Reaction of mixed-ligand iron-sulfur cluster [Fe4(Cp*)3(Ph2C2S2)(μ3-S)3(μ-S2)] (Cp* = C5Me5) with methyl iodide.: Synthesis, structure, and redox behaviour of [Fe4(Cp*)3(Ph2C2S2)(μ3-S)3(μ3-S2Me)]

The reaction of the mixed-ligand iron-sulfur cluster [Fe-4(Cp*)(3)(Ph2C2S2)(mu(3)-S)(3)(mu(3)-S-2)] ([3]) (Cp* = C5Me5) with iodomethane gave a methylated cluster, [Fe-4(Cp*)(3)(Ph2C2S2)(mu(3)-S)(3)(mu(3)-S2Me)]I ([4]I), in 60% yield. The anion exchange of [4]I with KPF6 gave [4]PF6 as a pure sample. A similar treatment of [3] using iodoethane afforded an ethylated cluster, [Fe-4(Cp*)(3)(Ph2C2S2)(mu(3)-S)(3)(mu(3)-S2Et)]I ([5]I), and oxidized parent cluster [3]I. The reaction of [3] with 2-iodopropane did not give an alkylated cluster. An unreacted cluster [3] was recovered with a small amount of oxidized cluster [3]I. The molecular structure of [Fe-4(Cp*)(3)(Ph2C2S2)(mu(3)-S)(3)(mu(3)-S2Me)] ([4]), which was obtained by the reduction of [4]PF6 with cobaltocene, was determined by an X-ray diffraction study. Crystallographic data are: Monoclinic, P2(1)/a, a = 21.707(2) Angstrom, b = 21.382(2) Angstrom, c = 11.433(1) Angstrom, beta = 98.98(1)degrees, V = 5241.5(9) Angstrom(3), Z = 4, and R = 0.067 for 7412 reflections with \F-0\ > 3sigma(F-0). The methyl group transferred from MeI is located on the singly ligating sulfur atom in the disulfide ligand of the parent cluster [3]. A cyclic voltammogram of [4]PF6 in 0.1 mol dm(-3) tetrabutylammonium tetrafluoroborate-CH3CN showed five reversible one-electron redox waves at E-1/2 = +1.42 V, +0.92 V, +0.41 V, -0.38 V, and -1.22 V vs SCE, corresponding to 4+/3+, 3+/2+, 2+/1+, 1+/0, and 0/1- charged cluster couples, respectively. An irreversible two-electron reduction wave was also observed at E-pe = 1.97 V vs SCE.