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, LxH, 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, H-1 NMR, C-13 NMR, ESR spectroscopy, magnetic susceptibility measurements, as well as their oxidation with PbO2 and reduction (for Cu(L-x)(2)) with PPh3 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 PPh3 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. (C) 2003 Elsevier B.V. All rights reserved.