INVESTIGATION OF O-1(2) GENERATION BY WATER-SOLUBLE ALPHA-DIIMINE COMPLEXES OF PLATINUM(II) AND PALLADIUM(II) WITH 3,4-DIHYDROXYBENZOIC ACID AS PHOTOSENSITIZERS

Eight complexes with the formula [M(N-N)(DHBA)] (where M=Pd(II) or Pt(II), N-N is 2,2'-bipyridine (BPY), 2,2'-biquinoline (BIQ), 1,10-phenanthroline (PHEN), 4,7-diphenyl-1,10-phenanthroline (DPP) and DHBA is 3,4-dihydroxybenzoic acid dianion) were found to photosensitize the oxidation of 2,2,6,6-tetramethyl-4-piperidinol (NH) in NN-dimethylformamide (DMF) to the nitroxide radical. This photo-oxidation reaction involves singlet molecular oxygen (O-1(2)) as an intermediate and its presence was confirmed by quenching studies using bis(diethyldithiocarbamato)nickel(II), a well known O-1(2) quencher. The ability of these complexes to photosensitize the above photo-oxidation reaction follows the order, [Pt(PHEN)(DHBA)] . H2O > [Pt(DPP)(DHBA)] . H2O > [Pt(BIQ)(DHBA)] > [Pd(PHEN)(DHBA)] > [Pt(BPY)(DHBA)] > [Pd(DPP)(DHBA)] > [Pd(BPY)(DHBA)] . CH3OH > [Pd(BIQ)(DHBA)]. This order depends on the metal ion, the nature of the alpha-diimine ligand and the geometry of the metal complex.