PHOTOCHEMICALLY PRODUCED COBALT(II) COMPLEXES WITH COORDINATED FREE-RADICALS - INTRAMOLECULAR OXIDATION OF THE METAL CENTER BY THE COORDINATED ALKYL RADICAL

Cobalt(III) complexes of the type [Co(bpy)(Am)(AA)]2+, where bpy is 2,2'-bipyridine, Am is ethylenediamine or propylenediamine, and AA is an amino acid, on photolysis in aqueous solution show the formation of cobalt(III)-alkyl complexes. In all the cases investigated, the flash photolysis technique is used to study the kinetics of the formation of the cobalt(III)-alkyl complex and subsequent reactions. In the case of the [Co(bpy)2(gly)]2+ ion, a stable cobalt(III)-alkyl complex is formed on photolysis, while in all the other cases the cobalt(III)-alkyl compound formed decomposes. The kinetics of the decomposition of the complexes has been investigated. It is observed that when two polypyridyl ligands are present in the coordination sphere, the cobalt(III)-alkyl complex formed is stabilized, while when only one bpy and an amine are present, the cobalt(III)-alkyl complex undergoes decomposition. Quantum yields for cobalt(II) formation have been determined in all the cases. The presence of dissolved oxygen does not seem to affect the photochemistry in aqueous solution.