Asymmetric Hydrogenation Of Acetophenone And Derivatives Catalyzed By Nickel Phosphine Complex And Supported Iridium Catalysts With Modifier Of Chiral Diamine

The asymmetric hydrogenation of carbonyl compounds is an important field for the pharmaceuticals and fine chemicals. The asymmetric hydrogenation include homogeneous and heterogeneous catalysis. Two catalytic systems were well developed because of their own merits. The development of excellent catalysts easily prepared has received more attention.The catalytic performance of NiCl₂(PPh₃)₂ modified with (S,S)-1,2-diphenylethylenediamine(DPEN) has been investigated in the asymmetric hydrogenation of acetophenone and its derivatives. The effects of reaction temperature, hydrogen pressure, concentration of (S,S)-DPEN and KOH on the activity and enantioselectivity have been studied in detailed. Under the optimum conditions: 15℃, 8.0MPa, (S,S)-DPEN 1.7×10^-2 mol/L and KOH 0.51mol/L, ethanol as solvent, the conversion of acetophenone and the e.e. value of (R)-phenylethanol were 98.1% and 77.2%, respectively. The chiral diamine not only improves the enantioselectivity but also accelerates the reaction rate.The supported iridium catalysts have been prepared and exhibited good catalytic activity and enantioselectivity for the asymmetric hydrogenation of acetophenone and its derivatives in the pressure of chiral modified (S,S)-DPEN, especially, Ir/γ-Al₂O₃-2TPP and Ir/SiO₂-2TPP. In this paper, the reaction parameters and different phosphines as stabilizer have been investigated. Under the optimum conditions, the 57.6% and 69.0% e.e. were observed in the asymmetric hydrogenation of acetophenone catalyzed by catalysts Ir/γ-Al₂O₃-2TPP and Ir/SiO₂-2TPP, respectively. The e.e. value of (S)-2-hydroxyphenylethanol was 77.2% catalyzed by Ir/SiO₂-2TPP in asymmetric hydrogenation of 2-hrdorxyacetophenone. After six times of recycle, the enantioselectivity of catalyst didn't decrease obviously.