Photochemische Untersuchungen von Vitamin B12-Modellverbindungen mit Azid bzw. Thiolat als Axialliganden – Precursorverbindungen für koordinativ ungesättigte Cobalt(II)-Komplexe

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; 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 wavelength of irradiation, the light-intensity as well as the solvents and substrates used during the photochemical experiments. Further, sensitization experiments using [Ru(bipy)₃]Cl₂ as sensitizer are described and the redox potentials of the investigated complexes are discussed.