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 CO2 conversion often face limitations in activity, selectivity, and stability under mild conditions, hindering their practical application and effective utilization of CO2. 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 −NH2 defects, the coexistence of imine and aminal linkages, and the successful anchoring of single-atom Fe3+ sites. Compared to nonmetallized counterparts, the dPOP-OFe-X catalysts exhibited significantly enhanced activity in both CO2/epoxide cycloaddition and CO2-mediated amine N-formylation under mild conditions. Specifically, the optimized dPOP-OFe-10 catalyst achieved a 93% yield of chloropropene carbonate from epichlorohydrin/CO2 (90 °C, 0.1 MPa, 8 h) and a 92% yield of N-methylformanilide from N-methylaniline/CO2 (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 CO2 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 CO2 utilization.