Ambient Chemical Fixation of CO₂ Using a Robust Ag₂₇ Cluster-Based Two-Dimensional Metal-Organic Framework

Unprecedented double S^2- templated Ag₂₇ clusters have been stabilized by 5,10,15,20-tetra(4-pyridyl)porphyrin (TPyP-H₂ ) ligands to afford a robust 2D metal-organic framework (Ag27-MOF). This silver cluster-assembled material serves as a highly efficient heterogeneous catalyst for the cyclization of both terminal and internal propargylamines with CO₂ under atmospheric pressure. Density functional theory (DFT) calculations illustrate that the high catalytic activity and broad substrate scope are attributable to the saddle-shaped metallic node in Ag27-MOF, which features an accessible platform with high-density silver atoms as π-Lewis acid sites for activating C≡C triple bonds. As a result, different sterically hindered alkyne substrates can be effectively activated through π-interactions with these cationic silver centers.