Homogeneous Catalysis for C-H Activation and Other Approaches to Shale Gas Utilization!

Shannon S. Stahl!University of Wisconsin–Madison!

CH4

H2/CO

H2C CH2

R

CH3OH

[O]

(existing)!

What will be the source of aromatics, C4s and propylene?!

Bruijnincx and Weckhuysen!ACIE 2013, 52, 11980!

Why Homogeneous Catalysis?!• !Homogeneous catalysts are used in numerous major industrial processes!!- !olefin oligomerization, polymerization (ethylene) !! ! !• metallocenes and other single-site Ti/Zr/Hf!! ! !• [(P,O)Ni–H]+ (SHOP catalysts)!! ! !• Cr(EH)3/Me2pyrrole/AlR3!!- !hydroformylation (syngas)!! ! !• Rh/phosphine, HCo(CO)4 ± phosphine!!- !aerobic oxidation - Wacker and Mid-Century processes (O2)!!- !many others…!

!• !Is Homogeneous vs. Heterogenous Catalysis an appropriate dividing line? !!Is this an artifact of US academic science (Chemistry vs. Chem. Engr. departments and associated language barriers)?!!- !Molecular vs. Nanoparticle vs. Bulk Heterogeneous!!- !Liquid phase vs. gas phase chemistry!!- !How should single-site supported catalysts (e.g., metallocene and related olefin!! !polymerization catalysts) and MOFs be classified?!

!• !This presentatiion will emphasize "molecular" processes and/or concepts!!- !biological transformations/oxidations reflect this perspective!! !(enzymes are molecules)!!- !molecular/atomistic concepts are increasingly relevant and applied to !! !"heterogenous" catalysis (zeolites, MOFs)!

α-Olefin Synthesis and Applications!

Alpha Olefins Market Analysis By Product (1-Butene, 1-Hexene, 1-Octene), By Application (Polyethylene, Detergent Alcohol, Synthetic Lubricant) And Segment Forecasts To 2020!Published: March 2015 | ISBN Code: 978-1-68038-356-0!

“Increasing 1-hexene usage in LLDPE

production is expected to drive the market growth

over the forecast period.”!

Major Applications!•  LLDPE!•  HDPE!•  Detergent Alcohols!•  Synthetic Lubricants!

α-Olefin Synthesis!•  Shell Higher Olefin Process (oligomerization/methathesis) - ethylene!•  Oligomerization (INEOS) - ethylene!•  Fischer-Tropsch (Sasol) - syngas!

•  Butadiene telomerization (Dow) – naphtha cracking!•  Ethylene trimerization/tetramerization - ethylene

(Chevron Phillips, Sasol)!

Homogeneous Catalysts!Selective for primarily!a single alpha olefin!

5.2M tons!3.7M !tons!

courtesy of C. R. Landis!

Discovered in 1930s (Co) & 1960s (Rh)

– Oxo Process –

Hydroformylation: (α-)Olefins and Syngas!

Linear (and branched) Aldehydes > 18 billion lbs/year

R + H2/CO R H

OHRh or Co

Discovered in 1955

– Mid-Century and Related Autoxidations –

Radical Chain (Liquid Phase) Aerobic Oxidation of Hydrocarbons!

H3C

CH3

+ 3 O2Co/Mn/Br-

HO2C

CO2H

+ 2 H2O

Radical-Chain (Catalytic) Aerobic Oxidation!> 100 billion lbs/year

In2In RH

R O2RH

R

RO2

RO2RO4R2 RO2

InH

RO2H

2 In

RO2R

RO2

R

R

Initiation

Propagation

Termination

Ri

+ +

++ +

+nonradical products + O2

also…!

airOOH

decompositionOH O

+

among others!

H2C CH2 + 1/2 O2 H3C H

O[Pd, Cu]

H2O 2 Cu2+

2 Cu+

HO

CH3

PdII

PdIIOH

PdII

H+

H2O

CH2

CH2

2+

+ 2 H+

+

+ H+

Pd0

1/2 O2

CH2 CH2

Discovered in 1959

Wacker Process: Ethylene to Acetaldehyde!

