title: On the Triple Role of Fluoride Ions in Palladium-Catalyzed Stille Reactions.
abstract: The mechanism of Stille reactions (cross-coupling of ArX with Ar'SnnBu3 ) performed in the presence of fluoride ions is established. A triple role for fluoride ions is identified from kinetic data on the rate of the reactions of trans-[ArPdBr(PPh3 )2 ] (Ar=Ph, p-(CN)C6 H4 ) with Ar'SnBu3 (Ar'=2-thiophenyl) in the presence of fluoride ions. Fluoride ions promote the rate-determining transmetallation by formation of trans-[ArPdF(PPh3 )2 ], which reacts with Ar'SnBu3 (Ar'=Ph, 2-thiophenyl) at room temperature, in contrast to trans-[ArPdBr(PPh3 )2 ], which is unreactive. However, the concentration ratio [F(-) ]/[Ar'SnBu3 ] must not be too high, because of the formation of unreactive anionic stannate [Ar'Sn(F)Bu3 ](-) . This rationalises the two kinetically antagonistic roles exerted by the fluoride ions that are observed experimentally, and is found to be in agreement with the kinetic law. In addition, fluoride ions promote reductive elimination from trans-[ArPdAr'(PPh3 )2 ] generated in the transmetallation step.
authors.affiliation: Ecole Normale Supérieure-PSL Research University, Département de Chimie, Sorbonne Universités-UPMC Univ Paris 06, CNRS UMR 8640 PASTEUR, 24 Rue Lhomond, 75231 Paris Cedex 5 (France).
authors.forename: Marius
authors.initials: M
authors.lastname: Hervé
authors.affiliation: CEA-Saclay, DSM-IRAMIS-NIMBE-LCMCE, UMR 3685, 91191 Gif Sur Yvette, Cedex (France).
authors.forename: Guillaume
authors.initials: G
authors.lastname: Lefèvre
authors.affiliation: University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp (Belgium).
authors.forename: Emily A
authors.initials: EA
authors.lastname: Mitchell
authors.affiliation: University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp (Belgium). bert.maes@uantwerpen.be.
authors.forename: Bert U W
authors.initials: BU
authors.lastname: Maes
authors.affiliation: Ecole Normale Supérieure-PSL Research University, Département de Chimie, Sorbonne Universités-UPMC Univ Paris 06, CNRS UMR 8640 PASTEUR, 24 Rue Lhomond, 75231 Paris Cedex 5 (France). Anny.Jutand@ens.fr.
authors.forename: Anny
authors.initials: A
authors.lastname: Jutand
keywords: Stille reaction; fluoride; kinetics; palladium; transmetallation