Mechanistic Insight into Thiophene Catalyst-Transfer Polymerization Mediated by Nickel Diimine Catalysts

Abstract

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.

Trials and tribulations of designing multitasking catalysts for olefin/thiophene block copolymerizations

“…We suspect dissociation might be occurring based on our concurrent work with precatalyst C1 , where we observe some catalyst dissociation. In this case, however, the catalyst preferentially re‐inserts into polymer chains rather than the monomer.…”

“…We initially selected Ni precatalyst C1 (Chart ), which was chosen based on its reported living, chain‐growth olefin polymerization behavior as well as its ability to synthesize P3HT with a targeted number‐average molecular weight ( M n ) and moderate dispersity (Đ) . Due to the high sensitivity of the olefin polymerization to coordinating substrates, including thiophene and THF, we synthesized the polyolefin block first, followed by polythiophene.…”

Diversifying Cross‐Coupling Strategies, Catalysts and Monomers for the Controlled Synthesis of Conjugated Polymers

“…This allows for tunability of the substituents to improvep olymerization behavior.T he linker can also be modulated, but only the acenaphthene backbone has been used forC TP reactions to date. This class of catalyst can polymerize thiophenes, [143][144][145] as well as benzotriazoles in ac hain-growthf ashion. [146,147] Excitingly,e xternally initiated nickel diimines have recently been developed.…”

“…[148] Significant opportunities exist with this catalyst framework due to the modularn ature of the ligand and the ease of synthesis for these compounds. Some chain transfer issues have been noted, [143,144] and further development of these catalysts is necessary.…”

Investigation of Bimetallic Nickel Catalysts in Catalyst‐Transfer Polymerization of π‐Conjugated Polymers

“…To further advance the field of conjugated polymers using CTP, a better understanding of monomer‐catalyst interactions is essential . Recent studies to improve the methodology of CTP primarily focused on the reactive ligands, ancillary ligands, and the transition metal . Baker et al designed a catalyst that incorporated an unsymmetrical propyl‐bridged diphosphine ligand as a new approach to tune catalyst reactivity .…”