Kinetic effects of increased proton transfer distance on proton-coupled oxidations of phenol-amines.
Kinetic effects of increased proton transfer distance on proton-coupled oxidations of phenol-amines.
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DOI：
10.1021/ja2056853
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发表时间：
2011-11-02
影响因子：
15
通讯作者：
Mayer, James M.
中科院分区：
文献类型：
--
作者：
Markle, Todd F.;Rhile, Ian J.;Mayer, James M.
为了测试在质子耦合电子转移（PCET）反应中改变质子供体-受体距离的影响，将双环氨基-茚满醇（2）的氧化与具有邻位CPh 2NH 2取代基的密切相关的苯酚（1）的氧化进行比较。光谱，结构，热化学和计算研究表明，这两个氨基苯酚是非常相似的，除了O <$N距离（dON）是>0.1 <$比1在2。根据X射线晶体学，dON的差异为0.13 ± 0.03 μ m，根据DFT计算，dON的差异为0.165 μ m。这些酚类化合物被外层氧化剂氧化后，通过协同质子-电子转移（CPET）反应生成二阶自由基阳离子·OAr-NH 3+。简单的隧道效应和经典的动力学模型都预测，2中较长的供体-受体距离将导致反应较慢，约。两个数量级，以及更大的H/D动力学同位素效应（KIE）。然而，动力学研究表明，具有较长的质子转移距离的化合物，2，表现出较小的KIE和速率常数是非常接近的1。例如，2被三芳基酰胺基阳离子N（C6 H4 OMe）3·+（3a+）氧化的速率为（1.4 ± 0.1）× 104 M-1 s-1，仅比1与N（C6 H4 OMe）2（C6 H4 Br）·+（3b+）的密切相关反应慢两倍。速率常数的这种差异很好地解释了反应自由能的略微不同：ΔG°（2 + 3a+）= +0.078 V vs. ΔG°（1 + 3b+）= +0.04 V。两种酚胺确实显示出一些细微的动力学差异：例如，化合物2的CPET速率常数对驱动力的依赖性较浅（Brønsted α，Δln（k）/Δln（Keq））。这些结果表明，简单的隧道模型是不是一个很好的预测质子给体-受体距离的影响，在协调电子转移反应涉及强氢键系统。计算分析所观察到的两种苯酚的相似性强调了高度非谐O H N势能面的重要性和质子振动激发态的影响。
To test the effect of varying the proton donor-acceptor distance in proton-coupled electron transfer (PCET) reactions, the oxidation of a bicyclic amino-indanol (2) is compared with that of a closely related phenol with an ortho CPh2NH2 substituent (1). Spectroscopic, structural, thermochemical and computational studies show that the two amino-phenols are very similar, except that the O⋯N distance (dON) is >0.1 Å longer in 2 than in 1. The difference in dON is 0.13 ± 0.03 Å from X-ray crystallography and 0.165 Å from DFT calculations. Oxidations of these phenols by outer-sphere oxidants yield distonic radical cations •OAr–NH3+ by concerted proton-electron transfer (CPET). Simple tunneling and classical kinetic models both predict that the longer donor-acceptor distance in 2 should lead to slower reactions, by ca. two orders of magnitude, as well as larger H/D kinetic isotope effects (KIEs). However, kinetic studies show that the compound with the longer proton-transfer distance, 2, exhibits smaller KIEs and has rate constants that are quite close to those of 1. For example, the oxidation of 2 by the triarylamminium radical cation N(C6H4OMe)3•+ (3a+) occurs at (1.4 ± 0.1) × 104 M-1 s-1, only a factor of two slower than the closely related reaction of 1 with N(C6H4OMe)2(C6H4Br)•+ (3b+). This difference in rate constants is well accounted for by the slightly different free energies of reaction: ΔG°(2 + 3a+) = +0.078 V vs. ΔG°(1 + 3b+) = +0.04 V. The two phenol-amines do display some subtle kinetic differences: for instance, compound 2 has a shallower dependence of CPET rate constants on driving force (Brønsted α, Δln(k)/Δln(Keq)). These results show that the simple tunneling model is not a good predictor of the effect of proton donor-acceptor distance on concerted-electron transfer reactions involving strongly hydrogen-bonded systems. Computational analysis of the observed similarity of the two phenols emphasizes the importance of the highly anharmonic O⋯H⋯N potential energy surface and the influence of proton vibrational excited states.
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影响因子：
15
作者：
Costentin, Cyrille;Robert, Marc;Saveant, Jean-Michel
通讯作者：
Saveant, Jean-Michel
影响因子：
4
作者：
Benisvy, L;Bill, E;Wilson, C
通讯作者：
Wilson, C
影响因子：
--
作者：
BRAGA, TG;WAHL, AC
通讯作者：
WAHL, AC
DOI：
10.1524/zpch.217.12.1507.20477
发表时间：
2003-01-01
影响因子：
2.5
作者：
Doslic, N;Kühn, O
通讯作者：
Kühn, O
影响因子：
15
作者：
Bonin, Julien;Costentin, Cyrille;Saveant, Jean-Michel
通讯作者：
Saveant, Jean-Michel