Role of Fluoride Ions in Palladium-Catalyzed Cross-Coupling Reactions

Fluoride ions are known to promote Suzuki-Miyaura, Hiyama, and Stille reactions [cross-coupling between aryl halides ArX and nucleophiles Ar'B(OH)(2), Ar'Si(OMe)(3), and Ar'SnBu3, respectively], where they exert a similar triple role: (1) They favor transmetalation by formation of trans-ArPdFL2 (L = PPh3) complexes that react with the nucleophiles in contrast to trans-ArPdXL2. (2) They catalyze the reductive elimination from trans-ArPdAr'L-2. generated in the transmetalation. (3) The final role is negative, by formation of unreactive anionic species [Ar'BF(OH)(2)](-), [Ar'SiF(OMe)(3)](-), or [Ar'SnFBu3](-), respectively. Consequently the rate of the rate-determining transmetalation is controlled by the concentration ratio [F-]/[nucleophile] which must be less or close to one to ensure fast transmetalation. 1 Introduction 2 Reaction of Fluoride Ions with ArPdXL2 Complexes 3 The Triple Role of Fluoride Ions in Suzuki-Miyaura Reactions 4 The Triple Role of Fluoride Ions in Hiyama Reactions 5 The Triple Role of Fluoride Ions in Stille Reactions 6 Conclusion