Reaction of strong nucleophiles with molybdenum-iron-sulfur edge-bridge double cubanes

INOR 108

Mark L. Hlavinka, hlavinka@fas.harvard.edu, Taichi Miyaji, and Richard H. Holm, holm@chemistry.harvard.edu. Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford St., Cambridge, MA 02138
Under investigation is the insertion of strong nucleophile (X) into the core of high-nuclearity molybdenum-iron-sulfur clusters in an attempt to approach the FeMo-cofactor (MoFe7S9X; X = C, N, or O) of nitrogenase. We have recently utilized edge-bridged double cubane cluster (Tp)2Mo2Fe6S8(PEt3)4 (EBDC, Tp = hydrotris-(pyrazolyl)borate (1-)) as an effective precursor to structural analogs of the PN cluster of nitrogenase. The addition of hydrosulfide or hydroselenide nucleophile to EDBC effects a core rearrangement yielding, [(Tp)2Mo2Fe6(ì2-Q)(ì2-S)(ì3-S)6(ì6-S)(QH)2]3- (Q = S, Se) where the fate of the attacking nucleophile is a ì2 bridging position. The question arises whether other strong nucleophiles (X) could attack the core of EBDC, yielding clusters approaching the FeMo-cofactor of nitrogenase. In this presentation we report the synthesis and certain properties of a series of oxygen ligated PN-type clusters prepared by the addition of oxygen nucleophiles to high-nuclearity molybdenum-iron-sulfur clusters.