Fabrication And Catalytic Property Of Ordered Cyclopalladated Thiophen Imine Self-assembly Monolayer Supported On Graphene Oxide For Catalyzing Suzuki Coupling Reaction

In this paper,graphene oxide supported ordered thiophenimine palladium self-assembled catalytic monolayer?denoted as GO@TA-Pd?was designed and synthesized.The oxygen-containing functional groups on the surface of graphene oxide?GO?were chemically modified with APTES,resulting in a large number of amino groups appeared on the surface of graphene oxide,then,2-thiophene formaldehyde was used to react with amino groups to form Schiff base structure.Finally,the prepared monolayer was coordinated with Pd Li₂Cl₄ to yield the catalytic monolayer.The synthesis process of GO@TA-Pd was characterized by X-ray diffraction?XRD?,Raman spectrscopy,Scanning electron microscopy?SEM?,Transmission electron microscope?TEM?,FTIR,X-ray Photoelectron Spectroscopy?XPS?and Inductively Coupled Plasma Atomic Emission Spectroscopy?ICP-AES?.The structure of GO hardly changed during modifying according to the results obtained by XRD and Raman,indicating that GO kept its structure.The morphological changes of catalyst at each step showed no different characteracters,indicating that every step was proceded.The elements,such S and Pd etc on the surface were detected by EDS.The changes of functional groups in each stage,such as-NH₂,-NH=CH-were also confirmed by FTIR.The elements on the catalyst were analyzed by XPS,in which two valence of palladium was observed.Based on the analysis above,the designed graphene oxide supported ordered thiophenimine palladium self-assembled catalytic monolayer catalyst was successfully prepared.The content of palladium was obtained by ICP-AES.Suzuki coupling reaction was used as templet to test the catalytic performance of GO@TA-Pd.The high performance liquid chromatography was used to analyze the yield of catalytic reaction.The advantages and disadvantages of several analytical methods of HPLC used for the yield analysis were explored.The optimization condition of Suzuking coupling reaction catalyzed by GO@TA-Pd was initially carried out by screening various solvents,time,bases,temperatures,in which the optimized reaction was selected?K₂CO₃,H₂O/Et OH mixture?v/v=1:1?,at 70°C,6 h?.The higher yield could be obtained by treating the catalyst with ultrasonic way.Under the optimized conditions,different substrates were used for screening,in which higher and moderate yields could be obtained.The catalytic performance was also compared with other catalysts reported.GO@TA-Pd could be recycled at least 5 times.The catalytic mechanism of the catalyst was studied by hot filtration experiment,poisoning test,Rct IR,SEM,XRD and Raman.It was proved that the catalytic reaction was heterogeneous catalysis,which occoured on the surface of catalytic monolayer.The possible mechanism was also proposed.