Mechanism of Alkyne Alkoxycarbonylation at a Pd Catalyst with P,N Hemilabile Ligands: A Density Functional Study |
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| Authors: | Luke Crawford Prof David J Cole‐Hamilton Prof Eite Drent Prof Michael Bühl |
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| Institution: | 1. University of St. Andrews, School of Chemistry, North Haugh, St. Andrews, Fife, KY16 9ST (UK);2. Leiden Institute of Chemistry, Leiden University PO Box 9502, 2300 RA Leiden (The Netherlands) |
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| 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 Pd0 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. |
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| Keywords: | alkynes density functional calculations homogeneous catalysis palladium reaction mechanisms |
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