• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Chemistry: A European journal >Chiral Modification of Platinum by Co-Adsorbed Cinchonidine and Trifluoroacetic Acid: Origin of Enhanced Stereocontrol in the Hydrogenation of Trifluoroacetophenone
【24h】

Chiral Modification of Platinum by Co-Adsorbed Cinchonidine and Trifluoroacetic Acid: Origin of Enhanced Stereocontrol in the Hydrogenation of Trifluoroacetophenone

机译：共吸附的金可可宁和三氟乙酸手性修饰铂：三氟苯乙酮加氢中立体控制增强的起源

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Cinchonidine (CD) adsorbed onto a platinum metal catalyst leads to rate acceleration and induces strong stereocontrol in the asymmetric hydrogenation of trifluoroacetophenone. Addition of catalytic amounts of trifluoroacetic acid (TFA) significantly enhances the enantiomeric excess from 50 to 92 %. The origin of the enantioselectivity bestowed by co-adsorbed CD and TFA is investigated by using in situ attenuated total reflection infrared spectroscopy and modulation excitation spectroscopy. Molecular interactions between the chiral modifier (CD), acid additive (TFA) and the trifluoro-activated substrate at the solid–liquid interface are elucidated under conditions relevant to catalytic hydrogenations, that is, on a technical Pt/Al_2O_3 catalyst in the presence of H_2 and solvent. Monitoring of the unmodified and modified surface during the hydrogenation provides an insight into the phenomenon of rate enhancement and the crucial interactions of CD with the ketone, corresponding product alcohol, and TFA. Comparison of the diastereomeric interactions occurring on the modified surface and in the liquid solution shows a striking difference for the chiral preferences of CD. The spectroscopic data, in combination with calculations of molecular structures and energies, sheds light on the reaction mechanism of the heterogeneous asymmetric hydrogenation of trifluoromethyl ketones and the involvement of TFA in the diastereomeric intermediate surface complex: the quinuclidine N atom of the adsorbed CD forms an N-H-O-type hydrogen-bonding interaction not only with the trifluoro-activated ketone but also with the corresponding alcohol and the acid additive. Strong evidence is provided that it is a monodentate acid/base adduct in which the carboxylate of TFA resides at the quinuclidine N-atom of CD, which imparts a better stereochemical control.
机译：吸附在铂金属催化剂上的辛可尼定（CD）导致速率加速，并在三氟苯乙酮的不对称氢化中引起强烈的立体控制。加入催化量的三氟乙酸（TFA）可将对映体过量从50％提高至92％。通过使用原位衰减全反射红外光谱和调制激发光谱研究了共吸附CD和TFA赋予的对映选择性的起源。在与催化氢化有关的条件下，即在工业Pt / Al_2O_3催化剂存在下，阐明了手性改性剂（CD），酸添加剂（TFA）和三氟活化底物在固液界面上的分子相互作用。 H_2和溶剂。氢化过程中未修饰和修饰表面的监测提供了速率增加现象以及CD与酮，相应的产物醇和TFA的关键相互作用的见解。比较在改性表面和液体溶液中发生的非对映异构体相互作用，发现CD的手性偏好存在显着差异。光谱数据与分子结构和能量的计算相结合，揭示了三氟甲基酮的非均相不对称氢化和TFA参与非对映异构体中间表面络合物的反应机理：吸附的CD的喹核苷N原子形成NHO型氢键键合不仅与三氟活化的酮发生相互作用，而且还与相应的醇和酸添加剂发生相互作用。提供有力的证据表明，它是单齿酸/碱加合物，其中TFA的羧酸盐位于CD的奎核苷N原子上，可以提供更好的立体化学控制。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号