A Common Active Intermediate in the Oxidation of Alkenes, Alcohols and Alkanes with H₂O₂ and a Mn(II)/Pyridin-2-Carboxylato Catalyst

The mechanism and the reactive species involved in the oxidation of alkenes, and alcohols with H₂O₂, catalysed by an in situ prepared mixture of a Mn^II salt, pyridine-2-carboxylic acid and a ketone is elucidated using substrate competition experiments, kinetic isotope effect (KIE) measurements, and atom tracking with ¹⁸O labelling. The data indicate that a single reactive species engages in the oxidation of both alkenes and alcohols. The primary KIE in the oxidation of benzyl alcohols is ca. 3.5 and shows the reactive species to be selective despite a zero order dependence on substrate concentration, and the high turnover frequencies (up to 30 s⁻¹) observed. Selective ¹⁸O labelling identifies the origin of the oxygen atoms transferred to the substrate during oxidation, and is consistent with a highly reactive, e. g., [Mn^V(O)(OH)] or [Mn^V(O)₂], species rather than an alkylperoxy or hydroperoxy species.