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)(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, [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 ¹⁸ O-labeling experiments proposed that the aliphatic hydroxylation occurred via a Co^IV-oxo (or Co^III-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 mono-nuclear cobalt complexes with peroxo, hydroperoxo, and oxo ligands.