Mononuclear metal-O2 complexes bearing macrocyclic N-tetramethylated cyclam ligands.
Mononuclear metal-O2 complexes bearing macrocyclic N-tetramethylated cyclam ligands.
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DOI：
10.1021/ar3000019
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发表时间：
2012-08-21
影响因子：
18.3
通讯作者：
Wonwoo Nam
中科院分区：
文献类型：
--
作者：
Cho, Jaeheung;Sarangi, Ritimukta;Wonwoo Nam
金属酶激活分子氧以进行多种生物反应，包括天然存在的分子的生物转化、外源性物质的氧化代谢和氧化磷酸化。在酶的催化位点处的分子氧活化通过几个步骤发生，例如O2在还原的金属中心处的结合，金属-超氧和-过氧物种的产生，以及金属-氢过氧络合物的O-O键断裂以形成高价金属-氧氧化剂。由于这些单核金属-双氧（M-O2）加合物是金属酶催化的双氧活化反应中的关键中间体，因此对这些物种的合成仿生类似物的结构和光谱性质以及反应性的研究有助于我们对其生物化学的理解。用于研究金属配合物对分子氧的活化作用的一类特别通用的仿生配位配合物是带有大环N-四甲基化cyclam（TMC）配体的M-O2配合物。本帐户描述了合成，结构和光谱表征，和反应性研究的M-O2配合物轴承四氮杂大环n-TMC配体，其中M = Cr，Mn，Fe，Co，Ni和n = 12，13，和14，从我们的实验室最近的结果为基础。我们已经使用了各种光谱技术，包括共振拉曼和X射线吸收光谱，和密度泛函理论（DFT）的计算来表征几种新型的金属-O2配合物。值得注意的是，X-射线晶体结构表明，这些配合物是端对金属-超氧和侧对金属-过氧物种。大环TMC配体的金属离子和环尺寸控制金属-O2络合物的几何和电子结构，导致端对金属-超氧与侧对金属-过氧结构。反应性研究表明，它们可以进行亲电反应，如氧原子转移和C-H键活化的有机底物。金属过氧配合物是亲核反应中的活性氧化剂，如醛脱氨。我们还证明了一个完整的分子间O2-转移金属（III）-过氧配合物的Mn（II）配合物。本报告中的结果显示了金属离子和支持配体在调整生物学和仿生反应中相关的金属-O2中间体的几何和电子结构以及反应性方面的重要性。
Metalloenzymes activate dioxygen to carry out a variety of biological reactions, including the biotransformation of naturally occurring molecules, oxidative metabolism of xenobiotics, and oxidative phosphorylation. The dioxygen activation at the catalytic sites of the enzymes occurs through several steps, such as the binding of O2 at a reduced metal center, the generation of metal–superoxo and –peroxo species, and the O–O bond cleavage of metal–hydroperoxo complexes to form high-valent metal-oxo oxidants. Because these mononuclear metal–dioxygen (M–O2) adducts are implicated as key intermediates in dioxygen activation reactions catalyzed by metalloenzymes, studies of the structural and spectroscopic properties and reactivities of synthetic biomimetic analogues of these species have aided our understanding of their biological chemistry. One particularly versatile class of biomimetic coordination complexes for studying dioxygen activation by metal complexes is M–O2 complexes bearing the macrocyclic N-tetramethylated cyclam (TMC) ligand. This Account describes the synthesis, structural and spectroscopic characterization, and reactivity studies of M–O2 complexes bearing tetraazamacrocyclic n-TMC ligands, where M = Cr, Mn, Fe, Co, and Ni and n = 12, 13, and 14, based on recent results from our laboratory. We have used various spectroscopic techniques, including resonance Raman and X-ray absorption spectroscopy, and density functional theory (DFT) calculations to characterize several novel metal–O2 complexes. Notably, X-ray crystal structures had shown that these complexes are end-on metal-superoxo and side-on metal-peroxo species. The metal ions and the ring size of the macrocyclic TMC ligands control the geometric and electronic structures of the metal–O2 complexes, resulting in the end-on metal–superoxo versus side-on metal–peroxo structures. Reactivity studies performed with the isolated metal-superoxo complexes reveal that they can conduct electrophilic reactions such as oxygen atom transfer and C–H bond activation of organic substrates. The metal–peroxo complexes are active oxidants in nucleophilic reactions, such as aldehyde deformylation. We also demonstrate a complete intermolecular O2-transfer from metal(III)–peroxo complexes to a Mn(II) complex. The results presented in this Account show the significance of metal ions and supporting ligands in tuning the geometric and electronic structures and reactivities of the metal–O2 intermediates that are relevant in biology and in biomimetic reactions.
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