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Replacement of an Oxo by an Imido Group in Oxotransferase Model Compounds: Influence on the Oxygen Atom Transfer

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posted on 04.10.2010, 00:00 by Nadia C. Mösch-Zanetti, Dietmar Wurm, Manuel Volpe, Ganna Lyashenko, Bastian Harum, Ferdinand Belaj, Judith Baumgartner
Treatment of [MoO(N-t-Bu)Cl2(dme)] (dme = dimethoxyethane) with 2 equiv of the potassium salts of Schiff base ligands of the type KArNC(CH3)CHC(CH3)O afforded oxo imido molybdenum(VI) compounds [MoO(N-t-Bu)L2] {1, with Ar = phenyl (LPh), 2 with Ar = 2-tolyl (LMePh), 3 with Ar = 2,6-dimethylphenyl (LMe2Ph) and 4 with Ar = 2,6-diisopropylphenyl (LiPr2Ph)}. We have also prepared related bisimido complexes [Mo(N-t-Bu)2L2 (5 with L = LPh, 6 with L = LMePh, and 7 with L = LMe2Ph) by treatment of [Mo(N-t-Bu)2Cl2(dme)] with 2 equiv of the potassium salt of the respective ligand. 1, 3, 5, and 6 were characterized via single crystal X-ray diffraction. The oxo imido complexes exhibit oxygen atom transfer (OAT) reactivity toward trimethyl phosphine. Kinetic data were obtained for 1 and 3 by UV/vis spectroscopy revealing decreased OAT reactivity in comparison to related dioxo complexes with the same Schiff base ligands and decreased reactivity of 1 versus 3. Cyclic voltammetry was used to probe the electronic situation at the molybdenum center showing reversible reduction waves for 3 and [MoO2(LMe2Ph)2] at comparable potentials while 1 exhibits a significant lower potential. Density functional theory (DFT) calculations showed a higher electron density on oxygen in the oxo imido complexes.