84
24 Mw (Da) 264000 252500 246000 154500 97000
Mn (Da) 93000 88500 91000 67350 47850
PDI 2.84 2.85 2.70 2.29 2.03
Table 6.4.16. GPC Data for the Metathesis of NBR and 1-hexene using 5-15
Catalyst loading (phr)
Time (h)
0.007 0.014 0.028 0.05
1 Mw (Da) 256250 267000 267000 240000
Mn (Da) 66000 65000 62500 60000
PDI 3.88 4.11 4.27 4.00
2 Mw (Da) 272000 266000 263000 241500
Mn (Da) 64500 66000 63000 60000
PDI 4.22 4.03 4.17 4.03
3 Mw (Da) 279500 266000 270000 238000
Mn (Da) 67900 64500 64000 60000
PDI 4.12 4.12 4.22 3.97
4 Mw (Da) 272000 272000 268000 239000
Mn (Da) 65000 66250 64000 60000
PDI 4.18 4.11 4.19 3.98
24 Mw (Da) 271500 276000 266500 239000
Mn (Da) 64000 65000 63000 60000
PDI 4.24 4.25 4.23 3.98
148
Table 6.4.17. GPC Data for the Metathesis of NBR and 1-hexene using 5-17
Catalyst loading (phr)
Time (h)
0.007 0.014 0.028 0.05
0.25 Mw (Da) 267500 228500 196500 156500
Mn (Da) 81000 78000 70500 63500
PDI 3.30 2.93 2.79 2.46
1 Mw (Da) 267500 215500 192000 153000
Mn (Da) 81500 76700 71000 61750
PDI 3.28 2.81 2.70 2.48
2 Mw (Da) 220500 217000 189000 152500
Mn (Da) 71500 75600 69750 60900
PDI 3.08 2.87 2.71 2.50
3 Mw (Da) 238500 216000 194000 155000
Mn (Da) 80500 75550 70650 62150
PDI 2.96 2.86 2.75 2.49
4 Mw (Da) 243000 213500 187000 151000
Mn (Da) 79850 74850 69500 60350
PDI 3.04 2.85 2.69 2.50
24 Mw (Da) 241000 220500 198500 160000
Mn (Da) 80600 75400 71800 63400
PDI 2.99 2.92 2.76 2.52
6.4.2.3 Hydrogenation of NBR
A standard procedure for the hydrogenation of NBR is as follows. A 5 wt% solution of NBR in
chlorobenzene was prepared. In a glovebox 2 mL of the NBR solution was place in a vial with a
stirbar. The catalyst solution was prepared by dissolving the precatalyst (10 or 5 µmol) in
CH2Cl2 (0.2 mL) and if required the appropriate amount of BCl3 was added. The catalyst
solution was added to the NBR and the vials were placed in a high pressure Parr reactor. The
reactor was purged with H2 and charged to the required pressure. The reactor was heated to the
required temperature and the reaction was left for 20 hr. The degree of hydrogenation was
determined by IR spectroscopy following the procedure described by following literature
procedures.27
149
Table 6.4.18. Hydrogenation of NBR using 3-5, 5-5, 5-12
Compound
Catalyst
Loading (µmol)
Pressure
(bar)
Degree of
Hydrogenation
3-5 10 50 82%
5 82 71%
5-5 10 50 0%
10 82 0%
5-12 10 50 0%
10 82 0%
Table 6.4.19. Hydrogenation of NBR using 3-9, 5-9, 5-17
Compound
Catalyst Loading
(µmol)
Pressure
(bar)
Degree of
Hydrogenation
3-9 10 50 Major Cross Linking
5 82 Major Cross Linking
5-9 10 50 74%
10 82 99%
5-17 10 50 36%
10 82 96%
150
Chapter 6 References
1. (Ed.), R. H. G., Handbook of Metathesis. Wiley-VCH: Weinheim, 2003.
2. Astruc, D., New Journal of Chemistry 2005, 29 (1), 42-56.
3. Dragutan, I.; Dragutan, V.; Demonceau, A., RSC Advances 2012, 2 (3), 719-736.
4. Grubbs, R. H.; Chang, S., Tetrahedron 1998, 54 (18), 4413-4450.
5. Meek, S. J.; O'Brien, R. V.; Llaveria, J.; Schrock, R. R.; Hoveyda, A. H., Nature 2011,
471 (7339), 461-6.
6. Ong, C.; Mueller, J. M.; Soddemann, M.; Koenig, T. Metathesis of nitrile rubbers in the
presence of transition metal catalysts. WO2011023763A1, 2011.
7. Pederson, R. L.; Fellows, I. M.; Ung, T. A.; Ishihara, H.; Hajela, S. P., Advanced
Synthesis & Catalysis 2002, 344 (6-7), 728-735.
8. Grubbs, R. H.; Miller, S. J.; Fu, G. C., Accounts of Chemical Research 1995, 28 (11),
446-452.
