Mechanistic insights from reactions between copper(II)-phenoxyl complexes and substrates with activated C-H bonds.
Mechanistic insights from reactions between copper(II)-phenoxyl complexes and substrates with activated C-H bonds.
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从铜 (II)-苯氧基配合物与具有活化 C-H 键的底物之间反应的机理见解。
DOI：
10.1021/ic048695i
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
Stack,TDanielP
中科院分区：
文献类型：
--
作者：
Pratt,RussellC;Stack,TDanielP
金属酶半乳糖氧化酶的氧化活性形式的两种铜（II）−苯氧基类似物[1tBu2]+和[2tBu2]+的反应性已经使用底物苯甲醇和9，10-二氢蒽进行了研究，共进行了四次反应。在所有情况下，氧化剂与苯甲醛或蒽产物的化学计量比均为2：1，表明[1tBu2]+和[2tBu2]+最终仅表现为单电子氧化剂，但反应动力学均表明只有一个铜（II）−苯氧基络合物参与了速率决定步骤。对于每种底物，速率定律表明[1tBu2]+和[2tBu2]+通过不同的机制反应：一种通过简单的双分子反应进行，而另一种首先进入底物结合平衡，然后通过分子内反应进行反应。由后一种机制进行的反应具有更快的总体速率，这与底物结合机制的较低熵垒相关。反应速率与底物的C-H键离解能以及显著的氘动力学同位素效应的相关性表明，速率决定步骤涉及从活化的C-H键中提取氢原子。[1tBu2]+/苯甲醇反应的非经典KIE（298 K时kH/kD = 15）的变温研究（268 - 308 K）未能显示量子隧穿的证据。第二个1当量的铜（II）-苯氧基氧化剂在决定速率和产物的氢原子提取步骤之后完成反应的快速顺序不能用动力学来探测。与文献中报道的其他铜（II）-苯氧基络合物和半乳糖氧化酶本身的反应性进行了比较。
The reactivities of two copper(II)−phenoxyl analogues of the oxidized, active form of the metalloenzyme galactose oxidase, [1tBu2]+and [2tBu2]+, have been studied using the substrates benzyl alcohol and 9,10-dihydroanthracene, for a total of four reactions. The reaction stoichiometries in all cases show a 2:1 ratio of oxidant to benzaldehyde or anthracene product, indicating that [1tBu2]+and [2tBu2]+behave ultimately as only one-electron oxidants, but the reaction kinetics each indicate that only a single copper(II)−phenoxyl complex is involved in the rate-determining step. For each substrate, rate laws indicate that [1tBu2]+and [2tBu2]+react by different mechanisms: one proceeds by a simple bimolecular reaction, while the other first enters into a substrate-binding equilibrium before subsequently reacting by an intramolecular reaction. The reactions proceeding by the latter mechanism have faster overall rates, which correlates to a lower entropic barrier for the substrate-binding mechanism. Correlation of the reaction rates with the C−H bond dissociation energies of substrates as well as significant deuterium kinetic isotope effects indicates that the rate-determining steps involve hydrogen atom abstraction from the activated C−H bonds. A variable-temperature study (268−308 K) of the nonclassical KIE of the [1tBu2]+/benzyl alcohol reaction (kH/kD= 15 at 298 K) failed to show evidence for quantum tunneling. The rapid sequence by which a second 1 equiv of copper(II)−phenoxyl oxidant completes the reaction after the rate- and product-determining hydrogen atom abstraction step cannot be probed kinetically. Comparisons are made to the reactivities of other copper(II)−phenoxyl complexes reported in the literature and to galactose oxidase itself.
DOI：
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发表时间：
2003
期刊：
影响因子：
--
作者：
T.Nishigaki et al.;S.Itoh.et al.
通讯作者：
S.Itoh.et al.