Formation of XPhos‐Ligated Palladium(0) Complexes and Reactivity in Oxidative Additions

Understanding the nature of the intermediate species operating within a palladium catalytic cycle is crucial for developing efficient cross‐coupling reactions. Even though the XPhos/Pd(OAc) 2 catalytic system has found numerous applications, the nature of the active catalytic species remains elusive. A Pd 0 complex ligated to XPhos has been detected and characterized in situ for the first time using cyclic voltammetry and NMR techniques. In the presence of XPhos, Pd(OAc) 2 initially associates with the ligand to form a complex in solution, which has been characterized as Pd II (OAc) 2 (XPhos). This Pd II center is then reduced to the Pd 0 (XPhos) 2 species by an intramolecular process. This study also sheds light on the formation of Pd I –Pd I dimers. Finally, a kinetic study probes a dissociative mechanism for the oxidative addition with aryl halides involving Pd 0 (XPhos) as the reactive species in equilibrium with the unreactive Pd 0 (XPhos) 2 . Remarkably, the reportedly poorly reactive PhCl reacts at room temperature in the oxidative addition, which confirms the crucial role of the XPhos ligand in the activation of aryl chlorides.