Chromium(V)-oxo and chromium(III)-superoxo complexes bearing a macrocyclic TMC ligand in hydrogen atom abstraction reactions

Abstract

A Cr(V)-oxo complex bearing a macrocyclic TMC ligand, [Cr(V)(TMC)(O)(OCH(3))](2+), was synthesized, isolated, and characterized by various physicochemical methods, including UV-vis, ESI-MS, resonance Raman, EPR and X-ray analysis. The reactivity of the Cr(V)-oxo complex was investigated in C-H and O-H bond activation reactions. The reactivity of a Cr(III)-superoxo complex, [Cr(III) (TMC)(O(2))(Cl)](+), was investigated in O-H bond activation reactions as well. By comparing reactivities of the Cr(III)-superoxo and Cr(V)-oxo complexes under the identical reaction conditions, we were able to demonstrate that the Cr(III)-superoxo complex is more reactive than the Cr(V)-oxo complex in the activation of C-H and O-H bonds. The present results provide strong evidence that under certain circumstances, metal-superoxo species can be an alternative oxidant for high-valent metal-oxo complexes in oxygenation reactions.