Imidazolium Iodide-Containing Polycarbazole Networks as Efficient Catalysts for the Cycloaddition of CO₂ to Epoxides

In this study, a rigid, bulky, noncoplanar carbazolyl-terminated triphenylimidazole monomer (namely, TCPI) and its ionic salt, triphenylimidazolium iodide, (namely, TCPI-IL), are synthesized. Subsequently, triphenylimidazole- and triphenylimidazolium iodide-containing polycarbazole networks are separately synthesized by oxidative polymerization (namely, oTCPI and oTCPI-IL, respectively) and Friedel–Crafts alkylation reaction (namely, fTCPI and fTCPI-IL, respectively). As expected, the obtained fTCPI/fTCPI-IL and oTCPI/oTCPI-IL networks exhibit high specific surface areas, i.e., 743 and 713 m2 g–1 for fTCPI and oTCPI, and 560 and 532 m2 g–1 for fTCPI-IL and oTCPI-IL, respectively. Due to the high specific surface areas along with the presence of multiple interacting sites for CO2 molecules, i.e., imidazoliumyl, carbazolyl, and phenyl rings, the fTCPI-IL and oTCPI-IL networks display not only high CO2 adsorption capacities (2.53 and 1.99 mmol g–1, respectively) but also high catalytic activities for the chemical fixation of CO2 with epoxides. Remarkably, the fTCPI-IL network also displays a high catalytic activity in directly converting diluted CO2 (CO2/N2 = 15/85, v/v) into cyclic carbonates, in which high conversions (92–99%) and quantitative selectivity (99%) are achieved for a wide range of epoxides.