Computational Study of the Factors Controlling Enantioselectivity in Ruthenium(II) Hydrogenation Catalysts
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- 作者：Devis Di Tommaso ; Samuel A. French ; Antonio Zanotti-Gerosa ; Fred Hancock ; Erika J. Palin ; C. Richard A. Catlow
- 刊名：Inorganic Chemistry
- 出版年：2008
- 出版时间：April 7, 2008
- 年：2008
- 卷：47
- 期：7
- 页码：2674 - 2687
- 全文大小：6170K
- 年卷期：v.47,no.7(April 7, 2008)
- ISSN：1520-510X
文摘
The reduction of prochiral ketones catalyzed by Ru(diphosphine)(diamine) complexes has been studied at the DFT-PBE level of theory. Calculations have been conducted on real size systems [trans-Ru(H)2(S,S-dpen)(S-xylbinap) + acetophenone], [trans-Ru(H)2(S,S-dpen)(S-tolbinap) + acetophenone] and [trans-Ru(H)2(S,S-dpen)(S-xylbinap) + cyclohexyl methyl ketone] with the aim of identifying the factors controlling the enantioselectivity in Ru(diphosphine)(diamine) catalysts. The high enantiomeric excess (99%) in the hydrogenation of acetophenone catalyzed by trans-Ru(H)2(S,S-dpen)(S-xylbinap) has been explained in terms of the existence of a stable intermediate along the reaction pathway associated with the (R)-alcohol. The formation of this intermediate is hindered with the competitive pathways, which consequently increases the activation energy for the hydrogen transfer acetophenone/(S)-phenylethanol reaction. For the [trans-Ru(H)2(S,S-dpen)(S-tolbinap) + acetophenone] system, the lower enantioselectivity (i.e. 80%) is rationalized by the smaller differences in the activation energy between the competitive pathways which differentiate between the two diastereomeric approaches of the prochiral ketone. The DFT-PBE results suggest that this reaction is driven to the (R)-product only by the process of binding the acetophenone to the active site of the trans-Ru(H)2(S,S-dpen)(S-tolbinap) catalyst. For the hydrogenation of cyclohexyl methyl ketone catalyzed by trans-Ru(H)2(S,S-dpen)(S-xylbinap), the low performance in the enantioselective hydrogenation of the dialkyl ketone (i.e. 37%) is again explained by the small differences in the activation and binding energies which are the factors which could effectively differentiate between the two alkyl groups.