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 OO 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.