Synthesis Of Metal-organic Framework And Catalysis Of CO₂ Cycloaddition Reaction

Carbon dioxide（CO₂）is the main man-made greenhouse gas,which causes a series of environmental problems that affect human production and life.In recent decades,the focus of scientific research at home and abroad was mainly on how to enrich CO₂and catalyze its transformation into industrial products,and finally realized the resource utilization of CO₂.Due to the wide application of reaction products,the cycloaddition reaction of CO₂and epoxy compounds has attracted much attention.Metal-organic framework materials（MOFs）have become ideal catalysts for the cycloaddition reaction between CO₂and alkylene oxide because of their adjustable pore size,easily functional framework and highly dispersed catalytic active centers.Therefore,in order to make the cycloaddition reaction more practical,it is urgent to develop catalysts for cycloaddition reaction under mild conditions.In this paper,the structural characteristics,stability and catalytic performance of three newly synthesized MOF materials in catalytic cycloaddition reaction were mainly explored.The specific research contents are as follows:1.The exquisite combination of scarcely reported S-shaped[Pb₁₀K₂（μ₂-OH）₂（COO）₂₄]clusters and H₆TDP ligands under solvothermal condition generated a highly robust microporous framework of{（Me₂NH₂）₂[Pb₅K（TDP）₂（μ₂-OH）]·4DMF·6H₂O}_n（NUC-45）with1D open channels along a axis.Due to the excellent confined pore environments,such as large surface area,rich Lewis acid sites of Pb²⁺and K⁺,plentiful Lewis base sites ofμ₂-OH group and N_pyridineatom,and open channels,activated NUC-45a exhibits excellent catalytic performance on the cycloaddition of CO₂with various epoxides under mild conditions.This work shows that the use of multifunctional organic ligands and the introduction of alkali metal ions are conducive to the construction of porous cluster-based metal-organic materials with excellent heterogeneous catalysis.2.The solvothermal self-assembly by employing 2,4,6-tri（2,4-dicarboxyphenyl）pyridine（H₆TDP）as organic linker leads to a robust honeycomb skeleton of{[（CH₃）₂NH₂][In ^IIIPb ^II（TDP）（H₂O）]·3DMF·3H₂O}_n（NUC-52）with the advantages of large specific surface area,nanoscopic channels,high porosity（61.3%）,and thermal stability.To the best of our knowledge,this is the first 4p-5p heterometallic{In ^IIIPb ^II}cluster-based nano-porous host framework,whose activated state possesses the coexistence of Lewis acid-base sites including 7-coordinated Pb²⁺ions,4-coordinated In³⁺ions,uncoordinated carboxyl oxygen atoms,and N_pyridineatoms.Performed catalytic experiments exhibited that activated NUC-52aunder mild conditions owned the excellent catalytic performance on the cycloaddition of CO₂with various epoxideswith excellent turnover number（2475）and turnover frequency(619 h^-1).Hence,this work lays down the groundwork for constructing heterometallic cluster-based nanoporous MOFs with excellent Lewis acidic catalysis and chemical stability.3.The exquisite combination of scarcely reported[In₂（CO₂）₅（H₂O）₂（DMF）₂]clusters and 2,6-bis（2,4-dicarboxylphenyl）-4-（4-carboxylphenyl）pyridine（H₅BDCP）under solvothermal condition generated a highly robust nanoporous framework of{[In₂（BDCP）（DMF）₂（H₂O）₂]（NO₃）}_n（NUC-65）with nano-caged voids（14.1（?））and rectangular nanochannels（15.94（?）×11.77（?））along a axis.It is worth mentioning that In（1）ion displays the extremely low tetra-coordination modes after the thermal removal of its associated four solvent molecules of H₂O and DMF.After solvent exchange and vacuum drying,activated NUC-65a became a catalytic material because of its extremely unsaturated metal center.Catalytic experiments proved that the conversion of epichlorohydrin with 1 atm CO₂into 4-（chloromethyl）-1,3-dioxolan-2-one catalyzed by 0.11 mol%NUC-65a could reach 99%at 65°C within 24 hours.Moreover,with the aid of 5 mol%co-catalyst n-Bu₄NBr,heterogenous NUC-65ashowed the excellent universal catalytic perfromance on most of epoxides under mild conditions.Hence,this work offers a fresh insight into the design of structure-defect cationic metal-organic frameworks,which can be better applied to various fields because of their promoted performance.