Suzuki-Miyaura Coupling Reaction Catalyzed By Fiber State Pd/Pd-Ni Catalysts

C-C coupling reactions play an important role in the field of organic synthesis and have been widely used in the synthesis of medicine,natural products and materials.There are many types of C-C coupling reactions,including Suzuki-Miyaura coupling reaction,Heck coupling reaction,Ullmann coupling reaction,Negishi reaction,Sonogashira reaction and Stille reaction.Due to the advantages of mild reaction conditions,easy substrate acquisition,good functional group tolerance and high regional selectivity,Suzuki-Miyaura coupling reaction has been highly favored by researchers and has become one of the most effective methods to construct C-C bond at present.Pd catalyst has been widely studied for its high catalytic activity for the suzukia-miyaura coupling reaction.At the same time,Pd catalysts that have been studied most are mainly including two types:homogeneous Pd catalysts and heterogeneous Pd catalysts.In today's world,green chemistry technology has been paid more and more attention by chemical workers in various countries.Although homogeneous Pd catalyst has high catalytic activity,it is difficult to recover,not easy to purify its product,solvent pollution and other shortcomings,which greatly limit its practical industrial application.Heterogeneous catalysts successfully overcome these shortcomings and become the first choice to develop green catalysts.The paper aims to prepare carbon nanofibers loaded Pd?Pd-Ni?nanocomposites and explore the application in Suzuki-Miyaura coupling reaction.Carbon fibers have many excellent properties,such as low density,large specific surface area,and high corrosion resistance.Electrostatic spinning technology has developed into a mature technology with the advantages of simple equipment manufacturing,low cost and easy operation.Therefore,in recent years,the preparation of carbon nanofibers by electrostatic spinning technology is one of the focuses in the field of materials science.The specific research content is as follows:1.Using PAN/DMF solution containing PdCl₂ as spinning precursor solution,the polymer nanofiber membrane loaded with PdCl₂ was prepared by electrostatic spinning technology.Then the polymer nanofiber membrane was carbonized at high temperature under air atmosphere,and the one-dimensional carbon fiber supported palladium nanocluster composite catalyst?PdO@CNF?was obtained.Due to the small size of the active species of the catalyst,it showed high catalytic activity in the Suzuki-Miyaura coupling reaction?bromobenzene and phenylboronic acid almost completely reacted in only 3 hours?.In addition,the nano-composite catalyst has good recycling performance and has been used for 10 times continuously.The experimental results show that the active palladium oxide nanoclusters have strong interaction with the surface of carbon fiber,and the clusters are not easy to be detached from the carrier during the reaction process,which can improve their service efficiency and meet the requirements of atomic economy in green chemistry.2.Using PdCl₂ and NiCl₂ as metal precursor salts,the bimetallic Pd-Ni catalyst with synergetic catalytic effect was successfully prepared through the experimental steps of electrostatic spinning,ethanol reduction and high-temperature carbonization.The catalytic activity of the bimetallic catalyst in the Suzuki-Miyaura coupling reaction was significantly due to its single component Pd or Ni catalyst.X-ray photoelectron spectroscopy confirmed the existence of metal Pd in the form of Pd²⁺and Pd⁰,and metal Ni in the form of Ni²⁺.High resolution transmission electron microscopy showed that the particle size of the active species was very small and evenly distributed.The experimental results showed that the main catalyst was the active component Pd or PdO,and the co-catalyst was NiO,The additive element Ni and the carrier carbon nanofiber together prevent the agglomeration of the active component Pd,making it exist in a small size,so as to expose more reactive sites and improve the catalytic reaction rate.In addition,the bimetal nanocomposite catalyst has a good service life and no obvious agglomeration of the active components after 10 cycles,showing good thermal stability.A possible reaction mechanism was proposed for the catalytic reaction system.In a word,the research center of this paper is to improve the catalytic reactivity by reducing the size of nano-active components and introducing non-noble metal additives.