title: Sigma-alkylpalladium intermediates in intramolecular Heck reactions:isolation and catalytic activity.
abstract: The isolation of sigma-alkylpalladium Heck intermediates, possible when beta-hydride elimination is inhibited, is a rather rare event. Performing intramolecular Heck reactions on N-allyl-2-halobenzylamines in the presence of [Pd(PPh(3))(4)], we isolated and characterized a series of stable bridged palladacycles containing an iodine or bromine atom on the palladium atom. Indolyl substrates were also tested for isolation of the corresponding complexes. X-ray crystallographic analysis of one of the indolyl derivatives revealed the presence of a five-membered palladacycle with the metal center bearing a PPh(3) ligand and an iodine atom in a cis position with respect to the nitrogen atom. The stability of the sigma-alkylpalladium complexes is probably a consequence of the strong constraint resulting from the bridged junction that hampers the cisoid conformation essential for beta-hydride elimination. Subsequently, the thus obtained bridged five-membered palladacycles were proven to be effective precatalysts in Heck reactions as well as in cross-coupling processes such as Suzuki and Stille reactions.
authors.affiliation: DISMAB, Sezione di Chimica Organica A. Marchesini, Università di Milano, Via Venezian 21, 20133 Milano, Italy.
authors.forename: Egle M
authors.initials: EM
authors.lastname: Beccalli
authors.forename: Elena
authors.initials: E
authors.lastname: Borsini
authors.forename: Stefano
authors.initials: S
authors.lastname: Brenna
authors.forename: Simona
authors.initials: S
authors.lastname: Galli
authors.forename: Micol
authors.initials: M
authors.lastname: Rigamonti
authors.forename: Gianluigi
authors.initials: G
authors.lastname: Broggini