Phosphine-Borane Frustrated Lewis Pairs for Metal-Free CO₂/Epoxide Copolymerization

Abstract

The development of metal-free catalysts with excellent activity and controllability remains a significant obstacle for the copolymerization of CO2 and epoxides. In this study, we used the frustrated Lewis pair (FLP) composed of commercial tertiary phosphine and trialkylborane to catalyze the copolymerization of CO2 and propylene oxide (PO). The rational matching of the electronic and steric properties of Lewis bases and acids has a great influence on the activity and controllability of CO2 copolymerization. The FLP composed of PtBu3 and BnBu3 exhibits moderate catalytic activity (TOF up to 447 h–1) and high initiation efficiency toward CO2 and PO copolymerization, in which PtBu3 possesses strong nucleophilicity and large steric hindrance while BnBu3 possesses medium Lewis acidity and steric hindrance. The obtained polycarbonates had well-defined structures with the carbonate contents of 96–99%, tunable molecular weights (8.0–19.9 kDa), and narrow dispersities (<1.1). The favorable performance of the FLP confirms that FLP catalysis is a feasible catalytic methodology for CO2 and epoxide copolymerization.