Copolymerization of CO ₂ with Epoxides by Imidazolium Engineering in Bifunctional Organoboron Catalysts

Boron-based bifunctional catalysts are a novel class that has emerged recently, demonstrating exceptional catalytic activity for the copolymerization of epoxides with CO2. Nevertheless, the structure-performance relationship of these catalysts has remained inadequately explored. Here, we report a series of highly efficient metal-free catalysts. These catalysts are designed through the strategic integration of a Lewis acidic boron center and a Lewis basic imidazolium cation. Extensive tunability of catalytic activity was achieved by systematically modulating the steric and electronic properties of the imidazolium moiety, achieved through variations in the imidazole substituents and precise optimization of the spatial separation between the boron and nitrogen centers. These catalysts exhibited remarkable efficiency (TOF > 500 h–1), maintaining >99% polycarbonate selectivity over a wide temperature range (25–120 °C) and under moderate CO2 pressures (1.0–4.0 MPa). Mechanistic insights were garnered from reaction kinetics studies, control experiments, 11B NMR analysis, polymer MALDI-TOF mass spectrometry of the polymers, and density functional theory (DFT) calculations. These findings support an intramolecular cooperative catalytic mechanism. These results underscore the critical importance of cationic structure optimization in catalyst design and provide a rational pathway for developing advanced metal-free catalysts for future epoxide/CO2 copolymerization applications.