Palladium Catalyzed C-H Functionalization of Arenes via Metal-Ligand Cooperation

Palladium-catalyzed C-C coupling reactions that directly functionalize C-H bonds have emerged as a powerful tool for C-C bond formation. These reactions do not require a previous functionalization of every reaction partner and therefore conform to the principles of green chemistry, standing in a good position towards a more sustainable chemical synthesis. We have been looking closely at some of these transformations in order to better understand their mechanism and make them more efficient. The use of metal-ligand cooperation has proved to be a useful approach in C-H activation and, in particular, we have been using chelating cooperating ligands such as 2,2′-bipyridin]-6(1H)-one (bipy-6-OH). Palladium complexes derived from this ligand are capable of accelerating C-H functionalization reactions of simple arenes (non-chelate assisted C-H activation). Mechanistic studies show the cooperating effect of the ligand and its assistance in the C-H cleavage step by a concerted mechanism in the metal coordination sphere. In addition to the metal-ligand cooperation in the C-H activation, bipy-6-OH influences the product-forming step leading to chemoselective processes. The application of this type of ligands to direct arylations as well as aerobic oxidative Heck reactions of arenes will be discussed.