Syntheses, Structures, and Catalytic Activity of Copper(II)‐Aroylhydrazone Complexes

Abstract

AbstractTwo CuII complexes of tridentate Schiff base ligands, [Cu(L1)(CH3OH)2]NO3·CH3OH (1) and [Cu2(L2)2(CH3OH)2](NO3)2 (2), were prepared and characterized by elemental analyses and spectroscopic methods [H2L1 = (E)‐N‐(4‐hydroxy benzoic acid (2‐hydroxy‐3‐methoxybenzylidene)benzohydrazide, and H2L2 = (E)‐N‐4‐hydroxy benzoic acid (5‐bromo‐2‐hydroxybenzylidene)benzohydrazide]. The crystal structures of 1 and 2 were established by X‐ray crystallography. The complex cation in 1 is based on a square pyramid with the uninegative Schiff base coordinating in a tridentate mode via O, N, O′‐donor atoms with the remaining sites being occupied by two methanol oxygen atoms with one of these in the axial position. By contrast, the Schiff base coordinates in a tridentate ligand fashion in dinuclear compound 2 as the phenoxide oxygen atom bridges two central copper atoms. The NO4 coordination donor set is completed by a methanol oxygen atom, which occupies an axial position in the distorted square pyramidal arrangement. Complexes 1 and 2 are very active catalysts in clean epoxidation reactions using aqueous hydrogen peroxide and acetonitrile. The effects of reaction parameters such as solvent and oxidant in the epoxidation of cis‐cyclooctene were investigated and showed that cyclooctene and cyclohexene were oxidized efficiently to their corresponding epoxide with 100 and 31 % selectivity, respectively, in the presence of catalyst 2. This catalytic system showed also excellent selectivity in the oxidation of benzyl alcohol.