Designing nickel- and palladium-based precatalysts to improve catalyst-transfer polymerization towards conjugated polymer synthesis

Abstract

Catalyst transfer polymerization (CTP) is a versatile synthetic tool to obtain access to sequence specific π-conjugated polymers, which are attractive materials for organic electronics. CTP proceeds through a chain-growth mechanism creating polymers with precise molecular weights, narrow dispersities, and end-group functionalization. These parameters are desirable properties that can affect the overall performance of organic electronic and photonic devices. While CTP has made large advances in the synthesis of π-conjugated polymers in the past 15 years, its substrate scope has been limited to mainly simple and electron rich monomers. The need to expand the scope of CTP to access more complicated conjugated building blocks, such as alternating donor-acceptor monomers, necessitates the need to develop new strategies. This report presents an approach to improve CTP by exploring a model study involving nickel and palladium precatalysts to test the impact of cooperative catalysis and non-covalent π-π stacking interactions on the important metal π-aryl complex. Catalyst performance in CTP was evaluated using poly(3-hexylthiophene) as the model system. Monomer conversion, degree of polymerization, end-group identity, and molecular weight distribution were analyzed to determine the quality of the polymerizations. The information gained from this study provided insight into what structural features are desirable when designing a suitable catalyst that will exhibit a controlled polymerization.