Theoretical Research On Structural Control Of Palladium/Polyaniline Composites And Their Activity Law For C-C Coupling Reaction

Polyaniline-based composite materials have a wide range of applications in the fields of energy storage,corrosion protection,environmental protection,catalysis,etc.,because they have the advantages of easy preparation,controllable structure,and low price.In recent years,as an efficient new catalyst system,it has shown unique advantages in the fields of constructing C-C bonds and C-N bonds,and has achieved many results.However,as organic polymer-supported catalysts,there are still problems such as unsatisfactory catalytic activity,low recycling times.low degree of greening of the catalytic reaction,and insufficient structure-activity relationship of the catalyst.For this reason,this paper adopts a modified one-step in-situ self-stable dispersion polymerization(SSDP)technology route.By using a small amount of palladium chloride as a metal ion dopant,using(NH4)2S2Os as oxidant in acidic environment at-30?,obtained a series of new palladium/polyaniline composite catalysts.We focused on its catalytic performance in catalyzing nitro reduction and C-C coupling reactions,revealed the coordination mechanism of metal palladium and polyaniline,and obtained novel research results.The main research contents and results are shown as follows:(1)Using camphor sulfonic acid as the dopant,an ultra-low loading(0.047 w.t.%)networked Pd@PANI catalyst was prepared in one step.The catalyst has significant advantages in the nitro reduction reaction compared with similar catalysts reported in the literature:Only Using 0.026 mol%catalyst;Pure water as solvent at room temperature;Reduce the amount of reducing agent by about 40%(The amount of NaBH4 used is only 2.5 times the equivalent of the substrate);The reaction time is significantly shortened(15-300 min);The maximum yield of reduction of nitro to amino can reach 97%;The catalyst can be reused more than 8 times in this reaction system.(2)Through XRD.FR-IR,XPS,SEM.TEM and other test analysis,we systematically studied the influence of different acids(Hydrochloric acid,camphor sulfonic acid,glacial acetic acid,citric acid and pyromellitic acid)as acid media and dopants on the structural characteristics of the prepared Acid-PdCl2/PANI catalyst.The results of the study indicate that different acid media will significantly affect the morphology and structure of PdCl2/PANI catalysts;In particular,it has different effects on the essential structural characteristics of the carrier polyaniline(the content of the oxidized and reduced structure);We found for the first time that the structural characteristics of PANI in C-C coupling reactions are:the higher the content of the reduced structure contained in the support polyaniline,the better it is for improving the reactivity and catalytic efficiency of the catalyst.(3)By using HCl-PdCl2/PANI as the typical case catalyst,the result shows that HCl-PdCl2/PANI catalyst has excellent catalytic performance in Suzuki,Heck,polyaromatic coupling and Ullmann coupling reactions.Especially in Ullmann reaction,using DMF as solvent,2 times equivalents of diisopropylethylamine as base.140? for 2.5 h can obtain the yield more than 85%.Compared with other similar catalysts,the catalytic system no longer requires the use of an additional reducing agent,and the reaction system is more green and efficient.We analyzed the catalytic reaction mechanism in detail through real-time online infrared and XPS characterization,the organic bases play the dual roles of acid binding agent and reducing agent in the reaction system.After the catalyst was reused 8 times,the reaction product could still be obtained in 73%yield.(4)The coordination mechanism of metal palladium and polyaniline carrier was analyzed in detail by means of TG,XPS,Raman spectroscopy and solid nuclear magnetic characterization.The palladium in the initial prepared catalyst was in bivalent form and coordinated with nitrogen in polyaniline.During the catalytic reaction,part of palladium was reduced to zero valences,and the quinone structure in the polyaniline carrier was also reduced to benzene structure.It is precisely because of this unique structural change of the polyaniline carrier that the agglomeration of the metal palladium is prevented to some extent,and the divalent palladium in the material together with the zero-valent palladium formed by the reaction promotes the progress of the reaction.