Spectroscopic Characterization and Reactivity Studies of a Mononuclear Nonheme Mn(III)–Hydroperoxo Complex

[Image: see text] We report the first example of a mononuclear nonheme manganese(III)–hydroperoxo complex derived from protonation of an isolated manganese(III)–peroxo complex bearing an N-tetramethylated cyclam (TMC) ligand, [Mn(III)(TMC)(OOH)](2+). The Mn(III)-hydroperoxo intermediate is characterized with various spectroscopic methods as well as with density functional theory (DFT) calculations, showing the binding of a hydroperoxide ligand in an end-on fashion. The Mn(III)–hydroperoxo species is a competent oxidant in oxygen atom transfer (OAT) reactions, such as the oxidation of sulfides. The electrophilic character of the Mn(III)–hydroperoxo complex is demonstrated unambiguously in the sulfoxidation of para-substituted thioanisoles.