Design And Syntheses Of Metal-Organic Frameworks N-Heterocyclic Olefins Single-site Catalysts For CO₂ Conversions

The rapid increase in atmospheric CO₂ concentrations threatens human society,the natural environment and the synergies between the two.In order to improve the CO₂ problem from an environmental,legal and social point of view,the capture,activation and chemical conversion of CO₂ has attracted a great deal of attention in the last decades.CO₂ is a thermodynamically and kinetically stable molecule and there has been widespread interest in"taming"CO₂ into a potential alternative C1 source of fossil energy for the synthesis of high value-added compounds.（a）The palladium-catalyzed multi-component reaction of propargylamines,aryl iodides and CO₂ to form functionalised 2-oxazolidinone heterocycles is an industrially essential reaction.However,it has only been reported in homogeneous catalytic systems.A single-site metal palladium trifunctional catalyst（MOF-a NHO-Pd）was prepared by introducing NHO ligand site bonding on a classical MOF,and its structure and composition were characterised in detail by PXRD,NMR,XPS,SEM,HR-TEM,AC-TEM,XFAS and other techniques to investigate the role of MOF-a NHO-Pd in catalyzing the production of functionalised 2-oxazolidinones from propargylamines,aryl iodides and CO₂.The catalytic performance of MOF-a NHO-Pd in the preparation of functionalized 2-oxazolidinone heterocyclic compounds catalyzed by propargylamine,aryl iodide and CO₂ was investigated.MOF-a NHO-Pd was found to synergistically enhance its catalytic activity in CO₂ adsorption,activation and catalytic conversion,achieving a turnover frequency（TOF）of up to 148.8 h^-1,which is a significant advantage over reported homogeneous and non-homogeneous catalysts(<10 h^-1).Importantly,this is the first example of a non-homogeneous MOF-a NHO-Pd single-site catalyst used to catalyse a multicomponent reaction of propargylamines,aryl iodides and CO₂.（b）Metal heterocyclic olefins（M-NHO）on the pore wall of metal organic frameworks（MOF）can be used as active sites for efficient organocatalysis.However,conventional methods requiring the addition of strong bases or insoluble Ag₂O are not suitable for the introduction of metallic palladium on MOF-NHOs,as these reagents would destroy its host framework.Here,we prepared active M-NHO unit-site metallic palladium catalysts（Ui O-66-NHO-Pd）with covalent bond linkages by post-synthetic modification techniques and the use of soluble Pd（OAc）₂ as a palladium source.It was also characterised in detail by PXRD,FT-IR,XPS,TEM,HAADF-STEM and XFAS techniques.The performance of Ui O-66-NHO-Pd in the adsorption,activation and catalytic conversion of three-component CO₂ to 2-oxazolidinones reaction was investigated.the TOF was up to 735 h^-1 and the catalytic mechanism of the three-component cycloaddition reaction was proposed.（c）Two-component reactions of propargylamines and CO₂ can effectively reduce the release of CO₂ and provide many high value-added chemical products.However,most catalysts in such reactions are associated with noble metals to obtain high yields.Therefore,the search for noble metal-free catalysts for MOFs is essential and important.Therefore,we prepared active M-NHO unit-site metal-copper catalysts with covalent bond linkages（Ui O-66-NHOs-Cu）by post-synthetic modification techniques and the use of soluble Cu Cl as a copper source.It was also characterised in detail using PXRD,FT-IR,XPS,TEM,HAADF-STEM and XFAS techniques.The performance of Ui O-66-NHOs-Cu in the reaction of two-component CO₂ adsorption,activation and catalytic conversion to 2-oxazolidinones was investigated.Mechanistic studies showed that Ui O-66-NHOs-Cu can synergistically activate the substrate with the base work,and Ui O-66-NHOs-Cu can obtain TOF values up to 1548 h^-1 when simulated flue gas is used as the CO₂ source.