Search for: All records

Abstract Manganese catalysts that activate hydrogen peroxide have seen increased use in organic transformations, such as olefin epoxidation and alkane C−H bond oxidation. Proposed mechanisms for these catalysts involve the formation and activation of Mn^III‐hydroperoxo intermediates. Examples of well‐defined Mn^III‐hydroperoxo complexes are rare, and the properties of these species are often inferred from Mn^III‐alkylperoxo analogues. In this study, we show that the reaction of the Mn^III‐hydroxo complex [Mn^III(OH)(^6Medpaq)]⁺(1) with hydrogen peroxide and acid results in the formation of a dark‐green Mn^III‐hydroperoxo species [Mn^III(OOH)(^6Medpaq)]⁺(2). The formulation of2is based on electronic absorption,¹H NMR, IR, and ESI‐MS data. The thermal decay of2follows a first order process, and variable‐temperature kinetic studies of the decay of2yielded activation parameters that could be compared with those of a Mn^III‐alkylperoxo analogue. Complex2reacts with the hydrogen‐atom donor TEMPOH two‐fold faster than the Mn^III‐hydroxo complex1. Complex2also oxidizes PPh₃, and this Mn^III‐hydroperoxo species is 600‐fold more reactive with this substrate than its Mn^III‐alkylperoxo analogue [Mn^III(OO^tBu)(^6Medpaq)]⁺. DFT and time‐dependent (TD) DFT computations are used to compare the electronic structure of2with similar Mn^III‐hydroperoxo and Mn^III‐alkylperoxo complexes. 

Abstract Herein we report the electrochemical generation of a mononuclear Mn^III(OO) (peroxo) complex supported on a dpaq ligand (dpaq=2‐(bis(pyridin‐2‐ylmethyl)amino)‐N‐(quinolin‐8‐yl)acetamide) for the first time, and its reactivity inN,N‐dimethylformamide. The formation of the Mn^III(dpaq)(OO) complex is probed by low temperature electronic absorption spectro‐electrochemistry experiments. An analysis of the reduction of the Mn^III(dpaq)(OO) complex is carried out combining cyclic voltammetry and simulations. The involvement of a Mn^II(dpaq)(OOH) complex is proposed based on CV data and is corroborated by DFT computations.