Abstract
Platinum nanoparticles(Pt NPs)were easily prepared in imidazolium-based ionic liquids by simple H2 reduction of PtO2 in the presence of cinchona alkaloid stabilizers.TEM showed that well-dispersed Pt NPs of about 1.78 nm were obtained.With the modification of cinchona alkaloids,the Pt NPs catalysts exhibited excellent activity and enantioselectivity in the asymmetric hydrogenation ofα-ketoesters.With the stabilization and modification of cinconidine,the ethyl pyruvate asymmetric hydrogenation could reach up to 4640 h^-1 TOF,and the ee value ofα-ketoesters heterogeneous enantioselective hydrogenation could reach 70.0%~80.1%.Studies showed that the characteristics of the chiral center,conformation as well as steric hindrance of the stabilizer and/or the modifier synergistically affected the asymmetric catalytic performance.The combination of BMIMPF6 and acetic acid solvents was also necessary for achieving high activity and enantioselectivity.Catalysts can be reused several times without significiant loss of activity and enantioselectivity.
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