Organometallic Aerobic Oxidation Chemistry > 1 billion lbs/year

Regioselective Alkane Activation by Transition Metal Complexes!

Activation of 1° C-H bond is favored!!!but…!

reactions generally stoichiometric and incompatible with oxidants or other reagents needed to functionalize the metal-alkyl!

Labinger & Bercaw Nature 2002, 417, 507-514. !

IrMe3P H

HIr

Me3P H

hν

– H2+ Ir

Me3P H

110 °C, 14h

1.5:1

+

for M = Rh, only 1° C–H activation

+ CH4Zr NRR(H)NR(H)N

R = SiBut3

ZrN(H)RR(H)N

R(H)N

CH3

Sc CH3 + 13CH4 Sc 13CH3 + CH4

Oxidative Addition (Bergman, Graham, Jones, …)!

Sigma-Bond Metathesis (Bercaw, Watson, Marks, …)!

1,2-Addition (Wolczanski, Bergman, …)!

1980s, 1990s!

Selective "C–H Functionalization"!2000s – Applications to organic chemistry, pharmaceutical synthesis…!

DG

H3C

H3C CH3

OH3C

H3C

OO

OO

OH

OH

Jiadifenolide

Huw Davies Emory University

NSF Center for Chemical Innovation (CCI)!

120° CCH3OH + PtCl42- + 2 HClCH4 + PtCl62- + H2O

PtCl42-

! [O]!The

Oxidant Problem!

Organometallic Methane Oxidation!The Shilov System (1971)!

PtIIClClClCl PtII

ClClCH3Cl

PtIVClClClCl

2-

CH3

Cl

2-

2-

CH3OH + H+

CH4 HCl

PtIVCl62-

PtIICl42-H2O

Shilov System!

+25% conversion

80%

OH OHHO OHCl

CH4 vs. CH3OH

k1 k2

k1 ~ k2cf. H atom abstraction:

k1

k2~ 10-6

C2H6 vs. C2H5OH

H–CH2CH3 > H–CH2CH2OH > H–CH(OH)CH3

→ direct oxidation of ethane to ethylene glycol!

Propanol Oxidation

CH4 CH3OH CH2O

Biological Methane Oxidation!

CH4 + O2 + NADH + H+ CH3OH + H2O + NAD+MMO45 °C

! e– The

Reductant Problem!

Methane Monooxygenase (Fe)!

Graphic:!Kopp & Lippard Curr. Opin. Chem. Biol., 2002, 568.!

Biological Methane Oxidation!

CH4 + O2 + NADH + H+ CH3OH + H2O + NAD+MMO45 °C

The Reductant Problem!

Methane Monooxygenase (Fe)!

CH4 + H2O2 → CH3OH + H2O !

O2 + 2 H+ + 2 e– → H2O2 !

CH4 + 2 H2O → CO2 + 8 H+ + 8 e– !

x 4!

5 CH4 + 4 O2 → 4 CH3OH + 2 H2O + CO2 !

* Max 80% selectivity *!

Biological Aerobic Oxidation

Mn+

H2O SubH2

Subox 1/2 O2

M(n+2)+

+ 2 H+ + 2 H+S(O)

S

O

Mn+

O2

H2O

+ 2 H++ 2 e-

M(n+2)+

L

N NNN

CO2- CO2-

Fe

O +•

FeO

OFe

OGluOGluNHis NHis

OH2OGlu

O OGlu

CuO

OCu

NHis

NHisNHis

NHisNHis

NHis

Oxidases substrate oxidation and !

dioxygen reduction occur in independent steps

Oxygenases substrate oxidation coupled!to oxygen atom transfer !

from dioxygen!

H2O or!H2O2!

HgX2 & Pt(bpym)-Catalyzed Oxidation of Methane!

