Chiral η6‐Arene/N‐Tosylethylenediamine–Ruthenium(II) Complexes: Solution Behavior and Catalytic Activity for Asymmetric Hydrogenation |
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| Authors: | Christian?A Sandoval Dr Fusheng Bie Aki Matsuoka Yoshiki Yamaguchi Dr Hiroshi Naka Prof?Dr Yuehui Li Koichi Kato Prof?Dr Noriyuki Utsumi Kunihiko Tsutsumi Takeshi Ohkuma Prof?Dr Kunihiko Murata Dr Ryoji Noyori Prof?Dr |
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| Institution: | 1. Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Linging Rd, Shanghai 200032 (P.R. China), Fax: (+86)?21‐6416‐6128;2. Department of Chemistry, Shanghai University, Shanghai 200444 (P.R. China);3. Department of Chemistry and Research Center for Materials Science, Nagoya University, Chikusa, Nagoya 464‐8602 (Japan), Fax: (+81)?52‐783‐4177;4. Graduate School of Pharmaceutical Sciences, Nagoya City University, Mizuho, Nagoya 467‐8603 (Japan);5. Central Research Laboratory, Technology and Development Division, Kanto Chemicals Co., Inc. Soka, Saitama 340‐0003 (Japan);6. Division of Chemical Process Engineering, Graduate School of Engineering, Hokkaido University, Sapporo 060‐8628 (Japan) |
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| Abstract: | Aromatic ketones are enantioseletively hydrogenated in alcohols containing RuX{(S,S)‐Tsdpen}(η6‐p‐cymene)] (Tsdpen=TsNCH(C6H5)CH(C6H5)NH2; X=TfO, Cl) as precatalysts. The corresponding Ru hydride (X=H) acts as a reducing species. The solution structures and complete spectral assignment of these complexes have been determined using 2D NMR (1H‐1H DQF‐COSY, 1H‐13C HMQC, 1H‐15N HSQC, and 1H‐19F HOESY). Depending on the nature of the solvents and conditions, the precatalysts exist as a covalently bound complex, tight ion pair of Ru+(Tsdpen)(cymene)] and X?, solvent‐separated ion pair, or discrete free ions. Solvent effects on the NH2 chemical shifts of the Ru complexes and the hydrodynamic radius and volume of the Ru+ and TfO? ions elucidate the process of precatalyst activation for hydrogenation. Most notably, the Ru triflate possessing a high ionizability, substantiated by cyclic voltammetry, exists in alcoholic solvents largely as a solvent‐separated ion pair and/or free ions. Accordingly, its diffusion‐derived data in CD3OD reflect the independent motion of Ru+(Tsdpen)(cymene)] and TfO?. In CDCl3, the complex largely retains the covalent structure showing similar diffusion data for the cation and anion. The Ru triflate and chloride show similar but distinct solution behavior in various solvents. Conductivity measurements and catalytic behavior demonstrate that both complexes ionize in CH3OH to generate a common Ru+(Tsdpen)(cymene)] and X?, although the extent is significantly greater for X=TfO?. The activation of RuX(Tsdpen)(cymene)] during catalytic hydrogenation in alcoholic solvent occurs by simple ionization to generate Ru+(Tsdpen)(cymene)]. The catalytic activity is thus significantly influenced by the reaction conditions. |
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| Keywords: | asymmetric hydrogenation asymmetric transfer hydrogenation diffusion constants NMR spectroscopy ruthenium |
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