ALKYL RADICAL SUBSTITUTION ON DISULFIDE IN THE PRESENCE OF COBALT(II)COMPLEXES

Photolysis of methyl(L)cobaloxime (L=trans ligand) (1) or methyl(L)-O, O'-bis(difluoroboryl)cobaloxime (2) in the presence of bis(4-chlorophe nyl) disulfide gave 4-chlorophenyl methyl sulfide together with 4-chlo rophenylthio(L)cobaloxime (5) or orophenylthio(L)-O,O'-bis(difluorobor yl)cobaloxime (6). Similar photolysis in the presence of 2,2,6,6-tetra methyl-1-piperidyloxyl (TEMPO) gives 1-methoxy-2,2,6,6-tetramethylpipe ridine. The reactivity of the cobaloximes 1 and 2 to the disulfide and TEMPO increases when the cobaloximes have a trans ligand (L) of large r steric requirement and low pka, or when the equatorial ligand is an electronegative O-(difluoroboryl)dimethylglyoxime. Two probable mechan isms are proposed for the reaction. The first is a direct radical subs titution on the disulfide with a methyl radical, and the second involv es the initial interaction between the disulfide and the (L)cobaloxime radical to afford arylthio(L)cobaloxime (5 or 6) and an arylthio radi cal. The latter radical reacts with methyl(L)cobaloxime to give aryl m ethyl sulfide.