Bio-inspired oxidation catalysis based on proton-coupled electron transfer: Toward efficient and selective oxidation of methane to methanol.

In this paper, a trail of my research is described starting from oxidation of alkanes by FeIII-TPA (TPA = tris(2-pyridylmethyl)amine) complexes with alkyl hydroperoxides to Ru-pyridylamine complexes which can be converted to RuIV-oxo complexes in different spin states (S = 1 or 0) through proton-coupled electron-transfer oxidation of the corresponding RuII-aqua complexes, clarifying that those spin states do not affect the reactivity in water. The introduction of strongly donating N-heterocyclic carbene (NHC) moiety allows us to create a RuIII-oxyl complex showing different reactivity from that of RuIV-oxo complexes. Manipulation of second coordination spheres (SCSs) of Ru-TPA complexes is also described, visualizing unique functionality. The introduction of hydrophobic SCS to a FeII-NHC complex enables to catalyze selective oxidation of methane to form methanol in high selectivity in aqueous media based on the "catch-and-release" strategy, which can also allow us to achieve highly selective two-electron oxidation of aromatic compounds.