Solvent-Assisted Ligand Exchange (SALE) For Enhancement of the Capability of Epoxide Ring-Opening Reaction Catalysis Based on Three Amide-Functionalized Metal-Organic Frameworks
Over the past years, functionalized pillar ligands have been considered significantly due to their important role in MOFs structure performance. Synthesis of MOFs compound with particular functionalized ligand is not always successful, and sometimes it cannot be synthesized easily and directly even by means of several methods. Hence, this limitation can be overcome by applying a post synthesis way which is swapping functional groups without changing the whole backbone of pillar ligand. Solvent-assisted ligand exchange (SALE) is a post synthesis method which has been assisted to confront this challenge by replacing functional groups together. Through this investigation, we tried to improve the properties of the MOFs compound and increase their catalytic efficiency by importing a new functional group into their structures. N1, N3-di (pyridine-4-yl) malonamide linker (S) is one the pillar ligands which does not easily enter to the structure in order to synthesize MOFs compound. Therefore, to solve this issue , amide functionalized benzene-cored ligand derivatives were designed as linkers for manufacture of new 3D structures of [Co(oba)(bpta)]•(DMF)2 TMU-50, [Co2(oba)2(bpfn)]•(DMF)2.5 TMU-51 and one novel 2D [Co(oba)(bpfb)]•(DMF)2 TMU-49 , layered of compound via hydrothermal reaction. Moreover, their ability as catalysts were figured out in the methanolysis reaction of the epoxides. To increase the MOFs catalytic efficiency, we designed N1, N3-di (pyridine-4-yl) malonamide linkers (S) as a malonamide pillar ligand, which consists of an acidic hydrogen which is suitable for catalysis an epoxide ring-opening reaction that enhance the catalytic activity. Due to the synthesis the MOFs structure via this linker was not possible, we tried to design three new structures with incorporating different percentages of S linkers and exchange acylamide functional group was with malonamide via SALE pathway. The acylamide functional group was successfully replaced and produced daughter MOFs TMU-49S, TMU-50S and TMU-51S. PXRD and NMR spectroscopy confirmed that the S linker is incorporated to acylamide-MOFs structure. The obtained materials TMU-49S, TMU-50S and TMU-51S, are isostructural to their parent frameworks. The S spacer significantly improved the catalytic properties of MOFs compound in ring-opening reaction of epoxides and TMU-50S showed 98% catalytic efficiency after incorporated S linker. They can be recycled without any significant loss of the catalytic efficiency.