Bis[N-(2,6 Palladium(II) Complexes and Their Radical Intermediates Generated by PbO2 and PPh3

Abstract

New bis[N-(2,6-di-t-butyl-1-hydroxyphenyl)salicylideneminato] palladium(II) [Pd(Lx)<inf>2</inf>] complexes bearing HO and MeO substituents on the salicyaldehyde moiety were prepared, and their spectroscopic properties, as well as redox reactivity towards PbO<inf>2</inf> and PPh<inf>3</inf>, examined by e.s.r. and u.v. spectroscopy. The complexes display charge-transfer bands in the 670-692 nm range in polar solvents, which are assigned to the d(Pd) → π* (chelated quinoid) transition. One-electron oxidation of Pd(Lx)<inf>2</inf> produces PdII-stabilized radicals in which the unpaired electrons are localized on the phenoxy fragments and do not couple with the two radical centers. The complexes are easily reduced with PPh<inf>3</inf> via intramolecular electron-transfer from ligand to metal to give various radical intermediates and Pd. All detected radical species have been characterized by e.s.r. spectroscopy.