Oxygen-Atom Transfer by a Naked Manganese(V)-Oxo-Porphyrin Complex Reveals Axial Ligand Effect
Oxygen-Atom Transfer by a Naked Manganese(V)-Oxo-Porphyrin Complex Reveals Axial Ligand Effect
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DOI：
10.1002/chem.200901361
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发表时间：
2009-01-01
影响因子：
4.3
通讯作者：
Lanucara, Francesco
中科院分区：
文献类型：
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作者：
Crestoni, Maria Elisa;Fornarini, Simonetta;Lanucara, Francesco
高价过渡金属-氧配合物是参与多种生物过程和化学转化的亲电氧化剂。 [1]锰 (V)-氧代物种被认为是多种烯烃环氧化中的关键中间体，它们为含血红素单加氧酶（包括细胞色素 P450 酶）的活性物种提供了有用的功能模型。锰-氧单元也存在于 photoACHTUNGTRENNUNG 系统 II 的核心，将水氧化为氧。 [2]MnV-氧-卟啉复合物类似于所谓的化合物 I 中间体，被描述为 FeIV-氧-卟啉自由基阳离子复合物。它们首先由 Groves 在水溶液中制备，并被表征为抗磁性低自旋 d2 基态。 [3]还描述了带有与大环和 salen 配体结合的 MnV-oxo 单元的配合物的其他例子。 [4]有趣的是，可溶于水的 MnV-氧代-卟啉复合物的氧原子转移 (OAT) 反应性被发现强烈依赖于 pH 值。在低 pH 值下观察到的显着增强可以通过轴向配体反式到 MnV-oxo 单元对进入反应性高自旋态所需的电子促进能量的影响以及方程 (1) 中描述的水中质子平衡的存在来解释。
High-valent transition-metal–oxo complexes are electrophilic oxidants implicated in a variety of biological processes and chemical transformations.[1] Manganese (V)–oxo species are suggested to be crucial intermediates in the epoxidation of a wide range of alkenes and they provide useful functional models for the active species of heme-containing monooxygenases, including cytochrome P450 enzymes. Manganese–oxo units are also found at the core of photoACHTUNGTRENNUNGsystem II, performing oxidation of water to oxygen.[2]MnV–oxo–porphyrin complexes are analogous to the socalled Compound I intermediate, described as an FeIV–oxo–porphyrin radical cation complex. They were first prepared by Groves in aqueous solution and characterised as diamagnetic low-spin d2 ground state.[3] Other examples of complexes bearing a MnV–oxo unit bound to macrocyclic and salen ligands have also been described.[4] Interestingly, the oxygen-atom-transfer (OAT) reactivity of MnV–oxo–porphyrin complexes soluble in water is found to be strongly pH-dependent. The pronounced enhancement observed at low pH has been explained by the effect of the axial ligand trans to the MnV–oxo unit on the electron promotion energy required to access the reactive high-spin states and by the existence of the prototropic equilibria in water depicted in Equation (1).