title: Mechanism of alkyne alkoxycarbonylation at a Pd catalyst with P,N hemilabile ligands: a density functional study.
abstract: A detailed mechanism for alkyne alkoxycarbonylation mediated by a palladium catalyst has been characterised at the B3PW91-D3/PCM level of density functional theory (including bulk solvation and dispersion corrections). This transformation, investigated via the methoxycarbonylation of propyne, involves a uniquely dual role for the P,N hemilabile ligand acting co-catalytically as both an in situ base and proton relay coupled with a Pd(0) centre, allowing for surmountable barriers (highest ΔG(≠) of 22.9 kcal mol(-1) for alcoholysis). This proton-shuffle between methanol and coordinated propyne accounts for experimental requirements (high acid concentration) and reproduces observed regioselectivities as a function of ligand structure. A simple ligand modification is proposed, which is predicted to improve catalytic turnover by three orders of magnitude.
authors.affiliation: University of St. Andrews, School of Chemistry, North Haugh, St. Andrews, Fife, KY16 9ST (UK).
authors.forename: Luke
authors.initials: L
authors.lastname: Crawford
authors.forename: David J
authors.initials: DJ
authors.lastname: Cole-Hamilton
authors.forename: Eite
authors.initials: E
authors.lastname: Drent
authors.forename: Michael
authors.initials: M
authors.lastname: Bühl
keywords: alkynes; density functional calculations; homogeneous catalysis; palladium; reaction mechanisms