Charged dioxomolybdenum(VI) complexes with pyridoxal thiosemicarbazone ligands as molybdenum(V) precursors in oxygen atom transfer process and epoxidation (pre)catalysts

The reaction of [MoO2(acac)(2)] with hydrochloric salts of pyridoxal thiosemicarbazone ligands. H2L1-3 center dot HCl, in dry methanol or acetonitrile resulted in the formation of the mononuclear complex [MoO2(HL1) (CH3OH)]Cl center dot 1.5CH(3)OH (1a) or polynuclear complexes [{MoO2(HL1-3))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(HL1-3)(2)]Cl-2 (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 la 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 versus olefin. (C) 2011 Elsevier Ltd. All rights reserved.