[1 3] SITE-DIFFERENTIATED AND SULFIDE-BRIDGED CUBANE CLUSTERS IN CHEMISTRY AND BIOLOGY/

A subset of protein-bound Fe4S4 cubane-type clusters occurs in a [1:3] iron site-differentiated form in which the terminal ligand at the uni que site is not a cysteinyl group. Reactions of synthetic site-differe ntiated [Fe4S4](2+) clusters are summarized, including removal of the unique iron atom to afford the [Fe3S4](0) cuboidal cluster, thereby co mpleting the synthesis of analogues of native iron-sulfur clusters wit h nuclearity 14. The cuboidal cluster supports metal ion insertion rea ctions leading to a set of heterometal cubane type clusters MFe3S4, wh ose redox potentials have been determined as a function of M. Sulfide- bridged double cubanes [MFe3S4]-S-[MFe3S4] (M = Mo, Fe; M-2 = MoFe), a nother type of site-differentiated cluster, have been prepared as prec ursors in potential cluster rearrangement reactions leading to the cor e [MFe6S9] with the same topology as the FeMo-cofactor of nitrogenase.