Suzuki Coupling:Aqueous and Anhydrous Synthesis of

Ferrocene-Capped Thiophene

Bill Mitchell2003-04

Fe

S

Fe

Polythiophene

Introduction

• Polythiophene– p-type semiconducting organic polymer– Tuneable electronic properties

S

*

*

n

Introduction

• Applications– Photovoltaics (solar cells)

• Cheaper

• Higher voltage

• Activated by visible light

• Tuning will improve efficiency

– Transistors, light emitting diodes• Cheaper

• More efficient

• Smaller

S

*

*

n

Introduction

• Problem– No cyclic voltammetry

• Polymerization

• Ferrocene– End-cap for thiophene– Electrochemically active

Fe

Ferrocene

Introduction

• Short chain vs. long chain– Solubility– Yield– Accuracy

n= 1, 2, 3

Short chainn= 3, 4

Long chain

Fe

S

Fe

n

Fe

S

S

S

Fe

n

Procedure 1:Aqueous 2,5-Diferrocenyl-Thiophene

• Suzuki Coupling– Aqueous

• Highly contaminated

• Low yield

S

Br

Br

Fe

B

O

H

O

H

Fe

S

Fe

2 + + 2 NaOH(aq)

PdCl2(dppf)

In dimethoxy-ethanereflux 120 hr.

Side Reaction

Fe

B

O

H

O

H

Fe

H

O

H

+ + B(OH)3

Anhydrous CouplingOrganic soluble

– Boronic ester– Less contamination– Higher yield

1-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-ferrocene

Fe

O

O

B

Procedure 2:1-(4,4,5,5-Tetramethyl-1,3,2-Dioxabolan-2-yl)-Ferrocene

(Boronic Ester)

Fe

O

O

B

Fe

B

O

H

O

H

O

H

O

H

H

O

H

+ in pentane +

Procedure 3:Anhydrous 2,5-Diferrocenyl-

Thiophene

Pd

P

P

h

3

P

P

h

3

P

P

h

3

P

P

h

3

Pd

P

P

h

3

P

P

h

3

S

X

Br

Fe

S

Pd

P

P

h

3

P

P

h

3

Br

X

S

Pd

P

P

h

3

P

P

h

3

X

Fe

Fe

S

X

Fe

O

O

B

K

3

P

O

4

Fe

Br

-

K

B

r

K

2

P

O

4

O

O

B

+ 2 PPh3

X = Br,

+

+ -

+In dioxaneReflux 96-120 hr.

Solvent Catalyst Excess Ligand Reducing Agent Base Time Yield5-10 mol% equivalent equivalent on catalyst 3 equiavalents on (starting materials)dependant on scale on catalyst fully reduced boronic ester

THF NiBr2(PPh3)2 1 PPh3 2 n-BuLi potassium t-butoxide 72 hrs 0% (~100%)dioxane PdCl2(dppf) none 2 n-BuLi potassium t-butoxide 48 hrs 0% (~0%)dioxane NiBr2(PPh3)2 none 2 n-BuLi potassium t-butoxide 72 hrs 0% (~0%)dioxane NiCl2(dppe) 2 dppe .5 n-BuLi potassuim t-butoxide 44 hrs 0% (~0%)dioxane NiCl2(dppe) 2 dppe none potassium t-butoxide 18 hrs 0% (~0%)

dioxane PdCl2(dppf) none .5 n-BuLi potassium carbonate 48 hrs 0% (~100%)dioxane (PPh3)4Pd(0) open bottle 2 PPh3 none potassium carbonate 24 hrs 0% (~100%)dioxane (PPh3)4Pd(0) fresh bottle 2 PPh3 none potassium carbonate 120 hrs 2.5% (N/A)

dioxane NiCl2(dppe) 2 dppe .25 added after 20 hr. potassium phosphate 44 hrs 0% (90%)dioxane NiCl2(dppe) 2 dppe .375 n-BuLi potassium phosphate 120 hrs 0% (~100%)dioxane PdCl2(dppf) none .375 n-BuLi potassium phosphate 44 hrs 0% (~95%)dioxane (PPh3)4Pd(0) fresh bottle 2 PPh3 none potassium phosphate 96 hrs trace (42%)dioxane (PPh3)4Pd(0) fresh bottle 2 PPh3 none potassium phosphate 96 hrs 5% (69%)

Results

Results:Aqueous 2,5-Diferrocenyl-Thiophene

1H NMR spectrum

250 MHz

Fe

S

Fe

Conclusion

• Synthesize Ferrocene-Capped Thiophene– Aqueous method– Chromatography eluent less polar

• 50:50 hexane:dichloromethane

• 70:30 hexane:dichloromethane

Further Research

• Make Derivatives– Electron donating and withdrawing– Electrochemical characterization

• Variable temperature

Applications

• Photovoltaics

• Transistors

Suzuki Coupling:Aqueous and Anhydrous Synthesis of

Ferrocene-Capped Thiophene

Bill Mitchell2003-04

Fe

S

Fe

Chemical Shift

€ δ=observed shift (Hz)*106250*106 (Hz)