Synthesis, spectroscopic characterization and redox reactivity of some transition metal complexes with salicylaldimines bearing 2,6-di-phenylphenol

Abstract

New bidentate N-(2,6-di-phenyl-1-hydroxyphenyl) salicylaldimines bearing X=H and 3,5-di- t-butyl substituents on the salicylaldehyde ring, L x H, and their copper(II) complexes, M(L x ) 2, (M=Cu(II), Co(II), Pd(II), Ni(II) and Zn(II)) have been synthesized and characterized by IR, UV/vis, 1H NMR, 13C NMR, ESR spectroscopy, magnetic susceptibility measurements, as well as their oxidation with PbO 2 and reduction (for Cu(L x ) 2) with PPh 3 were investigated. ESR studies indicate that oxidation of M(L x ) 2 produces ligand-centered M II-phenoxyl radical species. The Cu(L x ) 2 complexes, unlike others M(L x ) 2, are readily reduced by PPh 3 via intramolecular electron transfer from ligand to copper(II) to give unstable radical intermediates which are converted to another stable secondary radical species. The analysis of ESR spectra of Cu(L x ) 2, Co(L 1) 2 and generated phenoxyl radicals are presented.