State Key Laboratory of Elemento-organic Chemistry, Department of Chemistry, Nankai University, Tianjin 300071.
J Org Chem. 2013 Jul 19;78(14):7076-85. doi: 10.1021/jo400915f. Epub 2013 Jul 1.
The pKa values of 41 chiral phosphoric acid-family catalysts in DMSO were predicted using the SMD/M06-2x/6-311++G(2df,2p)//B3LYP/6-31+G(d) method for the first time. The study showed that the calculated pKa's range from -4.23 to 6.16 for absolute pKa values and from -4.21 to 6.38 for relative pKa values. Excellent agreement between the calculated and experimental pKa's was achieved for the few available cases (to a precision of around 0.4 pKa unit), indicating that this strategy may be suitable for calculating highly accurate pKa's. A good linear correlation between the pKa's for 3 and 3' disubstituted phenyl BINOL phosphoric acids and the Hammett constants was obtained. The relationship between the acidities of phosphoric acid catalysts and their reaction activity and selectivity was also discussed. Knowledge of the pKa values of phosphoric acids should be of great value for the understanding of chiral Brønsted acid-catalyzed reactions and may aid in future catalyst design.
首次使用 SMD/M06-2x/6-311++G(2df,2p)//B3LYP/6-31+G(d) 方法预测了 41 种手性磷酸催化剂在 DMSO 中的 pKa 值。研究表明，绝对 pKa 值的计算 pKa 值范围为-4.23 至 6.16，相对 pKa 值的计算 pKa 值范围为-4.21 至 6.38。对于少数可用情况，计算出的 pKa 值与实验值之间具有极好的一致性（精度约为 0.4 pKa 单位），表明该策略可能适用于计算高精度的 pKa 值。3 和 3'取代苯基 BINOL 磷酸的 pKa 值与哈米特常数之间存在良好的线性相关性。还讨论了磷酸催化剂的酸度与其反应活性和选择性之间的关系。了解磷酸的 pKa 值对于理解手性布朗斯特酸催化反应应该具有重要价值，并可能有助于未来的催化剂设计。
