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

摘要

The reaction of [MoO _2(acac) _2] with hydrochloric salts of pyridoxal thiosemicarbazone ligands, H _2L ~(1-3)·HCl, in dry methanol or acetonitrile resulted in the formation of the mononuclear complex [MoO _2(HL ~1)(CH _3OH)]Cl·1.5CH _3OH (1a) or polynuclear complexes [{MoO _2(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 [Mo _2O _3(HL ~(1-3)) _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 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 versus olefin.