New macrocycles derived from dibenzo-18-crown-6 and molecules derived from pentaethylene glycol were designed and investigated as catalysts for nucleophilic fluorination of alkyl mesylates with potassium fluoride by reliable computational methods. In addition, 3 known catalysts (18-crown-6, [2.2.2]-cryptand, and pentaethylene glycol) were also simulated. In the kinetic model, the solubilization of the salt by the macrocycle, the possible dimerization of the KF(cat) complex and the reaction of the solubilized KF(cat) complex were considered. The calculated free energy barriers for the known catalysts are in very good agreement with published experimental data. For the new designed catalysts, all of them were predicted to be effective in promoting fluorination. A novel macrocycle based on a thiourea-crown-ether structure, named TCEbut, was calculated to be the most effective catalyst, even overcoming [2.2.2]-cryptand. This catalyst works by complexing the potassium ion and making four hydrogen bonds provided by the thiourea groups to the S_N2 transition state.

中文翻译：

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用于KF亲核氟化的新大环的理论设计：硫脲-冠醚预计将克服[2.2.2] -cryptand

设计并研究了衍生自二苯并-18-冠-6的新大环和衍生自五甘醇的分子，并通过可靠的计算方法研究了它们用氟化钾对烷基甲磺酸酯进行亲核氟化的催化剂。此外，还模拟了3种已知的催化剂（18-crown-6，[2.2.2] -cryptand和五乙二醇）。在动力学模型中，考虑了盐通过大环的增溶，KF（cat）配合物可能的二聚作用以及溶解的KF（cat）配合物的反应。计算出的已知催化剂的自由能垒与已公开的实验数据非常吻合。对于新设计的催化剂，预计所有这些催化剂都能有效促进氟化。基于硫脲-冠醚结构的新型大环化合物，名为TCEbut，被认为是最有效的催化剂，甚至可以克服[2.2.2] -cryptand。该催化剂通过络合钾离子并使硫脲基团与S形成四个氢键而起作用_N 2过渡态。