Study of the mechanism of copper-activated NHC–R and NHC=O coupling under the conditions of the Chan–Evans–Lam reaction system

In this work, the phenomena of copper-induced formation of NHC-R and NHC=O particles in the Chan–Evans–Lam arylation reaction system of aniline are discussed for the first time. The considered combinations between NHC and arylboronic acid residues have been demonstrated using 5 different arylboronic acids and three Cu/NHC complexes. It is also shown that the formation of the azolone NHC=O is due to copper-mediated oxygen transfer from the atmosphere to the carbene center of the NHC. Using a set of experimental physicochemical methods of analysis, as well as with the help and methods of quantum chemistry, it is shown for the first time that the degradation pathway of Cu/NHC complexes through the formation of NHC–R is controlled kinetically, and through the formation of NHC=O - thermodynamically, which makes a significant contribution to the understanding of the observed phenomena.