title: Primary products and mechanistic considerations in alkane metathesis.
abstract: Alkane metathesis, a reaction catalyzed by the silica-supported tantalum hydride [(SiO)2Ta-H], 1, which transforms acyclic alkanes into their higher and lower homologues, was reported in 1997. New studies conducted in a continuous flow reactor in the case of propane indicate that, by varying the contact time, hydrogen and olefins are primary products. This crucial observation, as well as the known properties of tantalum alkyls to perform alpha-H or beta-H eliminations, supports the proposition of a new mechanism involving metallacyclobutane intermediates just like in olefin metathesis. The observed selectivities for linear and branched Cn+1 and Cn+2 products as well as the linear/branched ratio can be well-explained on the basis of the minimization of steric interactions between 1,2- or 1,3-substituents in the various tantallacyclobutane intermediates or during their formation. Hydrogen plays a specific role in the cleavage of metal alkyls to complete the catalytic cycle.
authors.affiliation: Laboratoire de Chimie Organométallique de Surface (UMR 9986 CNRS-ESCPE Lyon), ESCPE Lyon, 43 Bd du 11 Novembre 1918, 69616 Villeurbanne, Cédex, France. basset@cpe.fr
authors.forename: Jean Marie
authors.initials: JM
authors.lastname: Basset
authors.forename: Christophe
authors.initials: C
authors.lastname: Copéret
authors.forename: Laurent
authors.initials: L
authors.lastname: Lefort
authors.forename: Barry M
authors.initials: BM
authors.lastname: Maunders
authors.forename: Olivier
authors.initials: O
authors.lastname: Maury
authors.forename: Erwan
authors.initials: E
authors.lastname: Le Roux
authors.forename: Guillaume
authors.initials: G
authors.lastname: Saggio
authors.forename: Sophie
authors.initials: S
authors.lastname: Soignier
authors.forename: Daravong
authors.initials: D
authors.lastname: Soulivong
authors.forename: Glenn J
authors.initials: GJ
authors.lastname: Sunley
authors.forename: Mostafa
authors.initials: M
authors.lastname: Taoufik
authors.forename: Jean
authors.initials: J
authors.lastname: Thivolle-Cazat