Revisiting Alkane Hydroxylation with m-CPBA (m-Chloroperbenzoic Acid) Catalyzed by Nickel(II) Complexes

Mechanistic studies are performed on the alkane hydroxylation with m-CPBA (m-chloroperbenzoic acid) catalyzed by nickel(II) complexes, Ni-II(L). In the oxidation of cycloalkanes, Ni-II(TPA) acts as an efficient catalyst with a high yield and a high alcohol selectivity. In the oxidation of adamantane, the tertiary carbon is predominantly oxidized. The reaction rate shows first-order dependence on [substrate] and [Ni-II(L)] but is independent on [m-CPBA]; v(obs)=k(2)[substrate][Ni-II(L)]. The reaction exhibited a relatively large kinetic deuterium isotope effect (KIE) of 6.7, demonstrating that the hydrogen atom abstraction is involved in the rate-limiting step of the catalytic cycle. Furthermore, Ni-II(L) supported by related tetradentate ligands exhibit apparently different catalytic activity, suggesting contribution of the Ni-II(L) in the catalytic cycle. Based on the kinetic analysis and the significant effects of O-2 and CCl4 on the product distribution pattern, possible contributions of (L)Ni-II-O-. and the aroyloxyl radical as the reactive oxidants are discussed.