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

An amide-bound [Fe4S4]3+ cluster, [Fe4S4{N­(SiMe3)2}4]− (1), was found to serve as a convenient precursor for synthetic analogues of the oxidized form of high-potential iron–sulfur proteins. Treatment of 1 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 (2a), Tbt (2b), Eind (2c), Dxp (2d), Dpp (2e); 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-s-hydrindacen-4-yl, Dxp = 2,6-di­(m-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 (2a), −0.86 V (2b), −0.84 V (2c), −0.74 V (2d), and −0.63 V (2e) vs Ag/Ag+ in THF, are significantly more negative than that of [Fe4S4(SPh)4]−/2– (−0.21 V).