Generation of Tertiary Phosphine-Coordinated Pd(0) Species from Pd(OAc)2 in the Catalytic Heck Reaction

Palladium(II) diacetate reacted with water (1 equiv./Pd) and (R)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl ((R)-BINAP) (3 equiv./Pd) in benzene in the presence of Et3N to give the palladium(0) species Pd[(R)-BINAP]2 (1 equiv./Pd), (R)-BINAP monoxide (1 equiv./Pd), and Et3N·HOAc (2 equiv./Pd). The progress of reaction strongly affected by the content of water in the reaction solution. The reduction of Pd(OAc)2 in the presence of PPh3 proceeded in a similar process to give Pd(PPh3)4 and OPPh3.