Hyper-Cross-Linked Ionic Polymer Bearing Phosphate and Hydroxyl for Catalytic Cycloaddition of CO2 with Epoxide under Atmospheric Pressure

Abstract

Converting CO2 to valuable chemicals under mild conditions remains a significant challenge. Herein, we accomplish a solvent-, metal-, and additive-free catalytic transformation of epoxides with CO2 under atmospheric pressure using an ionic polymer (H-IPyBPOH) as the catalyst. This polymer is synthesized via Friedel–Crafts alkylation between a phosphate-bearing hydrogen-bond donor and an imidazolium-based ionic linker. The resulting material contains potent hydrogen-bonding sites (P–OH), imidazolium cations, and bromide anions as nucleophiles. It exhibits excellent catalytic activity and recyclability for the cycloaddition of CO2 to epoxides. Combined DFT calculations and experimental results reveal that the high performance arises from the synergistic cooperation of hydrogen-bonding sites for epoxide activation, basic pyridine sites for CO2 activation, and bromide ions for the ring-opening attack. Moreover, the catalyst shows broad substrate compatibility and an outstanding structural stability. It can be easily recovered by filtration and reused for at least six cycles without a significant loss of activity.