Probing concerted proton-electron transfer in phenol-imidazoles
Probing concerted proton-electron transfer in phenol-imidazoles
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DOI：
10.1073/pnas.0708967105
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发表时间：
2008-06-17
影响因子：
11.1
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.
一系列七种取代的 4,6-二叔丁基-2-(4,5-二芳基咪唑基)-苯酚以及两种相关的苯并咪唑化合物已被制备和表征。所有化合物的X射线晶体结构表明，苯酚环和咪唑环接近共面，并通过分子内ArOH中心点中心点N氢键连接。这些化合物的单电子氧化发生在酚质子通过协同质子电子转移（CPET）移动到咪唑基上时，产生相当稳定的双子自由基阳离子。这些酚基化合物是一个有价值的系统，可用于检查 CPET 的主要特征。双分子 CPET 氧化的动力学测量，E-rxn 在 +0.04 和 -0.33 V 之间，给出从 (6.3 +/- 0.6) x 10(2) 到 (3.0 +/- 0.6) x 10(6) M-1 s(-1) 的速率常数。log(k) 与 Delta G 度有良好的相关性，15 个速率常数中只有一个下降超过一个因子5.2 从相关线。咪唑上的取代基影响（O-H 中心点中心点中心点 N）氢键，如 H-1 NMR 和计算的振动光谱和几何形状的变化所标记。晶体学 d(O 中心点 中心点 N) 值似乎更受晶体堆积力的影响。然而，速率常数与任何这些测量或计算的参数几乎没有相关性。在来自同一结构家族的这一系列化合物中，速率常数差异的主要贡献者是驱动力 Delta G 度。
A series of seven substituted 4,6-di-tert-butyl-2-(4,5-diarylimidazolyi)-phenols have been prepared and characterized, along with two related benzimidazole compounds. X-ray crystal structures of all of the compounds show that the phenol and imidazole rings are close to coplanar and are connected by an intramolecular ArOH center dot center dot center dot N hydrogen bond. One-electron oxidation of these compounds occurs with movement of the phenolic proton to the imidazole base by concerted proton-electron transfer (CPET) to yield fairly stable distonic radical cations. These phenol-base compounds are a valuable system in which to examine the key features of CPET. Kinetic measurements of bimolecular CPET oxidations, with E-rxn between +0.04 and -0.33 V, give rate constants from (6.3 +/- 0.6) x 10(2) to (3.0 +/- 0.6) x 10(6) M-1 s(-1).There is a good correlation of log(k) with Delta G degrees, with only one of the 15 rate constants falling more than a factor of 5.2 from the correlation line. Substituents on the imidazole affect the (O-H center dot center dot center dot N) hydrogen bond, as marked by variations in the H-1 NMR and calculated vibrational spectra and geometries. Cry stallographic d(O center dot center dot center dot N) values appear to be more strongly affected by crystal packing forces. However, there is almost no correlation of rate constants with any of these measured or computed parameters. Over this range of compounds from the same structural family, the dominant contributor to the differences in rate constant is the driving force Delta G degrees.