Brunclik Samuel A, Grotemeyer Elizabeth N, Aghaei Zahra, Mian Mohammad Rasel, Jackson Timothy A
Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas, Lawrence, KS 66045, USA.
Protein Structure and X-ray Crystallography Laboratory, University of Kansas, Lawrence, KS 66045, USA.
Molecules. 2024 Apr 18;29(8):1849. doi: 10.3390/molecules29081849.
Manganese catalysts that activate hydrogen peroxide carry out several different hydrocarbon oxidation reactions with high stereoselectivity. The commonly proposed mechanism for these reactions involves a key manganese(III)-hydroperoxo intermediate, which decays via O-O bond heterolysis to generate a Mn(V)-oxo species that institutes substrate oxidation. Due to the scarcity of characterized Mn-hydroperoxo complexes, Mn-alkylperoxo complexes are employed to understand factors that affect the mechanism of the O-O cleavage. Herein, we report a series of novel complexes, including two room-temperature-stable Mn-alkylperoxo species, supported by a new amide-containing pentadentate ligand (dpaq). We use a combination of spectroscopic methods and density functional theory computations to probe the effects of the electronic changes in the ligand sphere to the hydroxo and alkylperoxo units to thermal stability and reactivity. The structural characterizations for both Mn(OTf)(dpaq) and Mn(OH)(dpaq) were obtained via single-crystal X-ray crystallography. A perturbation to the ligand sphere allowed for a marked increase in reactivity towards an organic substrate, a modest change in the distribution of the O-O cleavage products from homolytic and heterolytic pathways, and little change in thermal stability.
能活化过氧化氢的锰催化剂可高效立体选择性地进行多种不同的烃氧化反应。这些反应通常提出的机理涉及一个关键的锰（III）-氢过氧中间体，该中间体通过O-O键异裂分解生成一个启动底物氧化的Mn（V）-氧物种。由于已表征的锰-氢过氧配合物稀缺，因此采用锰-烷基过氧配合物来理解影响O-O键裂解机理的因素。在此，我们报道了一系列新型配合物，包括两种由新型含酰胺五齿配体（dpaq）支撑的室温稳定的锰-烷基过氧物种。我们结合光谱方法和密度泛函理论计算来探究配体球中电子变化对羟基和烷基过氧单元的热稳定性和反应性的影响。通过单晶X射线晶体学获得了Mn（OTf）（dpaq）和[Mn（OH）（dpaq）]（OTf）的结构表征。对配体球的扰动使得对有机底物的反应性显著增加，O-O键裂解产物从均裂和异裂途径的分布有适度变化，而热稳定性几乎没有变化。
