Carboxylation of terminal alkynes with CO2 using novel silver N-heterocyclic carbene complexes

Four novel N-heterocyclic carbene (NHC) silver complexes, I-IV, have been synthesized and characterized. The single X-ray crystal diffraction data indicate a dinuclear solid-state structure for I and III and a mononuclear structure for II and IV. These complexes have been successfully used as efficient catalysts for the C-H activating carboxylation of terminal alkynes with CO2. A wide range of substrates with various functional groups afforded the corresponding aryl or alkyl substituted propiolic acids in good yields under mild conditions. Moreover, the role of bases and the reaction mechanism is thoroughly discussed.