Design of Heterogeneous Catalysts for Selective Asymmetric Hydrogenation

1. (E)- α -苯基肉桂酸在cinchonidine修饰Pd催化剂上的不对称加氢反应(1)研究了催化剂制备方法、载体和预还原对负载型Pd催化剂活性和对映选择性的影响。在473K左右预还原的钛载体催化剂效果最好。(2)改性剂和底物在Pd上的吸附量受到载体的强烈影响，表明改性剂的表面浓度对于获得高对映选择性的重要性。具有相当数量的酸性和碱性位点且具有中等比表面积的载体是优选的。(3)钯的分散性和钯上的余氯影响催化剂的对映选择性。(4)极性溶剂。与在金鸡纳生物碱修饰的Pt催化剂上进行α -酮酯的加氢反应相比，较低的氢压力和较低的底物浓度更适合该反应。(5)在最佳反应条件下，以5%的pdtio_2为催化剂，烯烃对映选择性加氢反应的光学产率最高，达到72%。(1)光产率的转换依赖关系表明了底物与改性剂在Pd表面吸附平衡的重要性。(2)基于反应条件影响的动力学研究以及底物和改性剂结构影响的研究目前正在进行中，以解释该反应的机理。

1. Asymmetric hydrogenation of (E)-alpha-phenylcinnamic acid on cinchonidine-modified Pd catalysts(1) The effects of the catalyst preparation method, supports, and the pre-reduction on the activity and enantioselectivity of supported Pd catalysts have been investigated. A titania-supported catalyst pre-reduced at around 473K was found most effective.(2) The amounts of the modifier and the substrate adsorbed on Pd are strongly influenced by the support employed, indicating the importance of the surface concentration of the modifier for obraining a high enantioselectivity. A support having appreciable amounts of both acidic and basic sites with a moderate specific surface area is preferable.(3) The Pd dispersion and the residual chlorine on Pd affect the enantioselectivity of the catalyst.(4) Polar solvents. lower hydrogen pressures, and lower substrate concentrations are preferable for this reaction, in contrast with the hydrogenation of alpha-ketoesters on cinchona alkaloid-modified Pt catalysts.(5) The highest optical yield of 72%ee in the enantioselective hydrogenation of alkenes with heterogeneous catalysts, was obtained with a 5%PdTiO_2 catalyst under optimal reaction conditions.2. Studies on the reaction mechanism(1) The conversion dependencies of optical yields showed the importance of adsorption equilibrium between the substrate and the modifier on Pd surface.(2) Kinetic studies based on the effects of reaction conditions and studies of the effects of the structures of the substrate and the omdifier are now currently underway to interpret the mechanism of this reaction.