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Catalysis of Methyl Transfer Reactions by Oriented External Electric Fields: Are Gold-Thiolate Linkers Innocent?
Journal of the American Chemical Society ( IF 15.0 ) Pub Date : 2018-03-07 , DOI: 10.1021/jacs.8b00192
Rajeev Ramanan 1 , David Danovich 1 , Debasish Mandal 2 , Sason Shaik 1
Affiliation  

Oriented external electric fields (OEEFs) are potent effectors of chemical change and control. We show that the Menshutkin reaction, between substituted pyridines and methyl iodide, can be catalyzed/inhibited at will, by just flipping the orientation of the EEF ( F Z) along the "reaction axis" ( Z), N---C---I. A theoretical analysis shows that catalysis/inhibition obey the Bell-Evans-Polanyi principle. Significant catalysis is predicted also for EEFs oriented off the reaction axis. Hence, the observation of catalysis can be scaled up and may not require orienting the reactants vis-à-vis the field. It is further predicted that EEFs can also catalyze the front-side nucleophilic displacement reaction, thus violating the Walden-inversion paradigm. Finally, we considered the impact of gold-thiolate linkers, used experimentally to deliver the EEF stimuli, on the Menshutkin reaction. A few linkers were tested and proved not to be innocent. In the presence of F Z, the linkers participate in the electronic reorganization of the molecular system. In so doing, these linkers induce local electric fields, which map the effects of the EEF and induce catalysis/inhibition at will, as in the pristine reaction. However, as the EEF becomes more negative than -0.1 V/Å, an excited charge transfer state (CTS), which involves one-electron transfer from the 5p lone pair of iodine to an antibonding orbital of the gold cluster, crosses below the closed-shell state of the Menshutkin reaction and causes a mechanistic crossover. This CTS catalyzes nucleophilic displacement of iodine radical from the CH3I•+ radical cation. The above predictions and others discussed in the text are testable.

中文翻译:

定向外部电场催化甲基转移反应:金硫醇连接体是无辜的吗?

定向外部电场 (OEEF) 是化学变化和控制的有效效应器。我们表明,取代吡啶和甲基碘之间的 Menshutkin 反应可以随意催化/抑制,只需沿“反应轴”(Z)翻转 EEF(FZ)的方向,N---C-- -一世。理论分析表明催化/抑制遵循 Bell-Evans-Polanyi 原理。对于偏离反应轴的 EEF,也预测了显着的催化作用。因此,可以扩大对催化的观察,并且可能不需要将反应物定向到场。进一步预测,EEFs 也可以催化前端亲核置换反应,从而违反瓦尔登反演范式。最后,我们考虑了金硫醇接头的影响,实验上用于传递 EEF 刺激,对 Menshutkin 反应。测试了一些链接器并证明不是无辜的。在 FZ 存在下,接头参与分子系统的电子重组。这样做时,这些连接子会诱导局部电场,从而映射 EEF 的影响并随意诱导催化/抑制,就像在原始反应中一样。然而,当 EEF 变得比 -0.1 V/Å 更负时,激发电荷转移态 (CTS) 涉及从 5p 孤对碘到金簇的反键轨道的单电子转移,穿过闭合的Menshutkin 反应的壳状态并导致机械交叉。该 CTS 催化碘自由基从 CH3I•+ 自由基阳离子的亲核置换。
更新日期:2018-03-07
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