The complexes [Pd(η²-dmfu)(P–N)] [P–N = 2-(PPh₂)C₆H₄-1-CHNR, R = C₆H₄OMe-4; CHMe₂; C₆H₃Me₂-2,6; C₆H₃(CHMe₂)-2,6] react with an excess of BrC₆H₄R¹-4 (R¹ = CF₃; Me) yielding the oxidative addition products [PdBr(C₆H₄R¹-4)(P–N)] at different rates depending on R [C₆H₄OMe-4 > C₆H₃(CHMe₂)-2,6 > CHMe₂ ≈ C₆H₃Me₂-2,6] and R¹ (CF₃ ≫ Me). In the presence of K₂CO₃ and activated olefins (ol = dmfu, fn), the latter compounds react with an excess of 4-R²C₆H₄B(OH)₂ (R² = H, Me, OMe, Cl) to give [Pd(η²-ol)(P–N)] and the corresponding biaryl through transmetallation and fast reductive elimination. The transmetallation proceeds via a palladium(II) intermediate with an O-bonded boron anion, the formation of which is markedly retarded by increasing the bulkiness of R. The intermediate was isolated for R = CHMe₂, R¹ = CF₃ and R² = H. The boron anion is formulated as a diphenylborinate anion associated with phenylboronic acid and/or as a phenylboronate anion associated with diphenylborinic acid. In general, the oxidative addition proceeds at a lower rate than transmetallation and represents the rate-determining-step in the coupling reaction of aryl bromides with arylboronic acids catalyzed by [Pd(η²-dmfu)(P–N)].