Mechanism of alkyne alkoxycarbonylation at a Pd catalyst with P,N hemilabile ligands : a density functional study
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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.
Crawford , L , Cole-Hamilton , D J , Drent , E & Buehl , M 2014 , ' Mechanism of alkyne alkoxycarbonylation at a Pd catalyst with P,N hemilabile ligands : a density functional study ' Chemistry - A European Journal , vol 20 , no. 43 , pp. 13923-13926 . DOI: 10.1002/chem.201403983
Chemistry - A European Journal
This is the accepted version of the following article: Crawford, L., Cole-Hamilton, D. J., Drent, E. and Bühl, M. (2014), Mechanism of Alkyne Alkoxycarbonylation at a Pd Catalyst with P,N Hemilabile Ligands: A Density Functional Study. Chem. Eur. J., 20: 13923–13926, which has been published in final form at http://dx.doi.org/10.1002/chem.201403983
The authors thank the School of Chemistry and EaStCHEM for support