Synthesis, Characterization And Applications Of Copper And Nickel Complexes Of Multidentate N-Heterocyclic Carbenes

N-heterocyclic carbenes (NHCs) are a class of a-donor with strong electron-donating ability. And their transition metal complexes have a wide range of applications in catalysis, medicine and materials. Development of the application of N-heterocyclic carbene complexes based on the first row transition metals such as Ni, and Cu is of importance for their relatively low price and toxicity compared with precious metals. The study is focused on the use of polydentate N-heterocyclic carbenes to build complexes possessing metal-metal interactions, and screening out catalysts with the cooperative catalytic effect. Meanwhile, the convenient synthetic method of NHC transition metal catalysts also is developed.This dissertation is divided into three parts:In part one, treatment of1,10-phenanthroline functionalized imidazolium salts (1,2,4-triazole salts) with Ag2O afforded a series of Ag(Ⅰ)-NHC complexes, including binuclear silver compounds and one tetranuclear silver compound having a ligand-unsupported Ag-Ag interaction. Further reaction of the Ag-NHCs with copper powder, or direct reaction of imidazolium salts (1,2,4-triazole salts) with copper powder generated a series of binuclear copper(Ⅰ)-NHC complexes. Among these copper complexes, the three-center two-electron bond bridged by acetonitrile is the first example in the reported Cu-NHC complexes. We also successfully screened out the efficient catalyst of1,3-dipolar cycloaddition reaction between azide and terminal alkynes. The TON value could be up to2,000. Besides, the reaction could be carried out smoothly without inert gas protection and reducing agents.In part two, reactions of pyrazole-bridged imidazolium salts or their corresponding silver-carbene complexes with copper powder afforded unusual copper(Ⅱ) hydroxides complexes of N-heterocyclic carbenes. The complexes have been fully characterized by X-ray diffraction analysis, elemental analysis, IR and ESI-MS spectrum. A catalytic study shows that these copper(Ⅱ) complexes are highly active in the N-arylation reactions of imidazoles and aromatic amines with arylboronic acids in methanol at room temperature under base-free conditions. In part three, we describe a new synthetic procedure of transition metal N-heterocyclic carbenes complexes. A number of Pd(Ⅱ), Pt(Ⅱ), Co(Ⅲ), and Ru(Ⅱ) complexes containing functionalized NHCs have been obtained in good to excellent yields using Ni(Ⅱ)-NHC complexes as carbene transfer reagents. Ni(Ⅱ)-NHC complexes are easily prepared from the direct reactions of corresponding imidazolium salts with commercially available Raney nickel powder. The by-product NiCl2of transmetallation reactions can be easily removed by simple filtration. This study offers a new economical and practical synthetic method for metal-NHC complexes.