Synthesis, characterization and catalytic properties of dinuclear complexes of copper(II) and nickel(II): Oxidation of cyclohexane, toluene and cyclopentane

Abstract

Oxidation of saturated hydrocarbon by transition metal complexes is of great importance because this would give industrially valuable organic fine chemicals. Here, dinuclear copper(II) and dinuclear nickel(II) complexes with same N,O donor ligand have been used as catalyst for the oxidation of cyclohexane, toluene and cyclopentane using hydrogen peroxide as the oxidant to examine their catalytic activity and effect of nature of metal center on catalysis. [Cu2(L1)2(μ2-Cl)Cl]·2.5H2O (1) and [Ni2(L1)2(μ2-N3)2 (CH3OH)2]·CH3OH (2) have been synthesized under mild conditions where HL1 is 1-((2-hydroxyethylimino)methyl)naphthalen-2-ol. These complexes have been characterized by elemental analysis, FT-IR, UV-Vis, mass spectroscopy, TGA-DTA and cyclic voltametric studies. Their structures have been confirmed by single crystal X-ray diffraction analysis. Some theoretical calculations have been performed to investigate spectral transitions. Copper(II) complex shows effective catalytic ability towards oxidation of the saturated hydrocarbons such as cyclohexane, toluene and cyclopentane in the presence of hydrogen peroxide when corresponding alcohols and ketones have been obtained as major products. However, complex 2 has been found to be inactive as catalyst for the oxidation. It is possible that Cu-hydroperoxo or Cu-peroxo species is formed during catalysis (as revealed from UV-vis spectral analysis) which could be the active species for the oxidation reaction.