The Hydrogenation/Transfer Hydrogenation Network in Asymmetric Reduction of Ketones Catalyzed by [RuCl2(binap)(pica)] Complexes |
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| Authors: | Christian A. Sandoval Prof. Dr. Yuehui Li Kuiling Ding Prof. Dr. Ryoji Noyori Prof. Dr. |
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| Affiliation: | 1. Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032 (China), Fax: (+86)?21‐5492‐5480;2. Department of Chemistry and Research Center for Materials Science, Nagoya University, Chikusa, Nagoya 464‐8602 (Japan), Fax: (+81)?52‐783‐4177 |
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| Abstract: | Chiral binap/pica‐RuII complexes (binap=(S)‐ or (R)‐2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl; pica=α‐picolylamine) catalyze both asymmetric hydrogenation (AH) of ketones using H2 and asymmetric transfer hydrogenation (ATH) using non‐tertiary alcohols under basic conditions. The AH and ATH catalytic cycles are linked by the metal–ligand bifunctional mechanism. Asymmetric reduction of pinacolone is best achieved in ethanol containing the Ru catalyst and base under an H2 atmosphere at ambient temperature, giving the chiral alcohol in 97–98 % ee. The reaction utilizes only H2 as a hydride source with alcohol acting as a proton source. On the other hand, asymmetric reduction of acetophenone is attained with both H2 (ambient temperature) and 2‐propanol (>60 °C) with relatively low enantioselectivity. The degree of contribution of the AH and ATH cycles is highly dependent on the ketone substrates, solvent, and reaction parameters (H2 pressure, temperature, basicity, substrate concentration, H/D difference, etc.). |
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| Keywords: | asymmetric catalysis homogeneous catalysis hydrogenation reaction mechanisms ruthenium |
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