Bifunctional Pyridinium-Based Ionic-Liquid-Immobilized Diindium Tris(diphenic acid) Bis(1,10-phenanthroline) for CO2 Fixation

A pyridinium-based ionic-liquid-decorated 1D metal-organic framework (MOF; IL-[In-2(dpa)(3)(1,10-phen)(2)]; IL = ionic liquid; dpa = diphenic acid; 1,10-phen = 1,10-phenanthroline) was developed as a bifunctional heterogeneous catalyst system for CO2-oxirane coupling reactions. An aqueous-microwave route was employed to perform the hydrothermal reaction for the synthesis of the [In-2(dpa)(3)(1,10-phen)(2)] MOF, and the IL-[In-2(dpa)(3)(1,10-phen)(2)] catalyst was synthesized by covalent postfunctionalization. As a result of the synergetic effect of the dual-functional sites, which include Lewis acid sites (coordinatively unsaturated In sites) and the I- ion in the IL functional sites, IL-[In-2(dpa)(3)(1,10-phen)(2)] displayed a high catalytic activity for CO2-epoxide cycloaddition reactions under mild and solvent-free conditions. Microwave pulses were employed for the first time in MOF-catalyzed CO2-epoxide cycloaddition reactions to result in a high turnover frequency of 2000-3100 h(-1). The catalyst had an excellent reusability and maintained a continuous high selectivity. Furthermore, only a small amount of leaching was observed from the spent catalyst. A plausible reaction mechanism based on the synergistic effect of the dual-functional sites that catalyze the CO2-epoxide cycloaddition reaction effectively is proposed.