Microwave-assisted Magnetic Ni@Pd-Ni₂O₃ Core/Shell Nanoparticles Applied In Organic Synthesis

Noble metal nanocatalysts,such as Palladium,Ruthenium,Rhodium,Iridium,etc.,have all played a good catalytic role in C-H bond activation and C-C bond coupling reactions.Thereby,they can be well applied in drug synthesis,material synthesis or other organic synthetic fields.Typical examples are Suzuki coupling,Ullmann coupling,Songashira coupling,and Heck coupling.However,noble metal nanocatalysts have the disadvantages of difficult recovery and insufficient environmental protection during preparation.According to relevant researches,the recovery method of noble metal nanocatalysts mainly includes: firstly loading it on graphene,hydrotalcite,resin and other polymers;and then recovering the supported catalyst by centrifugation or filtration.In the preparation of noble metal nanocatalysts,the preparation methods provided in most researches use oleylamine,oleic acid,and sodium borohydride,which are not environmentally friendly and green reducing agents.In order to solve the above mentioned issues,a method for preparing magnetic nickel-palladium alloy nano-catalyst using ethylene glycol as a reducing agent and microwave as a heating energy source is designed.Compared with reducing agents such as oleylamine,oleic acid,and sodium borohydride,ethylene glycol is less polluting to the environment,and therefore more in line with the requirements of environmentally friendly preparation.Microwave as a heating energy source,which can continuously maintain a high temperature environment,is able to strengthen the reducibility of ethylene glycol,shorten the catalyst preparation time and achieve the effect of saving energy.The prepared magnetic nickel-palladium catalyst can be recovered by suction through a magnet,which is more convenient than centrifugation or filtration.At the same time,the preparation of nickel and palladium into alloy nanoparticle morphology can strengthen the electron transfer effect in the particle structure,thereby enhancing the catalytic activity of palladium.After the preparation of the nickel-palladium alloy nanoparticles,in order to study the material chemical structure in the field of material chemistry,we performed XPS,XRD,TEM,EDS mapping,and SEM characterization.Combining TEM and EDS mapping results,we can confirm that the nickel-palladium nanocatalyst has a core-shell structure with nickel as the core and palladium and nickel oxide as the shell.Therefore,we named the nano-palladium catalyst Ni@Pd-Ni₂O₃ core/shell nanoparticles.At the same time,we also found that the prepared nanoparticles are about 20 nm in diameter and relatively uniform in size.They can remain uniform Ly dispersed and non-agglomerated in the liquid phase.In order to prove the catalytic activity of the nickel-palladium alloy nanoparticles in the field of organic chemical synthesis,we applied the nickel-palladium alloy nanoparticles to Suzuki coupling,Ullmann coupling,and directed C-H bond activation reaction under microwave heating conditions,and the application in organic reactions such as photocatalytic dehydrogenation coupling.In catalyzing the Suzuki coupling reaction,we used water and ethanol and other environmentally friendly solvents for the reaction and obtained the coupling product.Compared with the results of the same type of reaction catalyzed by the palladium nanomaterials described in other researches,we are getting the same high yield under these conditions.The reaction time is shortened and the number of cycles is extended.In catalyzing the Ullmann coupling reaction,we used ethylene glycol,a green and environmentally friendly reducing agent and solvent.Compared with the results of the same type of reaction catalyzed by other palladium nanomaterials described in other literatures,we also shortened the process at the same high yield Thereaction time is increased,and the number of cycles is extended.In order to further prove the catalytic activity of the catalyst,we applied the nickel-palladium alloy nanoparticles to an acetoxylation reaction to perform a reactivity test.Since the acetoxylation reaction is a type-directed carbon-hydrogen bond activation reaction,it is more difficult to perform than the Suzuki coupling and the Ullmann couplingrecations.Our catalytic reaction results show that the yield is low.However,we still successfully isolated the catalytic products,which proved that the catalyst still has a certain catalytic activity in catalyzing the difficult organic reactions such as activation of carbon-hydrogen bonds.Finally,in order to prove that the palladium nanocatalyst has a certain photocatalytic activity,we also applied it to the photocatalytic thiocyanation reaction,and also achieved a high yield of the thiocyanation product.