Theoretical Study of C-H Bond Cleavage via Concerted Proton-Coupled Electron Transfer in Fluorenyl-Benzoates
Theoretical Study of C-H Bond Cleavage via Concerted Proton-Coupled Electron Transfer in Fluorenyl-Benzoates
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DOI：
10.1021/jacs.8b10461
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发表时间：
2018-11-21
影响因子：
15
通讯作者：
Hammes-Schiffer, Sharon
中科院分区：
文献类型：
--
作者：
Sayfutyarova, Elvira R.;Goldsmith, Zachary K.;Hammes-Schiffer, Sharon
开发新的策略来激活和裂解 C-H 键对于广泛的应用来说非常重要。最近报道了一种使用多位点协同质子耦合电子转移（PCET）激活C-H键的新方法，涉及分子间电子转移到氧化剂以及分子内质子转移。对于与 2-(9H-芴-9-基)苯甲酸酯反应的一系列氧化剂，实验研究揭示了非典型的布朗斯台德 a，定义为 PCET 速率常数的对数与平衡常数或缩放驱动力的对数的斜率。在此，该反应采用振动非绝热 PCET 理论进行建模。氢隧道效应、质子供体-受体模式的热采样、溶质和溶剂重组以及激发振动电子态的贡献被发现发挥着重要作用。计算定性地再现了布朗斯台德 a 明显小于 0.5 的实验观察结果，并用电子质子振动态对之间的放热过程解释了这种浅斜率。这些基本机制的见解可以指导设计更有效的 C-H 键激活和裂解策略。
Developing new strategies to activate and cleave C-H bonds is important for a broad range of applications. Recently a new approach for C-H bond activation using multi-site concerted proton-coupled electron transfer (PCET) involving intermolecular electron transfer to an oxidant coupled to intramolecular proton transfer was reported. For a series of oxidants reacting with 2-(9H-fluoren-9-yl)benzoate, experimental studies revealed an atypical Bronsted a, defined as the slope of the logarithm of the PCET rate constant versus the logarithm of the equilibrium constant or the scaled driving force. Herein this reaction is modeled with a vibronically nonadiabatic PCET theory. Hydrogen tunneling, thermal sampling of the proton donor-acceptor mode, solute and solvent reorganization, and contributions from excited vibronic states are found to play important roles. The calculations qualitatively reproduce the experimental observation of a Bronsted a significantly less than 0.5 and explain this shallow slope in terms of exoergic processes between pairs of electron proton vibronic states. These fundamental mechanistic insights may guide the design of more effective strategies for C-H bond activation and cleavage.