Synthesis Of Heterogeneous Palladium Catalysts Containing Nitrogen Or Phosphorus And Their Applications In Suzuki-Miyaura Coupling Reaction

The composition of the palladium-catalyzed C-C bond in modern organic synthetic chemical reactions is one of the most basic and important reactions,in this field,Suzuki-Miyaura coupling reaction of aryl halides and arylboronic acids catalyzed by palladium are the most useful synthetic transformations to construct fine chemicals,pharmaceuticals,and agrochemicals.In general,the coupling reaction can efficiently proceed in the presence of homogeneous palladium complexes.Despite there are significant progress for Suzuki-Miyaura reaction has been achieved in recent years,there are some drawbacks of homogeneous palladium catalysis including the difficulty in recovery and reuse of the usually expensive catalysts,as well as product contamination by incomplete separation of metal catalysts.The typical way to solve these problems is anchoring palladium catalysts on suitable support.However,some of these heterogeneos palladium catalysts show lower catalytic activity in comparison with the homogeneous counterparts.Therefore progress for the heterogeneous palladium catalysts with enhanced activity are still highly desirable.In this paper,the corresponding organic palladium metal polymer catalysts were synthesized by using polyphosphazene ring and polyphenylphosphine as the basic skeleton unit respectively.They were applied to the heterogeneous catalyzed Suzuki-Miyaura coupling reaction.The recovery of the catalyst can be achieved by simply centrifuging.First of all,a highly cross-linked polymer was formed by the substitution reaction of hexachlorocyclotriphosphazene with 4,4'-diaminobiphenyl,then using Pd?OAc?₂ as a palladium precursor,the divalent palladium is supported on the polymer in toluene.The target organic polymer catalyst was obtained and applied to Suzuki-Miyaura coupling reaction.The reaction of 4-bromoanisole and phenylboronic acid was chosen as template reaction to optimize conditions,in terms of solvent,temperature and base.The condition of 50?,EtOH/H₂O?1:1,v/v?,K₂CO₃,0.3mol%of Pd catalyst in the N₂ atmosphere was tested as the optimum condition.And the catalytic effect was better than that of commercially available palladium catalyst in comparison with the catalytic effect of commercial small molecule palladium catalyst.After the catalyst was selected under the optimal conditions,a series of representative substrates were selected for the application of the catalyst with relatively high yields was obtained,and the catalytic efficiency of the catalyst after 6 times did not show a significant decline.Secondly,1,4-dibromobenzene and 4,4'-dibromobenzene were made into Grignard reagent and then reacted with chlorodiphenylphosphine respectively to get the corresponding two kinds of polyphenylphosphonium chloride,then coordination reaction with PdCl₂ afforded two kinds of organic palladium metal polymer catalysts.The reaction of 4-bromoanisole and phenylboronic acid was chosen as the template reaction to compare the catalytic effect of the two catalysts.A series of representative substrates were selected in the air atmosphere at 25?,EtOH/H₂O?1:1,v/v?,K₂CO₃,0.3mol%Pd catalyst to test the application of the two catalysts,both of them afford the coupling products in high yields.The catalyst with more stable structure was also chosen by comparing the recovery effect of the two catalysts at the same time.Thirdly,the corresponding structure of material was confirmed by ¹H NMR,¹³C NMR,³¹P NMR and IR,and the loading of palladium in two catalysts was determined by ICP-AES.The thermal stability and morphology of the catalysts were characterized by TGA,SEM and TEM.The results show that the catalysts have good thermal stability and morphology are spherical and irregular granule,respectively.The data of XPS show that Pd exist in both catalysts in the form of+2 valence.In summary,a serial of Pd catalysts were synthesized in this paper which can effectively catalyze the Suzuki-Miyaura coupling reaction.And the yield is high,the recovery of the catalysts can be facilely realized.Therefore,all of the expected design goals were achieved.