Reaction landscape of a mononuclear Mn III -hydroxo complex with hydrogen peroxide.

Peroxomanganese species have been proposed as key intermediates in the catalytic cycles of both manganese enzymes and synthetic catalysts. However, many of these intermediates have yet to be observed. Here, we report the formation of a series of intermediates, each generated from the reaction of the mononuclear Mn III -hydroxo complex [Mn III (OH)(dpaq 2Me )] + with hydrogen peroxide under slightly different conditions. By changing the acidity of the reaction mixture and/or the quantity of hydrogen peroxide added, we are able to control which intermediate forms. Using a combination of electronic absorption, 1 H NMR, EPR, and X-ray absorption spectroscopies, as well as density functional theory (DFT) and complete active space self-consistent field (CASSCF) calculations, we formulate these intermediates as the bis(μ-oxo)dimanganese(III,IV) complex [Mn III Mn IV (μ-O) 2 (dpaq 2Me ) 2 ] + , the Mn III -hydroperoxo complex [Mn III (OOH)(dpaq 2Me )] + , and the Mn III -peroxo complex [Mn III (O 2 )(dpaq 2Me )]. The formation of the Mn III -hydroperoxo species from the reaction of a Mn III -hydroxo complex with hydrogen peroxide mimics an elementary reaction proposed for many synthetic manganese catalysts that activate hydrogen peroxide.