[1:3] Site-differentiated and sulfide-bridged cubane clusters in chemistry and biology
A subset of protein-bound Fe,S, cubane-type clusters occurs in a (1:3) iron site-differentiated form in which the terminal ligand at the unique site is not a cysteinyl group. Reactions of synthetic site-differentiated (Fe,S,)" clusters are summarized, including removal of the unique iron atom to afford the (Fe,S,)' cuboidal cluster, thereby completing the synthesis of analogues of native iron-sulfur clusters with nuclearity $4. The cuboidal cluster supports metal ion insertion reactions leading to a set of heterometal cubane type clusters MFe,S,, whose redox potentials have been determined as a function of M. Sulfide-bridged double cubanes (MFe,S,)-S-(MFe$,) (M = Mo, Fe; h'& = MoFe), another type of site-differentiated cluster, have been prepared as precursors in potential cluster rearrangement reactions leading to the core (MFe,S,) with the same topology as the FeMo-cofactor of nitrogenase.