Kumada Catalyst-Transfer Polycondensation of Thiophene-Based Oligomers: Robustness of a Chain-Growth Mechanism

Abstract

Polymerization of conjugated oligomers is an efficient approach for band gap engineering of conjugated polymers. On the other hand, a recently discovered chain-growth Ni-catalyzed Kumada polycondensation of monothiophenes becomes an important tool in engineering of macromolecular architectures. In this paper we evaluate the feasibility for chain-growth polycondensation of model monomers comprising one, two, or three thiophene rings. We found that Ph−Ni(PPh3)2−Br-mediated polycondensations of HT-coupled bi- and terthiophenes lead predominantly to Ph-terminated polymers indicating the chain-growth polymerization mechanism. Although an increase of the monomer molecular length somewhat decreases the fraction of the Ph-terminated products as a result of increased probability of a chain-termination and chain-transfer reactions, chain-growth elementary steps remain dominating even for lengthy monomers. Such results reflect that in the key polycondensation step the Ni catalyst undergoes selective intramolecular “...