title: Palladium(II) complexes of new bulky bidentate phosphanes: active and highly regioselective catalysts for the hydroxycarbonylation of styrene.
abstract: The synthesis of four new bulky bidentate phosphines that possess both tert-butyl and trifluoromethylphenyl substituents is described. Symmetric ligands were readily obtained by alkylation of phosphidoboranes of the type Li[P(BH(3))(tBu)(Ar)] with dihaloalkanes. Non-symmetric ligands were prepared from a new stable precursor, tBu(2)P(BH(3))(CH(2))(3)Br, that should prove useful for other ligand syntheses. Palladium(II) complexes of the four new ligands were prepared and were characterised by spectroscopic methods, microanalysis and X-ray crystallography. The new [PdCl(2)(L)] complexes were evaluated as catalysts for the hydroxycarbonylation of styrene and found to give unprecedented regioselectivity and yields for a diphosphine-based catalyst. A study on promoter effects reveals that the presence of acid and chloride is necessary to achieve such selectivities. It has been proposed in the literature that such conditions result in a new pathway in which styrene is converted into 2-phenethyl chloride, with the latter being the real substrate in the reaction. However, a deuterium labelling study seems to rule out this mechanism, at least under the conditions used herein.
authors.affiliation: School of Chemistry, University of St Andrews, EaStCHEM, St Andrews, Fife, KY16 9ST, UK.
authors.forename: Jamie J R
authors.initials: JJ
authors.lastname: Frew
authors.forename: Karen
authors.initials: K
authors.lastname: Damian
authors.forename: Hendrik
authors.initials: H
authors.lastname: Van Rensburg
authors.forename: Alexandra M Z
authors.initials: AM
authors.lastname: Slawin
authors.forename: Robert P
authors.initials: RP
authors.lastname: Tooze
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Clarke