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Elucidation of the Enantioselection Mechanism of Transition Metal-Catalyzed Asymmetric Reactions

过渡金属催化不对称反应的对映选择机制的阐明

基本信息

批准号：
13440186
负责人：
IMAMOTO Tsuneo
金额：
$ 9.02万
依托单位：
CHIBA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

项目摘要

This study is directed toward the elucidation of the enantioselection mechanism of rhodium-catalyzed asymmetric hydrogenation that is one of the representative asymmetric catalyses. P-Chirogenic, electron-rich diphosphines such as BisP^* and MiniPHOS were used in this study because of their simple molecular structure and very high enantioinduction ability in rhodium-catalyzed asymmetric hydrogenations of α- or β-and dehydroamino acid derivatives, enamides, and enol esters. One of the most important findings is the detection and characterization of the rhodium dihydride complexes bearing diphosphine ligands. The dihydride complexes reacted readily with the alkene substrates even at -100 - -90 ℃ to give the corresponding monohydride intermediates, and subsequent reductive elimination occurred at about -50 ℃. These results are interpreted by considering a dihydride mechanism. It is concluded that the enantioselection is determined at the stage of the migratory insertion of the Rh-H to the C-C double bond. The main factors to control the enantioselection are 1. Trans effect of by the coordinated phosphorus atom, 2. The orbital interaction between of the Rh-H and the C-C double bond, 3. Formation of the chelate cycle, 4. The steric interaction between the bulky group at the phosphorus and the chelate cycle, 5. Electronic effect of the substituent at the olefic group. It is also concluded that the enantioselection of these Rh-catalyzed asymmetric hydrogenations is governed by multi stereo regulation factors. A new quadrant rule to correlate between the stereochemistry of the hydrogenation products and the structure of the catalyst structures has been proposed. A new, highly efficient chiral diphosphine ligand has been designed and synthesized based on these research results.

本研究旨在阐明铑催化不对称氢化反应的对映体选择机理，铑催化不对称氢化反应是典型的不对称催化反应之一。由于分子结构简单，在铑催化的α-或β-和脱氢氨基酸衍生物、酰胺和烯醇酯的不对称氢化反应中具有很高的对映诱导能力，因此本研究使用了富含电子的P-Chirogenic二膦化合物，如BisP^*和MiniPHOS。其中最重要的发现之一是检测和表征二氢化铑配合物携带二膦配体。二氢化物配合物在-100 ~ -90℃时也能与烯烃底物反应生成相应的一氢化物中间体，随后在-50℃左右发生还原消除。这些结果可以通过考虑二氢化物机理来解释。结果表明，对映体选择是在Rh-H向C-C双键迁移插入阶段决定的。控制对映体选择的主要因素有：1。2.配位磷原子的反式效应。氢原子和碳碳双键之间的轨道相互作用，3。4.螯合循环的形成；在磷和螯合循环中，大基团之间的空间相互作用，5。取代基在烯烃基团上的电子效应。结果表明，这些铑催化的不对称氢化反应的对映体选择受多重立体调控因素的控制。提出了加氢产物立体化学与催化剂结构之间的象限规则。在此基础上设计并合成了一种新的高效手性二膦配体。