The Preparation Of Magnetic Mesoporous Egg Yolk-shell Bifunctional Catalyst And Its Asymmetric Catalysis

In recent years,many magnetic functionalized catalysts have been reported in various catalytic reactions,and a large number of literature reviews have been conducted.Despite these tremendous achievements,the inherent defects of magnetic aggregation often lead to a reduction in catalytic efficiency.Especially in some enantioselective reactions,this magnetic aggregation will also have a negative effect on the delicate chiral catalytic microenvironment,thereby reducing the enantioselectivity.Fortunately,in the preparation of magnetic catalysts,some improved methods,such as the SiO2 coating method and the yolk-shell structured magnetic catalyst,overcome the shortcomings of magnetic aggregation,and the surface has rich silicon hydroxyl groups to facilitate the modification of functional groups.Some enantioselective reactions with higher enantioselectivity can be overcome.However,its application in multi-step tandem enantioselective organic conversion is less explored.Therefore,taking advantage of superparamagnetic materials,it is very desirable to rationally design dual-functional catalysts for series reactions.In this paper,the magnetic core material with egg core-type structure is used as a carrier.It is expected to use its structural characteristics to load the two catalysts on the inner core and the outer shell,so that the different active centers of the catalyst can be separated,and the interaction between the two catalysts Influence,improve the performance of the catalyst.The main research content is divided into the following two parts:?1?By modifying the Pd/C catalytic center on the inner magnetic egg yolk and introducing a chiral diamine ruthenium catalyst into the nanochannel of the outer silicon shell,a magnetically recyclable bifunctional catalyst with an egg yolk shell structure was synthesized.The dual-functional catalyst exhibits good catalytic activity in the one-pot serial reaction of Suzuki coupling/asymmetric hydrogen transfer of iodoacetophenone and arylboronic acid,and can be reduced by a carbon-carbon double bond/asymmetric hydrogen transfer pair The styryl-substituted aromatic ketones undergo continuous reduction/asymmetric hydrogen transfer in a one-pot series reaction,providing a series of important chiral aryl alcohol compounds with a yield of up to 97%and a stereoselectivity of 99%.The catalyst can also be easily recovered and reused nine times with an external magnet,and there is no significant change in catalytic activity.?2?Magnetic nanoparticles Fe₃O₄@SiO₂were synthesized by the improved St?ber method,and then using cetyltrimethylammonium bromide?CTAB?as a template agent,through 1,2-bis?triethoxysilyl?ethane?BTEE?and?R,R?-4-?trimethoxymethylsilane?ethylphenylsulfonyl-1,2-diphenyldiamine functional silicon source hydrolyzed and copolymerized under alkaline conditions,based on hydrothermal strategy Nano silicon spheres with magnetic double-layer egg yolk shell structure were synthesized.Then the chiral diamine ruthenium catalyst was introduced into the nanochannel of the outer silicon shell,and then 1,3-bis?2,6-di-isopropylphenyl?imidazole-2-gold?I?The tetrafluoroborate catalyst is supported on the material,and finally the magnetic double-layer egg yolk shell bifunctional catalyst is synthesized and successfully applied to the one-pot hydrolysis/asymmetric hydrogen transfer of phenylacetylene compounds to generate chiral aromatic alcohols In the series reaction.The experimental results show that in the whole series reaction system,the catalyst can not only catalyze the series reaction with a high yield of 99%and a stereoselectivity of 99%,but also can be used six times after the series reaction is completed,and still maintain Efficient catalytic activity.