title: Mechanistic studies on the Pd-catalyzed vinylation of aryl halides with vinylalkoxysilanes in water: the effect of the solvent and NaOH promoter.
abstract: The mechanism of the Pd-catalyzed vinylation of aryl halides with vinylalkoxysilanes in water has been studied using different catalytic precursors. The NaOH promoter converts the initial vinylalkoxysilane into a highly reactive water-soluble vinylsilanolate species. Similarly, deuterium-labeling experiments have shown that, irrespective of the catalytic precursor used, vinylation occurs exclusively at the CH vinylic functionality via a Heck reaction and not at the C-Si bond via a Hiyama cross-coupling. The involvement of a Heck mechanism is interpreted in terms of the reduced nucleophilicity of the base in water, which disfavors the transmetalation step. The Heck product (β-silylvinylarene) undergoes partial desilylation, with formation of a vinylarene, by three different routes: (a) hydrolytic desilylation by the aqueous solvent (only at high temperature); (b) transmetalation of the silyl olefin on the PdH Heck intermediate followed by reductive elimination of vinylarene; (c) reinsertion of the silyl olefin into the PdH bond of the Heck intermediate followed by β-Si syn-elimination. Both the Hiyama and Heck catalytic cycles and desilylation mechanisms b and c have been computationally evaluated for the [Pd(en)Cl2] precursor in water as solvent. The calculated Gibbs energy barriers support the reinsertion route proposed on the basis of the experimental results.
authors: Departamento de Química Orgánica y Química Inorgánica, Universidad de Alcalá , Edificio de Farmacia, Campus Universitario, E28871 Alcalá de Henares, Madrid, Spain.
authors: Alvaro
authors: A
authors: Gordillo
authors: Manuel A
authors: MA
authors: Ortuño
authors: Carmen
authors: C
authors: López-Mardomingo
authors: Agustí
authors: A
authors: Lledós
authors: Gregori
authors: G
authors: Ujaque
authors: Ernesto
authors: E
authors: de Jesús
mesh_terms: D002384:Catalysis; D015394:Molecular Structure; D010165:Palladium / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry*; D012972:Sodium Hydroxide / Q000737:chemistry*; D012995:Solubility; D013237:Stereoisomerism; D014753:Vinyl Compounds / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D012821:Silanes; D014753:Vinyl Compounds; D014867:Water; D012972:Sodium Hydroxide; D010165:Palladium