Polymer-supported chiral Co(salen) complexes: Synthetic applications and mechanistic investigations in the hydrolytic kinetic resolution of terminal epoxides
Polymer-supported chiral Co(salen) complexes: Synthetic applications and mechanistic investigations in the hydrolytic kinetic resolution of terminal epoxides
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DOI：
10.1021/ja984410n
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发表时间：
1999-05-05
影响因子：
15
通讯作者：
Jacobsen, EN
中科院分区：
文献类型：
--
作者：
Annis, DA;Jacobsen, EN
本文介绍了聚苯乙烯和二氧化硅键合的手性Co（salen）配合物的合成及其在不对称催化中的应用。一个通用的方法为共价连接的salen配合物的两种类型的支持已被设计出来，和相应的固定化钴衍生物被证明是有效的和高对映选择性催化剂的水解动力学拆分（HKR）的末端环氧化物。这些系统为与从HKR分离反应产物相关的某些技术困难提供了实际解决方案。的拔除.通过过滤和重复循环的负载型催化剂的证明，没有反应性或对映选择性的损失。该催化剂体系介导的酚类化合物与末端环氧化物的对映选择性加成反应提供了一种简便、高产率的合成相应的对映体富集的芳基醚的方法。固定化催化剂已被调整为连续流动过程，用于以高产率和ee产生反应产物，仅需要非常简单的产物纯化技术。这些催化剂进行高效和对映选择性的环氧开环的机制已解决使用二氧化硅结合的Co（salen）配合物。已经观察到催化剂位点隔离的程度和反应速率之间的显著相关性，这与这些反应中的协同反应机理一致。
This paper describes the synthesis of polystyrene- and silica-bound chiral Co(salen) complexes and their application in asymmetric catalysis. A general method for the covalent attachment of salen complexes to both types of support has been devised, and the corresponding immobilized cobalt derivatives an shown to be efficient and highly enantioselective catalysts for the hydrolytic kinetic resolution (HKR) of terminal epoxides. These systems provide practical solutions to certain technical difficulties associated with the isolation of reaction products from the HKR. Removal. of the supported catalyst by filtration and repeated recycling is demonstrated with no loss of reactivity or enantioselectivity. The enantioselective addition of phenols to terminal epoxides mediated by this catalyst system provides a facile, high-yielding synthesis of the corresponding enantioenriched aryl ethers. The immobilized catalysts have been adapted to a continuous flow process for the generation of reaction products in high yield and ee, requiring only very simple techniques for product purification. The mechanism by which these catalysts perform highly efficient and enantioselective epoxide ring opening has been addressed using a silica-bound Co(salen) complex. A dramatic correlation between the degree of catalyst site-isolation and reaction rate has been observed, consistent with a cooperative bimetallic mechanism in these reactions.