Mechanism of Enantioselective Ti-Catalyzed Strecker Reaction: Peptide-Based Metal Complexes as Bifunctional Catalysts
详细信息 查看全文
- 作者：Nathan S. Josephsohn ; Kevin W. Kuntz ; Marc L. Snapper ; and Amir H. Hoveyda
- 刊名：Journal of the American Chemical Society
- 出版年：2001
- 出版时间：November 28, 2001
- 年：2001
- 卷：123
- 期：47
- 页码：11594 - 11599
- 全文大小：102K
- 年卷期：v.123,no.47(November 28, 2001)
- ISSN：1520-5126
文摘
Kinetic, structural, and stereochemical data regarding the mechanism of Ti-catalyzed addition ofcyanide to imines in the presence of Schiff base peptide ligands are disclosed. The reaction is first order in theTi·ligand complex; kinetic studies reveal 
S
= -45.6 ± 4.1 cal K-1 mol-1, indicating a highly organizedtransition structure for the turnover-limiting step of the catalytic cycle. A mechanistic model consistent withthe kinetic and stereochemical data is presented, where the Ti center is coordinated to the Schiff base unit ofthe ligand and the AA2 moiety of the peptidic segment of the chiral ligand associates and delivers HNC to theactivated bound substrate. Thus, these studies illustrate that these non-C2-symmetric catalysts likely operate ina bifunctional fashion.
S = -45.6 ± 4.1 cal K-1 mol-1, indicating a highly organizedtransition structure for the turnover-limiting step of the catalytic cycle. A mechanistic model consistent withthe kinetic and stereochemical data is presented, where the Ti center is coordinated to the Schiff base unit ofthe ligand and the AA2 moiety of the peptidic segment of the chiral ligand associates and delivers HNC to theactivated bound substrate. Thus, these studies illustrate that these non-C2-symmetric catalysts likely operate ina bifunctional fashion.