Mechanism of enantioselective Ti-catalyzed strecker reaction: Peptide-based metal complexes as bifunctional catalysts
Mechanism of enantioselective Ti-catalyzed strecker reaction: Peptide-based metal complexes as bifunctional catalysts
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DOI：
10.1021/ja011875w
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发表时间：
2001-11-28
影响因子：
15
通讯作者：
Hoveyda, AH
中科院分区：
文献类型：
--
作者：
Josephsohn, NS;Kuntz, KW;Hoveyda, AH
动能。公开了在希夫碱肽配体存在下，钛催化氰化物加成亚胺的机理的结构和立体化学数据。该反应在钛配体配合物中为一级反应；动力学研究表明，δ（双匕首）= -45.6 +/- 4.1 cal K-1 mol(-1)，表明催化循环的周转限制步骤具有高度组织化的过渡结构。提出了一个与动力学和立体化学数据相一致的机制模型，其中Ti中心与配体的希夫碱单位协调，手性配体肽段的AA2部分结合并将HNC传递给活化的结合底物。因此，这些研究表明，这些非c -2对称催化剂可能以双功能方式运作。
Kinetic. structural, and stereochemical data regarding the mechanism of Ti-catalyzed addition of cyanide to imines in the presence of Schiff base peptide ligands are disclosed. The reaction is first order in the Ti-ligand complex; kinetic studies reveal DeltaS(double dagger) = -45.6 +/- 4.1 cal K-1 mol(-1), indicating a highly organized transition structure for the turnover-limiting step of the catalytic cycle. A mechanistic model consistent with the kinetic and stereochemical data is presented, where the Ti center is coordinated to the Schiff base unit of the ligand and the AA2 moiety of the peptidic segment of the chiral ligand associates and delivers HNC to the activated bound substrate. Thus, these studies illustrate that these non-C-2-symmetric catalysts likely operate in a bifunctional fashion.