Application Of Metal-Organic Framework To The Preparation Of Chiral Amines By Dynamic Kinetic Resolution

How to efficiently and selectively obtain chiral optically pure amine has always been a hot and difficult research topic.Among them,dynamic kinetic resolution(DKR)is one of the common methods for the preparation of chiral amines.The chemical racemization catalyst and the biocatalyst are coupled in reaction system,which has the advantages of theoretical yield 100%and ease of separation after the application.Recent studies have found that the catalytic efficiency of chemical racemization catalysts could not match with the high efficiency of biocatalysts,so the focus of the research was on how to improve the efficiency of catalysts.The morphology and size uniformity of traditional supported materials were poor,and the supported noble metal nanoparticles were prone to agglomeration and oxidation,selective leaching,and had poor dispersibility.In addition,slow molecular diffusion rate led to the low catalytic efficiency.Therefore,developing a carrier with a high loading capacity that prevented noble metal nanoparticles aggregation and accelerated the diffusion and mass transfer of substrate molecules is the key.Metal-organic frameworks(MOFs),as a new type of microporous hybrid crystal materials,has tunable pore structure,chemical stability,and other characteristics,which are suitable carriers for noble metal nanoparticles.Among them,hollow core-shell MOFs had the advantages of high porosity,and fast mass transfer ability,showing great potential in improving catalytic activity and selectivity.In this paper,hollow core-shell MOFs were developed as carriers of noble metal nanoparticles to solve the problems of easy agglomeration and oxidation of nanoparticles.Hollow amorphous MOFs were developed as common carriers loaded with enzymes and noble metal nanoparticles to solve the problems of the long mass transfer distance of molecules.Core-shell MOFs nanocatalyst with a hollow structure and stable shell was developed.Firstly,MIL-101 was synthesized by hydrothermal method,and hollow mesoporous MIL-101(HM-MIL)was formed by etching with acetic acid.Using HMMIL as a carrier for palladium nanoparticles(Pd NPs)to synthetize HM-MIL@Pd.Proposing a facile HM-MIL-template strategy that ZIF-8 shells overgrew uniform on hollow MIL-101@Pd to synthetize HM-MIL@Pd@ZIF-8-30min.The crystal combination of ZIF-8 and HM-MIL was proved successful by X-ray diffraction and infrared spectroscopy.The core-shell HM-MIL@Pd@ZIF-8-30min material exhibited a hierarchical porous structure by using transmission electron microscopy,thermogravimetric analysis,and specific surface area analyzer.It was found that the thickness and roughness of ZIF-8 crystal deposition increased with the prolongation of ZIF-8 modification time further through transmission electron microscopy characterization test.The DKR system for catalyzing 1-phenylethylamine was successfully constructed.First,the catalytic activity of the HM-MIL@Pd@ZIF-8-30min catalyst in the racemzation reaction was evaluated by using(S)-1-phenethylamine as the substrate.The results showed that compared with unmodified HM-MIL@Pd and solid MIL101(Cr)@Pd@ZIF-8(S-MIL@Pd@ZIF-8),HM-MIL@Pd@ZIF-8-30min had higher racemization activity,conv.50%and eeamine 2%.Second,the DKR reaction of 1phenethylamine was catalyzed by HM-MIL@Pd@ZIF-8-30min with Novozym 435,using 4-chlorophenylvalerate as the acyl donor,obtaining excellent conversion 99%and SelR-amide 94%.In addition,the catalyst exhibited excellent stability,with conversion and selectivity reaching 95%and 93%after ten catalytic cycles.Through density functional theory and computer simulation study,it was found that ZIF-8 had better adsorption of imines than HM-MIL,promoting the hydrogenation of imines on the surface of Pd(111)and reducing side reactions.According to the calculation results of the Pd(111)surface racemization reaction,it was further indicated that the endothermic reaction required a higher temperature,and the adsorption stability of the catalyst to the intermediate imine played a more critical role in the reaction process.Hollow amorphous ZIF-90(HamZIF-90)as the carrier,a combination catalyst loaded with noble metal nanoparticles and lipase was constructed and applied to the dynamic kinetic resolution of chiral amines.Firstly,melamine and salicylic acid were used as the hydrogel template of zinc,combined with organic ligands,and the hydrogel was removed at a high temperature to obtain HamZIF-90.The Pd NPs and lipase were co-immobilized on the carrier to prepare HamZIF-90@Pd@CalB catalyst.The successful synthesis of the amorphous hollow structure material was confirmed by diverse characterization.Its catalytic activity was tested with 1-phenylethylamine and 4-chlorophenylvalerate as substrates,and the consequence show that the conversion 98%and SelR-amide 93%.In addition,the catalytic efficiency of the HamZIF-90@Pd@CalB catalyst was higher than ZIF-90@Pd@CalB,due to the hollow structure of HamZIF-90.