Non‐Chelate‐Assisted Palladium‐Catalyzed Aerobic Oxidative Heck Reaction of Fluorobenzenes and Other Arenes: When Does the C−H Activation Need Help?

Abstract The pyridone fragment in the ligand [2, 2’‐bipyridin]‐6(1 H )‐one (bipy‐6‐OH) enables the oxidative Heck reaction of simple arenes with oxygen as the sole oxidant and no redox mediator. Arenes with either electron‐donating or electron‐withdrawing groups can be functionalized in this way. Experimental data on the reaction with toluene as the model arene shows that the C−H activation step is turnover limiting and that the ligand structure is crucial to facilitate the reaction, which supports the involvement of the pyridone fragment in the C−H activation step. In the case of fluoroarenes, the alkenylation of mono and 1,2‐difluoro benzenes requires the presence of bipy‐6‐OH. In contrast, this ligand is detrimental for the alkenylation of 1,3‐difluoro, tri, tetra and pentafluoro benzenes which can be carried out using just [Pd(OAc) 2 ]. This correlates with the acidity of the fluoroarenes, the most acidic undergoing easier C−H activation so other steps of the reaction such as the coordination‐insertion of the olefin become kinetically important for polyfluorinated arenes. The use of just a catalytic amount of sodium molybdate as a base proved to be optimal in all these reactions. magnified image