Synthesis, spectroscopic characterization and ESR studies on electron transfer reactions of bis[N-(2,6-di-tert-butyl-1-hydroxyphenyl)salicylaldiminato]-copper(II) complexes with PbO2 and PPh3

New bis[N-(2,6-di-t-buty1-1-hydroxyphenyl)salicylideneminato]copper(II) com plexes bearing HO and CH3O substituents on the salicyaldehyde moiety were p repared, and their spectroscopic properties, as well as redox reactivity to wards PbO2 and PPh3, examined by ESR and UV spectroscopy. In the process of synthesis of HO complexes unlike CH,O the oxidative C-C coupling of coordi nated salicylaldimine ligands does not takes place. The powder ESR spectra of CI-I,O substituted complexes unlike of HO analogues are typical of a tri plet state Cu(II) dimers with a half-field forbidden (DeltaM = +/-2) transi tion and the allowed transitions (Deltam = +/-1) dimeric form of the comple xes at 300 and 113 K. The one-electron oxidation of 3-CH3O and all of the O H complexes with PbO2 to give indophenoxyl type secondary radicals which ar e significantly different from those observed for analogues Cl, Br and NO2 substituted chelates. The presented complexes unlike their electron-withdra wing analogues are readily reduced by PPh3 via intramolecular electron tran sfer from ligand to copper(II) to give various radical intermediates as wel l as Cu(I) radical ligand compounds. The analysis of ESR spectra all of the complexes and radical intermediates are presented. (C) 2001 Elsevier Scien ce B.V. All rights reserved.