咪唑-2-亚基的水解,Journal of the American Chemical Society

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咪唑-2-亚基的水解
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2011-02-02 , DOI: 10.1021/ja103578y
Oldamur Hollóczki , Péter Terleczky , Dénes Szieberth , Georgios Mourgas ₁ , Dietrich Gudat ₁ , László Nyulászi

Affiliation

首次研究了咪唑-2-亚基在主要水性环境中的直接反应 [H(2)O (>60%)/THF 溶剂系统中的约 0.1 M 溶液]。该反应产生了相应的咪唑鎓-氢氧化物的稳定溶液，pH 值为 13，这与从头分子动力学模拟的结果一致。相比之下，卡宾在主要非质子环境 (>80% THF) 中的水解产生了氢桥连的卡宾 - 水复合物，可以通过核磁共振和红外光谱首次检测到。该复合物缓慢转化为两种异构的开环产物，并且在与咪唑鎓氢氧化物的动态平衡中处于较高的水浓度。随着水分子数量逐渐增加，卡宾水解的计算机制研究表明，咪唑鎓-氢氧化物结构只能以三个或更多水分子作为反应物进行优化，并且随着水分子数量的增加，其稳定性也随之增加。到卡宾-水复合物。与实验结果一致，这些发现指出溶剂稳定性和氢氧根离子的碱性在反应中起着至关重要的作用。随着水分子数量的增加，连接反应中间体的势垒越来越小，开环水解产物可以衍生自咪唑鎓-氢氧化物类型的中间体。对非芳香族咪唑烷-2-亚基类似物水解的计算研究清楚地表明，类似的开环产物比适当的离子对和卡宾 - 水复合物稳定 10-12 kcal/mol，与已知的一致咪唑-2-亚基的芳香稳定化。因此，这些分子水解并独家形成开环产物。

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Hydrolysis of Imidazole-2-ylidenes

The direct reaction of an imidazole-2-ylidene in a predominantly aqueous environment [about 0.1 M solution in a H(2)O (>60%)/THF solvent system] was investigated for the first time. The reaction yielded a stable solution of the corresponding imidazolium-hydroxide of pH 13, which is in agreement with results from an ab initio molecular dynamics simulation. In contrast, hydrolysis of the carbene in a mainly aprotic environment (>80% THF) gives a hydrogen-bridged carbene-water complex which could be detected by NMR and IR spectroscopies for the first time. This complex converts slowly to two isomeric ring opened products and is at higher water concentration in dynamic equilibrium with the imidazolium hydroxide. A computational mechanistic study of the carbene hydrolysis with a gradually increasing number of water molecules revealed that the imidazolium-hydroxide structure can only be optimized with three or more water molecules as reactants, and with the increasing number of water molecules its stability is increasing with respect to the carbene-water complex. In agreement with the experimental results, these findings point out that solvent stabilization and basicity of the hydroxide ion plays a crucial role in the reaction. With increasing number of water molecules the barriers connecting the reaction intermediates are getting smaller, and the ring opened hydrolysis products can be derived from imidazolium-hydroxide type intermediates. Computational studies on the hydrolysis of a nonaromatic imidazolidine-2-ylidene analogue clearly indicated the analogous ring-opened product to be by 10-12 kcal/mol more stable than the appropriate ion pair and the carbene-water complex, in agreement with the known aromatic stabilization of imidazol-2-ylidenes. Accordingly, these molecules hydrolyze with exclusive formation of the ring-opened product.

更新日期：2011-02-02

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