Burger Veronika, Franta Maximilian, O'Donoghue AnnMarie C, Ofial Armin R, Gschwind Ruth M, Zipse Hendrik
Department of Chemistry, Ludwig-Maximilians Universität München, Butenandtstr. 5-13, 81377 München, Germany.
Institute for Organic Chemistry, University Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany.
J Org Chem. 2025 Feb 14;90(6):2298-2306. doi: 10.1021/acs.joc.4c02668. Epub 2025 Jan 30.
A comprehensive analytical protocol combining conductivity, diffusion-ordered NMR (DOSY), and photometric kinetic measurements is employed to analyze the nucleophilic reactivity of pyridinamide ion pairs in low-polarity organic solvents. The association patterns of these systems are found to strongly depend on cation size, with larger cations favoring the formation of cationic triple ion sandwich complexes together with free and highly nucleophilic anions. Kinetic studies using the ionic strength-controlled benzhydrylium method demonstrate that pyridinamide ions exhibit significantly higher nucleophilicities as compared to established organocatalysts, particularly in low-polarity solvents. Nucleophilicities are furthermore found to correlate well with Brønsted basicities measured in water and with Lewis basicities calculated in dichloromethane. Taken together, these findings provide quantitative guidelines for the future design of highly active Lewis base catalysts.
采用一种结合电导率、扩散有序核磁共振（DOSY）和光度动力学测量的综合分析方法，来分析低极性有机溶剂中吡啶酰胺离子对的亲核反应活性。发现这些体系的缔合模式强烈依赖于阳离子大小，较大的阳离子有利于形成阳离子三联离子夹心配合物以及游离且具有高亲核性的阴离子。使用离子强度控制的二苯甲基鎓方法进行的动力学研究表明，与已有的有机催化剂相比，吡啶酰胺离子表现出显著更高的亲核性，特别是在低极性溶剂中。此外，还发现亲核性与在水中测得的布朗斯特碱性以及在二氯甲烷中计算出的路易斯碱性具有良好的相关性。综上所述，这些发现为未来设计高活性路易斯碱催化剂提供了定量指导。
