School of Chemistry, University of New South Wales, UNSW Sydney, NSW 2052, Australia.
Org Biomol Chem. 2020 Mar 14;18(10):1910-1917. doi: 10.1039/d0ob00036a. Epub 2020 Feb 25.
A series of imidazolinium salts, their six-, seven- and eight-membered homologues, and the related formamidinium salts were prepared, and their pK values were determined in DMSO at 25 °C using the bracketing indicator method. The effect of each type of structural variation on the acidity of each salt was considered, particularly noting the importance of ring size and the effect of the steric and electronic nature of the N-aryl substituents. The effect of a cyclic structure was also probed through comparing the cyclic systems with the corresponding formamidinium salts, noting the importance of conformational flexibility in the latter cases. Along with allowing choice of appropriate bases for deprotonation of these species, it is anticipated that the data presented will aid in the understanding of the nucleophilicity, and potentially catalytic efficacy, of the corresponding carbenes.
一系列咪唑啉盐、它们的六元、七元和八元同系物，以及相关的甲脒盐被制备，并使用指示缓冲剂法在 25°C 的 DMSO 中测定了它们的 pK 值。考虑了每种结构变化对每种盐的酸度的影响，特别注意了环大小的重要性以及 N-芳基取代基的空间和电子性质的影响。还通过将环状系统与相应的甲脒盐进行比较来探究环状结构的影响，注意到在后一种情况下构象灵活性的重要性。除了允许为这些物种的去质子化选择合适的碱之外，预计所呈现的数据将有助于理解相应卡宾的亲核性和潜在的催化效力。
