Reaction landscape of a pentadentate N5-ligated Mn(II) complex with O2˙- and H2O2 includes conversion of a peroxomanganese(III) adduct to a bis(μ-oxo)dimanganese(III,IV) species.

Herein we describe the chemical reactivity of the mononuclear [Mn(II)(N4py)(OTf)](OTf) (1) complex with hydrogen peroxide and superoxide. Treatment of 1 with one equivalent superoxide at -40 °C in MeCN formed the peroxomanganese(III) adduct, [Mn(III)(O2)(N4py)](+) (2) in ~30% yield. Complex 2 decayed over time and the formation of the bis(μ-oxo)dimanganese(III,IV) complex, [Mn(III)Mn(IV)(μ-O)2(N4py)2](3+) (3) was observed. When 2 was formed in higher yields (~60%) using excess superoxide, the [Mn(III)(O2)(N4py)](+) species thermally decayed to Mn(II) species and 3 was formed in no greater than 10% yield. Treatment of [Mn(III)(O2)(N4py)](+) with 1 resulted in the formation of 3 in ~90% yield, relative to the concentration of [Mn(III)(O2)(N4py)](+). This reaction mimics the observed chemistry of Mn-ribonucleotide reductase, as it features the conversion of two Mn(II) species to an oxo-bridged Mn(III)Mn(IV) compound using O2(-) as oxidant. Complex 3 was independently prepared through treatment of 1 with H2O2 and base at -40 °C. The geometric and electronic structures of 3 were probed using electronic absorption, electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD), variable-temperature, variable-field MCD (VTVH-MCD), and X-ray absorption (XAS) spectroscopies. Complex 3 was structurally characterized by X-ray diffraction (XRD), which revealed the N4py ligand bound in an unusual tetradentate fashion.