PHOTOCHEMISTRY OF AZIDO AND THIOLATO VITAMIN-B12 MODEL COMPLEXES AS PRECURSOR COMPOUNDS FOR COORDINATIVELY UNSATURATED COBALT(II) COMPLEXES

The photolysis of [LCo(chelat)B] complexes (1-3) (L = azide, N-3(-); thiolate, RS(-); chelat = dimethylglyoxime, dmg; N,N'-o-phenylene-bis(salicylidenimine), salphen; N,N'-ethylene-bis(salicylidenimine), salen; B = pyridine, imidazole, triphenylphosphine) leads upon the homolytic cleavage of the Co-L bond to both coordinatively unsaturated reactive cobalt(II) chelates [Co(chelat)B] and ligand radicals L(.). The efficiency of these photochemical redox reactions is described in relation to the structure of the cobalt(III) chelates, the wavelenght of irradiation, the light-intensity as well as the solvents and substrates used during the photochemical experiments. Further, sensitization experiments using [Ru(bipy)(3)]Cl-2 as sensitizer are described and the redox potentials of the investigated complexes are discussed.