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

A pyridinium-based ionic-liquid-decorated 1 D metal-organic framework (MOF; IL-[In2 (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 [In2 (dpa)3 (1,10-phen)2 ] MOF, and the IL-[In2 (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-[In2 (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.