Charged Dioxomolybdenum(VI) Complexes with Pyridoxal Thiosemicarbazone Ligands as Molybdenum(V) Precursors in Oxygen Atom Transfer Process and Epoxidation (pre)Catalysts
Résumé
The reaction of [MoO2(acac)2] with hydrochloric salts of pyridoxal thiosemicarbazone ligands, H2L 1-3 •HCl, in dry methanol or acetonitrile resulted in the formation of the mononuclear complex [MoO2(HL 1)(CH3OH)]Cl•1.5CH3OH (1a) or polynuclear complexes [{MoO2(HL 1-3)}Cl]n (1-3) containing a different substituent on the nitrogen atom of the N-thioureide fragment: Ph (1 and 1a), Me (2) or H (3). New dinuclear molybdenum(V) complexes [Mo2O3(HL 1-3)2]Cl2 (4-6) were obtained by oxygen atom abstraction from 1-3 with triphenylphosphine. All compounds were characterized by chemical analysis, IR spectroscopy, one-and two-dimensional NMR methods, TGA and in selected cases by DSC measurements. In addition, the crystal and molecular structure of 1a was determined by single crystal X-ray diffraction. All molybdenum(VI) species were used as (pre)catalysts for olefin epoxidation under solvent-free conditions with a 0.05% Mo loading vs. olefin.
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