Active Species of Nonheme Iron and Manganese-Catalyzed Oxidations

The intense catalytic and spectroscopic studies of the last decade provided important insights into the mechanisms of some nonheme iron-catalyzed oxidations with hydrogen peroxide. For manganese-based analogs, direct spectroscopic data on the structure of the reactive intermediates are scarce; mechanistic proposals are mainly based on catalytic studies and on analogy with iron systems. Herein, these data are summarized and contemporary mechanistic landscape is presented. We have mainly focused on iron and manganese complexes with N ₄-donor aminopyridine ligands, which are one of the most successful catalysts for chemo-, regio- and enantioselective transformations of organic substrates with H₂O₂ and H₂O₂/CH₃COOH as oxidants. The low-spin Fe^III–OOH, Fe^IV = O and Fe^V = O species can be spectroscopically trapped in the catalyst systems studied, low-spin Fe^V = O intermediate being the most likely key oxidizing agent.