Mechanism-Inspired Upgradation of Phosphonium-Containing Organoboron Catalysts for Epoxide-Involved Copolymerization and Homopolymerization

The dynamic Lewis multicore system (DLMCS) which integrates the Lewis acidic boron center(s) and an ammonium salt in one molecule has shown good catalytic performance in polymer synthesis. Inspired by the insightful intramolecular ammonium cation assisted mechanism, herein, we communicated a superior organoboron system by replacing a nitrogen atom with a phosphorus atom. The upgraded mono-, di-, and trinuclear organoboron catalysts show significantly improved catalytic performance and heat resistance for versatile epoxide-involved transformations, including ring-opening copolymerization of epoxides and cyclic anhydrides, copolymerization of CO2 and epoxides, and ring-opening polymerization of epoxides. 11B NMR, single-crystal X-ray diffraction, and DFT results imply that the replacing nitrogen with phosphorus in an onium cation led to an effective epoxide activation and nucleophilic attack of the counterion on the activated epoxide, which remarkably shortened the initiation period and accelerated chain expansion, resulting in the obvious improvement of the activity. The upgraded phosphonium-containing organoboron system combined with the mechanism study and insightful understanding would be instructive in designing advanced metal-free catalysts.