Experimental and theoretical investigations of zwitterionic hypercrosslinked polymers as robust catalysts for CO2 fixation under cocatalyst- and solvent-free conditions

The development of highly stable and active single-component catalysts for transformation of CO2 into organic carbonates remains challenging. Here several novel triazinyl- and pyridinium-based zwitterionic hypercrosslinked polymers (TPHCPs) were constructed via a simple one-pot strategy and their structures were characterized. The TPHCPs exhibit excellent porosity and multiple adjustable functional units, including nucleophilic Br- anions formed in situ. The obtained TPHCPs were used in the cycloaddition reaction of CO2 and epoxide, and the effects of TPHCP structures and reaction parameters were studied respectively. TPHCP superset of 3Br(-) was determined to be the most excellent catalyst, the multiple active sites of TPHCP superset of 3Br- are beneficial for the simultaneous adsorption and activation of CO2 and epoxide. It could efficiently catalyze the reaction of CO2 with various epoxides to form corresponding cyclic carbonates without a co-catalyst under mild conditions. In addition, the recovery and reuse performances of TPHCP33Br(-) were examined. The catalytic activity did not change obviously upon reusing five times. Finally, a reasonable mechanism of the cycloaddition reaction under the synergistic actions of multiple active sites was proposed by using a DFT calculation method.