Insights into the Mechanism of Modern Ullmann–Goldberg Coupling Reactions

Abstract

This chapter focuses on the mechanisms of the Ullmann-Goldberg-type cross-coupling reactions. These reactions have been extensively studied from a mechanistical point of view. The chapter explains the oxidation state of copper catalysts. The addition of ligands of copper salts in the catalytic reactions may prevent the formation of less reactive, multiply ligated, cuprate structures. An alternative approach is to synthesize and study well-defined, stable, and soluble copper(I) complexes, species that have been shown to have good activities in copper-catalyzed C-heteroatom bond formation reactions. This strategy is described in the chapter. The chapter also illustrates that the nature as well as the concentration of the auxiliary ligand used in Ullmann-type condensation reactions have a strong impact on the equilibriums between the different copper(I) complexes present in solution, and in the formation of the active catalyst as well. The chapter further discusses the activation mode of aryl halides by copper complexes.