Synthesis, Spectroscopic Characterization and Redox Reactivity of Some Transition Metal Complexes with Salicylaldimines Bearing 2,6-Di

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<inf>x</inf>H, and their copper(II) complexes, M(L<inf>x</inf>)<inf>2</inf>, (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<inf>2</inf> and reduction (for Cu(L<inf>x</inf>)<inf>2</inf>) with PPh<inf>3</inf> were investigated. ESR studies indicate that oxidation of M(L<inf>x</inf>) <inf>2</inf> produces ligand-centered MII-phenoxyl radical species. The Cu(L<inf>x</inf>)<inf>2</inf> complexes, unlike others M(L<inf>x</inf>) <inf>2</inf>, are readily reduced by PPh<inf>3</inf> 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<inf>x</inf>)<inf>2</inf>, Co(L <inf>1</inf>)<inf>2</inf> and generated phenoxyl radicals are presented. © 2003 Elsevier B.V. All rights reserved.