Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 20, Issue 43, Pages 13923-13926Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201403983
Keywords
alkynes; density functional calculations; homogeneous catalysis; palladium; reaction mechanisms
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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 Pd-0 centre, allowing for surmountable barriers (highest Delta G double dagger 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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