A Convenient Route to Synthetic Analogues of the Oxidized Form of High-Potential Iron–Sulfur Proteins

Abstract

An amide-bound [Fe₄S₄]³⁺ cluster, [Fe₄S₄{N­(SiMe₃)₂}₄]⁻ (<b>1</b>), was found to serve as a convenient precursor for synthetic analogues of the oxidized form of high-potential iron–sulfur proteins. Treatment of <b>1</b> with 4 equiv of bulky thiols led to replacement of the amide ligands with thiolates, giving rise to a series of [Fe₄S₄(SR)₄]⁻ clusters (R = Dmp (<b>2a</b>), Tbt (<b>2b</b>), Eind (<b>2c</b>), Dxp (<b>2d</b>), Dpp (<b>2e</b>); Dmp = 2,6-di­(mesityl)­phenyl, Tbt = 2,4,6-tris­[bis­(trimethylsilyl)­methyl]­phenyl, Eind = 1,1,3,3,5,5,7,7-octaethyl-<i>s</i>-hydrindacen-4-yl, Dxp = 2,6-di­(<i>m</i>-xylyl)­phenyl, Dpp = 2,6-diphenylphenyl). These clusters were characterized by the mass spectrum, the EPR spectrum, and X-ray crystallography. The redox potentials of the [Fe₄S₄]^3+/2+ couple, −0.82 V (<b>2a</b>), −0.86 V (<b>2b</b>), −0.84 V (<b>2c</b>), −0.74 V (<b>2d</b>), and −0.63 V (<b>2e</b>) vs Ag/Ag⁺ in THF, are significantly more negative than that of [Fe₄S₄(SPh)₄]^−/2– (−0.21 V)