Water-soluble arylhydrazone complexes based on Mn(II) and Cu(II) as catalysts for liquid-phase toluene oxidation

Novel hydrosoluble coordination compounds based on arylhydrazones of β-diketones and bearing first row transition metals, namely [Mn(μ-1κO1,2κO2-HL1)2(H2O)2]n (1) and [Cu(κO1O2N-L2)(DEA)] (2; DEA = diethanolamine), were synthesised and characterized. Their structural features were investigated using single crystal X-ray diffraction. The catalytic performance of the complexes was explored for liquid phase oxidation of toluene in homogeneous medium using aqueous tert-butyl hydroperoxide (TBHP) and hydrogen peroxide (H2O2) as oxidants. Both catalysts demonstrated activity, producing a mixture of benzaldehyde, benzyl alcohol and benzoic acid. Under optimized conditions, in the presence of catalysts 1 and using an aqueous TBHP solution as oxidant, the oxidation of toluene yielded an overall 42.6% of oxygenated products. Contrary to what has been regularly reported regarding selectivity for benzaldehyde, benzoic acid was the predominant product in this study (71%).