New mononuclear dioxidomolybdenum(VI) complexes with hydrazone ligands: Synthesis, crystal structures and catalytic performance

Three new dioxomolybdenum (VI) complexes, [MoO2L1(MeOH)] (1), [MoO2L2(MeOH)] (2) and [MoO2L3(H2O)]center dot EtOH (3), where L-1, L-2 and L-3 are the dianionic form of N'-(2-hydroxybenzylidene)-3-methylbenzohydrazide, 4-bromo- N'-(2-hydroxybenzylidene)benzohydrazide and 2-bromo-N'-(2-hydroxy benzylidene) benzohydrazide, respectively, have been prepared and characterized by IR, UV-Vis and NMR spectra, as well as single crystal X-ray diffraction. The Mo atoms in the complexes are in octahedral coordination, with the ONO donor set of the hydrazone ligands, O atoms of the solvents, and two oxo groups. Crystals of the complexes are stabilized by hydrogen bonds of types O-H center dot center dot center dot N and O-H center dot center dot center dot O. Moreover, the catalytic properties of complexes 1-3 are compared in cyclohexane oxidation. It was found that sebacic acid and FeCl3 could promote the catalytic activities of the complexes.