New molybdenum (VI) catalyst for the epoxidation of alkenes and oxidation of sulfides: An experimental and theoretical study

The preparation and catalytic activity of molybdenum(VI) dioxido complex [MoO₂L(C₂H₅OH)] (L = N′-[1-(2- hydroxynaphthyl)ethylidene]-2-hydroxy benzohydrazide) are reported. The reaction of the respective benzohydrazide ligand and the Mo(VI) dioxido precursor, [MoO₂(acac)] (acac = acetylacetonate), in ethanol afforded the [MoO₂L(C₂H₅OH)] complex. Structure of the complex was unequivocally established by single-crystal X-ray crystallography. The X-ray structure of complex reveals a six coordinate molybdenum center with a distorted octahedral geometry. By using the AIM analysis, topological properties of the electron density were analyzed to define the bond path between atoms. The AIM calculations indicate that the ligand H₂L coordinates to the molybdenum ion in the enol-enamine form (not keto-amine). An insight in the electronic structure of the complex was also obtained by using the density functional theory (DFT). The [MoO₂L(C₂H₅OH)] complex was successfully applied as a catalyst in both, the epoxidation of olefins with tert-butyl hydroperoxide (TBHP) and the oxidation of sulfides with urea hydrogen peroxide (UHP), to form the corresponding sulfoxides.