Impact of Multiple Hydrogen Bonds with Fluoride on Catalysis: Insight from NMR Spectroscopy.
Impact of Multiple Hydrogen Bonds with Fluoride on Catalysis: Insight from NMR Spectroscopy.
复制标题
DOI：
10.1021/jacs.0c09832
复制
发表时间：
2020-11-18
影响因子：
15
通讯作者：
Gouverneur V
中科院分区：
文献类型：
--
作者：
Ibba F;Pupo G;Thompson AL;Brown JM;Claridge TDW;Gouverneur V
氢键相互作用已经在催化中进行了探索，使复杂的化学反应成为可能。最近，与金属碱金属氟化物的对映选择性亲核取代已经用BINAM衍生的双脲催化剂完成，为氟化物提供多达四个NH氢键供体（HBD）。这些催化剂将不溶性CsF和KF带入溶液中，控制氟化物亲核性，并提供手性微环境用于将对映选择性氟化物递送至亲电体。这些属性鼓励了1H/19 F NMR研究，以获得关于溶液中氟化物的氢键网络的信息，以及这些排列如何影响催化亲核加成的效率。在本文中，NMR实验能够确定HB与十三种双脲催化剂的氟化物接触的数量和量级。这些数据补充了诊断耦合常数1hJNH···F-，深入了解了多个H键对氟化物的影响反应性能。在二氯甲烷（DCM-d2）中，非烷基化的BINAM衍生的双脲催化剂使其四个NH基团中的两个与氟化物形成氢键，这种安排允许有效的相转移能力，但对氟化物递送的对映体选择性的控制较低。更有效的N-烷基化BINAM衍生的双脲催化剂在氟化物结合时经历脲异构化，并形成动态刚性的三叉氢键键合的氟化物络合物，其在结构上类似于它们在固态下的构象。深入了解如何抗衡阳离子影响氟化物络合提供的基础上，NMR数据表征形成的物种在DCM-D2反应时，双脲催化剂与四正丁基氟化铵（TBAF）或CsF。结构-活性分析表明，三种氢键与氟离子的接触对催化剂活性的贡献并不相等，这表明调节各个电子环境是控制相转移能力和对映选择性的一种可行方法.
Hydrogen-bonding interactions have been explored in catalysis, enabling complex chemical reactions. Recently, enantioselective nucleophilic fluorination with metal alkali fluoride has been accomplished with BINAM-derived bisurea catalysts, presenting up to four NH hydrogen-bond donors (HBDs) for fluoride. These catalysts bring insoluble CsF and KF into solution, control fluoride nucleophilicity, and provide a chiral microenvironment for enantioselective fluoride delivery to the electrophile. These attributes encouraged a 1H/19F NMR study to gain information on hydrogen-bonding networks with fluoride in solution, as well as how these arrangements impact the efficiency of catalytic nucleophilic fluorination. Herein, NMR experiments enabled the determination of the number and magnitude of HB contacts to fluoride for thirteen bisurea catalysts. These data supplemented by diagnostic coupling constants 1hJNH···F– give insight into how multiple H bonds to fluoride influence reaction performance. In dichloromethane (DCM-d2), nonalkylated BINAM-derived bisurea catalyst engages two of its four NH groups in hydrogen bonding with fluoride, an arrangement that allows effective phase-transfer capability but low control over enantioselectivity for fluoride delivery. The more efficient N-alkylated BINAM-derived bisurea catalysts undergo urea isomerization upon fluoride binding and form dynamically rigid trifurcated hydrogen-bonded fluoride complexes that are structurally similar to their conformation in the solid state. Insight into how the countercation influences fluoride complexation is provided based on NMR data characterizing the species formed in DCM-d2 when reacting a bisurea catalyst with tetra-n-butylammonium fluoride (TBAF) or CsF. Structure–activity analysis reveals that the three hydrogen-bond contacts with fluoride are not equal in terms of their contribution to catalyst efficacy, suggesting that tuning individual electronic environment is a viable approach to control phase-transfer ability and enantioselectivity.
登录
查看更多内容
影响因子：
16.6
作者：
Brak, Katrien;Jacobsen, Eric N.
通讯作者：
Jacobsen, Eric N.
影响因子：
2.2
作者：
Enthart, Andreas;Freudenberger, J. Christoph;Luy, Burkhard
通讯作者：
Luy, Burkhard
影响因子：
2.1
作者：
Kotke, M;Schreiner, PR
通讯作者：
Schreiner, PR
影响因子：
15
作者：
De, Chandra Kanta;Mittal, Nisha;Seidel, Daniel
通讯作者：
Seidel, Daniel
影响因子：
15
作者：
Birrell, James A.;Desrosiers, Jean-Nicolas;Jacobsen, Eric N.
通讯作者：
Jacobsen, Eric N.