A. Sen!

CH3CH3 + O2 + CO 5% Pd/C CH3CO2H + CO2H2O (0.1 M HCl)500 psi 100 psi 100 psi 2.7% yield

1138 TOs

References:!JACS 1992, 114, 7307.!Nature 1994, 368, 613.!JACS 1997, 119, 6048.!Acc. Chem. Res. 1998, 31, 550.!

in situ H2O2!production with!heterogeneous

catalyst!

Catalytic "monooxygenase" pathway for ethane oxidation:!

See also:!R. Neumann JACS 2004, 126, 10236.!Methane to Methanol/Acetaldehyde!

Alternative coupled process for methane to acetic acid ("oxidase"-type reactivity): !

Science 2003, 301, 814-818.!

PdSO4, 180 °C in H2SO4! R. Periana!

H2C CH2 + 1/2 O2 H3C H

O[Pd, Cu]

H2O 2 Cu2+

2 Cu+

HO

CH3

PdII

PdIIOH

PdII

H+

H2O

CH2

CH2

2+

+ 2 H+

+

+ H+

Pd0

1/2 O2

CH2 CH2

Discovered in 1959

Wacker Process: Ethylene to Acetaldehyde!

Organometallic Aerobic Oxidation Chemistry > 1 billion lbs/year

NO

NO

NO2

NO1/2 O2

H2Oe-

cathode

e-

2 H+

2

2

Homogeneous "Oxidase" Reactions

O2 + 4 H+ + 4 e- → H2O!

2 H+ + 2 e- → H2!

O2 + 2 H+ + 2 e- → H2O2 !

0.00!

1.23!

0.68!

Redox couples can facilitate oxidation reactions with O2!

•!A!•!B!

Gerken & Stahl, ACS Cent. Sci., 2015, 1, 234-243. !

2 H2

2 H2O

cathodeanode

O2 + 4 H+

e- e-

e-e- e-

e-

H+ membrane4 H+

(CH3OH)

(CO2)

η = 0.3 V!

Slow steps avoided through the use of synergistic mediators!

(Also Fast)!

Fast!Electrochemical!

Kinetics!

Fast !Aerobic!

Oxidation!

Slow!Aerobic!

Oxidation!

!Slow!

Electrochemical!Kinetics!

Electrocatalysis provide unique opportunities to address catalyst development and characterization!

Low Temperature, Direct Conversion of Natural Gas to Alcohols Using Commercial Wacker Plant Design

N2

Low  pressure  Air  (O2/N2)

Natural  Gas(CH4+  C2H6 +  C3H8)

ROH(Methanol  +  Ethanol+  Ethylene  glycol+  Isopropanol+  propylene  glycol)

Ox  +  HOP

H2Ox

H2Ox+  HOP

ROP

H2O

Separator  (SP)

Vent

STY  =  ~50  lbs/L.hr

Hydrocarbon  oxidizer  (HO)

Ox  Regenerator  (OR)

~200oCbubble-­‐column  reactors  are  among  the  least  expensive  reactors

No  O2 plant  required

Inherently  Safe

Modified, Commercial Wacker Process

New main group chemistry

Enables, new low cost process

Methanol Ethanol Ethylene Glycol Isopropanol Propylene Glycol

Natural Gas

Air

Courtesy of T.B. Gunnoe!

IO3- -based C-H activation reagent/oxidant:

Gunnoe, Groves et al. J. Am. Chem. Soc. 2014, 136, 8393−8401!

TlIII, PbIV, BiV, IIII-based C-H activation reagent/oxidant: Periana, Ess et al. Science 2014, 343, 1232-1237

T. Brent Gunnoe!University of Virginia!

Radical Chain (Aerobic) Oxidation of Hydrocarbons!

Bromine as a recyclable "chain carrier"!

(CH4, C2H6, …)!

Lorkovic, et al. !Catal. Today 2004, 98, 317-322 !

Radical Chain (Aerobic) Oxidation of Hydrocarbons!

Bromine as an O2-recyclable "chain carrier"!

