title: Borohydride, azide, and chloride anions as terminal ligands on Fe/Mo/S clusters. Synthesis, structure and characterization of [(Cl4-cat)(PPr3) MoFe3S4(X)2]2(Bu4N)4 and [(Cl4-cat)(PPr3)MoFe3S4 (PPr3)(X)]2(Bu4N)2 (X = N3-, BH4-, Cl-) double-fused cubanes. NMR reactivity studies of [(Cl4-cat)(PPr3) MoFe3S4(BH4)2]2(Bu4N)4.
abstract: Our explorations of the reactivity of Fe/Mo/S clusters of some relevance to the FeMoco nitrogenase have led to new double-fused cubane clusters with the Mo2Fe6S8 core as derivatives of the known (Cl4-cat)2Mo2Fe6S8(PPr3)6 (I) fused double cubane. The new clusters have been obtained by substitution reactions of the PPr3 ligands with Cl-, BH4-, and N3-. By careful control of the conditions of these reactions, the clusters [(Cl4-cat)(PPr3)MoFe3S4(BH4)2]2(Bu4N)4 (II), [(Cl4-cat)(PPr3)MoFe3S4(PPr3)(BH4)]2(Bu4N)2 (III), [(Cl4-cat)(PPr3)MoFe3S4(N3)2]2(Bu4N)4 (IV), [(Cl4-cat)(PPr3)MoFe3S4(PPr3)(N3)]2(Bu4N)2 (V), and [(Cl4-cat)(PPr3)MoFe3S4Cl2]2(Et4N)4 (VI) have been obtained and structurally characterized. A study of their electrochemistry shows that the reduction potentials for the derivatives of I are shifted to more positive values than those of I, suggesting a stabilization of the reduced clusters by the anionic ligands BH4- and N3-. Using 1H NMR spectroscopy, we have explored the lability of the BH4- ligand in II in coordinating solvents and its hydridic character, which is apparent in its reactivity toward proton sources such as MeOH or PhOH.
authors.affiliation: Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Markos
authors.initials: M
authors.lastname: Koutmos
authors.forename: Irene P
authors.initials: IP
authors.lastname: Georgakaki
authors.forename: Dimitri
authors.initials: D
authors.lastname: Coucouvanis
mesh_terms: D000838:Anions; D001386:Azides / Q000737:chemistry*; D040761:Biomimetic Materials / Q000737:chemistry; D001894:Borohydrides / Q000737:chemistry*; D002713:Chlorine / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008280:Magnetics; D008667:Metalloproteins / Q000737:chemistry; D015394:Molecular Structure; D008982:Molybdenum / Q000737:chemistry*; D009591:Nitrogenase / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry*
chemical_list: D000838:Anions; D001386:Azides; D001894:Borohydrides; D008024:Ligands; D008667:Metalloproteins; D002713:Chlorine; D013455:Sulfur; D008982:Molybdenum; D007501:Iron; D009591:Nitrogenase