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首页> 外文期刊>Bulletin of the Chemical Society of Japan >Quantum Chemical Studies on Dioxygen Activation and Methane Hydroxylation by Diiron and Dicopper Species as well as Related Metal-Oxo Species
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Quantum Chemical Studies on Dioxygen Activation and Methane Hydroxylation by Diiron and Dicopper Species as well as Related Metal-Oxo Species

机译：Dion和Dicopper物种的二恶英活化和甲烷羟基化的量子化学研究以及相关金属 - 氧代物种

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摘要

Quantum chemical studies by the author and co-workers on dioxygen activation and methane hydroxylation by diiron and dicopper enzyme species as well as related metal-oxo species are reviewed. The activation of the O-O bond of dioxygen at the mono- and dimetal sites of metalloenzymes is an essential process in the initial catalytic stages of naturally occurring oxygenation reactions. A way of orbital thinking about dioxygen activation at diiron and dicopper enzymes is developed at the extended Huckel level of theory. Two different reaction pathways that lead from dimetal peroxo complexes with mu-eta(1):eta(1)-O-2 and mu-eta(2):eta(2)-O-2 modes to the corresponding dioxo complexes are discussed in detail. In considering the mechanism of methane hydroxylation, special attention to FeO+-mediated methane hydroxylation that occurs under ion cyclotron resonance (ICR) conditions is given. Mechanistic aspects about methane hydroxylation by the bare transition-metal oxide ions ScO+, TiO+, VO+, CrO+, MnO+, FeO+, CoO+, NiO+, and CuO+ are systematically analyzed on the basis of density functional theory (DFT) calculations. An important feature in the reaction is the spin crossover between the high-spin and low-spin potential energy surfaces in particular in the C-H activation process. The spin inversion from the high-spin state to the low-spin state effectively decreases the barrier height of C-H activation. Another feature in the reaction is that no radical species is involved in the course of the hydroxylation because the methyl species formed as a result of the C-H bond cleavage can directly coordinate to the metal active site. The coupling of the OH and CH3 ligands occurs to produce methanol at the metal active center. The reaction profiles obtained from DFT calculations are similar to those of the Gif chemistry proposed by D. H. R. Barton, in particular the involvement of the HO-M-CH3 species as an intermediate in the hydroxylation of methane. The nonradical mechanism is extended to methane hydroxylation by the diiron and dicopper species of methane monooxygenase (MMO). This mechanism is possible when the metal active center is coordinatively unsaturated to have a space for the coordination of the OH and CH3 groups as ligands. Although compelling discussion to support the involvement of oxygen- and carbon-centered radicals is provided, the nonradical mechanism still seems to be applicable for methane hydroxylation from the viewpoint of reaction selectivity. Kinetic isotope effects (KIEs) in the C-H activation process by the bare FeO+ complex and diiron and dicopper enzyme models are compared with respect to the radical and nonradical mechanisms by using transition state theory.
机译：综述了作者和副工人的Quantum Chemical研究，DiOron和Dicopper酶物种以及相关金属 - 氧代物种的二恶英激活和甲烷羟基化。在金属酶单次和二十次位点处的二恶英O-O键的活化是天然存在的氧化反应的初始催化阶段的必要方法。在延伸的哈奇理论水平的延伸水平上显造了一种轨道思维关于DiOron和Dicpopper酶的轨道思维。讨论了来自Mu-eta（1）的二甲醛过氧化络合物的两种不同的反应途径：ETA（1）-O-2和MU-ETA（2）：ETA（2）-O-2模式进行了相应的DIOXO复合物的方法详细。在考虑甲烷羟基化机制时，给出了在离子回旋共振（ICR）条件下发生的Feo +介导的甲烷羟基。基于密度泛函理论（DFT）计算，系统地分析了裸趋介金属氧化物离子SCO +，TiO +，VO +，CRO +，MnO +，FeO +，CoO +，NiO +和CuO +的机械方面。反应中的一个重要特征是高旋转和低自旋电位能量表面之间的旋转交叉，特别是在C-H激活过程中。从高旋转状态到低旋转状态的旋转反转有效地降低了C-H激活的阻挡层。反应中的另一个特征是，由于C-H键裂解的结果形成的甲基物质可以直接与金属活性位点直接与金属活性位点相坐标，因此不参与羟基化的过程。 OH和CH3配体的偶联发生以在金属活性中心生产甲醇。从DFT计算中获得的反应谱与D.H.R.Barton提出的GIF化学的反应谱相似，特别是HO-M-CH3物种的涉及作为甲烷的羟基化中的中间体。甲烷单氧基酶（MMO）的二龙和二泊型物种延伸到甲烷羟基化的非静态机制。当金属活性中心是协调的时，这种机制是可能的，以具有oh和CH3基团作为配体的配位的空间。尽管提供了令人信服的讨论来支持氧和碳源自由基的参与，但从反应选择性的观点来看，非rrace机制似乎仍然适用于甲烷羟基化。通过使用过渡状态理论，将裸FEO +复合物和DiOron和DiCopper酶模型进行C-H激活过程中的动力学同位素效应（Kies）。

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