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

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, [Co-III(15-TMC)(O-2)](+), 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, [Co-III(15-TMC)(OOH)](2+). The cobalt(III)-hydroperoxo complex was further converted to [Co-III(15-TMC-CH2-O)](2+) by hydroxylation of a methyl group of the 15-TMC ligand. Kinetic studies and O-18-labeling experiments proposed that the aliphatic hydroxylation occurred via a Co-IV-oxo (or Co-III-oxyl) species, which was formed by OO 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.