Stabilizing Silver Single‐Atom Site via A Pore‐Confined Triphenylphosphine for CO ₂ Conversion With High Substrate‐Specificity

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 (PPh 3 ) 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 CO 2 with benzyl‐substituted propargylamines under mild, additive‐free aqueous conditions, achieving a turnover frequency up to 1051.3 ± 0.7 h −1 . Moreover, PPh 3 , 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 PPh 3 ‐coordinated silver site synergizes with the Zr 6 O 8 cluster to activate both the alkyne substrate and CO 2 , substantially lowering the energy barriers for CO 2 insertion and cyclization. This work presents a molecule‐enhanced confinement approach for designing stable and efficient single‐atom catalysts with controllable substrate‐specificity.