Journal of the American Chemical Society, Vol.138, No.18, 5817-5820, 2016
Four-Electron Oxidation of Phenols to p-Benzoquinone Imines by a (Salen)ruthenium(VI) Nitrido Complex
Proton-coupled electron-transfer reactions of phenols have received considerable attention because of their fundamental interest and their relevance to many biological processes. Here we describe a remarkable four electron oxidation of phenols by a (salen)ruthenium(VI) complex in the presence of pyridine in CH3OH to afford (salen)ruthenium(I) p-benzoquinone imine complexes. Mechanistic studies indicate that this reaction occurs in two phases. The first phase is proposed to be a two electron transfer process that involves electrophilic attack by Ru N at the phenol aromatic ring, followed by proton shift to generate a Ru(W) p-hydroxyanilido intermediate. In the second phase the intermediate undergoes infra molecular two-electron transfer, followed by rapid deprotonation to give the Ru(II) p-benzoquinone imine product.