Metal-Free Triazine-Incorporated Organosilica Framework Catalyst for the Cycloaddition of CO₂ to Epoxide under Solvent-Free Conditions

Abstract

The silicon-based materials with enriched superficial Si–OH groups are candidates in the field of the cycloaddition of CO2 to epoxide to cyclic carbonate; meanwhile, the triazine ring with a nitrogen-rich structure has shown a high adsorption affinity toward CO2 to polarize CO2. On this basis, a metal-free triazine-incorporated organosilica framework (SiTIOF) containing triazine rings, −NH, and Si–OH was prepared by substitution reaction and then a hydrothermal method. The prepared SiTIOF exhibited an outstanding catalytic activity for the cycloaddition of CO2 to epoxide with the cocatalyst tetrabutylammonium bromide (Bu4NBr) due to the triazine unit and multiple hydrogen bond donors (−NH, −OH). Besides, the SiTIOF catalyst could be reused six times and has good versatility to various epoxides with CO2 cycloaddition. Moreover, the possible reaction mechanism with a hydrogen bond donor (HBD) and halide anion synergistic catalysis was proposed.