Role of dppf Monoxide in the Transmetalation Step of the Suzuki–Miyaura Coupling Reaction

Diphosphine ligands are frequently used in palladium-catalyzed Suzuki–Miyaura (S-M) reactions. Despite their widespread application in both academic and industrial settings, their role in the B-to-Pd transmetalation has not been firmly established. We combined electrochemistry, NMR spectroscopy, and DFT calculations to elucidate the role of dppf (1,1′-bis(diphenylphosphino)ferrocene) in this key elementary step of the S-M reaction. We observed that excess dppf inhibits transmetalation involving PhB(OH)2 and dppf-ligated arylpalladium(II) complexes, while an optimal [base]/[PhB(OH)2] ratio maximizes the concentration of a [Pd–O–B] key intermediate. In situ oxidation of dppf to the diphosphine monoxide dppfO can take place in the presence of base, leading to dppfO-ligated arylpalladium(II) complexes, which readily undergo transmetalation at room temperature. These findings suggest guidelines for the rational optimization of diphosphine-promoted S-M reactions.