Shedding Light on the Precatalytic Mixture of Pd(OAc)2 and Cooperating Bipyridone Ligands for the C─H Functionalization of Arenes

Abstract

The use of a mixture of a precursor palladium compound and a ligand as precatalyst is a common practice in metal catalyzed organic synthesis. In general, little attention is paid to how these mixtures develop into the active species, but this is crucial for an efficient catalysis. We describe here the complexes that are obtained from Pd(OAc)2 and PdCl2 and the chelating bipyridones [2,2′- bipyridin]-6(1H)-one (bipy-6-OH) and 1,10-phenanthrolin-2(1H)-one (phen-2-OH). This type of ligands plays a cooperating role in the C─H activation step and are useful in many Pd-catalyzed C─H functionalization reactions. Both monomeric and dimeric complexes were obtained. The catalytic performance observed when using the isolated, well defined Pd-ligand complexes and the Pd(OAc2)/ligand mixtures in a model direct arylation of toluene have been analyzed, as well as the plausible pathway for the generation of Pd(0) active species under catalytic conditions.