Zwitterionic resorcinarene bifunctional organocatalyst for the cycloaddition of carbon dioxide to epoxide

The cycloaddition of carbon dioxide (CO₂) to epoxide (CCE) reaction is a highly attractive sustainable process due to its high atom economy and the versatility applications of the resulting cyclic carbonates. Conventional catalysts for CCE reactions were indispensable of halide cocatalyst, however, halides posed risk of corrosion to process steel equipment and the residue halide was environmentally harmful. To obviate halide, a new halide-free resorcinarene-based zwitterion (RES-Z) catalyst was designed and synthesized as organocatalyst for CCE reactions. The RES-Z catalyst exhibited excellent performance at 120 °C and 0.5 mol% catalyst loading under 1.0 MPa CO₂ pressure for 12 h, the commercially epoxide bisphenol A diglycidyl ether and 12 terminal epoxides were converted into the corresponding cyclic carbonates with 73–99 % conversion and 99 % selectivity. Bifunctional catalytic mechanism was proposed and validated by NMR titrations where the cationic moiety activated the epoxide and the anionic moiety activated the CO₂. Moreover, the catalyst demonstrated exceptional recyclability, exhibiting no decline in catalytic activity over five consecutive reaction cycles. These findings not only substantiate the efficacy of resorcinarene-based organocatalysts in halide-free catalytic systems but also advance the sustainable utilization of CO₂ in chemical synthesis.