Formation, Characterization, and O-O Bond Activation of a Peroxomanganese(III) Complex Supported by a Cross-Clamped Cyclam Ligand
Formation, Characterization, and O-O Bond Activation of a Peroxomanganese(III) Complex Supported by a Cross-Clamped Cyclam Ligand
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DOI：
10.1021/acs.inorgchem.5b02398
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发表时间：
2016-03-07
影响因子：
4.6
通讯作者：
Jackson, Timothy A.
中科院分区：
文献类型：
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作者：
Colmer, Hannah E.;Howcroft, Anthony W.;Jackson, Timothy A.
尽管有报道描述了过氧锰(III)中间体的亲核反应活性，以及它们转化为高价氧桥二聚体的情况，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个挑战。在这里，我们报道了由交叉夹持的大环Me2EBC配体(4，11-dimethyl-1，4，8，11-tetraazabicyclo[6.6.2]hexadecane).支撑的过氧锰加合物的生成、表征和活化已知该配体支持具有明确光谱性质的高价单核Mn-IV物种，这提供了从相应的Mn-III-Peroxo加合物的O-O键激活中识别单核Mn-IV产物的机会。在CH2C12中，通过在[Mn-II(Cl)(2)(Me2EBC)]中加入KO2，低温合成了过氧锰中间体[Mn-III(O-2)(Me2EBC)(+)]，并用电子吸收光谱、电子顺磁共振(EPR)和X射线吸收谱(XAS)对其进行了表征。用密度泛函理论(DFT)和含时密度泛函(TD)方法研究了[Mn-III(O-2)(Me2EBC)](+)中间体的电子结构。对[Mn-III(O-2)(Me2EBC)](+)的衰变产物进行了详细的光谱研究，发现存在单核的Mn-III-羟基物种或单核的Mn-IV和Mn-III-羟基物种的混合物。观察到的衰变产物的性质取决于用于产生Mn-III(O-2)(Me2EBC)](+)的KO2的量。Mn-III-羟基产物用MnK-Edge XAS进行了表征，边缘前跃迁能量和强度相对于[Mn-III(O-2)(Me2EBC)](+)的位移是过氧基和非过氧基之间共价性差异的标志。据我们所知，这项工作是第一次观察到单核Mn-IV中心在非卟啉类Mn-III-Peroxo中心衰变时的情况。
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, macro cyclic 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(O-2)(Me2EBC)(+), was prepared at low-temperature by the addition of KO2 to [Mn-II(Cl)(2)(Me2EBC)] in CH2C12, 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(O-2)(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(O-2)(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(O-2)(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(O-2)(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.