McFarland, Science, 2012, 338, 340-342. !

Alkane bromination:!Alkyl bromide conversion !

to valuable products:!

Br2 regeneration by O2:!

Pt(bpym)-Catalyzed Oxidation of Methane vs. Ethane!

Periana et al.!Science 1998, 280, 560-564.!

CH4 + H2SO4 + SO3 CH3OSO3H + H2O + SO2[Pt(bpym)X2]

180° C

HgX2 & Pt(bpym)-Catalyzed Oxidation of Methane!

CH4 + 2 Hg(O3SCF3)2 CH3O3SCF3 + HO3SCF3 + Hg2O3SCF3)2

alternative solvents: H2SO4 and CF3CO2H

CH4 + 2 H2SO4 CH3OSO3H + 2 H2O + SO2180 °C

100% !!

50% conversion, 85% selectivity: 43% yield

180 °C

HO3SCF3

HgII

Periana/Catalytica, 1993!

50% conversion, 85% selectivity: 43% yield!

90% conversion, 81% selectivity: 70% single-pass YIELD !!!CH4 + 2 H2SO4 CH3OSO3H + 2 H2O + SO2200 °C

PtII

Periana/Catalytica, 1998!

N N

NNPtII

X

XPtII =

Periana et al. Science 1993, 259, 340-343.!Periana et al. Science 1998, 280, 560-564.!

Notes!• H2SO4 is the oxidant!• the organic ligand remains stable in hot, fuming sulfuric acid!• the Pt(II) complex is thermodynamically stable!• no chloride inhibition (obviously) as in Shilov system!

HgX2 & Pt(bpym)-Catalyzed Oxidation of Methane!

Step 1: CH4 + 2 H2SO4Step 2: CH3OSO3H + H2OStep 3: SO2 + 1/2 O2 + H2ONet Rxn: CH4 + 1/2 O2

CH3OSO3H + 2 H2O + SO2 CH3OH + H2SO4 H2SO4

In principle. . .

CH3OH

multi-stage aerobic oxidation of alkanes... !

Step 1: 2 CH4 + 5 H2SO4Step 2: CH3CO2SO3H + H2OStep 3: 4 SO2 + 2 O2 + 4 H2ONet Rxn: 2 CH4 + 2 O2

CH3CO2SO3H + 7 H2O + 4 SO2 CH3CO2H + H2SO4 4 H2SO4

CH3CO2H + 2 H2O

(CONCEPT)!

Catalytica/Periana Pt(bpym) Catalyst!

+!+!

+! +!

+!

+!+!

+!+!+!+!+!

+!+!

+!+!

+!+!

+!

+!+!+!

+!

+!+!

+!+! +!+!

+! +!

+!+!

+!+!+!

+!+!+!+!

+!+!+!

+!+!+!+!+!+!+!+!+!+!+!

+!+!+!

+!+!+!+!+!+!+!+!+!+!+!

+!

+!

""

"

10! 20! 30! 40! 50! 60! 70!

100!

80!

60!

40!

20!

0!0! 80! 90! 100!

% One-Pass RH Conversion!

% P

rodu

ct S

elec

tivity!

"

"

"

+!

+!

"

"

CH3OH!

These catalysts all generate radicals

k1 << k2

+ OCM!

Methane Sulfonation!

Economic Window: k1 >> k2                    

courtesy of R. A. Periana!

R–H R–OH+ 1/2 O2 + n O2

CO2k1! k2!

N N

NNPtII

X

XPtII =H

First-generation non-radical catalyst!

Pt(bpym)-Catalyzed Oxidation of Methane vs. Ethane!

Periana and coworkers!J. Am. Chem. Soc. 2014, 136, 10085−10094!

CH3–CH3 + H2SO4 + SO3HO3S OSO3HCH3 OSO3H

[Pt(bpym)X2]

CH4 + H2SO4 + SO3 CH3OSO3H + H2O + SO2[Pt(bpym)X2]

180° C

Gunnoe, Herring, Trewyn; J. Am. Chem. Soc.  2016, 138, 116-125.!

