Radical substitution on a thioester by a methyl radical generated from methyl(L)cobaloxime

Abstract

Photolysis of methyl(L)cobaloxime 1, Me(L)[Co], in the presence of S-(4-chlorophenyl) thioacetate 5, yielded 4-chlorophenyl methyl sulfide 6. The reactivity of the methyl(L)cobaloxime with the thioester increases when the cobaloxime has a trans phosphine ligand (L) of larger steric requirement or a 4-substituted pyridine ligand (L) of lower basicity. Methyl(L)BF₂-cobaloxime 2, methyl(L)tetraphenylcobaloxime 3 and methyl(L)BF₂-tetraphenylcobaloxime 4 having electronegative or bulky equatorial ligands lose their reactivity with the thioester. The generation of the methyl radical from cobaloxime 2 is more efficient than from cobaloxime 1 in spite of its poor reactivity with the thioester. These features of the reaction are accounted for by ‘the effective concentration of the out-of-cage methyl radical’ and ‘the coordinative interaction of the thioester with the cobalt(II) complex’.