介孔载体负载Pt催化剂上α-酮酸酯的不对称氢化

Enantioselective Hydrogenation of α-Ketoesters on Mesoporous Matrix Supported Platinum Catalysts

以介孔材料SBA-15、经或未经Al2O3修饰的具有三维立方孔道结构的SiO2为载体,制备了负载型Pt催化剂,并用于催化α-酮酸酯底物2-氧代-4-苯基-丁酸乙酯(EOPB)和丙酮酸乙酯(Etpy)的不对称氢化反应中.结果表明,当SBA-15孔径由6.2,7.6和9.2nm依次增加时,EOPB不对称氢化的活性和手性选择性有所提高,氢化ee值分别为22.0%,36.0%和50.0%.两类拥有三维立方孔道结构的SiO2载体负载的Pt催化剂性能明显优于SBA-15负载的,表明传质或空间位阻因素对EOPB不对称氢化的手性选择性和反应活性影响很大.以Al2O3修饰的介孔硅为载体时,相应的Pt催化剂上EOPB氢化手性选择性最高(ee79.3%),且具有高氢化活性;用于丙酮酸乙酯不对称氢化反应时,活性和手性选择性(ee值达90.2%以上)均较高.由此可见,Al2O3修饰的三维立方介孔硅结构的复合纳米材料是一种新型的多相手性催化剂载体,具有良好的应用前景.

The asymmetric hydrogenation of ethyl 2-oxo-4-phenyl-butyrate（EOPB） over the Pt catalysts modified by cinchonidine usingmesoporous SBA-15,cubic mesoporous silica,and Al2O3 modified cubic mesoporous silica as matrix was studied.The results showed that inthe channels of mesoporous SBA-15,the enantioselectivity and conversion are enhanced in larger sized channels compared to those of thehydrogenation in smaller sized channels.When the channel size of SBA-15 increases from 6.2 nm to 7.6 nm and to 9.2 nm,the hydrogenation ee is 22.0%,36.0%,and 50.0%,respectively.The ee（53.8%） on the cubic mesoporous silica support is obviously higher than tha（36.0%） on the SBA-15 support with similar channel size,and the ee on the Al2O3 modified cubic mesoporous silica support reaches 79.3%These facts showed that the mass transfer or steric clash has important impacts on the enantioselectivity and conversion of the enantioselective hydrogenation of EOPB.In the enantioselective hydrogenation of ethyl pyruvate,the Al2O3-grafted cubic mesoporous silica supported Pcatalyst exhibits high activity and excellent enantioselectivity（ee over 90.2%）,which is comparable to that of the best commercial Pt/Al2O catalysts.The high catalytic performance is attributed not only to the developed cubic channel structure of the Pt catalyst support,but also tothe enhancement of the interaction of Pt nanoparticles and the Al2O3-grafted support,which would improve the modification of cinchonidineon the surface of Pt particles.These indicate that the Al2O3 modified cubic mesoporous silica is a novel,promising support material for theheterogeneous chiral catalysis.