Method for aerobic oxidative coupling of thiophenes with a ligand-supported palladium catalyst

1. A method for synthesizing a 2,2′-bithiophene from two thiophenes, the method comprising:

contacting the two thiophenes with oxygen gas and a catalyst comprising palladium and a ligand selected from the group consisting of a pyridine; a 1,10-phenanthroline; a 2,2′-bipyridine, a 2,2′-bipyrimidine; a 4,5-diazafluoren-9-one; a quinoline; a 1,10-phenanthroline-5,6-dione; a bis(arylimino)acenaphthene; and a 2,2′-biquinoline;

whereby the two thiophenes are covalently coupled by aerobic oxidation to form the 2,2′-bithiophene;

wherein the two thiophenes are not substituted exclusively with alkyl groups, alkoxy groups, alkanoate groups, alkanamide groups, alkoxyalkyl groups, and benzoalkyl groups.

2. The method of claim 1 , wherein the 2,2′-bithiophene that is synthesized has the chemical structure:

and

the two thiophenes have the chemical structure:

wherein X is a halogen, an alkyl, a trimethylsilyl (TMS), a thiophenyl, or a dioxolanyl:

and wherein R 1 and R 2 are each independently selected from the group consisting of hydrogen, bromine, chlorine, fluorine, an alkoxycarbonyl group, an oxoalkyl group, and an alkyl group.

3. The method of claim 2 , wherein the two thiophenes are 2,3-dibromothiophene, 2,4-dibromothiophene, 2-bromo-4-fluorothiophene 2-bromo-3-dodecylthiophene, 2-bromothiophene, 2-chlorothiophene, 2-bromo-3-methylthiophene, 2-bromo-3-hexylthiophene, 2-chloro-3-hexylthiophene,

and wherein the corresponding 2,2′-bithiophene is 4,4′,5,5′-tetrabromo-2,2′-bithiophene (X is bromine, R 1 is bromine, and R 2 is hydrogen), 3,3′,5,5′-tetrabromo-2,2′-bithiophene (X is bromine, R 1 is hydrogen, and R 2 is bromine), 5,5′-dibromo-3,3′-difluoro-2,2′-bithiophene (X is bromine, R 1 is hydrogen, and R 2 is fluorine), 5,5′-dibromo-4,4′-didocecyl-2,2′-bithiophene (X is bromine, R 1 is n-dodecyl, and R 2 is hydrogen), 5,5′-dibromo-2,2′-bithiophene (X is bromine, R 1 is hydrogen, and R 2 is hydrogen), 5,5′-dichloro-2,2′-bithiophene (X is chlorine, R 1 is hydrogen, and R 2 is hydrogen), 5,5′-dibromo-4,4′-dimethyl-2,2′-bithiophene (X is bromine, R 1 is methyl, and R 2 is hydrogen), 5,5′-dibromo-4,4′-dihexyl-2,2′-bithiophene (X is bromine, R 1 is n-hexyl, and R 2 is hydrogen) 5,5′-dichloro-4,4′-dihexyl-2,2′-bithiophene (X is chlorine, R 1 is n-hexyl, and R 2 is hydrogen),

4. The method of claim 1 , wherein the 2,2′-bithiophene that is synthesized is a 2,2′-bibenzo[b]thiophene, and wherein the two thiophenes are benzo[b]thiophenes.

5. The method of claim 4 , wherein the 2,2′-bibenzo[b]thiophene has the chemical structure:

and

the two benzo[b]thiophenes have the chemical structure:

wherein R 1 , R 2 , R 3 , R 4 and R 5 are independently selected from the group consisting of hydrogen and bromine.

6. The method of claim 5 , wherein the 2,2′-bibenzo[b]thiophene that is synthesized is 3,3′-dibromo-2,2′-bibenzo[b]thiphene or 2,2′-bibenzo[b]thiophene, and wherein the two benzo[b]thiophenes are 3-bromobenzo[b]thiophene (R 1 is bromine; R 2 , R 3 , R 4 and R 5 are all hydrogen) or unsubstituted benzo[b]thiophene R 2 , R 3 , R 4 and R 5 are all hydrogen).

