Catalyst-transfer polymerization (CTP) is a living, chain-growth method for accessing conjugated polymers with control over their length and sequence. Typical catalysts utilized in CTP are either Pd or Ni complexes with bisphosphine or N-heterocyclic carbene ancillary ligands. More recently, diimine-ligated Ni complexes have been employed; however, in most cases nonliving pathways become dominant at high monomer conversions and/or low catalyst loading. We report herein an alternative Ni diimine catalyst that polymerizes 3-hexylthiophene in a chain-growth manner at low catalyst loading and high monomer conversion. In addition, we elucidate the chain-growth mechanism as well as one chain-transfer pathway. Overall, these studies provide insight into the mechanism of conjugated polymer synthesis mediated by Ni diimine catalysts.

Block copolymers containing both insulating and conducting segments have been shown to exhibit improved charge transport properties and air stability. Nevertheless, their syntheses are challenging, relying on multiple post-polymerization functionalization reactions and purifications. A simpler approach would be to synthesize the block copolymer in one pot using the same catalyst to enchain both monomers via distinct mechanisms. Such multitasking polymerization catalysts are rare, however, due to the challenges of finding a single catalyst that can mediate living, chain-growth polymerizations for each monomer under similar conditions. Herein, a diimine-ligated Ni catalyst is evaluated and optimized to produce block copolymer containing both 1-pentene and 3-hexylthiophene. The reaction mixture also contains both homopolymers, suggesting catalyst dissociation during and/or after the switch in mechanisms. Experimental and theoretical studies reveal a high energy switching step coupled with infrequent catalyst dissociation as the culprits for the low yield of copolymer. Combined, these studies highlight the challenges of identifying multitasking catalysts, and suggest that further tuning the reaction conditions (e.g., ancillary ligand structure and/or metal) is warranted for this specific copolymerization.

The discovery of catalyst-transfer polymerization and its further developments have led to unprecedented control over the length and sequence of conjugated polymers. However, the methods themselves are technically challenging to perform due to the air-and moisture-sensitivities of the monomers and catalysts. Herein, we report a catalyst-transfer polymerization method that affords poly(3-hexylthiophene) in high yields without using an inert atmosphere. The synthesis capitalizes on a rapid Negishi cross-coupling using a moisturetolerant organozinc monomer mediated by an air-stable Pd precatalyst. This simple method should make conjugated polymer synthesis more accessible to a broader range of researchers and may be generalizable to other monomer scaffolds.