Preparation Of Magnetic Mesoporous Egg Yolk Core-shell Catalyst And Its Hydrolysis-reduction Tandem Catalytic Performance

In recent years,magnetic nanomaterials have been widely used in biomedical,catalytic and industrial fields due to their excellent magnetic response properties.Functional modification on the surface of magnetic nanoparticles can effectively reduce magnetic aggregation.For example,Si O₂-coated and yolk core-shell magnetic materials have abundant silica hydroxyl groups on the surface,which provides a basis for functional group modification and the application of magnetic materials.In this article,clear core-shell structure has been designed,good dispersion of egg yolk shell-nuclear magnetic material,through the internal cavity and core-shell surface metal catalyst solid loading respectively,obtained with the double active site of solid phase catalytic material,magnetic and explore the function of this series of dual core-shell materials in a pot of aromatic alkyne compounds series hydrolysis-reduction reaction of catalytic performance.The main research content is divided into the following two parts:（1）Hollow yolk core-shell nanospheres with vertical mesoporous channels and amphiphilic shells were prepared using monodisperse inorganic silica nanospheres as hard templates.The silicon-based materials were mercaptosilized by post grafting method,and chiral ruthenium/cyclohexanediamine compounds were grafted onto the outer surface of the core-shell by click reaction.1,3-bis（2,6-di-isopropylphenyl）imidoazole-2-gold（I）triflate（gold catalyst）was encapsulated in the cavity by the covalent bond between trifluoromethane and the hydroxyl group on the inner inorganic silicon material.Thus,a dual-function catalyst with hydrolytic activity in the cavity and reductive activity on the surface was obtained.The one-pot hydrolyzation-reduction series catalytic performance of catalyst for aromatic alkyne substrates was investigated.The results showed that catalyst had high catalytic activity（up to 98%yield）and enantioselectivity（up to 99%ee）,which could overcome the incompatibility of ruthenium-gold bimetallic compounds in homogeneous systems.（2）Synthesis based on non-magnetic catalysts,Fe₃O₄nanospheres coated with monodisperse silica were prepared by hydrothermal method,and a new type of yolk core-shell magnetic material was synthesized as a hard template.The surface of magnetic core-shell material was modified by post grafting method with thiol functional silicon source,and the chiral ruthenium/diamine catalyst was supported on the core-shell surface.Then,the gold catalyst was adsorbed to the inner magnetic core by decompression encapsulation strategy,and the gold catalyst was fixed under hydrogen bonding force,so as to obtain magnetic yolk core-shell functional mesoporous catalyst with double catalytic activity.The chiral ruthenium/gold bimetallic magnetic catalyst was characterized by XRD,SEM,TEM,¹³C NMR,²⁹Si NMR,BET,FT-IR and hysteresis loop.The catalytic yield and enantioselectivity of catalyst for the one-pot series hydrolysis-asymmetric hydrogen transfer reaction of aromatic alkynes were maintained to be equal to that of nonmagnetic catalyst.In particular,the stability and recoverability of the magnetic catalyst were investigated.The results showed that it could be completely recovered from the reaction solution by magnet adsorption,and still had a high enantioselectivity（95%ee）after 6 cycles.