[1:3] Site-differentiated and sulfide-bridged cubane clusters in chemistry and biology

Abstract

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 unique site is not a cysteinyl group. Reactions of synthetic site-differentiated [Fe4S4]2+ clusters are summarized, including removal of the unique iron atom to afford the [Fe3S4]0 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 MFe3S4, whose redox potentials have been determined as a function of M. Sulfide-bridged double cubanes [MFe3S4]-S-[MFe3S4] (M = Mo, Fe; M2 = MoFe), another type of site-differentiated cluster, have been prepared as precursors in potential cluster rearrangement reactions leading to the core [MFe6S9] with the same topology as the FeMo-cofactor of nitrogenase.