Grotemeyer Elizabeth N, Parham Joshua D, Jackson Timothy A
The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1567 Irving Hill Road, Lawrence, KS 66045, USA.
Dalton Trans. 2023 Oct 17;52(40):14350-14370. doi: 10.1039/d3dt02672h.
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-hydroxo complex [Mn(OH)(dpaq)] 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, 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 [MnMn(μ-O)(dpaq)], the Mn-hydroperoxo complex [Mn(OOH)(dpaq)], and the Mn-peroxo complex [Mn(O)(dpaq)]. The formation of the Mn-hydroperoxo species from the reaction of a Mn-hydroxo complex with hydrogen peroxide mimics an elementary reaction proposed for many synthetic manganese catalysts that activate hydrogen peroxide.
过氧锰物种被认为是锰酶和合成催化剂催化循环中的关键中间体。然而，这些中间体中的许多尚未被观测到。在此，我们报告了一系列中间体的形成，它们各自是在略有不同的条件下由单核锰-羟基配合物[Mn(OH)(dpaq)]与过氧化氢反应生成的。通过改变反应混合物的酸度和/或添加的过氧化氢量，我们能够控制生成哪种中间体。结合电子吸收光谱、¹H NMR、EPR和X射线吸收光谱，以及密度泛函理论(DFT)和完全活性空间自洽场(CASSCF)计算，我们将这些中间体确定为双(μ-氧代)二锰(III,IV)配合物[MnMn(μ-O)(dpaq)]、锰-氢过氧配合物[Mn(OOH)(dpaq)]和锰-过氧配合物[Mn(O)(dpaq)]。锰-羟基配合物与过氧化氢反应生成锰-氢过氧物种，这模拟了许多用于活化过氧化氢的合成锰催化剂所提出的一个基元反应。
