Reactions

The catalytic cycle begins with the oxidative addition of the aryl halide to the active palladium(0) complex, generating a palladium(II) intermediate (1). This latter then undergoes coordination of the amine, which increases the acidity of the amine proton (2). Subsequent deprotonation by a base (typically sodium tert-butoxide or cesium carbonate) yields a palladium(II) amido intermediate (3). Finally, reductive elimination occurs and affords the arylated amine product while simultaneously regenerating the active palladium(0) catalyst (4).

Competitive pathways: when the amine substrate possesses a hydrogen atom at the β position relative to nitrogen, a competitive β-hydride elimination side reaction can occur from the palladium(II) amide intermediate (A). This step yields a coordinated imine and a palladium(II) hydride species. Subsequently, reductive elimination occurs and gives the undesired aryl product and releases imine by-product (B).
To prevent this side reaction, the use of dialkyl phosphine ligands (XPhos for example) is a good solution. Indeed, these ligands are incredibly bulky and the steric congestion around the palladium center creates immense strain, which drives the complex to undergo rapid reductive elimination