In Situ Observation of Non‐Classical 2‐Norbornyl Cation in Confined Zeolites at Ambient Temperature,Angewandte Chemie International Edition

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In Situ Observation of Non‐Classical 2‐Norbornyl Cation in Confined Zeolites at Ambient Temperature
Angewandte Chemie International Edition ( IF 16.1 ) Pub Date : 2020-12-03 , DOI: 10.1002/anie.202013384
Xiaomin Tang _{1,

2} , Wei Chen ₁ , Xianfeng Yi ₁ , Zhiqiang Liu ₁ , Yao Xiao _{1,

2} , Zhongfang Chen ₃ , Anmin Zheng ₁

Affiliation

Carbonium ions are an important class of reaction intermediates, but their dynamic evolution is difficult to be monitored by in situ techniques under experimental conditions because of their extremely short lifetime. Probably the most famous case is 2‐norbornyl cation (2NB⁺): its existing form (classical or non‐classical) had been debated for decades, until the concrete proof of non‐classical geometry was achieved by X‐ray crystallographic characterization at ultra‐low temperature (40 K) and super acidic environment. However, we lack the understanding about 2NB⁺ at ambient conditions. Herein, by taking advantage of the confinement effect and delocalized acidic environment of zeolites, we successfully stabilized 2NB⁺ and unequivocally confirmed its “non‐classical” structure inside the ZSM‐5 zeolite by ab initio molecular dynamics simulations and ¹³C solid‐state nuclear magnetic resonance experiments. It is the first time to in situ observe the non‐classical 2NB⁺ without the super acidic environment at ambient temperature, which provides a new strategy to expand the carbocation chemistry.

中文翻译：

常温下受限沸石中非经典2-降冰片烯阳离子的原位观察

碳离子是一类重要的反应中间体，但由于其寿命极短，因此在实验条件下很难通过原位技术监测其动态演变。可能最著名的案例是2-降冰片烷基阳离子（2NB ⁺）：它的存在形式（经典或非经典）已经争论了数十年，直到通过X射线晶体学表征获得了非经典几何形状的具体证明。低温（40 K）和超酸性环境。但是，我们缺乏在环境条件下对2NB ⁺的了解。在此，通过利用沸石的约束作用和离域酸性环境，成功地稳定了2NB ⁺并且通过从头算分子动力学模拟和¹³ C固态核磁共振实验明确证实了ZSM-5沸石内部的“非经典”结构。这是第一次在环境温度下原位观察没有超酸性环境的非经典2NB ⁺，这为扩展碳正离子化学反应提供了新的策略。

更新日期：2020-12-03

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