Phosphine-Borane Frustrated Lewis Pairs for Metal-Free CO<sub>2</sub>/Epoxide Copolymerization
Ying Wang, Ziheng Liu, Wenqi Guo, Chengjian Zhang, Xinghong Zhang
Abstract
The development of metal-free catalysts with excellent activity and controllability remains a significant obstacle for the copolymerization of CO 2 and epoxides. In this study, we used the frustrated Lewis pair (FLP) composed of commercial tertiary phosphine and trialkylborane to catalyze the copolymerization of CO 2 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 CO 2 copolymerization. The FLP composed of P t Bu 3 and B n Bu 3 exhibits moderate catalytic activity (TOF up to 447 h –1 ) and high initiation efficiency toward CO 2 and PO copolymerization, in which P t Bu 3 possesses strong nucleophilicity and large steric hindrance while B n Bu 3 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 CO 2 and epoxide copolymerization.