Ceric Ammonium\nNitrate Oxidation of a Mn<sup>II</sup> Complex Generates a Bis(μ-oxo)dimanganese(IV,IV)\nProduct via\na Mn<sup>IV</sup>–Oxo Intermediate

The oxidation of manganese complexes using ceric ammonium\nnitrate\n(CAN) is often complicated by the fact that cerium(IV) can serve as\nboth an oxidant and a Lewis acid. In this work, we explore the reaction\nof CAN with the Mn<sup>II</sup> complex [Mn<sup>II</sup>(OTf)(<sup>DMM</sup>N4py)](OTf) (<sup>DMM</sup>N4py = <i>N</i>,<i>N</i>-bis(4-methoxy-3,5-dimethyl-2-pyridylmethyl)-<i>N</i>-bis(2-pyridyl)methylamine). We chose this complex as multiple oxidation\nproducts, including oxomanganese(IV) and bis(μ-oxo)dimanganese(III,IV)\ncomplexes, have previously been reported. We envisioned that knowledge\nof the spectral properties of these intermediates would aid in understanding\nthe potential complexities of CAN oxidation reactions. The oxidation\nof [Mn<sup>II</sup>(OTf)(<sup>DMM</sup>N4py)](OTf) with 2.0 equiv\nCAN in 9:1 (v/v) MeCN:H<sub>2</sub>O at 25 °C transiently forms\nthe Mn<sup>IV</sup>–oxo complex, but this species is formed\nin low yields and is unstable. The Mn<sup>IV</sup>–oxo complex\nevolves to a new intermediate that had not been previously observed.\nAt lower temperatures, the formation of this new intermediate is preceded\nby formation of the previously reported bis(μ-oxo)dimanganese(III,IV)\ncomplex. EPR and X-ray absorption experiments for the new intermediate\nprovide strong evidence for its formulation as [Mn<sup>IV</sup>Mn<sup>IV</sup>(μ-O)<sub>2</sub>(<sup>DMM</sup>N4py)<sub>2</sub>]<sup>4+</sup>. This work establishes dinuclear Mn<sup>IV</sup>Mn<sup>IV</sup> species as products that must be considered in CAN oxidation reactions\nof Mn<sup>II</sup> complexes and shows that both mononuclear Mn<sup>IV</sup>–oxo and dinuclear Mn<sup>III</sup>Mn<sup>IV</sup> complexes can be intermediates in such reactions.