Mechanosynthesis And C-S Cross-Coupling Catalysis Of Pyridine-Functionalized Ni(?)-NHC Complexes

N-heterocyclic carbene(NHC)complexes are a kind of organometallic compounds with special topological structures and become important substitutes for organic phosphine complexes due to their advantages of high stability and low toxicity.The functional modification of NHC can make them have different electronic and spatial properties,so they have certain adaptability in the fields of coordination,catalysis,and materials.Thioethers are important pharmaceutical intermediates,which widely exist in a variety of food and drug.Therefore,the construction of C-S bonds is of great significance.At present,both the synthesis of NHC complexes and the construction of C-S bonds are often completed by the traditional solution method.These processes are often accompanied by the extensive use of toxic reagents,which is not in line with the concept of green chemistry,so it is extremely important to develop a green synthesis pathway and catalytic system.The mechanochemical method through the application of mechanical force to stimulate the reaction has become an important means to construct green chemical systems due to the advantages of low solvent consumption,simple operation,time-saving and high efficiency.In this dissertation,mechanochemical techniques were used for the mechanosynthesis of NHC complexes and the catalysis of C-S cross-coupling.First,two benzimidazolium salts with different anions[H₂L]Br₂ and[H₂L](PF₆)₂([H₂L]=1,1'-di(2-picolyl)-3,3'-methylenedibenzoimidazolium)were prepared by a planetary ball mill.Then,their reactions with Ni(OAc)₂·4H₂O by grinding in a mortar afforded three nickel complexes,[Ni L]Br₂·CH₃OH(1),[Ni L]Br₂·2H₂O(1')and[Ni L](PF₆)₂·0.5CH₃CN(2)respectively.Finally,three Ni(?)-NHC complexes were used as raw materials,a five-coordinated complex[Ni LBr]PF₆(3)was further obtained by grinding in three methods,i.e.,mixing complex 1 or 1'and complex 2 in equal proportion(method 1),adding the same amount of NH₄PF₆ to complex 1 or 1'(method 2),adding the same amount of KBr to complex 2(method 3).The structure of the Ni(?)-NHC complex was characterized and analyzed by infrared spectrometer,nuclear magnetic resonance apparatus,X-ray powder diffractometer,X-ray single-crystal diffractometer and element analyzer.Further,the above-mentioned Ni(?)-NHC complexes 1-3 were taken as the research objects to explore their catalytic activity in the cross-coupling of C-S bond between 2-bromoacetophenone and 2-mercaptobenzothiazole.Complex 3 shows high catalytic activity,and the yield can reach 93%by screening and optimizing the experimental conditions.The green chemistry indicators E-factor and EcoScale were used to calculate the environment-friendly degree of the whole research process of the catalytic system,which was close to the ideal value,indicating that the whole process according to the concept of green chemistry environment-friendly.