Palladium–catalysed alkyne alkoxycarbonylation with P,N chelating ligands revisited : a density functional theory study
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A revised in situ base mechanism of alkyne alkoxycarbonylation via a Pd catalyst with hemilabile P,N-ligands (PyPPh2, Py = 2-pyridyl) has been fully characterised at the B3PW91-D3/PCM level of density functional theory. Key intermediates on this route are acryloyl (η3-propen-1-oyl) complexes that readily undergo methanolysis. With two hemilabile P,N-ligands and one of them protonated, the overall computed barrier is 24.5 kcal mol-1, which decreases to 20.3 kcal mol-1 upon protonation of the second P,N-ligand. This new mechanism is consistent with all of the experimental data relating to substituent effects on relative reaction rates and branched/linear selectivities, including new results on the methoxycarbonylation of phenylacetylene using (4-NMe2Py)PPh2 and (6-Cl-Py)PPh2 ligand. This ligand is found to decrease catalytic activity over PyPPh2, thus invalidating a formerly characterised in situ base mechanism.
Ahmad , S , Lockett , A , Shuttleworth , T , Miles-Hobbs , A , Pringle , P & Buehl , M 2019 , ' Palladium–catalysed alkyne alkoxycarbonylation with P,N chelating ligands revisited : a density functional theory study ' , Physical Chemistry Chemical Physics , vol. 21 , no. 16 , pp. 8543-8552 . https://doi.org/10.1039/C9CP01471C
Physical Chemistry Chemical Physics
Copyright © 2019 The Author(s). This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1039/C9CP01471C
DescriptionAuthors thank EaStCHEM and the School of Chemistry for support. The Bristol Chemical Synthesis Centre for Doctoral Training (BCS CDT) funded by the Engineering and Physical Sciences Research Council (EPSRC) (EP/G036764/1) and the University of Bristol are thanked for a PhD studentship (to T. A. S.).
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