9. Deiters, A.; Martin, S. F., Chemical Reviews 2004, 104 (5), 2199-2238.
10. Fu, G. C.; Nguyen, S. T.; Grubbs, R. H., Journal of the American Chemical Society 1993,
115 (21), 9856-9857.
11. Maier, M. E., Angewandte Chemie International Edition 2000, 39 (12), 2073-2077.
12. Schrock, R. R., Accounts of Chemical Research 1990, 23 (5), 158-165.
13. Buchmeiser, M. R., Ring-Opening Metathesis Polymerization. In Materials Science and
Technology, Wiley-VCH Verlag GmbH & Co. KGaA: 2006.
14. Piotti, M. E., Current Opinion in Solid State and Materials Science 1999, 4 (6), 539-547.
15. Kessler, M. R.; White, S. R., Journal of Polymer Science Part A: Polymer Chemistry
2002, 40 (14), 2373-2383.
16. Bazan, G. C.; Khosravi, E.; Schrock, R. R.; Feast, W. J.; Gibson, V. C.; O'Regan, M. B.;
Thomas, J. K.; Davis, W. M., Journal of the American Chemical Society 1990, 112 (23), 8378-
8387.
17. Bielawski, C. W.; Benitez, D.; Morita, T.; Grubbs, R. H., Macromolecules 2001, 34 (25),
8610-8618.
18. Chatterjee, A. K.; Choi, T.-L.; Sanders, D. P.; Grubbs, R. H., Journal of the American
Chemical Society 2003, 125 (37), 11360-11370.
151
19. Chatterjee, A. K.; Grubbs, R. H., Organic Letters 1999, 1 (11), 1751-1753.
20. Connon, S. J.; Blechert, S., Angewandte Chemie International Edition 2003, 42 (17),
1900-1923.
21. Marinescu, S. C.; Levine, D. S.; Zhao, Y.; Schrock, R. R.; Hoveyda, A. H., Journal of the
American Chemical Society 2011, 133 (30), 11512-11514.
22. Schrodi, Y.; Ung, T.; Vargas, A.; Mkrtumyan, G.; Lee, C. W.; Champagne, T. M.;
Pederson, R. L.; Hong, S. H., CLEAN – Soil, Air, Water 2008, 36 (8), 669-673.
23. Thomas, R. M.; Keitz, B. K.; Champagne, T. M.; Grubbs, R. H., Journal of the American
Chemical Society 2011, 133 (19), 7490-7496.
24. Ritter, T.; Hejl, A.; Wenzel, A. G.; Funk, T. W.; Grubbs, R. H., Organometallics 2006,
25 (24), 5740-5745.
25. Ong, C.; Mueller, J. M. Process for the preparation of low molecular weight
hydrogenated nitrile rubber. WO2011023788A1, 2011.
26. Xie, H.-Q.; Li, X.-D.; Guo, J.-S., Journal of Applied Polymer Science 2003, 90 (4), 1026-
1031.
27. Bhattacharjee, S.; Bhowmick, A. K.; Avasthi, B. N., Industrial & Engineering Chemistry
Research 1991, 30 (6), 1086-1092.
28. Occhipinti, G.; Bjørsvik, H.-R.; Törnroos, K. W.; Jensen, V. R., Organometallics 2007,
26 (24), 5803-5814.
29. Wasilke, J.-C.; Wu, G.; Bu, X.; Kehr, G.; Erker, G., Organometallics 2005, 24 (17),
4289-4297.
30. Sanford, M. S.; Love, J. A.; Grubbs, R. H., Journal of the American Chemical Society
2001, 123 (27), 6543-6554.
31. Sanford, M. S.; Ulman, M.; Grubbs, R. H., Journal of the American Chemical Society
2001, 123 (4), 749-750.
32. Furstner, A.; Furstner, A.; Picquet, M.; Bruneau, C.; H. Dixneuf, P., Chemical
Communications 1998, (12), 1315-1316.
152
Chapter 7 Summary and Future Work
7.1 Summary
The work presented herein was motivated by the desire to develop new olefin metathesis
catalysts for the cross metathesis of NBR and 1-hexene. Recognizing a gap in the patent
literature, the use of tridentate ligands for this new development was targeted. Specifically,
tridentate dianionic ligands were used to synthesize new ruthenium alkylidene complexes. These
complexes were inactive for olefin metathesis on their own but upon the stepwise addition of two
equivalents of BCl3 the resulting complexes were active for a variety of metathesis reactions.
Chapter 2 explores the coordination chemistry of tridentate dithiolate ligands on ruthenium. It
was found that only complexes with tridentate dithiolate ligands with a central ether donor could
be successfully isolated. These complexes were demonstrated to react with BCl3 to give new
6-coordinate ruthenium complexes. A chloride from BCl3 was transferred to ruthenium and the
remaining BCl2 fragment was bridged between the two thiolate ligands.
