Synthesis, Characterization, Crystal Structure and Catalytic Activity of New Dinuclear Cu(II) Complex in Oxidation of Benzyl Alcohol

Due to the wide application of carbonyl compounds as intermediates for many chemical compounds, drugs, vitamins and fragrances, the selective oxidation of aromatic alcohols to their corresponding aldehydes is one of the most important transformations in organic chemistry [1]. Therefore, numerous methods have been developed using a variety of reagents for this purpose. Traditional oxidants, such as KMnO4, CrO3, Br2, and TBHP (tert-butyl hydroperoxide), used in the oxidation of aromatic alcohols are usually toxic, corrosive or expensive. Thus, offering innovative, “clean” methods that use environmentally friendly oxidants such as hydrogen peroxide and molecular oxygen in non-toxic solvents in particular aqueous media could be a new challenge in this regard [2]. Recently, the catalytic oxidation of alcohols by transition metal complexes in the presence of H2O2 has been developed. Various compounds of Cu(II) salts and complexes have been widely used as catalysts in the oxidation of alcohols [3]. In the present work, we report synthesis, crystal structure, spectroscopic properties and catalytic activity of a new dinuclear copper(II) complex, [Cu(2-amp)(μ-OAc)2l]2 (1). Complex 1 was synthesized by the reaction of equimolar amounts of 2-(aminomethyl)pyridine (2-amp) and Cu(OAc)2∙3H2O in methanol. The blue crystals of complex 1 were obtained by thermal gradient method during one week. Single crystal X-ray analysis indicated that these crystals are related to a dinuclear Cu(II) complex which two Cu(II) ions are connected together by two acetate bridging groups. The catalytic potential of complex 1 was tested for the oxidation of benzyl alcohol as representative substrate for primary alcohols using H2O2 as a green oxidant. The oxidation products were identified by GC and the progress of the reaction and products were also checked by TLC. In order to obtain the optimum condition for catalytic oxidation of benzyl alcohol, the effects of various parameters, including molar ratio of oxidant to substrate, temperature and solvent were studied. The results of these studies showed that complex 1 catalyzed the oxidation of benzyl alcohol to the benzaldehydes but at higher temperatures a little amount of benzoic acids, produced by over oxidation of benzaldehyde, was also produced in the reaction mixture. The results indicate that the selectivity and the activity of this catalytic system depend on the reaction condition.