Molybdenum(VI) complexes with tridentate Schiff base ligands derived from isoniazid as catalysts for the oxidation of sulfides: synthesis, X-ray crystal structure determination and spectral characterization

Two new complexes, including [MoO2(L1)(CH3OH)] and [MoO2(L2)(CH3OH)], with tridentate ONO–donor Schiff base ligands (H2L1: (E)-N'-(2-hydroxy-3-methoxybenzylidene)isonicotinohydrazide and H2L2: (E)-N'-(5-chloro-2-hydroxybenzylidene)isonicotinohydrazide) have been synthesized and characterized spectroscopically through FT-IR and 1H-NMR and by elemental analyses. Their solid-state structures were also confirmed by single-crystal X-ray diffraction (SC-XRD) technique. These tridentate Schiff base ligands coordinated to the metal ion via phenolate oxygen, imine nitrogen and enolic oxygen atoms. In the complexes, the molybdenum center adapts a slightly distorted octahedral geometry, by using three O,N,O-donor atoms of the tridentate ligands, methanol and an oxo group employing the axial positions, while another oxo group makes the equatorial plane. Moreover, the complexes were utilized in oxidizing the different sulfides as an efficient homogeneous catalyst in the presence of tert-butyl hydroperoxide (TBHP) as an oxidizing agent in 1,2-dichloroethane (DCE) as a solvent under refluxed conditions. This method has numerous ascendancies such as high yield, short reaction time and excellent selectivity to produce corresponding sulfoxides without overoxidation to sulfones.