Multifunctional Immobilized Catalyst Based On Metal-Organic Framework For Synthesis Of Aryl-Oxazolidi Nones

Aryl-oxazolidinones are a kind of bioactive heterocyclic compounds,and widely applicable to many fields,such as medicine,pesticide,and weed control.Meanwhile,aryl-oxazolidinones are also a kind of important organic synthesis intermediates and play a key role in the total synthesis of natural products.However,the traditional synthetic methods of aryloxazolidinones usually regard highly toxic reactants like phosgene or phosgene-derived isocyanates as starting material.These synthetic methods seriously pollute the reactants,and the reaction conditions are very harsh.Among many new synthetic methods to obtain aryloxazolidinones,a more attractive one is to use carbon dioxide,epoxides,and anilines as raw materials,which is mainly divided into two synthetic routes.(1)Two-step method:carbon dioxide firstly reacts with epoxy compounds to prepare cyclic carbonates,then cyclic carbonates interact with aniline to synthesize aryl-oxazolidinones.(2)One-pot method:carbon dioxide,epoxy compounds,and aniline are simultaneously add to the reactor to directly synthesize aryl-oxazolidinones.Although the above two routes can obtain a good yield of aryloxazolidinones,all of them need two kinds of catalysts(ionic liquids and organic base)to participate in the reaction.As a result,the product separation process is complicated,and there is also the problem of difficulty in the recovery and reuse of the catalysts.It is an effective method that the active components of ionic liquids and organic base are immobilized on inorganic support to form a heterogeneous catalyst which used to synthesize aryloxazolidinones.At present,the carriers used for the immobilization of ionic liquids are mainly silicon dioxide,porous carbon materials and polymers.These carriers generally have problems such as few immobilization sites and single type of immobilized ionic liquid.NH2-MIL-101 is a metal-organic framework(MOF)material with a stable crystal structure,high area,and good hydrothermal stability.The amino group on the frame can be functionalized by the post-modification method to immobilize the ionic liquids,and the interaction of coordination bonds between the metal center coordination unsaturated site Cr(Ⅲ)and different organic bases to fix organic base.In this paper,NH2-MIL-101(Cr)was used as a carrier,the ionic liquids were in-situ synthesized and immobilized by "post-modification synthesis method"(PSM),meanwhile,the organic base is immobilized on NH2-MIL-101 by Cr(Ⅲ)coordinatively unsaturated metal sites(CUSs)to prepare different novel multifunctional immobilized catalysts.To improve the recyclability of the catalysts,NH2-MIL-101 carrier was grown on the surface of magnetic nanoFe3O4,then ionic liquids and organic base were immobilized simultaneously to prepare the magnetic multifunctional recoverable catalyst.The catalytic performance of the catalysts in the two-step and one-pot synthesis of aryl-oxazolidinones with carbon dioxide,propylene oxide,and aniline was systematically studied,and the structure-activity relationship between the catalyst structure and catalytic performance was discussed.The main findings are as follows:1.The carrier is based on NH2-MIL-101,the ionic liquids of 1-butyl-3methylimidazolium bromine(BmimBr)and 1-butyl-3-methylimidazolium acetate(BmimOAc)were respectively immobilized on it,denoted IL(Br-)-NH2-MIL-101 and IL(OAc-)-NH2-MIL101.The structure and physico-chemical properties of IL(Br-)-NH2-MIL-101 and IL(OAc-)NH2-MIL-101 were characterized by PXRD,SEM,FT-IR,DRS UV-Vis,nitrogen adsorptiondesorption,and elemental analysis.The results showed that BmimBr and BmimOAc were anchored in the NH2-MIL-101 skeleton via the acylamino group,which underwent a condensation reaction with N,N-dicarbonylimidazole(CDI)and the amino group on the carrier,which were