Tailoring of Unsaturated Metal Sites in Metal-Organic Frameworks to Promote the Conversion of CO2 into High-Value-Added Products

Well-defined metal-organic frameworks (MOFs) provide an attractive platform for catalysis. Understanding the intrinsic structure-activity relationship of MOFs helps guide the design of novel catalysts. In this work, a new three-dimensional (3D) MnII(salen)-based MOF (1) with strong adsorption capacity and high selectivity for CO2 was synthesized. Through sequential demetallization and remetallization, the flexible tailoring of the metal centers was realized to obtain a series of remetallized MOFs (r1 M ; M = Mn, Co, Cu, Ni, V). Among them, r1 Co was proved to be the most active catalyst for the cycloaddition of CO2 and epoxides. Mechanistic studies reveal that r1 Co displays a high CO2 affinity and Lewis acidity. In addition, kinetic studies suggest that r1 Co has a lower activation energy than the original MOF (1) and demetallized MOF (d1). Remarkably, r1 Co could be reused five times without affecting its catalytic activity.