Oxime derivative unsymmetrical azine, its Ni(II), Cu(II) and Zn(II) complexes: Synthesis, spectroscopy and catecholase activity

1-[(Z)-{(2E)-[(3E)-3-(hydroxyimino)butan-lidene]hydrazinylidene}methyl]naphthalen -2-ol, H2L (3) was synthesized by the agents of 2-hydroxy-1-naphtaldehyde, 2,3-butanedione monoxime and hydrazine in two steps. The structures of the compounds have been proposed by elemental analyses, spectroscopic data, that is, IR, ¹H NMR, UV-vis, X-ray, mass spectra (ESI or TOF), molar conductivities and magnetic susceptibility measurements. The ligand has potentially three nitrogens and an oxygen donor to be able to bind a metal center. In the light of analytical and physical results, it was suggested that the ligand may coordinate to by N,O/N2/N2O donor set to form square planar, octahedral, distorted square planar and tetrahedral complexes. Proton NMR evidence indicating that the ligand coordinates the metal ion through the phenolic oxygen and nitrogen of imine in the nickel and zinc complexes. Molar conductivity measurements reveal that all the complexes are non-electrolytes. In addition, catecholase activities of the complexes were studied. However, the only one of the complexes, 1b, behaves as an effective catalyst toward oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to its corresponding quinone derivative in MeOH saturated with O₂. The reaction follows Michaelis-Menten enzymatic reaction kinetics with turnover numbers (kcat) 1.19 × 10³/hour.