High-valent metal-oxo complexes generated in catalytic oxidation reactions using water as an oxygen source

High-valent metal-oxo complexes are produced by successive electron-transfer oxidation of metal complexes with one-electron oxidants in the presence of water, which is an oxygen source in the generation of the metal-oxo complexes. Then, metal-oxo complexes oxidize substrates to yield oxygenated substrates, accompanied by the regeneration of reduced metal complexes. Thus, the oxidation of substrates using one-electron oxidants can be catalyzed by metal complexes via formation of high-valent metal-oxo complexes by the electron-transfer oxidation of metal complexes in the presence of water as an oxygen source. When water is used as a substrate, water is oxidized by one-electron oxidants to evolve dioxygen via an O-O bond formation process. The one-electron oxidants used for the formation of high-valent metal-oxo complexes can be replaced by much weaker oxidants, when a photosensitizing metal complex, such as [Ru(bpy)(3)](2+) (bpy = 2,2'-bipyridine), is employed as a photocatalyst, an oxidized form of the photocatalyst, which is generated via photoinduced electron transfer from the excited state to a weaker oxidant, can oxidize metal complexes in the presence of water to afford the high-valent metal-oxo complexes. Thus, the oxidation of substrates, including water oxidation, by weak oxidants can be catalyzed by metal complexes under photoirradiation of the photocatalyst using water as an oxygen source. (C) 2016 Elsevier B.V. All rights reserved.