| Porphyrins and its derivatives,as one of the most important biomimetic catalysts,can effectively simulate cytochrome P450 and show excellent catalytic effect,making it has a very broad application prospects.However,the porphyrin compounds have the inherent defects,such as poor chemical stability in the homogeneous reaction,easily oxidized and difficult to separate and recover,and so on,which limited their application greatly.In order to solve the shortcomings of homogeneous catalysis of monometallic porphyrins,polymerization of a specific bridging agent into a polymer has become a new research trend.The polymerized porphyrin catalyst not only retains the original excellent catalytic properties,but also enhances its chemical stability,and at the same time improves the processability.Based on this,we synthesized a covalent porous metal porphyrin polymer with azo linkages.It was applied to the catalytic oxidation coupling reaction of benzyl alcohol and acetonitrile and the halogenation reaction of cyclohexane,which showed excellent catalytic performance.Based on the large amount of literature investigation,we used meso-tetra(4-nitrophenyl)metalporphyrin and P-phenylenediamine to synthesize the conjugated porous metal porphyrin polymer(Cu~Ⅱ-POP/Mn~Ⅲ-POP),and characterized using IR,TG,SEM and FEM detection methods.The test results show that Cu~Ⅱ-POP is a nanocatalyst that maded up of particles with a diameter of about 30 nm.The surface has a well-developed porous structure with a specific surface area of 226 m2/g and a major pore size distribution between 1.9 nm and 2 nm.The Cu~Ⅱ-POP catalyst has good thermal stability,can stably exist within 350℃.Then,we used Cu~Ⅱ-POP as a catalyst to catalyze the oxidative coupling of benzyl alcohol with acetonitrile to prepare the corresponding β-ketonitrile.Benzyl alcohol and acetonitrile were used as model reactions to compare the difference in catalytic activity between porphyrin polymers and copper porphyrin monomers.The effects of solvents,alkali additives,and oxidants on the reaction were examined,and the cycling performance of the catalysts was also investigated.The experimental results show that the yield of β-ketonitrile reaches 84%under optimal conditions,and Cu~Ⅱ-POP shows a good catalytic effect in the mild conditions.The polymer has strong stability,is insoluble in organic solvents,and has good cycle performance.It is reused five times and the catalytic effect is basically not reduced.At the same time,we can discuss the mechanism of this reaction.Finally,the halogenation reaction of cyclohexane with C-H bond was studied using the synthesized Mn~Ⅲ-POP polymer as a catalyst.A comparison of the two halogenated experimental schemes was conducted.It was found that when NaOCl was used as the halogen source and oxidant,the reaction was simple,efficient and easy to separate the product,the yield of chlorocyclohexane was as high as 89%.The optimal catalytic conditions for halogenation of C-H bonds were obtained by controlling several single-factor variables of the reaction.The catalyst has stable chemical properties,is easy to recycle,and has high catalytic activity after 5 cycles.Based on the experimental results and literature reports,we proposed the possible free radical reaction mechanism of the Mn~Ⅲ-POP catalyzed halogenation reaction of C-H bonds. |
