REACTIVITY OF CUBANE-TYPE [(OC)(3)MFE(3)S(4)(SR)(3)](3-) CLUSTERS (M=MO,W) - INTERCONVERSION WITH CUBOIDAL [FE3S4](0) CLUSTERS AND ELECTRON-TRANSFER

The title clusters, several examples of which have been reported earli er, have been prepared by two different methods and subjected to struc tural and reactivity studies. The compounds (Et(4)N)(3)[(OC)(3)MFe(3)S (4)(Smes)(3)]. MeCN (M = Mo/W) are isomorphous and crystallize in mono clinic space group P2(1)/n with a = 13.412(1)/13.297(1) Angstrom, b = 19.0380(1)/18.9376(3) Angstrom, c = 26.4210(1)/26.2949(1) Angstrom, be ta = 97.87(1)/97.549(1)degrees, and Z = 4. The clusters contain long M -S (2.62/2.59 Angstrom) and M-Fe (3.22/3.19 Angstrom) bonds, consisten t with the reported structure of [(OC)(3)MoFe3S4(SEt)(3)](3-) (3) Reac tion of [(OC)(3)MoFe3S4(LS(3))](3-) (7) With CO in the presence of NaP F6 affords cuboidal [Fe3S4(LS(3))](3-) (9), also prepared in this labo ratory by another route as a synthetic analogue of protein-bound [Fe3S 4](0) clusters. The clusters [Fe3S4(SR)(3)](3-) (R = mes, Et), of limi ted stability, were generated by the same reaction. Treatment of 9 wit h [M(CO)(3)(MeCN)(3)] affords 7 and its M = W analogue. The clusters [ (OC)(3)MFe(3)S(4)(SR)(3)](3-) form a four-member electron transfer ser ies in which the 3- cluster can be once reduced (4-) and twice oxidize d (2-, 1-) to afford clusters of the indicated charges. The correct as signment of redox couple to potential in the redox series of six clust ers is presented, correcting an earlier misassignment of the redox ser ies of 3. Carbonyl stretching frequencies are shown to be sensitive to cluster oxidation state, showing that the M sites and Fe3S4 fragments are electronically coupled despite the long bond distances. (LS(3) = phenyl)thio)-2,4,6-tris(p-tolylthio)benzenate(3-); mes = mesityl.).