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首页> 外文期刊>Chemistry: A European journal >Mechanistic Investigations into the Asymmetric Transfer Hydrogenation of Ketones Catalyzed by Pseudo-Dipeptide Ruthenium Complexes
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Mechanistic Investigations into the Asymmetric Transfer Hydrogenation of Ketones Catalyzed by Pseudo-Dipeptide Ruthenium Complexes

机译：假二肽钌配合物催化酮不对称转移加氢的机理研究

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摘要

The combination of N-Bocprotected a-amino acid hydroxyamides (pseudo-dipeptides) and [{RuACHTUNGTRENUNG(p-cymene) Cl2}2] resulted in the formation of superior catalysts for the asymmetric transfer hydrogenation (ATH) of nonactivated aryl alkyl ketones in propan- 2-ol. The overall kinetics of the ATH of acetophenone to form 1-phenylethanol in the presence of ruthenium pseudo-dipeptide catalysts were studied, and the individual rate constants for the processes were determined. Addition of lithium chloride to the reaction mixtures had a strong influence on the rates and selectivities of the processes. Kinetic isotope effects (KIEs) for the reduction were determined and the results clearly show that the hydride transfer is rate-determining, whereas no KIEs were detected for the proton transfer. From these observations a novel bimetallic outer-spheretype mechanism for these ATH process is proposed, in which the bifunctional catalysts mediate the transfer of a hydride and an alkali metal ion between the hydrogen donor and the substrate. Furthermore, the use of a mixture of propan-2-ol and THF (1:1) proved to enhance the rates of the ATH reactions. A series of aryl alkyl ketones were reduced under these conditions in the presence of 0.5 mol% of catalyst, and the corresponding secondary alcohols were formed in high yields and with excellent enantioselectivities (>99% ee) in short reaction times.
机译：N-Boc保护的a-氨基酸羟酰胺（伪二肽）和[{RuACHTUNGTRENUNG（p-cymene）Cl2} 2]的组合导致形成了高级催化剂，用于非活化芳基烷基酮的不对称转移氢化（ATH）。丙-2-醇。研究了在钌假二肽催化剂存在下苯乙酮的ATH生成1-苯基乙醇的整体动力学，并确定了该过程的各个速率常数。向反应混合物中加入氯化锂对方法的速率和选择性有很大的影响。确定了还原的动力学同位素效应（KIEs），结果清楚地表明，氢化物转移是决定速率的，而未检测到质子转移的KIE。从这些观察结果，提出了用于这些ATH过程的新颖的双金属外球型机理，其中双官能催化剂介导氢化物和碱金属离子在氢供体和底物之间的转移。此外，证明使用丙-2-醇和THF（1：1）的混合物可以提高ATH反应的速率。在0.5mol％的催化剂存在下，在这些条件下还原了一系列芳基烷基酮，并且在短的反应时间内以高收率和优异的对映选择性（＞ 99％ee）形成了相应的仲醇。

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