Three Roles for the Fluoride Ion in Palladium-Catalyzed Hiyama Reactions: Transmetalation of [ArPdFL2] by Ar'Si(OR)3

摘要

From the kinetic data on the transmetalation/ reductive elimination in fluoride-promoted Hiyama reactions, obtained using electrochemical techniques, it has been established that fluoride ions play three roles. F~-reacts with trans-[ArPdBrL,] (L = PPh3) to form trans-fArPdFLJ, which reacts with AtJSi(OMe)3 in the rate-determining transmetalation, whereas trans-/ArPdBrLJ does not react with Ar'Si-(OMe)3. F reacts with ArSi(OMe)3 to deliver the unreactive silicate Ar'SiF(OMe)3~-, thus leading to two antagonistic kinetic effects. In addition, F~ catalyzes the reductive elimination from intermediate trans-[ArPdAr'L2].