Precatalysts Involved in Copper-Catalyzed Arylations of Nucleophiles

In spite of the importance of ligand/copper-catalyzed arylations of nucleophiles in organic chemistry, their mechanism and in particular the interactions between ligands and copper have not been well understood until now. In this work, we synthesized a precatalyst involving one of the best ligands of the literature, the tetradentate chelator 1, and characterized it at the solid state and in solution (NMR, electrochemistry, X-ray crystallography). Thanks to the information collected, we now have a better understanding of the role of the ligand (influence on the solubility of copper and on its electrochemical properties) and the role of the solvent and can propose a description of the various reactions taking place at the early stages of copper-catalyzed arylations of nucleophiles. We thus showed that, in acetonitrile, the association of tetradentate ligand and copper(I) salts leads to the formation of an insoluble dimeric complex, behaving like a copper(I) reservoir. A very small part of the latter is soluble, but its structure is lost to the benefit of a monomeric form. This monomer, in which the copper center is at the +I oxidation level and made electron-rich by the ligand, is the only species present at the beginning of the catalytic process.