Low Temperature Electrocatalytic Oxidation of CH4

OMC-4Bp-Pt-Cl2 Electrocatalysis provides a unique opportunity to assess catalytic efficiency!

Oxidative C–C Coupling�

H

[Pd], O2

O

O

O

O

O

O

N

O

O

N

O

O

n

NH2

NH2

polyimide

+

Upilex (UBE)!#2 polyimide resin!

!high thermal and chemical resistance, high electrical insulating properties

and high mechanical strength!

CO2MeCO2Me+ MeOH [Pd], O2

CO2MeMeO2C

MeO2C CO2Me

CO2HHO2C

HO2C CO2H

- H2OO

O

O

O

O

O

- H2O

[V], O2

OO

O

+ H2O- MeOH

CH4 + CH4 CH3–CH3 CH2=CH2Pd/O2 Pd/O2

Methane?!

Oxidative Dehydrogenation of Saturated C–C Bonds!

R R'+ H2Ocat. PdII

+ 1/2 O2H H

R'R

O2 as the hydrogen acceptor!

R R'

XLnPdII

H

HydrideEliminationβ-

LnPdIIX2HX

XLnPdII

R R'

H H

RR'

H

C–HActivation

LnPd

LnPd0

HX

2 HX

OO

O2

H2O2(1/2 O2 + H2O)

Oxidative Dehydrogenation!Pd-Catalyzed Dehydrogenation of Cyclohexanones to Phenols!

Izawa, Pun, Stahl Science, 2011, 333, 209.!

catalyst!

Pd(TFA)2 /N NMe2

O O OH

R R R

[Pd], O2 [Pd], O2

– H2O – H2O

"Interrupted" Dehydrogenation of Cyclohexanones:!

Diao, Stahl JACS 2011, 133, 14566.!

catalyst!Pd(DMSO)2(TFA)2!

O O OH

R R R

[Pd], O2 [Pd], O2

– H2O – H2O

O O

O OH

Molecular PdII !Species!

Soluble Pd!Nanoparticles!

Heterogeneous Pd!Aggregates!

fast! moderate! inactive!

slow! moderate! inactive!

(kinetic burst)!

(induction period)!

(steady-state!turnover)!

(steady-state!turnover)!

X!Molecular vs. Nanoparticle Catalysis!

Non-Oxidative Hydrocarbon Conversion!

Activation of 1° C-H bond is favored!!!but…!

reactions generally stoichiometric and incompatible with oxidants or other reagents needed to functionalize the metal-alkyl!

Labinger & Bercaw Nature 2002, 417, 507-514. !

IrMe3P H

HIr

Me3P H

hν

– H2+ Ir

Me3P H

110 °C, 14h

1.5:1

+

for M = Rh, only 1° C–H activation

+ CH4Zr NRR(H)NR(H)N

R = SiBut3

ZrN(H)RR(H)N

R(H)N

CH3

Sc CH3 + 13CH4 Sc 13CH3 + CH4

Oxidative Addition (Bergman, Graham, Jones, …)!

Sigma-Bond Metathesis (Bercaw, Watson, Marks, …)!

1,2-Addition (Wolczanski, Bergman, …)!

Sadow & Tilley!JACS, 2003, 125, 7971–7977.!

Center  for  Enabling  New  Technologies  Through  Catalysis  A  NSF  Center  for  Chemical  Innova=on  CHE-­‐1205189  

Karen  I.  Goldberg,  University  of  Washington,  Principal  Inves=gator  www.nsfcentc.org  

OO

O

OO

OH

OH

OHOH

OH

OH

OH

H3COO

OH

OHO

OHO

O

OH

O

H3CO

OH

OH

H3CO OHHO OCH3

OHO

OOCH3

OH

OOH

H3CO O

OH

OHOCH3

O

OOH

OCH3

O

OOHOCH3

O

OH

OCH3

OCH3

HO

O OHH3CO

HO

lignin

ligninCO  +  H2  

CO2  

cellulose

hemicellulose

lignin

waste oil

OOHO OH

O

OH

OHO

OH

O

OH

O

O

O

O

O

O

R

R

R

Karen Goldberg!

