Triazine-containing polytriphenylimidazolium network for heterogeneous catalysis of CO2 conversion to cyclic carbonates

Abstract

In this work, novel triazine-linked triphenylimidazole (TPIM) and triphenylimidazolium (TPIM-IL) monomers have been synthesized and fully characterized. Subsequently, their corresponding networks, namely PTPIM and PTPIM-IL, respectively, have been synthesized by Friedel-Crafts alkylation reaction. Owing to the dendritic-like, bulky and rigid structure of the two monomers, the resultant PTPIM and PTPIM-IL networks display relatively high specific surface areas of 982 m2/g and 570 m2/g, respectively. More importantly, PTPIM network can be readily transformed into PTPIM-IL network via a facile post-modification process. The presence of abundant CO2-affinity sites, i.e., imidazolium and triazine rings, together with high nucleophilicity of iodine anion endows PTPIM-IL network with not only high CO2 uptake capacity (2.69 mmol g−1), but also high activity toward the cycloaddition of CO2 to epoxides. For example, PTPIM-IL network has proven very effective in converting epibromohydrin to its corresponding cyclic carbonate under mild conditions (60 °C, 0.1 MPa), yielding quantitative conversion (99%) and selectivity (99%). The catalytic activity of PTPIM-IL network is superior to most previously reported imidazolium-based heterogeneous catalysts.