| Transition metal-catalyzed coupling reaction is an important method for constructing new carbon-carbon bonds and carbon-heteroatomic bonds in modern organic chemistry.Since the beginning of the 20 th century,transition metal-catalyzed coupling reactions have made great progress,of which Ullmann reaction is a very important type of reaction.The Ullmann reaction made a major breakthrough from the initial use of copper catalysts to nickel catalysts,and especially with the discovery and wide application of palladium catalyst in the 1970 s.However,the Ullmann reactions still have many drawbacks such as harsh reaction conditions and so on which limit its’ the practical application.Chemists have made great efforts to making the reaction under more mild conditions by changing catalysts,ligands and so on.Catalysis is divided into homogeneous catalysis and non-homogeneous catalysis,in the homogeneous catalysis,the catalyst has larger contact area,more active sites,higher catalytic rate which make it generally has a good catalytic effect.Therefore,there are relatively more studies on homogeneous reactions.However,the disadvantages of homogeneous catalysts are also very obvious,that the catalyst is difficult to recover and reuse,which led to a series of problems such as metal residues,environmental pollution,and increased production costs.The use of heterogeneous catalysts can solve these problems to an extent.This not only and bring great atomic economic benefits,but also is more in line with the concept of green chemistry.Therefore,heterogeneous catalysts have a good application prospects.The main work of this paper is to synthesize a novel heterogeneous catalyst,and explore its’ application in Ullmann coupling reactions.The main contents include the following aspects:1.In the previous study,using divalent palladium salt and divalent nickel salt to react with titanate,our group synthesized a palladium-nickel-titanium-based catalyst Pd@Pd Ni-Ti-EG through a simple one-pot method under mild conditions.This method can prepare gram catalyst in laboratory conditions,which has good potential applications.In previous study,the catalyst showed excellent catalytic activity and stability in the Suzuki coupling reaction.In this paper,the catalyst was used to catalyze the Ullmann reaction to further explore its’ application scope.After a series of optimization of reaction conditions,the catalyst exhibited good catalytic activity in the C-C Ullmann coupling reaction.Self-coupling of aryl bromides yields up to 98% and have good compatibility for substrates containing different substituents.In addition,in the reaction system,the Pd@Pd Ni-Ti-EG catalyst also showed good stability and recyclability.The catalytic activity was not significantly reduced after 6 cycles.The XRD and TEM characterization of recovered catalyst showed that although the catalyst morphology was destroyed,palladium was still evenly distributed in the catalyst at a smaller size.This experimental results showed that our synthesis method could give palladium good dispersion and stability in the catalyst.2、Copper,as a relatively cheap transition metal with abundant reserves on the earth,has attracted the attention of chemists.In this paper,a titanium-based copper nanomaterial Cu@Ti-EG was prepared by using the reaction of divalent copper salts with titanate.Through a simple hydrothermal method,the catalyst could also be prepared in large quantities at one time and then used to catalyze the C-N Ullmann coupling reaction.After the optimization of the reaction conditions,it was found that the catalyst could realize C-N coupling under mild reaction conditions with good substrate compatibility.The yield was not significantly reduced after the catalyst was recycled three times which indicated the good stability of the catalyst.Characterization of the recovered catalyst also found that the catalyst morphology was not destroyed in the reaction system,and the content of Cu was not significantly lost. |
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