Synthesis and characterization of alumina-supported Mn(II), Co(II), Ni(II) and Cu(II) complexes of bis(salicylaldiminato)hydrazone as catalysts for oxidation of cyclohexene with tert-buthylhydroperoxide

Complexes of type [M(SAH)(OH2)] where M is Mn(II),Co(II),Ni(II) and Cu(II), and SAH is the Schiff-base formed by condensation of salicylaldehyde (2 equiv.) and hydrazine (1 equiv.), bis(salicylaldiminato)hydrazone, or 2-({(z)-2-[(E)-1-(2-hydroxyphenyl)methylidene}hydrazonolmethyl)phenol have been prepared and characterized by elemental analysis, IR, UV-vis spectroscopy, conductometric, small area X-ray photoelectron spectroscopy and magnetic measurements. Elemental analysis suggests the stoichiometry to be 1: 1 (metal:ligand). The results indicate that the Schiff-base ligand coordinates through one azomethine nitrogen and two phenolic oxygen to the metal ions. Conductance measurements suggest the non-electrolytic nature of the complexes. The atomic concentration of the complexes showed the ratio of M:N:O = 1:23, that indicates that a water molecule was in the complex. Alumina-supported complexes [M(SAH)OH2]-Al2O3 catalyze the oxidation of cyclohexene with tert-butylhydroperoxide (TBHP). The major products of the reaction were 2-cyclohexene-1-ol, 2cyclohexene-1-one and 2-cyclohexene-1-(tert-butylperoxy). The influence of solvent on the oxidation reaction has been studied. [M(SAH)OH2]-Al2O3 shows significantly higher catalytic activity than other alumina-supported complexes. These catalysts can also be reused in the oxidation of cyclohexene several times. The new materials [M(SAH)OH2]-Al2O3 were characterized by several techniques: chemical analysis and spectroscopic methods (Fr-IR, UV-vis, XRD, DRS). (c) 2005 Elsevier B.V. All rights reserved.