Carboxylation of Terminal Alkynes with Carbon Dioxide Catalyzed by an In Situ Ag₂O/N-Heterocyclic Carbene Precursor System

A carboxylation of terminal alkynes with carbon dioxide (CO₂) at ambient conditions was developed in situ using a series of N-heterocyclic carbene (NHC) precursors and Ag₂O. The unique structure of NHCs largely increases the solubility of active Ag species and meanwhile activates CO₂ by forming the NHC–CO₂ adduct. This novel catalytic system demonstrated quite low Ag loading, very high activities, wide substrate generality and excellent tolerance for a variety of functionalities. In addition, avoiding cumbersome synthesis procedures, processing, and reserving of the photosensitive Ag complex, this system could be stored and operated as straightforward as the inorganic Ag salt catalysts.