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) Mn^II(salen)-based MOF (<b>1</b>) 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 (<b>r1</b>^<b>M</b>; M = Mn, Co, Cu, Ni, V). Among them, <b>r1</b>^<b>Co</b> was proved to be the most active catalyst for the cycloaddition of CO₂ and epoxides. Mechanistic studies reveal that <b>r1</b>^<b>Co</b> displays a high CO₂ affinity and Lewis acidity. In addition, kinetic studies suggest that <b>r1</b>^<b>Co</b> has a lower activation energy than the original MOF (<b>1</b>) and demetallized MOF (<b>d1</b>). Remarkably, <b>r1</b>^<b>Co</b> could be reused five times without affecting its catalytic activity.