Chiral eta(6)-arene/N-tosylethylenediamine-ruthenium(II) complexes: solution behavior and catalytic activity for asymmetric hydrogenation.
Aromatic ketones are enantioseletively hydrogenated in alcohols containing [RuX{(S,S)-Tsdpen}(eta(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.
Sandoval
Christian A
CA
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Linging Rd, Shanghai 200032, PR China. sandoval@mail.sioc.ac.cn
Bie
Fusheng
F
Matsuoka
Aki
A
Yamaguchi
Yoshiki
Y
Naka
Hiroshi
H
Li
Yuehui
Y
Kato
Koichi
K
Utsumi
Noriyuki
N
Tsutsumi
Kunihiko
K
Ohkuma
Takeshi
T
Murata
Kunihiko
K
Noyori
Ryoji
R
D002384:Catalysis; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D005029:Ethylenediamines / Q000737:chemistry*; D006865:Hydrogenation; D007659:Ketones / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D012428:Ruthenium / Q000737:chemistry*; D013237:Stereoisomerism
D056831:Coordination Complexes; D005029:Ethylenediamines; D007659:Ketones; C031234:ethylenediamine; D012428:Ruthenium