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Abstract：
In this paper, the origins of enantioselectivity in asymmetric ketone hydrogenation catalyzed by RuH(2)(binap)(cydn) (cydn = trans-1,2-diaminocyclohexane) were discussed. Fifteen substrates involving aromatic, heteroaromatic, olefinic and dialkyl prochiral ketones were used to probe the catalytic mechanism and find an effective way to predict the chirality of the products. The calculated results demonstrate that the hydrogen transfer (HT) step from the Ru complex to the ketone substrate is the chirality-determining step in the H(2)-hydrogenation of ketones. The hydrogenation of aromatic-alkyl ketones can give higher enantiomeric excess (ee) values than that of dialkyl ketones. An interesting intermediate (denoted as ) could be formed if there is an α-hydrogen for R/R\' groups of the ketone due to the H(2)-H(α) interaction. Two substituent groups of the ketone could rotate around the C=O axis in two directions, clockwise or counter-clockwise. This rotation, with the big or conjugative substituent group away from/toward the closer binap ligand of the Ru catalyst, will form favorable/unfavorable chiral products with an Re-/Si- intermediate structure. On the contrary, if there is no such α-hydrogen in any substituent group of the ketone, ABS and another intermediate (denoted as INT) would not exist. This study indicates that the conjugative effect of the substituent groups of the ketone play an important role in differentiating the R/R\' groups of the ketone, while steric and electrostatic effects contribute to a minor extent. Furthermore, the disparity of the R and R\' groups of the ketone is of importance in the enantioselectivity and the favorable chiral alcohol is formed when the structure of the conjugative/big substituent group is away from the closer binap ligand of the RuH(2)(binap)(cydn) catalyst. According to the three factors of the substituent group and the fourth quadrant theory, the enantioselectivity of 91 prochiral ketones catalyzed by a series of Ru catalysts were predicted. All of the predictions are consistent with the experimental results.
摘要：
在本文中,讨论了RuH（2）（binap）（cydn）（cydn=反式-1,2-二氨基环己烷）催化的不对称酮氢化中对映选择性的起源。涉及芳香的15种底物，杂芳族，使用烯属和二烷基原手性酮来探索催化机理，并找到一种预测产物手性的有效方法。计算结果表明，从Ru络合物到酮底物的氢转移（HT）步骤是酮的H（2）氢化中的手性确定步骤。芳族烷基酮的氢化可以得到比二烷基酮更高的对映体过量(ee)值。如果由于H（2）-H（α）相互作用，酮的R/R\'基团存在α-氢，则可以形成有趣的中间体（表示为）。酮的两个取代基可以绕C=O轴在两个方向上旋转，顺时针或逆时针。这个旋转，大的或共轭的取代基远离/朝向Ru催化剂的更接近的binap配体，将形成具有Re-/Si-中间体结构的有利/不利的手性产物。相反,如果在酮的任何取代基中没有这样的α-氢，ABS和另一种中间体(表示为INT)将不存在。这项研究表明，酮的取代基的共轭作用在区分酮的R/R\'基团中起重要作用。而空间和静电效应贡献较小。此外，酮的R和R\'基团的差异在对映选择性方面很重要，并且当共轭/大取代基的结构远离RuH（2）（binap）（cydn）催化剂的更紧密的binap配体时，形成有利的手性醇。根据取代基的三个因素和第四象限理论，预测了一系列Ru催化剂催化91种前手性酮的对映选择性。所有的预测与实验结果一致。
