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.