Autoxidation catalysed by transition metal complexes. I. The coordinative mechanism for phenylmethanethiol autoxidation catalysed by Bis[dimercaptomaleonitrilato(2 -)]cobaltate(2-) [Co(mnt)₂]₂^2- in acetonitrile solution

Abstract

The homogeneous catalysis of phenylmethanethiol autoxidation

                       2PhCH₂SH+O₂ → PhCH₂SSCH₂Ph+H₂O₂

by [Co(mnt)₂]₂^2- (mnt, doubly deprotonated dimercaptomaleonitrile) in acetonitrile solution buffered with excess PhMe₂N and PhMe₂NH⁺ClO₄^- at 18.0°C is described. Effective catalysis occurs in this medium, with catalyst complex decomposition less than 1 mole % of the turnover. Spectrophotometric and oxygen-consumption kinetic data indicate that the mechanism involves initial coordination of the thiolate to [Co(mnt)₂]^- to form an intermediate which then, with Bronsted acid assistance, interacts with oxygen to form a second intermediate, which dissociates to products and regenerates [Co(mnt)₂]₂^2-. It is concluded that the role of the catalyst is to sequentially coordinate and activate the reactants and facilitate intramolecular electron transfer from thiolate to oxygen, without itself undergoing reduction or oxidation or dithiolene ligand substitution.