Synthesis, Characterization, and Reactivity of Cobalt(III)-Oxygen Complexes Bearing a Macrocyclic N-Tetramethylated Cyclam Ligand

Abstract

Mononuclear metal-dioxygen species are key intermediates that are frequently observed in the catalytic cycles of dioxygen activation by metalloenzymes and their biomimetic compounds. In this work, a side-on cobalt(III)-peroxo complex bearing a macrocyclic N-tetramethylated cyclam (TMC) ligand, [CoIII(15-TMC)(O2)]+, was synthesized and characterized with various spectroscopic methods. Upon protonation, this cobalt(III)-peroxo complex was cleanly converted into an end-on cobalt(III)-hydroperoxo complex, [CoIII(15-TMC)(OOH)]2+. The cobalt(III)-hydroperoxo complex was further converted to [CoIII(15-TMC-CH2-O)]2+ by hydroxylation of a methyl group of the 15-TMC ligand. Kinetic studies and 18O-labeling experiments proposed that the aliphatic hydroxylation occurred via a CoIV-oxo (or CoIII-oxyl) species, which was formed by O-O bond homolysis of the cobalt(III)-hydroperoxo complex. In conclusion, we have shown the synthesis, structural and spectroscopic characterization, and reactivities of mononuclear cobalt complexes with peroxo, hydroperoxo, and oxo ligands. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.