Background: The carbon-dioxide reduction to obtain important chemicals such as fuels is a
topic of high current interest. Recently, monomeric thiophenes and terthiophenes linked to a bipyridine
ligand were designed and their polymeric films achieved very high turnover numbers during electrocatalytic
CO2 reduction. In this paper we improved the protocol to access the ligand that shows the best
performances, in view of opening the way to a general method to obtain side-functionalized terthiophenes.
Methods: Several reactions were attempted to improve the synthetic pathway. Different approaches
were attempted to convert the 3-bromothiophene into its 3-iodo analog and to brominate it to obtain the
2,5-dibromo-3-iodothiophene. The synthetic pathway was completed by using Pd-catalyzed crosscoupling
reactions such as Sonogashira and Suzuki. The removal of a trimethylsilyl protection was attempted
by common methods. However, with the use of a one-pot reaction, both the alkyne deprotection
and the final Sonogashira coupling were performed as the key point of the pathway to obtain the
Results: The key intermediate 2,5-dibromo-3-iodothiophene was obtained by a CuI assisted electrophilic
aromatic substitution, followed by a bromination with NBS in ethyl acetate. This compound was
reacted with TMS-acetylene to obtain the ((2,5-dibromothiophen-3-yl)ethynyl)trimethylsilane which,
by a Suzuki reaction, afforded the ([2,2':5',2''-terthiophen]-3'-ylethynyl)trimethylsilane. Using a onepot
reaction for the last step, the deprotection of the TMS-protected alkyne and its coupling with 4-
bromo-2,2’-bipyridine was accomplished easily. A final 52% yield was achieved over 5 steps.
Conclusion: The ligand 4-([2,2':5',2''-terthiophen]-3'-ylethynyl)-2,2'-bipyridine was prepared in a 52%
yield, over 5 steps, improving the previous protocol (17% yield over 4 steps). The rhenium complex of
this ligand is still under study for CO2 reduction. This novel protocol can be used to produce a series of
analog terthiophene monomers bearing side-attached ligands.