Dioxomolybdenum(VI) complexes of hydrazone phenolate ligands - syntheses and activities in catalytic oxidation reactions

The new cis-dioxomolybdenum (VI) complexes [MoO2(L-2)(H2O)] (2) and [MoO2(L-3)(H2O)] (3) containing the tridentate hydrazone- based ligands (H2L2 = N'-(3,5-di-tert-butyl-2-hydroxybenzylidene)-4-methylbenzohydrazide and H2L3 = N'-(2-hydroxybenzylidene)-2-(hydroxyimino)propanehydrazide) have been synthesized and characterized via IR, H-1 and C-13 NMR spectroscopy, mass spectrometry, and single crystal X-ray diffraction analysis. The catalytic activities of complexes 2 and 3, and the analogous known complex [MoO2(L-1)(H2O)] (1) (H2L1 = N'-(2-hydroxybenzylidene)-4-methylbenzohydrazide) have been evaluated for various oxidation reactions, viz. oxygen atom transfer from dimethyl sulfoxide to triphenylphosphine, sulfoxidation of methyl-p-tolylsulfide or epoxidation of different alkenes using tert-butyl hydroperoxide as terminal oxidant. The catalytic activities were found to be comparable for all three complexes, but complexes 1 and 3 showed better catalytic performances than complex 2, which contains a more sterically demanding ligand than the other two complexes.

Automated summary

The new cis-dioxomolybdenum (VI) complexes containing tridentate hydrazone-based ligands have been synthesized and evaluated for their catalytic activities in various oxidation reactions. Complexes 1 and 3 showed better catalytic performances than complex 2 due to the differences in their steric properties.