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 understand them better and make them more efficient. Two examples will be discussed in detail.
On one hand, a detailed study on the direct arylation of pyridine and other arenes using the ligand [2,2′-bipyridin]-6(1H)-one) (bipy-6-OH) will be presented. Palladium complexes derived from this ligand are capable of accelerating these reactions, considerably reducing the reaction times. 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.
On the other hand, the mechanism of the Pd-catalyzed oxidative homocoupling of alkynes using oxygen as oxidant has been studied by a combined experimental and computational approach. Besides its synthetic interest, this reaction is a competitive process in coupling reactions involving terminal alkynes but no detailed study had been carried out so far on how this process actually occurs. The nature of the active species in the reaction and how oxygen interacts with palladium complexes to induce a productive catalytic transformation will be analyzed.