In Chapter 3, the ligands used in Chapter 2 were used for the synthesis of ruthenium alkylidene
complexes from Grubbs Catalysts. A library of compounds was synthesized with variations to
the central donor of the tridentate ligand including ether, thioether and phosphino. A ligand with
an aryl backbone and a tridentate dialkoxide ligand were also used. In most cases, complex
derivatives where the 5th ligand was either PCy3 or SIMes were prepared.
Due to the motivation to prepare the targeted olefin metathesis catalysts independently of Grubbs
Catalyst, Chapter 4 describes the development of a new method to prepare ruthenium
alkylidenes. Using a Ru(0) source such as Ru(cod)(cot) or Ru(PPh3)4H2 and dithioacetals derived
from the ligands used in Chapter 3, tridentate, dithiolate ruthenium alkylidene complexes could
be synthesized. This method provides a convenient route to these complexes by installing the
tridentate dithiolate ligand and the alkylidene on to ruthenium in one step.
Chapter 5 describes the reactivity of the complexes prepared in Chapters 3 and 4 with BCl3.
Similar to the reactivity observed in Chapter 2, these complexes react with 1 equivalent of BCl3
to form new 6-coordinate complexes. In the new complexes a chloride has transferred from BCl3
153
to ruthenium and the remaining BCl2 fragment is bridged between the thiolate ligands. Due to the
trans effect, the tridentate ligand rearranges on the metal centre. However, in some cases two
isomers are formed. In one isomer the ligand has rearranged and in the other it has not. With
some complexes the addition of a second equivalent of BCl3 results in abstraction of the chloride
from ruthenium to give a 5-coordinate cationic complex. In contrast, the parent complexes react
with Bronsted acids by protonation of the alkylidene carbon. The reactivity with both Lewis and
Bronsted acids is reversible by the addition of a base such as PtBu3 to give the parent tridentate
dithiolate ruthenium alkylidene complexes.
Finally, in Chapter 6 the ruthenium alkylidene complexes prepared were tested for catalytic
olefin metathesis. The tridentate dithiolate ruthenium alkylidene complexes described in
Chapters 3 and 4 were inactive for olefin metathesis. This was also the case for the complexes
formed by the addition of 1 equivalent of BCl3. The 5-coordinate cationic ruthenium alkylidenes
generated by the addition of a second equivalent of BCl3 were found to be active for a variety of
olefin metathesis reactions including ring closing metathesis (RCM), ring opening metathesis
polymerization (ROMP) and cross metathesis (CM). In general the catalysts containing SIMes
were more active than the PCy3 derivatives. The three most active catalysts were screened for
CM of NBR and 1-hexene. It was found that in order to achieve the same activity as 2nd
Generation Grubbs Catalyst, higher catalyst loadings were required. A series of these complexes
were also tested for the hydrogenation of NBR and shown to be active hydrogenation catalysts.
The successful development of new olefin metathesis catalysts presented herein has afforded a
large volume of new ruthenium chemistry. The knowledge gained from this work can be used in
the development of new, more active olefin metathesis catalysts.
7.2 Future Work
The activation of all the catalysts presented herein were done with the Lewis acid BCl3. An
obvious area of further development would be to investigate the effect of different Lewis acids.
Perhaps the use of a more electron withdrawing Lewis acid would result in a more active
catalyst. A Lewis acid activation method which is non-reversible may improve catalyst
performance also. Since the activation with BCl3 was shown to be reversible this could be a
potential path of catalyst decomposition and deactivation. Using a Lewis acid activator which
154
performs the activation in a non-reversible fashion could prevent this possible decomposition
pathway.
A rational design of precatalyst/activator could be performed if the catalyst decomposition was
better understood. This would be the motivation behind a study of catalyst deactivation and
decomposition pathways. The isolation and characterization of ruthenium species after catalytic
olefin metathesis would be of great interest. Once the decomposition products were isolated a
detailed mechanistic study of the pathway to these species would prove to be invaluable in the
design of longer living and thus more active catalysts.
Due to the easy variability of the dithioacetals used in the independent synthesis of these
complexes the scope of this reaction could be easily determined. This would provide convenient
access to a number of new catalyst variants. Modifications could be made to the ligand itself
using different tridentate dithiols in the dithioacetal synthesis. Modifications could include
different central donors and varied ligand backbones. Easy modification to the resulting
ruthenium alkylidene could be accomplished simply by using different aldehydes in the
dithioacetal preparation. The effect of electron withdrawing or donating substituents on the
phenyl ring could be investigated and alkyl variants could also be easily prepared.
The catalyst with the tridentate dialkoxide ligand was shown to be the most active for the
standard metathesis reaction. However, this catalyst could not be synthesized independently of
Grubbs Catalyst. It would therefore be beneficial if an independent synthesis of this catalyst was
developed. Developing a new method for synthesizing ruthenium alkylidenes could also allow
access to a variety of new complexes.
Finally the scope of metathesis reactions that these catalysts can perform should be broadened.
Although these catalysts were demonstrated to be active for the standard metathesis reactions
and the metathesis of NBR, knowledge of the scope of these catalysts would be useful for
developing new uses and applications for them.