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

https://doi.org/10.1016/j.jics.2021.100006Get rights and content
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Highlights

  • New cis-Mo(VI)O2 complexes of three tridentate O,N,O′-donor hydrazone ligands have been synthesized and characterized.

  • The complexes function as catalysts for oxo atom transfer to phosphine, sulfoxidation and epoxidation reactions.

  • The presence of a sterically demanding ligand substituent leads to low catalytic activity for the Mo(VI) oxo complex.

Abstract

The new cis-dioxomolybdenum (VI) complexes [MoO2(L2)(H2O)] (2) and [MoO2(L3)(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, 1H and 13C 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(L1)(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.

Keywords

Dioxomolybdenum(VI) complexes
Hydrazone
Schiff base
Oxidation
Epoxidation
Sulfoxidation

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