Studies on photochemically produced metal complexes with coordinated free radicals

Abstract

In cobalt(III) amine complexes containing amino acids, photolysis in the chargetransfer bands leads to the formation of alkyl cobalt(III) complexes. Steady and flash photolysis of complexes [Co(LL)2X]2+ and [Co(LL)2Y2]+ (LL = ethylene diamine, polypyridyl or propylenediamine, X = amino acid and Y = nitro ligand) were carried out. Steady irradiation of [Co(bpy)2(gly)]2+ ion (bpy = bipyridine, gly = glycine) in aqueous medium (pH 1–7) produces the six-coordinated complex [Co(bpy)2(CH2NH2)]2+. Flash photolysis of the complex under identical conditions gives an alkyl complex. The alkyl complex formed in the case of [Co(bpy)2(gly)]2+ ion is stable and could be isolated; the corresponding alkyl complex formed from [Co(bpy)(en)(gly)]2+ ion leads to the labilisation of the ethylenediamine ligand in acidic solutions. Photolysis of the nitro complexes of the type [Co(en)2(NO2)2]+ ion in acetonitrile, methanol and ethanol produces aπ-bonded transient nitro complex which reacts with molecular oxygen to give the mononuclear superoxo, dinuclear superoxo and dinuclear peroxo complexes in sequence. The formation of these products from the free radical coordinated cobalt(II) complex has been followed by the flash photolysis method and the rate constants have been determined. The details of the mechanisms are discussed.