Fe-Metal Organic Framework Catalyzed C-N Coupling And N-N Coupling Of Dioxazolones

Nitrogen-containing molecules are important components of most natural products,medicinal chemistry,bioactive substances and functional materials.The effective introduction of nitrogen element is an important research direction in organic synthesis and drug synthesis.Direct amidation of molecules requires the formation of nitrene precursors,but acylazide compounds are not suitable for this process because they are inherently unstable and difficult to separate and store.Dioxazolones,as the effective nitrene precursors,has many advantages such as easy synthesis,activation by transition metal at relatively low reaction temperature,and the only by-product produced by the reaction with dioxazoldones is carbon dioxide.Many new amidation reactions are generated during the homogeneous transition metal catalysis,which provides a new idea for the introduction of nitrogen in organic molecules.These methods are undoubtedly effective,but they also have some limitations,such as the need for precious metal catalysts（Rh,Ru,Ir,etc.）and the difficulty of catalyst separation.Therefore,the development of a heterogeneous cheap metal catalyst for the introduction of nitrogen is still an important scientific research direction in the field of chemistry.MOFs are a new class of photocatalysts with structural diversity,designability and high specific surface area,which show excellent performance in heterogeneous photocatalytic reactions.The porous structure of MOFs can make the substrate and product diffuse rapidly,shorten the carrier transport distance and improve the catalytic efficiency;crystallinity can avoid the formation of structural defects;the large surface area makes it easier for the substrate to reach the catalytic active site.Especially compared with traditional photocatalysts,the diversity and designability of MOFs catalysts can achieve the light response of MOFs by adjusting the building unit or the specific functional group of the target structure.In this paper,three kinds of Fe-based MOFs were studied as heterogeneous photocatalysts,and dioxazolones were used as nitrene precursors to photocatalyze the N-N coupling of dioxazolones with aromatic amines and the C-N coupling of 1,3-dicarbonyl compounds.In the first part of this paper,three kinds of Fe-based MOF,MIL-101（Fe）,NH₂-MIL-101（Fe）and Fe（BTC）-MOF,were synthesized by hydrothermal solvethermal method according to previous literatures,the three MOFs were characterized by SEM and XRD,according to the surface morphology and diffraction peak pattern of the synthesized MOFs,the successful synthesis of the three MOFs was proved.Then the characterization of UV-visible near-infrared spectrometer showed that it had a certain range of wavelengths of light absorption,confirming its feasibility as a photocatalytic material.In the second part,MIL-101（Fe）with high catalytic activity was selected as the photocatalyst for the N-N coupling reaction of three Fe-based MOFs with aromatic amines,and a series of hydrazide compounds with high yield were obtained.The system has a wide range of substrates and a wide range of functional group tolerance,including aromatic amines and nitrogen heterocyclic groups that replace the electron-drawing and electron-giving groups on the benzene ring.N-methyl aniline was selected as the representative model substrate to expand the range of dioxazolones.The XRD and infrared spectrum analysis of the catalyst in the cycle experiment proved that the structure of MIL-101（Fe）was stable during the catalytic process,and the yield analysis proved that the catalytic performance was stable.It was proved that MIL-101（Fe）hardly leached Fe ions during the catalytic process,and MIL-101（Fe）played a crucial role in the reaction.In the third part,MIL-101（Fe）photocatalytic system was applied to the C-N coupling reaction between dioxazolones and 1,3-dicarbonyl compound,and 1,4,2-dioxazole-5-one and 3-phenyl-1,4,2-dioxazole-5-one were used as representative nitrene precursors to expand the substrate.The C-N bond is formed directly from the C-H bond without prefunctionalization of any substrate.These methods provide a new idea for the construction of bioactive molecules and the introduction of N element in total drug synthesis,and have important application value for the synthesis of drug intermediates.