Synthesis, Spectroscopic Characterization and Redox Reactivity of the Copper(II) Salicylaldiminates Containing Sterically Hindered 2,6-Diphenylphenol

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 xH, and their copper(II) complexes, Cu(Lx)<inf>2</inf>, have been synthesized and characterized by i.r., u.v./vis., 1H-n.m.r., 13C-n.m.r., e.s.r. spectroscopy and magnetic susceptibility measurements. E.s.r. study has shown that chemical oxidation of Cu(Lx)<inf>2</inf> with PbO<inf>2</inf> produces ligand-centered CuII-phenoxyl radical species. The complexes are easily reduced with PPh<inf>3</inf> via intramolecular electron transfer from ligand to copper(II) to give unstable radical intermediates, which in time are converted to another stable secondary radical species. The analysis of e.s.r. spectra of Cu(L x)<inf>2</inf> and generated radical intermediates are presented.