Fabrication And Catalytic Performance Of Schiff Base Palladium-copper Bimetallic Catalytic Films For Suzuki Coupling Reaction

Schiff base has strong thermal and chemical stability and can coordinate well with different metals,which be used in a variety of organic reactions.Moreover,its activity increases exponentially in the presence of hydroxyl groups,especially in the ortho position of the imine group.In this paper,o-phenylenediamine and salicylaldehyde were used as raw materials to synthesize 2-[[(2-Aminophenyl)imino]methyl]phenol ligand(Apimp)which was grafted onto graphene oxide(GO)to form modified GO@Apimp by self-assembly.Bimetallic catalysts with different ratios of palladium-copper were prepared by coordinating GO@Apimp with palladium/copper salts(called as GO@Apimp-Pd/Cu).Their catalytic properties and catalytic mechanism for Suzuki coupling reaction were explored.Specific research contents are as follows:1.The designed aromatic imine ligand(Apimp)containing hydroxyl groups was synthesized by reacting o-phenylenediamine with salicylaldehyde,and was characterized by HNMR,high resolution mass spectrometer and infrared spectroscopy,PNO was grafted onto graphene oxide treated with acylation by self-assembly,and five bimetallic catalysts were prepared(denoted as GO@Apimp-Pd1Cu5,GO@Apimp-Pd1Ni5,GO@Apimp-Pd1Ru5,GO@Apimp-Pd1Fe5 and GO@Apimp-Pd1Co5),and their catalytic performance in the same Suzuki reaction were investigated under the same condition,in which the palladium-copper bimetallic catalyst had a higher catalytic activity than that of others.2.A series of bimetallic catalysts with different ratios of Pd/Cu(called as GO@Apimp-Pd,GO@Apimp-Cu,GO@Apimp-Pd1Cu2.5,GO@Apimp-Pd1Cu5,GO@Apimp-Pd1Cu5.5,GO@Apimp-Pd1Cu6.5,GO@Apimp-Pd1Cu7.5)were prepared and characterized by XRD,TEM,SEM,FT-IR,ICP-AES and SEM-EDS.Their catalytic performances of Pd/Cu bimetallic catalysts with different proportions for catalyzing Suzuki reaction were investigated.The results showed that the single copper catalyst had no activity for template reaction.Although the single palladium catalyst has a good catalytic yield,its TOF value is low due to the large palladium load.The TOF of the optimal metal ratio(GO@Apimp-Pd1Cu6.5)is as high as 1532258 h-1,which was 7.6 times more than that of single palladium catalyst,and could be recycled at least 5 times,indicating that the bimetallic catalyst has excellent catalytic activity.3.Catalytic mechanism in Suzuki reaction catalyzed by GO@Apimp-Pd1Cu6.5 was investigated and the catalytic deactivation of the bimetallic catalysts was also explored.According to the experimental data and analysis,the bimetallic catalyst generated nanoparticles of CuPd alloy in the process of catalysis,resulting in loss of active,which might be one of the important reasons for the loss of catalytic activity.Kinetics,thermal filtration and poisoning experiments were carried out to study the catalytic mechanism in Suzuki reaction catalyzed by GO@Apimp-Pd1Cu6.5.It was found that the process of catalytic reaction occurred at the interface of catalyst without leaching of Pd species.The catalytic mechanism was proposed based on the experiment data above:electrons of GO transferred to Cu through the ligand and then transferred to Pd via synergistic.It made Pd more negative which made it easier to carry out oxidation addition with aryl halide,which promoted the most important step in Suzuki coupling reaction.