Synthesis, characterization and catalytic oxyfunctionalization of cyclohexene with tert-butylhydroperoxide and hydrogen peroxide in the presence of alumina-supported Mn(II), Co(II), Ni(II) and Cu(II) bis(2-hydroxyanil)benzil complexes

New square-planar Mn(II), Cu(II), Ni(II) and Co(II) complexes of a tetradentate Schiff-base ligand “bis(2-hydroxyanil)benzil, H2[habenzil]; have been prepared and characterized by elemental analyses, IR, UV–vis, conductometric and magnetic measurements. The results suggest that the symmetrical Schiff-base is a bivalent anion with tetradentate N2O2 donors derived from the phenolic oxygen and azomethine nitrogen. The formulae was found to be [M(habenzil)] for the 1:1 non-electrolytic complexes. Alumina-supported metal complexes (ASMC; [M(habenzil)/Al2O3]) catalyze the oxidation of cyclohexene with tert-buthylhydroperoxide (TBHP) and H2O2. Oxidation of cyclohexene with TBHP gave 2-cyclohexene-1-one, 2-cyclohexene-1-ol and 1-(tert-butylperoxy)-2-cyclohexene whereas, oxidation with H2O2 resulted in the formation of cyclohexene oxide and cyclohexene-1,2-diol. Manganese(II) complex supported on alumina “[Mn(habenzil)]/Al2O3” shows significantly higher catalytic activity than other catalysts. The activity of the immobilized catalyst remains nearly the same after three cycles, suggesting the true heterogeneous nature of the catalyst.

Graphical abstractNew square-planar Mn(II), Cu(II), Ni(II) and Co(II) complexes of a tetradentate Schiff-base ligand “bis(2-hydroxyanil)benzil, H2[habenzil]”; have been prepared and characterized by elemental analyses, IR, UV–vis, conductometric and magnetic measurements. Alumina-supported metal complexes (ASMC; [M(habenzil)/Al2O3]) catalyze the oxidation of cyclohexene with tert-buthylhydroperoxide (TBHP) and H2O2. Oxidation of cyclohexene with TBHP gave 2-cyclohexene-1-one, 2-cyclohexene-1-ol and 1-(tert-butylperoxy)-2-cyclohexene whereas, oxidation with H2O2 resulted in the formation of cyclohexene oxide and cyclohexene-1,2-diol. Manganese(II) complex supported on alumina “[Mn(habenzil)]/Al2O3” shows significantly higher catalytic activity than other catalysts. Figure optionsDownload full-size imageDownload as PowerPoint slide