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Rhodium nanoparticles (Rh NPs) stabilized by natural cinchona alkaloids were synthesized in imidazolium-based ionic liquids using H2 as the reductant. Characterization showed well-dispersed Rh NPs of about 1.96 nm (TEM and HRTEM) and confirmed the ionic liquid and cinchona alkaloid stabilization to the Rh(0) NPs (XPS). When modified by chiral diamine, including (1R,2R)-diphenylethylenediamine ((1R,2R)-DPEN) or cinchona alkaloid derivatives, the Rh NPs catalysts exhibited good activity, chemoselectivity and enantioselectivity in the heterogeneous enantioselective hydrogenation of aromatic ketones. Synergistic effect between (1R,2R)-DPEN and cinchonidine was also observed, which significantly accelerated the reaction rate and enhanced the enantioselectivity. 63.0% enantioselectivity and 98.9% chemoselectivity could be achieved in the acetophenone enantioselective hydrogenation; up to 70.2% enantioselectivity and 100% chemoselectivity was obtained in the isobutyrylbenzene catalytic enantioselective hydrogenation. Catalytic system could be reused several times without significant loss in activity, chemoselectivity as well as enantioselectivity. This catalytic protocol opens the door to heterogeneous enantioselective hydrogenation of aromatic ketones with metal Rh NPs immobilized in ionic liquid.

Nickel nanoparticles (Ni NPs) were conveniently synthesized from the reduction of nickel(II) salt with NaBH4 or hydrazine in the presence of the ionic liquid 1-butyl-2,3-dimethylimidazolium (S)-2-pyrrolidinecarboxylic acid salt. UV/Vis spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy were employed to characterize the interaction between the metal and the ionic liquid. The face-centered cubic structure of the Ni NPs(0) was confirmed by X-ray diffraction characterization. Transmission electron microscopy images revealed well-dispersed Ni particles of approximately 5.1 nm in average diameter. The ionic liquid immobilized Ni NPs were employed as highly efficient catalysts in chemoselective hydrogenation of quinoline and relevant compounds, as well as aromatic nitro compounds under mild reaction conditions. The Ni NPs can be efficiently recovered and reused.

The heterogeneous enantioselective hydrogenation of α-ketoesters catalyzed by rhodium nanoparticles (Rh NPs) in ionic liquid was studied with the stabilization and modification of cinchona alkaloids. TEM characterization showed that well-dispersed Rh NPs of about 1.96 nm were obtained in ionic liquid. The results showed that cinchona alkaloids not only had good enantiodifferentiating ability but also accelerated the catalytic reaction. Under the optimum reaction conditions, the enantiomeric excess in ethyl benzoylformate hydrogenation could reach as high as 60.9%.

In this communication, we describe the highly enantioselective heterogeneous hydrogenation of aromatic ketones catalyzed by Ph3P stabilized Ru/γ-Al2O3, and modified by chiral diamines derived from cinchona alkaloids. A broad range of aromatic ketones over this catalyst can be hydrogenated to the corresponding alcohols with impressive enantioselectivity.

A series of silica (SiO 2 ) supported iridium catalysts stabilized by cinchona alkaloids was prepared and applied in the heterogeneous asymmetric hydrogenation of acetophenone. Cinchona alkaloids exhibited a marked ability to stabilize and disperse the Ir particles. In the presence of (1 S ,2 S )-diphenylethylenediamine ((1 S ,2 S )-DPEN)) as chiral modifier, the cinchonidine (CD) stabilized catalyst 5%Ir/2CD-SiO 2 exhibited excellent catalytic performance in the asymmetric hydrogenation of acetophenone in MeOH. Under the optimum conditions, the ee value of ( R )-phenylethanol achieved 79.8% and no other product was produced, a higher enantioselectivity than that reported up to now for acetophenone hydrogenation catalyzed by the supported metal catalysts modified by chiral reagents. In particular, a synergistic effect between (1 S ,2 S )-DPEN and CD was observed, which significantly accelerated the reaction rate and enhanced the enantioselectivity. The catalyst can be reused several times without a significant loss of activity and enantioselectivity.

Chiral imidazole hydrolytic metalloenzyme models with characteristics of chiral centers directly link to imidazole N-atoms and varieties in both alkyl chain length and number of alkyl chains, have been synthesised and investigated for enantioselective hydrolysis of Boc-α-amino acid esters. The result indicates that both hydrolysis rates and enantioselectivities are increased with increases in the alkyl chain length and the number of the alkyl chains in the lipophilic chiral imidazole-type surfactants in many cases. The lipophilic chiral imidazole 4d (( S )-1-hexadecoxy-2-(1-imidazolyl)-propane), which has one long alkyl chain, shows higher hydrolysis rate and enantioselectivity ( k D = 132.5 × 10 −5 , k D / k L = 5.38), 5d (( S )-1,5-dihexadecoxy-2-(1-imidazolyl)-pentane), which has two long alkyl chains, shows the highest hydrolysis rate and enantioselectivity ( k D = 201.5 × 10 −5 , k D / k L = 11.72). Additionally, the effects of the metals, the additives, the solvents and the substrates on the hydrolysis rates and enantioselectivities are examined.