Co−C Bond Reactivity and Cis Influence Relationship in Benzylcobaloximes with Glyoxime and Dimesitylglyoxime

Benzyl cobaloximes, ArCH2Co(dioxime)2Py, with two different dioximes, glyoxime (gH) and dimesitylglyoxime (dmestgH), have been synthesized and characterized by 1H and 13C NMR and UV−vis spectroscopy. The dioxy adducts, ArCH2(O2)Co(dioxime)2Py, were prepared by the insertion of molecular oxygen into the Co−C under photochemical conditions. The rate of insertion depends upon the nature of the dioxime and follows the order dmestgH ≫ dpgH > chgH > dmgH > gH. The steric cis influence of the dioximes on the Co−C bond also follows the same order. The study also suggests that the interactions between the axial benzyl group and the dioximes have significant influence on the Co−C bond reactivity. Such interactions are also seen in the molecular structure of [C6H4CH2Co(gH)2(4-tBuPy)] and in the dioxy complexes 4-CN-C6H4CH2(O2)Co(dmestgH)2Py and 2-naphthylCH2(O2)Co(dmestgH)2Py. On the basis of the results we have supported the cage mechanism for the oxygen insertion into the Co−C bond.