BRIDGING CH2 ADDITION TO THE DISULFUR LIGANDS OF AN IRON-SULFUR CLUSTER COMPOUND - X-RAY STRUCTURE OF S)2((MU-3-S2)-CH2-(MU-3-S2))(C5H4ME)4]2-((FECL4)2)

The nucleophilic sulfur atoms of the disulfur ligands in Fe4S6(C5H4R)4 (1) (R = H, Me) react easily with the alkyl halides CH2X2 (X = Cl, I) or CH3I, to give the cluster compounds [Fe4(mu3-S)2((mu3-S2)-CH2-(mu3 -S2))-(C5H4R)4]2+ (FeCl4)2-(R = H,2a[FeCl4]; R = Me,2b[FeCl4]), [Fe4(m u3-S)2((mu3-SSCH3)2)(C5H5)4](PF6)2(3[PF6]2), [Fe4(mu3-S)2((mu3-SSCH3)( mu3-S2)(C5H5)4](I)(4[I]). The structure of 2b[FeCl4], determined by X- ray diffraction, shows that a CH2 bridge is present between the sulfur atoms of each of the disulfido ligands. In this way a new, mu6-bonded ligand SSCH2SS is produced. 2b[FeCl4] crystallizes in the monoclinic system, space group Cc, with cell dimensions a = 15.847(2) angstrom, b = 13.050(2) angstrom, c = 16.395(2) angstrom, beta = 107.15-degrees, V = 3166.1 angstrom3, and Z = 4. Refinement of 392 parameters on 5859 observed reflections gave an R value of 0.047 (R(w) = 0.048). The stru cture of the new iron-sulfur cluster compound 2 differs from the paren t compound 1 in that only the S-S bond distances increase from 2.04 to 2.19 angstrom. The Fe-Fe and Fe-S bond distances remain unchanged. Th e H-1 NMR spectrum of 2 recorded in CD3CN indicates that the iron-sulf ur core is rigid with nonfluxional disulfur units. In solution, 1 reac ts immediately with CH3I to form the monomethylated product 4+. Stirri ng 1 in pure Mel for 48 h affords the dimethylated product 3(2+). This indicates the diminished nucleophilic character of 4+ as compared to 1.