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Cooperative catalytic methoxycarbonylation of alkenes: uncovering the role of palladium complexes with hemilabile ligands

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Abstract

Mechanistic studies of the catalyst [Pd2(dba)3/1,1′-bis(tert-butyl(pyridin-2-yl)phosphanyl)ferrocene, L2] for olefin alkoxycarbonylation reactions are described. X-ray crystallography reveals the coordination of the pyridyl nitrogen atom in L2 to the palladium center of the catalytic intermediates. DFT calculations on the elementary steps of the industrially relevant carbonylation of ethylene (the Lucite α-process) indicate that the protonated pyridyl moiety is formed immediately, which facilitates the formation of the active palladium hydride complex. The insertion of ethylene and CO into this intermediate leads to the corresponding palladium acyl species, which is kinetically reversible. Notably, this key species is stabilized by the hemilabile coordination of the pyridyl nitrogen atom in L2. The rate-determining alcoholysis of the acyl palladium complex is substantially facilitated by metal–ligand cooperation. Specifically, the deprotonation of the alcohol by the built-in base of the ligand allows a facile intramolecular nucleophilic attack on the acyl palladium species concertedly. Kinetic measurements support this mechanistic proposal and show that the rate of the carbonylation step is zero-order dependent on ethylene and CO. Comparing CH3OD and CH3OH as nucleophiles suggests the involvement of (de)protonation in the rate-determining step.

Graphical abstract: Cooperative catalytic methoxycarbonylation of alkenes: uncovering the role of palladium complexes with hemilabile ligands

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Publication details

The article was received on 06 Jul 2017, accepted on 19 Jan 2018 and first published on 07 Feb 2018


Article type: Edge Article
DOI: 10.1039/C7SC02964K
Citation: Chem. Sci., 2018, Advance Article
  • Open access: Creative Commons BY license
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    Cooperative catalytic methoxycarbonylation of alkenes: uncovering the role of palladium complexes with hemilabile ligands

    K. Dong, R. Sang, Z. Wei, J. Liu, R. Dühren, A. Spannenberg, H. Jiao, H. Neumann, R. Jackstell, R. Franke and M. Beller, Chem. Sci., 2018, Advance Article , DOI: 10.1039/C7SC02964K

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