Stabilizing Silver Single-Atom Site via A Pore-Confined Triphenylphosphine for CO2 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 (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.