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Chiral η 6 ‐Arene/ N ‐Tosylethylenediamine–Ruthenium(II) Complexes: Solution Behavior and Catalytic Activity for Asymmetric Hydrogenation
Author(s) -
Sandoval Christian A.,
Bie Fusheng,
Matsuoka Aki,
Yamaguchi Yoshiki,
Naka Hiroshi,
Li Yuehui,
Kato Koichi,
Utsumi Noriyuki,
Tsutsumi Kunihiko,
Ohkuma Takeshi,
Murata Kunihiko,
Noyori Ryoji
Publication year - 2010
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.200900461
Subject(s) - ruthenium , catalysis , asymmetric hydrogenation , noyori asymmetric hydrogenation , chemistry , medicinal chemistry , enantioselective synthesis , organic chemistry
Aromatic ketones are enantioseletively hydrogenated in alcohols containing [RuX{( S,S )‐Tsdpen}(η 6 ‐ p ‐cymene)] (Tsdpen=TsNCH(C 6 H 5 )CH(C 6 H 5 )NH 2 ; 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 ( 1 H‐ 1 H DQF‐COSY, 1 H‐ 13 C HMQC, 1 H‐ 15 N HSQC, and 1 H‐ 19 F 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 NH 2 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 CD 3 OD reflect the independent motion of [Ru + (Tsdpen)(cymene)] and TfO − . In CDCl 3 , 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 CH 3 OH 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.