Synergy of Dual Functional Sites for Conversion of CO2 in a Cycloaddition Reaction under Solvent-Free Conditions by a Zn(II)-Based Coordination Network with a Ladder Motif

Coordination polymers (CPs)/metal-organic frameworks (MOFs) are promising catalytic materials for selective carbon capture and utilization (CCU) as a C1 feedstock for the synthesis of value-added chemicals to mitigate the growing CO2 concentration in the atmosphere. Herein, we report the synthesis of a Zn(II)-based coordination network with a ladder motif (ADES-3) constructed on an acylamide functionalized bipyridyl-based Schiff base (E)-N'-(pyridin-4-ylmethylene)-isonicotinohydrazide (L) and 5-nitroisophthalic acid (5NO(2)-IP ligands and its utilization as an efficient binary heterogeneous catalyst for CO2 fixation. ADES-3 material has been characterized by various analytical techniques including single-crystal X-ray diffraction, which revealed a ladder motif with highly distorted trigonal bipyramidal geometry with unsaturated Lewis acid metal sites. ADES-3 with bulk phase purity was synthesized via room temperature stirring and exploited as a multifunctional heterogeneous catalyst for a CO2 cycloaddition reaction with aliphatic and aromatic epoxides to produce cyclic carbonates in a moderate reaction condition. Systematic experiments to explore the effect of various reaction parameters toward the optimization of cycloaddition reaction were performed, and ADES-3 offered good conversion ability for almost all tested epoxides under the optimum condition. Moreover, based on structural indication, a plausible mechanism for the cycloaddition reaction is proposed. ADES-3 exhibits a decent chemical and thermal stability during the reaction and can be reused up to four catalytic cycles with retention in catalytic activity suggesting good prospects for the application as a heterogeneous catalyst for CO2 fixation.