Kinetics and Mechanism of Ruthenacycle-Catalyzed Asymmetric Hydrogen Transfer

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• 作者：Nicolas Pannetier ; Jean-Baptiste Sortais ; Pape Sylla Dieng ; Laurent Barloy ; Claude Sirlin ; Michel Pfeffer
• 刊名：Organometallics
• 出版年：2008
• 出版时间：November 24, 2008
• 年：2008
• 卷：27
• 期：22
• 页码：5852-5859
• 全文大小：255K
• 年卷期：v.27,no.22(November 24, 2008)
• ISSN：1520-6041

文摘

The mechanism of asymmetric hydrogen transfer catalyzed by a ruthenacycle has been studied. Ruthenium-hydride intermediates have been characterized by ¹H NMR and IR. These hydride complexes appeared as a diastereomeric mixture (de = 64%) responsible for the enantiomeric excess of the hydrogen transfer reaction (ee = 60%). Kinetic measurements have been performed as a function of substrate concentration and temperature. Michaelis−Menten kinetics were observed indicating substrate−catalyst complex formation (thermodynamic data for the complexation reaction: ΔG⁰ = −13 kJ mol⁻¹ at 273 K, ΔH⁰ = −58 kJ mol⁻¹, ΔS⁰ = −170 J K⁻¹ mol⁻¹). The complexation process is accomplished prior to an intracomplex chemical reaction. As the substrate is still bound to the catalyst, pericyclic hydrogen transfer is deduced with an activation energy E_a = 83 kJ mol⁻¹. On the basis of these data, a mechanism is proposed for the overall hydrogen transfer reaction.