7. The method of claim 1 , wherein the 2,2′-bithiophene that is synthesized is a 5,5′-bis-(1-oxoalkyl)-2,2′-bithiophene, and wherein the two thiophenes are 2-(1-oxoalkyl)thiophenes.

8. The method of claim 7 , wherein the 5,5′-bis-(1-oxoalkyl)-2,2′-bithiophene has the chemical structure:

and

the two 2-(1-oxoalkyl)thiophenes have the chemical structure:

wherein R 1 is selected from the group consisting of an alkyl group and hydrogen.

9. The method of claim 8 , wherein the 5,5′-bis-(1-oxoalkyl)-2,2′-bithiophene that is synthesized is 5,5′-bis(trimethylacetyl)-2,2′-bithiophene or 5,5′-bis(carbaldehyde)-2,2′-bithiophene, and wherein the two 2-(1-oxoalkyl)thiophenes are 2-trimethylacetylthiophene (R 1 is tert-butyl; R 2 and R 3 are hydrogen) or thiophene-2-carbaldehyde (R 1 , R 2 , and R 3 are all hydrogen).

10. The method of claim 1 , wherein the 2,2′-bithiophene analog that is synthesized is a 5,5′-bithiazole, and wherein the two thiophene analogs are thiazoles.

11. The method of claim 10 , wherein the 5,5′-bithiazole has the chemical structure:

and

the two thiazoles have the chemical structure:

wherein R 1 is hydrogen and R 2 is bromine.

12. The method of claim 1 , wherein the ligand is selected from the group consisting of a 1,10-phenanthroline-5,6-dione; a 2,2′-bipyridine, a 2,2′-bipyrimidine; a 4,5-diazafluoren-9-one; a quinoline; a 1,10-phenanthroline; a bis(arylimino)acenaphthene; and a 2,2′-biquinoline.

13. The method of claim 12 , wherein the ligand is selected from the group consisting of:

(a) a 1,10-phenanthroline-5,6-dione having the chemical formula:

wherein

(i) 1, 2, 3, 4, or 5 of R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are hydrogen, or

(ii) all six of R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are hydrogen (the ligand is 1,10-phenanthroline-5,6-dione (phd));

(b) a 2,2′-bipyridine having the chemical formula:

wherein one or more of R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 and R 5 are independently selected from the group consisting of hydrogen, tert-butyl, methoxy, methyl, phenyl, and trifluoromethyl;

(c) a 2,2′-bipyrimidine having the chemical formula:

wherein one or more of R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 is hydrogen;

(d) a 4,5-diazafluoren-9-one having the chemical formula:

wherein one or more of R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 is hydrogen;

(e) a quinoline having the chemical formula:

wherein one or more of R 1 , R 2 , R 3 , R 4 , R 5 , R 6 and R 7 is hydrogen;

f) a 1,10-phenanthroline having the chemical formula:

wherein one or more of R 1 , R 2 , R 3 , R 4 , R 5 , R 6 R 7 , and R 8 is independently selected form the group consisting of hydrogen, methyl, and phenyl;

(g) a bis(arylimino)acenaphthene having the chemical formula:

wherein one or more of R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 is hydrogen, and wherein one or both of Ar 1 and Ar 2 are selected from the group consisting of 4-methylphenyl and 1,3,5-trimethylphenyl; and

(h) a 2,2′-biquinoline having the chemical formula:

wherein one or more of R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 , R 10 , R 11 and R 12 is hydrogen.

14. The method of claim 1 , wherein the catalyst further comprises a transition metal.

15. The method of claim 14 , wherein the transition metal is selected from the group consisting of zinc, copper, manganese, nickel, iron, cobalt and silver.

16. The method of claim 1 , wherein the catalyst further comprises a redox-active organic mediator, wherein the redox-active organic mediator is a substituted or unsubstituted benzoquinone, or a substituted or unsubstituted hydroquinone.