Direct observation of CuI/CuIII redox steps relevant to Ullmann-type coupling reactions

Abstract

A series of aryl–copper(III)-halide complexes have been synthesized and characterized by NMR and UV-visible spectroscopy, cyclic voltammetry and X-ray crystallography. These complexes closely resemble elusive intermediates often invoked in catalytic reactions, such as Ullmann–Goldberg cross-coupling reactions, and their preparation has enabled direct observation and preliminary characterization of aryl halide reductive elimination from CuIII and oxidative addition to CuI centers. In situ spectroscopic studies (1H NMR, UV-visible) of a Cu-catalyzed C–N coupling reaction provides definitive evidence for the involvement of an aryl-copper(III)-halide intermediate in the catalytic mechanism. These results provide the first direct observation of the CuI/CuIII redox steps relevant to Ullmann-type coupling reactions.