New NHC- silver and gold complexes active in A3-coupling (aldehyde-alkyne-amine) reaction

Silver and gold complexes bearing unsaturated N-heterocyclic carbene ligands, with unsymmetrical N-substituents and hydrogen or chlorine on backbone, have been synthetized and their efficiency tested in A3-coupling (aldehyde–alkyne–amine) reactions. Gold complexes showed higher activity than corresponding silver ones, even if the significant role of the backbone substituents should not be neglected. Indeed, complexes with chlorine substituted backbone were more efficient than hydrogen analogous. According to DFT calculations, electronic differences among complexes are able rationalize the different catalytic behavior, whereas steric properties play a minor part.