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.