New molybdenum(VI) complexes with thiazole-hydrazone ligand: Preparation, structural characterization, and catalytic applications in olefin epoxidation

Abstract

The reaction of [MoO2(acac)2] with (E)-2-((2-(benzo[d]thiazol-2-yl)hydrazono)methyl)-6-methoxyphenol (H2L), in acetonitrile and ethanol resulted in the formation of {[MoO2(HL)(H2O)]2[Mo6O19]·2MeCN} (1) (mononuclear cationic complex with hexamolybdate anion) and [MoO2L(EtOH)] (2) (neutral mononuclear complex), depending on the reaction conditions. In these compounds, the ligand is coordinated to the cis-MO22+ core via phenolic-oxygen, thiazole and azomethine nitrogen atoms, while the remaining sixth coordination site is occupied by the oxygen atom from the solvent molecule. Crystal and molecular structures of the compounds 1 and 2 were determined by the single crystal X-ray diffraction method. All of the investigated compounds were further characterized by elemental analysis, FT-IR and NMR spectroscopy. The molybdenum(VI) species were used as catalyst for olefin oxidation in the presence of tert-butylhydroperoxide (TBHP) as an oxidant. Under similar experimental conditions with equal Mo loading, the presence of the {[MoO2(HL)(H2O)]2[Mo6O19]·2MeCN} (1) resulted in higher oxidation conversion than [MoO2L(EtOH)] (2). It seems 1 contains two potentially active parts, the [MoO2(HL)H2O]+ cation and the Mo6O19−2 anion.