Synthesis,Characterization And Catalytic Properties Of Pyridyl Salen Complexes

Salen ligand is a Schiff base containing amine functional groups that are easily modified and can be combined with metal ions to increase stability.It can also introduce chiral structures and form valuable chiral metal catalysts.MOFs constructed with salen complexes allow regular alignment of the active sites of metals in the channels,thus improving catalytic efficiency and promoting separation and recovery.Therefore,the study of salen complexes is significant and valuable.This paper designed and synthesized novel salicylic aldehyde with multiple substituents,and pyridine salen ligands L1,L2,and L3 were synthesized with three diamines with different structures.The introduction of the tert-butyl group could prevent dimerization with metal.They were fully characterized by employing characterization（e.g.,IR spectrum,¹H NMR）.Nine complexes were synthesized,and the L2-Cu crystal structure was obtained by the solution volatilization method.A metal-organic framework was constructed with the L3-Zn complex.The crystals were analyzed by X-ray single-crystal diffraction,X-ray powder diffraction,and thermogravimetry.The complex L2-Cu catalyzed the formation of the C-N bond.The optimal conditions for forming the C-N bond catalyzed by the L2-Cu complex were as follows:DMSO as a solvent,adding 2 mmol Na OH or sodium tert-butanol as the promoter,6 mol%L2-Cu as a catalyst,reaction at 140℃for 8 h,the yield could reach 86.7%.The yield of the catalyst can still be more than 70%after three cycles,indicating that the catalyst has good repeatability.The scope and generality of the L2-Cu catalyzed cross-coupling reaction were explored,and the reaction mechanism was proposed.It can be seen from the above experiments that the complex L2-Cu is an excellent catalyst for C-N bond formation,which can make the reaction get a good yield and have good repeatability.Based on the structural advantages of MOFs,MOFs with photoadsorption capacity can be constructed to obtain more efficient photocatalytic activity.A binuclear metal-organic framework consisting of complex L3-Zn was used as a catalyst to degrade methyl orange.The optimal experimental conditions were as follows:methyl orange concentration 14 mg/L,catalyst mass 3 mg,H₂O₂ dose 60μL,p H=7,and the degradation rate could reach 96%.The degradation of MO follows the pseudo-first-order kinetic model,and the temperature increase accelerates the degradation of MO.The mechanism of catalytic degradation of methyl orange was studied.After four cycles,the degradation of methyl orange was still sound.The X-ray diffraction of L3-Zn coordination polymer before and after degradation is consistent with the XRD single-crystal simulation,and the SEM images show that they are uniform cubic particles.These results indicate that L3-Zn coordination polymers are heterogeneous catalysts with high purity and stability.Based on the above experiments,it is concluded that the synthesized L3-Zn coordination polymer is a very effective photodegradation catalyst.