confined in the nanocages.The catalyst IL(Br-)-NH2-MIL-101 can catalyze the cycloaddition reaction of carbon dioxide and propylene oxide to obtain propylene carbonate in high catalytic activity and yield.When the molar ratio of aniline,propylene carbonate,and catalyst IL(OAc-)-NH2-MIL-101 was 1:10:0.1,propylene carbonate and aniline reacted at 140℃ for 9 h,the yield of aryl-oxazolidinones was 92%.The catalysts exhibited good stability and recoverability after five cycles.Compared with the traditional synthesis methods,this synthesis method has mild reaction conditions,simple post-treatment,and the catalyst can be well recycled.2.The carrier is based on NH2-MIL-101,the ionic liquid of 1-butyl-3-methylimidazolium bromine(BmimBr)was anchored in the nanocages by post-modification synthesis method and the organic base of N,N-dimethylethylenediamine(DMEDA)was grafted on the carrier by NCr coordinate covalent bonds.Thus,a novel multifunctional immobilized catalyst with double catalytic activitice centers of ionic liquid and basic sites had been synthesized,denoted DMEDA/IL-NH2-MIL-101.The bulk structure and texture properties of DMEDA/IL-NH2MIL-101 were characterized by PXRD,SEM,FT-IR,nitrogen adsorption-desorption,and elemental analysis.The results showed that the ionic liquid of BmimBr was anchored to the NH2-MIL-101 skeleton by the acylamino group,and the organic base of DMEDA was immobilized in the NH2-MIL-101 framework by the N-Cr bond.Both active components were successfully synthesized and immobilized in the NH2-MIL-101 nanocages,and this conclusion was further proved by XPS and density functional theory(DFT)calculation.The catalyst DMEDA/IL-NH2-MIL-101 can effectively catalyze the one-pot synthesis of aryloxazolidinones with carbon dioxide,epoxide,and aniline in high catalytic activity and yield.Under 1.0 MPa carbon dioxide pressure,the molar ratio of aniline,propylene oxide,and catalyst DMEDA/IL-NH2-MIL-101 was 1:15:0.1,carbon dioxide,epoxide,and aniline reacted at 130℃ and sustained 10 h,the yield of aryl-oxazolidinones reached to 90%.The DMEDA/ILNH2-MIL-101 catalyst could be separated and reused after five runs,which exhibited good recyclability and stability.It was pointed out that the NH2-MIL-101 skeleton exhibited high carbon dioxide adsorption capacity,which can increase carbon dioxide concentration and accelerate the reaction even in the low pressure.3.The carrier is based on NH2-MIL-101 which was grown on the surface of superparamagnetic nano-Fe3O4 to prepare superparamagnetic Fe3O4@NH2-MIL-101 composite materials.Then the ionic liquid of 1-butyl-3-methylimidazolium bromine(BmimBr)was anchored in the nanocages by the post-modification synthesis method and the organic base of N,N-dimethylethylenediamine(DMEDA)was grafted on the carrier by N-Cr coordinate bonds.The obtained catalyst Fe3O4@DMEDA/IL-NH2-MIL-101 was characterized by a variety of characterization methods.The results showed that the dual active components of BmimBr and DMEDA were successfully synthesized and immobilized in the NH2-MIL-101 nanocages.The catalyst Fe3O4@DMEDA/IL-NH2-MIL-101 exhibited stable paramagnetism and good thermal stability,and can successfully catalyze the one-pot synthesis of aryl-oxazolidinones from carbon dioxide,epoxide,and aniline in high catalytic activity and yield.At a carbon dioxide pressure of 1.0 MPa,the molar ratio of aniline,propylene oxide,and catalyst Fe3O4@DMEDA/lL-NH2-MIL-101 was 1:15:0.1,carbon dioxide,epoxide,and aniline was reacted at 130℃ and sustained 10 h,the yield of aryl-oxazolidinones can reach to 88%.Besides,the catalyst can be efficiently recovered magnetically,and the reaction activity had not decreased significantly after repeated for five times.More importantly,the restricted microenvironment of the catalyst Fe3O4@DMEDA/IL-NH2-MIL-101 offered distinct sizeselective catalytic properties for the discrimination of reactants.