CHEMISTRY-A EUROPEAN JOURNAL, v.19, no.42, pp.14112 - 14118
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 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.