On the reduction of iron–sulphur clusters under carbon monoxide

Abstract

Multi-electron reduction of [Fe₄S₄(SPh)₄]^2– at platinum or mercury cathodes under CO at 1 atm (101 325 Pa) gives [Fe₂S₂(CO)₆]^2–via the formation of a stable tetranuclear intermediate [Fe₄S₄(CO)₁₂]^2–. The product, the intermediate, and [Fe₂S₂(CO)₆] are interrelated by a sequence of electrochemically irreversible electron-transfer steps which involve chemically reversible intra- and inter-molecular coupling or cleavage of S–S bonds. Hydrogenases and nitrogenases possessing [4Fe–4S] centres are inhibited by CO but rapid interaction of the synthetic cluster with this substrate only occurs when the highly reduced [Fe₄S₄(SPh)₄]^4– state is accessed and this corresponds to a physiologically unusual reduction level.