Mechanistic insights into the oxidation of substituted phenols via hydrogen atom abstraction by a cupric-superoxo complex.
Mechanistic insights into the oxidation of substituted phenols via hydrogen atom abstraction by a cupric-superoxo complex.
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DOI：
10.1021/ja503105b
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发表时间：
2014-07-16
影响因子：
15
通讯作者：
Karlin, Kenneth D.
中科院分区：
文献类型：
--
作者：
Lee, Jung Yoon;Peterson, Ryan L.;Ohkubo, Kei;Garcia-Bosch, Isaac;Himes, Richard A.;Woertink, Julia;Moore, Cathy D.;Solomon, Edward I.;Fukuzumi, Shunichi;Karlin, Kenneth D.
为了深入研究Cu（I）-O2加合物的反应机理，合成了一种新的铜超氧配合物[（DMM-tmpa）CuII（O2·-）]+（2）[DMM-tmpa =三（（4-甲氧基-3，5-二甲基吡啶-2-基）甲基）胺]，并研究了其在苯酚氧化-加氧反应中的作用.化合物2通过UV-vis、共振拉曼和EPR光谱表征。它与一系列对位取代的2，6-二叔丁基苯酚（p-X-DTBP）反应，以高达50%的产率得到2，6-二叔丁基-1，4-苯醌（DTBQ）。显着的氘动力学同位素效应和二阶速率常数（K2）的正相关性相比，p-X-DTBPs加枯基过氧自由基反应的速率常数表明，涉及限速氢原子转移（HAT）的机制。（kBT/e）ln k2与p-X-DTBP的Eox的弱相关性表明HAT反应通过电子转移/质子转移途径中的部分电荷转移而不是完全电荷转移进行。产品分析，18 O-标记实验，并采用2，4，6-三叔丁基苯氧基自由基的单独的反应性提供了进一步的机制的见解。在初始HAT之后，第二摩尔当量的2与最初形成的苯氧基自由基偶联，得到CuII-OO-（ArO′）中间体，其在p-OR-DTBP底物的情况下通过涉及释放H2 O2和相应醇的水解步骤的双电子氧化反应进行。相比之下，p-R-DTBP主要发生四电子氧化（O-O断裂），产生18 O标记的DTBQ和R基团的消除。
To obtain mechanistic insights into the inherent reactivity patterns for copper(I)–O2 adducts, a new cupric–superoxo complex [(DMM-tmpa)CuII(O2•–)]+ (2) [DMM-tmpa = tris((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)amine] has been synthesized and studied in phenol oxidation–oxygenation reactions. Compound 2 is characterized by UV–vis, resonance Raman, and EPR spectroscopies. Its reactions with a series of para-substituted 2,6-di-tert-butylphenols (p-X-DTBPs) afford 2,6-di-tert-butyl-1,4-benzoquinone (DTBQ) in up to 50% yields. Significant deuterium kinetic isotope effects and a positive correlation of second-order rate constants (k2) compared to rate constants for p-X-DTBPs plus cumylperoxyl radical reactions indicate a mechanism that involves rate-limiting hydrogen atom transfer (HAT). A weak correlation of (kBT/e) ln k2 versus Eox of p-X-DTBP indicates that the HAT reactions proceed via a partial transfer of charge rather than a complete transfer of charge in the electron transfer/proton transfer pathway. Product analyses, 18O-labeling experiments, and separate reactivity employing the 2,4,6-tri-tert-butylphenoxyl radical provide further mechanistic insights. After initial HAT, a second molar equiv of 2 couples to the phenoxyl radical initially formed, giving a CuII–OO–(ArO′) intermediate, which proceeds in the case of p-OR-DTBP substrates via a two-electron oxidation reaction involving hydrolysis steps which liberate H2O2 and the corresponding alcohol. By contrast, four-electron oxygenation (O–O cleavage) mainly occurs for p-R-DTBP which gives 18O-labeled DTBQ and elimination of the R group.
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影响因子：
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作者：
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