Colmer Hannah E, Howcroft Anthony W, Jackson Timothy A
Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , Lawrence, Kansas 66045, United States.
Inorg Chem. 2016 Mar 7;55(5):2055-69. doi: 10.1021/acs.inorgchem.5b02398. Epub 2016 Feb 23.
Although there have been reports describing the nucleophilic reactivity of peroxomanganese(III) intermediates, as well as their conversion to high-valent oxo-bridged dimers, it remains a challenge to activate peroxomanganese(III) species for conversion to high-valent, mononuclear manganese complexes. Herein, we report the generation, characterization, and activation of a peroxomanganese(III) adduct supported by the cross-clamped, macrocyclic Me2EBC ligand (4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane). This ligand is known to support high-valent, mononuclear Mn(IV) species with well-defined spectroscopic properties, which provides an opportunity to identify mononuclear Mn(IV) products from O-O bond activation of the corresponding Mn(III)-peroxo adduct. The peroxomanganese(III) intermediate, Mn(III)(O2)(Me2EBC), was prepared at low-temperature by the addition of KO2 to [Mn(II)(Cl)2(Me2EBC)] in CH2Cl2, and this complex was characterized by electronic absorption, electron paramagnetic resonance (EPR), and Mn K-edge X-ray absorption (XAS) spectroscopies. The electronic structure of the Mn(III)(O2)(Me2EBC) intermediate was examined by density functional theory (DFT) and time-dependent (TD) DFT calculations. Detailed spectroscopic investigations of the decay products of Mn(III)(O2)(Me2EBC) revealed the presence of mononuclear Mn(III)-hydroxo species or a mixture of mononuclear Mn(IV) and Mn(III)-hydroxo species. The nature of the observed decay products depended on the amount of KO2 used to generate Mn(III)(O2)(Me2EBC). The Mn(III)-hydroxo product was characterized by Mn K-edge XAS, and shifts in the pre-edge transition energies and intensities relative to Mn(III)(O2)(Me2EBC) provide a marker for differences in covalency between peroxo and nonperoxo ligands. To the best of our knowledge, this work represents the first observation of a mononuclear Mn(IV) center upon decay of a nonporphyrinoid Mn(III)-peroxo center.
尽管已有报道描述过氧锰（III）中间体的亲核反应活性，以及它们转化为高价氧桥联二聚体的过程，但激活过氧锰（III）物种以转化为高价单核锰配合物仍然是一项挑战。在此，我们报道了一种由交叉钳位的大环Me2EBC配体（4,11-二甲基-1,4,8,11-四氮杂双环[6.6.2]十六烷）支撑的过氧锰（III）加合物的生成、表征和活化。已知该配体可支撑具有明确光谱性质的高价单核Mn（IV）物种，这为从相应Mn（III）-过氧加合物的O-O键活化中鉴定单核Mn（IV）产物提供了机会。过氧锰（III）中间体[Mn（III）（O2）（Me2EBC）]+是在低温下通过向CH2Cl2中的[Mn（II）（Cl）2（Me2EBC）]中加入KO2制备的，该配合物通过电子吸收、电子顺磁共振（EPR）和Mn K边X射线吸收（XAS）光谱进行了表征。通过密度泛函理论（DFT）和含时（TD）DFT计算研究了[Mn（III）（O2）（Me2EBC）]+中间体的电子结构。对[Mn（III）（O2）（Me2EBC）]+衰变产物的详细光谱研究揭示了单核Mn（III）-羟基物种或单核Mn（IV）和Mn（III）-羟基物种混合物的存在。观察到的衰变产物的性质取决于用于生成[Mn（III）（O2）（Me2EBC）]+的KO2的量。通过Mn K边XAS对Mn（III）-羟基产物进行了表征，相对于[Mn（III）（O2）（Me2EBC）]+，前边缘跃迁能量和强度的变化为过氧配体和非过氧配体之间共价性的差异提供了一个标记。据我们所知，这项工作代表了在非卟啉类Mn（III）-过氧中心衰变时首次观察到单核Mn（IV）中心。
