Design And Synthesis Of Molybdenum And Vanadium Hydrazone Complexes And Their Catalytic Activity For Cyclohexane Reaction

Catalytic oxidation of cyclohexane is a representative selective oxidation reaction.In recent years,researchers have made many attempts around the catalysts for the reaction,including the application of silicon-based mesoporous materials,metal-organic framework materials,ionic liquids,heterogeneous photocatalysts and transition metal complexes.Among them,the study of transition metal complexes has been attracted extensive attention.Compared with industrial conditions,the reaction conditions are relatively mild,and the conversion of cyclohexane and the selectivity of products are also high when transition metal complexes,especially vanadium and molybdenum complexes are used as catalysts.Therefore,the development of transition metal complexes catalysts is an important research direction in the catalytic oxidation of cyclohexane.In this paper,three hydrazone molybdenum complexes and three hydrazone vanadium complexes were synthesized from MoO₂(acac)₂and VO(acac)₂for the first time.The three molybdenum complexes are[MoO₂L¹(Me OH)](1),[MoO₂L²(Me OH)](2)and[MoO₂L³(H₂O)]·Et OH(3)[H₂L¹=N?-(2-hydroxybenzylidene)-3-methyl benzohydrazide,H₂L²=4-bromo-N?-(2 hydroxybenzylidene)benzohydrazide,H₂L³=2-bromo-N?-(2-hydroxybenzylidene)benzohydrazide].The three vanadium complexes are[V₂O₂(?-O)₂(L⁴)₂](4),[VO₂L⁵](5)and[VOL⁶L']·CH₃OH(6)[HL⁴=4-tert-butyl-N'-(1-(pyridin-2-yl)ethylidene)benzohydrazide,HL⁵=2-hydroxy-N'-(1-(pyridin-2-yl)ethylidene)benzohydrazide),H₂L⁶=N'-(2-hydroxy-3-methoxy)benzyl idene-3-methyl benzohydrazide.H₂L'=2-hydroxybenzohydroxamate].They were characterized by FT-IR and UV-vis,and the crystal structure of them were determined by X-ray single crystal diffractometer.To investigate the catalytic properties of molybdenum and vanadium complexes in cyclohexane oxidation,complexes 2 and 6 are used as catalysts in this experiment.the effects of the amount of H₂O₂,the kinds of solvents,the amount of HNO₃,the reaction time,the reaction temperature and the kinds of acid promoters for the catalytic activity of the catalysts are discussed in this experiment and the optimum reaction conditions of two complexes under homogeneous catalysis were obtained.At the same time,the catalytic activities of the different complexes are compared under the optimum conditions.Three factors affecting the catalytic activity are found,namely,the active center of the complexes,the number of ligands and the electron absorption of ligand end groups.In addition,the catalytic activities of vanadium complexes and molybdenum complexes are compared with similar structure.It is found that compared with Mo complex,when vanadium complexes are used as catalysts,less H₂O₂and more HNO₃are need for the reaction,lower catalytic activity is shown at high temperature,and more cyclohexanone is produced,which is valuable for study.