Ag(I)-Catalyzed C–H Activation: The Role of the Ag(I) Salt in Pd/Ag-Mediated C–H Arylation of Electron-Deficient Arenes

The use of stoichiometric Ag(I)-salts as additives in Pd-catalyzed C–H functionalization reactions is widespread. It is commonly proposed that this additive acts as an oxidant or as a halide scavenger promoting Pd-catalyst turnover. We demonstrate that, contrary to current proposals, phosphine ligated Ag(I)-carboxylates can efficiently carry out C–H activation on electron-deficient arenes. We show through a combination of stoichiometric and kinetic studies that a (PPh3)Ag-carboxylate is responsible for the C–H activation step in the Pd-catalyzed arylation of Cr(CO)3-complexed fluorobenzene. Furthermore, the reaction rate is controlled by the rate of Ag(I)-C–H activation, leading to an order zero on the Pd-catalyst. H/D scrambling studies indicate that this Ag(I) complex can carry out C–H activation on a variety of aromatic compounds traditionally used in Pd/Ag-mediated C–H functionalization methodologies.