Enzymatic C-H activation by metal-superoxo intermediates.

The mechanisms of four enzymes that initiate oxidation of their substrates by using mid-valent metal-superoxo intermediates, rather than the more frequently described high-valent iron-oxo complexes, to cleave relatively strong C-H bonds have come into focus in the past several years. In two of these reactions, the alternative manifold for O2 and C-H activation enables unique four-electron oxidation reactions, thus significantly augmenting Nature's arsenal for transformation of aliphatic carbon compounds. General principles of this alternative manifold, including common kinetic characteristics and thermodynamic limitations, are emerging. Recent, combined experimental and computational studies on other systems have shown how a more thorough understanding of the structures of the metal-superoxo intermediates and the mechanisms by which they cleave C-H bonds might be achieved.