Asymmetric Hydrogenation Of Ethyl Pyruvates And Aromatic Ketones Catalyzied By Supported Rhodium And Ruthenium Catalysts And Ruthenium Phosphine Complexes With Modifier Of Chiral Compounds

The asymmetric hydrogenation of prochiral ketones is an important field in a variety of chemical processes for the synthesis of pharmaceuticals and fine chemical. It has become one of the most attractive field. Because of the inherent practical advantages of heterogeneous catalysis connected with the easy separation and handling, therefore, its investigation has received more and more attention in the recent years. The alumina supported rhodium catalysts which were stabilized by cinchonidine or quinine have been prepared with an improved method. The catalyst system using quinine (QN) or cinchonidine (CD) as chiral modifier exhibited excellent performance in the asymmetric hydrogenation of ethyl pyruvate. QN was a better chiral inducing reagent than that CD. The e.e. value of products in ethyl pyruvate hydrogenation was 5-6% higher for QN than that for CD and could reach 71.6% e.e. It was possible that the steric effect of methoxy group in QN exerted a favorable influence on the transition state of R-configuration. The studies showed that chiral modifier has not only a good enantiodifferentiating ability but also a considerable accelerating effect for the reaction. The PVP stabilized rhodium catalysts supported on alumina were prepared by hydrogen reduction in aqueous solution. The copolymers (MA-CD or MA-QN) of CD or QN and methyl acrylate were synthesized. When they were used as chiral modifier in the asymmetric hydrogenation of ethyl pyruvate, the catalyst 0.5%Rh/10PVP-γ-Al2O3 showed a good catalytic activity and enantiodifferentiating ability. The results indicated that MA-CD or MA-QN was the better chiral inducing reagent than that CD or QN. TOF value achieved 2060h-1 at 10℃. The e.e. value of R-ethyl lactate was about 72% under the optimized conditions. Alumina supported ruthenium catalysts (Ru/γ-Al2O3) , which were stabilized by phosphine ligands, were prepared under milder reduction conditions. The asymmetric hydrogenation of aromatic ketones and five-number heterocyclic ketones catalyzed by Ru/γ-Al2O3, which was modified with chiral reagent (1S, 2S)-(-)-1,2-diphenyl-1,2-ethylenediamine ((S,S)-DPEN) or L-proline, was investigated. The results indicated that the TPP stabilized rhodium catalysts (Ru/2TPP-γ-Al2O3) exhibited high catalytic activity and enantioselectivity. When (S, S)-DPEN is used as chiral modifider, the e.e. value of (R) –α-aromatic alcohols produced from acetophenone and its derivatives hydrogenation could reach 79.5 %～85.0 % under the reaction conditions: 10 oC～20 oC, PH2=5.0 MPa in KOH/i-PrOH solution. The e.e. value of the hydrogenation product of 2-acetothiophene was 86.2 % at 20 ℃and PH2=7 Mpa. The e.e. value of (S)-α-phenylethanol and (S)-α-phenylpropyl alcohol could achieve 59.5% and 72% when L-proline was used as chiral modifider, respectively. At the same time, the synergistic effect between (1S,2S)―DPENDS or L-proline and KOH was observed again, which significantly accelerated the reaction rate and enhanced the enantioselectivity. The catalyst was easily separated from the product and could bereused several times without obvious change of enantioselectivity. The water-soluble ruthenium phosphine complexes, (S, S)-1,2-diphenyl-1,2-ethylene diamine sulfonate disodium ((1S, 2S)-DPENDS) and a series hydrophilic ionic liquids [RMIM]+[p-CH3C6H4SO3]-( R=ethyl, butyl, octyl, dodecyl ) were synthesized. The asymmetric hydrogenation of aromatic ketones catalyzed by the ruthenium phosphine complexes modified with chiral ligand (1S, 2S)-DPENDS) was investigated in aqueous/organic and ionic liquid/oil biphasic catalytic system, respectively. The results showed that the influence of (1S, 2S)-DPENDS and KOH concentration on the asymmetric hydrogenation of acetophenone was very significant. In ionic liquid/oil biphasic catalytic system, the conversion of acetophenone was only 1.1% and e.e. value was zero in the absence of (1S, 2S)-DPENDS. If there was no addition of KOH into the reaction solution in the presence of (1S, 2S)-DPENDS, the conversion was only 0.6 %. When the concentrations of (1S, 2S)-DPENDS and KOH were 4.8×10-2 mol/L and 0.36 mol/L, the conversion and e.e. value could achieve 100% and 79.2%, respectively. The results suggested that the combination of chiral diamine and KOH was an essential factor for the formation of a chiral induction microcircumstance and the active catalytic species. The synergistic effect between (1S,2S)―DPENDS and KOH significantly accelerated the reaction rate and enhanced the enantioselectivity. The products were conveniently separated with decantation, both the ruthenium catalyst and (1S, 2S)-DPENDS were kept in the aqueous phase or ionic liquids phase and could be reused.