Synthesis, Characterization and X-Ray Crystal Structures of cis-Dioxomolybdenum(VI) Complexes of Similar Tridentate Aroylhydrazone Schiff Bases with Catalytic Epoxidation Activity

Two new cis-dioxomolybdenum(VI) complexes with general formula [MoO2L(MeOH)], where L = L-1 = N'-(3,5-dibromo-2-hydroxybenzylidene)-4-trifluoromethylbenzohydrazide for complex 1, and L = L-2 = N'-(3-bromo-5-chloro-2-hydroxybenzylidene)- 4-trifluoromethylbenzohydrazide for complex 2, have been synthesized and fully characterized on the basis of elemental analysis, FT-IR, molar conductivity, and electronic spectra. The complexes are also characterized by single crystal X-ray diffraction. The complexes have distorted octahedral structures in which the aroylhydrazones behave as dianionic ligands. It is also revealed from the crystal structures that the Mo(VI) center adopts NO5 donor environment, and the octahedral coordination is furnished by two oxido groups and oxygen atoms of neutral methanol molecules. The catalytic properties were investigated for epoxidation of cyclooctene using aqueous tert-butyl hydroperoxide as the oxidant.