Direct Cyclopalladation of Fluorinated Benzyl Amines by Pd₃(OAc)₆: The Coexistence of Multinuclear Pd_n Reaction Pathways Highlights the Importance of Pd Speciation in C-H Bond Activation

Palladacycles are key intermediates in catalytic C-H bond functionalization reactions and important precatalysts for cross-couplings. It is commonly believed that palladacycle formation occurs through the reaction of a substrate bearing a C-H bond ortho to a suitable metal-directing group for interaction with, typically, mononuclear "Pd(OAc)₂" species, with cyclopalladation liberating acetic acid as the side product. In this study, we show that N,N-dimethyl-fluoro-benzyl amines, which can be cyclopalladated either ortho or para to fluorine affording two regioisomeric products, can occur by a direct reaction of Pd₃(OAc)₆, proceeding via higher-order cyclopalladated intermediates. Regioselectivity is altered subtly depending on the ratio of substrate:Pd₃(OAc)₆ and the solvent used. Our findings are important when considering mechanisms of Pd-mediated reactions involving the intermediacy of palladacycles, of particular relevance in catalytic C-H bond functionalization chemistry.