Stabilizing Silver Single-Atom Site via A Pore-Confined Triphenylphosphine for CO₂ Conversion With High...

Ensuring the dispersion and anti-aggregation of single-atom sites under catalytic conditions remains a critical challenge in heterogeneous catalysis. Here, we report a dual-confinement strategy for constructing a metal-organic framework (MOF) based catalyst, MEC-88, by spatially confining triphenylphosphine (PPh₃) within the pores of MOF-808 to anchor silver single-atom sites. MEC-88 exhibits exceptional activity and pronounced substrate selectivity for the carboxylative cyclization of CO₂ with benzyl-substituted propargylamines under mild, additive-free aqueous conditions, achieving a turnover frequency up to 1051.3 ± 0.7 h^-1. Moreover, PPh₃, as a soft-base ligand, provides robust coordination to silver atoms, effectively inhibiting their aggregation to endow the catalyst with good recyclability. Mechanistic studies reveal that the PPh₃-coordinated silver site synergizes with the Zr₆O₈ cluster to activate both the alkyne substrate and CO₂, substantially lowering the energy barriers for CO₂ insertion and cyclization. This work presents a molecule-enhanced confinement approach for designing stable and efficient single-atom catalysts with controllable substrate-specificity.