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

Thedevelopment of metal-free catalysts with excellent activityand controllability remains a significant obstacle for the copolymerizationof CO2 and epoxides. In this study, we used the frustratedLewis pair (FLP) composed of commercial tertiary phosphine and trialkylboraneto catalyze the copolymerization of CO2 and propylene oxide(PO). The rational matching of the electronic and steric propertiesof Lewis bases and acids has a great influence on the activity andcontrollability of CO2 copolymerization. The FLP composedof (PBu3)-Bu- t and (BBu3)-Bu- n exhibits moderate catalytic activity(TOF up to 447 h(-1)) and high initiation efficiencytoward CO2 and PO copolymerization, in which (PBu3)-Bu- t possesses strong nucleophilicity andlarge steric hindrance while (BBu3)-Bu- n possesses medium Lewis acidity and steric hindrance. Theobtained polycarbonates had well-defined structures with the carbonatecontents of 96-99%, tunable molecular weights (8.0-19.9kDa), and narrow dispersities (<1.1). The favorable performanceof the FLP confirms that FLP catalysis is a feasible catalytic methodologyfor CO2 and epoxide copolymerization.