CO + H2

n-alkanes

Stochas(c  Distribu(on  

Fischer  -­‐Tropsch  

GAS FUEL

(Diesel)

Cn

X (not

useful as

fuel) HIGH-MW 3 9 19

Alkane Metathesis:Diesel from Any Carbon Source!

Gas, Coal, Shale, Tar Sands, Biomass…

hydrocracking alkane

metathesis

n-Alkanes are ideal transportation fuel (C10-C19 diesel): !  Burns more cleanly than oil-based fuels. Reduces CO emissions and particulate matter!  Diesel engines 30 - 40% more efficient than ! gasoline engines!

Alkane Methathesis via Tandem Catalysis!

Goldman, A. S. et al, Science, 2006, 312, 257.!U.S. Patent 7,902,417, issued March 8, 2011!

Alan Goldman Maurice Brookhart Richard Schrock

Comparable rates !but desired !

MW-selectivity achieved with tBuPCP, !

not with tBuPOCOP. !(tBuPOCOP)Ir!!

e.g. for reaction: 2 C6 → C10 + C2!!

PtBu2O

OPtBu2

Ir HH

Subtle catalyst variations are key:!

PtBu2

PtBu2

Ir HH

(tBuPCP)Ir!

with!Schrock!catalyst!!or!

CHC(CH3)2Ph

Mo

NRF6O

RF6O

Ar

R2

M MH2

dehydrogenation

X

Y

Ir

PR'2

PR2

M = Z

hydrogenation

R2

RRH3C CH3

olefinmetathesis

RR

Mo

NAr

CHR"R'O

R'O

Or

Re2O7/Al2O3MoO3/CoO/Al2O3

H2C CH2

From Ethylene and Alkanes to Aromatics!

Lyons, T. W. et al. J. Am. Chem. Soc. 2012, 134, 15707-15711. Brookhart, et al. “Synthesis of para-xylene and toluene.” (2012) WO 2012061272 A2.

Maurice Brookhart (iPr)2P Ir P(iPr)2

Brookhart, Goldman, et al. Nature Chemistry, 2011, 3, 167-171.

(CH2)nH

O PiPr2

PiPr2

Ir

170 °C (CH2)nH+

(CH2)nH

R RAlan Goldman Maurice Brookhart

[Cr]CatalystPhillipsProcess

Dehydrogenation 2 H2

major minor

Feedstock3

catalyst

250 °C 250 °C

Pd/C or Pt/Al2O3

Opportunities for Homogeneous Catalysis!1.  Oxygen management and reactivity!

a.  Sacrificial reductant?!b.  O2-Recyclable co-oxidant (Br2, NOx, etc.)!

2.  Oxidative vs. Non-Oxidative Transformations!a.  Reactions with ethylene (selective oligomerization)!b.  Dehydrogenative coupling, aromatization!c.  Methane as a C1 source!d.  Oxygenation reactions !e.  Oxidative C–C coupling (fundamentals, practical opportunities?)!f.  Oxidative dehydrogenation!

3.  Broader exploration of "Extreme" conditions (homogen. catal. perspective)!a.  Strong acid solvents!b.  "High" temperature (200 °C)!c.  Stable ligands to prevent catalyst decomp., oxidatively stable !!(previous examples: pincers, bpym)!

4.  Electrocatalysis and other tools !a.  A (new) tool for catalyst development and understanding!b.  Practical application opportunites? (smaller scale plants to avoid flaring)!

5.  Funding – to reinvigorate the field!a.  Small-team grants but programmatically interconnected – e.g., req'd participation in

annual/bi-annual workshop/symposium!b.  Active industrial engagement (consultation, funding?)!!!