H2O Activation for Hydrogen-Atom Transfer: Correct Structures and Revised Mechanisms
H2O Activation for Hydrogen-Atom Transfer: Correct Structures and Revised Mechanisms
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DOI：
10.1002/anie.201107556
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
van Gastel, Maurice
中科院分区：
文献类型：
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作者：
Gansaeuer, Andreas;Behlendorf, Maike;van Gastel, Maurice
通过氢原子转移（HAT）将自由基还原成烃是基本的自由基反应。[1]该领域的最新进展集中在醇和H2O作为HAT试剂，在硼烷[2]和[Cp 2 TiCl]存在下，[3]（Cp= C5 H5）使用H2作为最终还原剂，[4]和BH 3-NHC络合物（NHC= N-杂环卡宾）。[5]在[Cp_2TiCl]存在下，H_2O作为HAT试剂的倾向可通过使O_2H键的键离解能（BDE）降低约60kcalmol_2 ~（-1）来解释。[3]在本文中，我们通过EPR光谱和循环伏安法（CV）证明了所提出的HAT试剂1 [3c]不存在于[Cp 2 TiCl 2]和H2O的锌还原的THF溶液中。相反，我们的结果表明2和3是活性HAT试剂（图1）。此外，我们还表明，之前支持1 [3c]的数据也与2、3a和3b一致，并且较旧的计算研究[3c]需要扩展和改进。
The reduction of radicals to hydrocarbons through hydrogenatom transfer (HAT) is a fundamental radical reaction.[1] Recent developments in the field concentrate on alcohols and H2O as HAT reagents in the presence of boranes [2] and [Cp2TiCl],[3](Cp= C5H5) the use of H2 as the final reductant,[4] and on BH3–NHC complexes (NHC= N-heterocyclic carbene).[5] All cases feature a weakening of otherwise strong HÀX bonds.The propensity of H2O to act as a HAT reagent has been explained by a reduction of the bond dissociation energy (BDE) of the OÀH bond by about 60kcalmolÀ1 in the presence of [Cp2TiCl].[3] Herein, we demonstrate by EPR spectroscopy and cyclic voltammetry (CV) that the proposed HATreagent 1 [3c] is not present in zinc-reduced THF solutions of [Cp2TiCl2] and H2O. Instead, our results suggest that 2 and 3 are the active HAT reagents (Figure 1). Moreover, we show that previous data in support of 1 [3c] are also in agreement with 2, 3a, and 3b, and that an older computational study [3c] needs extension and refinement.