Formation of stable metal-phenoxyl radical complexes from metal-phenol(ate) species under aerobic conditions

The oxidized phenol species play important roles in biological systems as cofactors in some enzymes, such as galactose oxidase and copper amine oxidase, where the Cu II -phenoxyl radical species formed by O 2 could be detected. Many metal-phenoxyl radical complexes have hitherto been studied for understanding their detailed properties and reactivities. However, the formation of metal-phenoxyl radical species from metal(II)-phenol or -phenolate complexes by reaction with O 2 have not been fully discussed yet. In this review, we focus on the formation of the metal-phenoxyl radical species from metal(II)-phenol or phenolate complexes by O 2 and discuss the reaction mechanisms.