Biomimetic thiyl radical formation from diphenyl disulfide with the low valent Ni(i) state of a cofactor F430 model

Abstract

Cofactor F430 is a nickel-containing hydrocorphinato complex that plays important roles in the enzymatic formation and oxidation of methane. In methanotrophic bacteria, F430-dependent methyl-coenzyme M reductase (MCR) catalyses the endergonic conversion of the heterodisulfide adduct of coenzymes M and B with methane to methyl-coenzyme M and coenzyme B. In a radical mechanism, the Ni(i)-induced formation of a transient thiyl radical of coenzyme B from the heterodisulfide has been proposed. Herein, we introduce a new semi-artificial Ni-complex derived from vitamin B12 as functional model of F430. We demonstrate with electrochemical studies that the low valent Ni(i) complex cleaves the biomimetic model compound diphenyl disulfide into approx. 0.5 equivalents of thiophenol and a transient thiophenyl radical at a potential of −1.65 V vs. Fc/Fc+. Thiyl radicals are trapped in solution with phenylacetylene as thiophenyl-substituted olefins, but also lead to degradation of the Ni-complex.