Rational Construction of Missing-Linker Defects for Single-Atom Anchoring on Imine/Aminal-Bonded POPs to Boost Multifunctional CO 2 Conversion

Conventional heterogeneous catalysts for CO 2 conversion often face limitations in activity, selectivity, and stability under mild conditions, hindering their practical application and effective utilization of CO 2 . To address these challenges, this study presents a synergistic strategy integrating defect engineering and postsynthetic modification to fabricate metallized defective porous organic polymers (dPOP-OFe- X, X = 5, 10, 20) as efficient heterogeneous catalysts. Comprehensive characterization confirmed the controlled introduction of missing-linker −NH 2 defects, the coexistence of imine and aminal linkages, and the successful anchoring of single-atom Fe 3+ sites. Compared to nonmetallized counterparts, the dPOP-OFe- X catalysts exhibited significantly enhanced activity in both CO 2 /epoxide cycloaddition and CO 2 -mediated amine N -formylation under mild conditions. Specifically, the optimized dPOP-OFe-10 catalyst achieved a 93% yield of chloropropene carbonate from epichlorohydrin/CO 2 (90 °C, 0.1 MPa, 8 h) and a 92% yield of N -methylformanilide from N -methylaniline/CO 2 (100 °C, 1.0 MPa, 6 h). Additionally, dPOP-OFe-10 displayed broad substrate compatibility with diverse epoxides and amines, maintained high activity over five catalytic cycles, and retained structural integrity after recycling. Combined theoretical calculations and in situ FT-IR spectroscopy elucidated the interaction modes and energy profiles between catalytic sites and model reactants, revealing the synergistic catalytic mechanism involving multiple active sites in the CO 2 cycloaddition reaction. This work establishes a practical and universal approach for designing high-performance catalysts via a defect engineering strategy, paving the way for efficient CO 2 utilization.