Palladium(II)-Catalyzed C----H Activation/C----C Cross-Coupling Reactions: Versatility and Practicality

Pick your Pd partners: A number of catalytic systems have been developed for palladium-catalyzed C---H activation/C---C bond formation. Recent studies concerning the palladium(II)-catalyzed coupling of C---H bonds with organometallic reagents through a PdII/Pd⁰ catalytic cycle are discussed (see scheme), and the versatility and practicality of this new mode of catalysis are presented. Unaddressed questions and the potential for development in the field are also addressed.In the past decade, palladium-catalyzed C---H activation/C---C bond-forming reactions have emerged as promising new catalytic transformations; however, development in this field is still at an early stage compared to the state of the art in cross-coupling reactions using aryl and alkyl halides. This Review begins with a brief introduction of four extensively investigated modes of catalysis for forming C---C bonds from C---H bonds: PdII/Pd⁰, PdII/PdIV, Pd⁰/PdII/PdIV, and Pd⁰/PdII catalysis. A more detailed discussion is then directed towards the recent development of palladium(II)-catalyzed coupling of C---H bonds with organometallic reagents through a PdII/Pd⁰ catalytic cycle. Despite the progress made to date, improving the versatility and practicality of this new reaction remains a tremendous challenge.