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Mechanisms in the Reaction of Palladium(II)–π-Allyl Complexes with Aryl Halides: Evidence for NHC Exchange Between Two Palladium Complexes

  1. Adrien T. Normand Dr.1,2,
  2. Mikhail S. Nechaev Dr.3,
  3. Kingsley J. Cavell Prof.1

Article first published online: 2 JUL 2009

DOI: 10.1002/chem.200900373

Issue

Chemistry - A European Journal

Chemistry - A European Journal

Volume 15, Issue 29, pages 7063–7073, July 20, 2009

Additional Information

How to Cite

Normand, A., Nechaev, M. and Cavell, K. (2009), Mechanisms in the Reaction of Palladium(II)–π-Allyl Complexes with Aryl Halides: Evidence for NHC Exchange Between Two Palladium Complexes. Chemistry - A European Journal, 15: 7063–7073. doi: 10.1002/chem.200900373

Author Information

  1. 1

    School of Chemistry, Cardiff University, 51 Park Place, Cardiff CF10 3AT, Wales (UK), Fax: (+44) 29-208-74075

  2. 2

    Present address: Department of Chemistry and Center for Catalysis Research and Innovation, University of Ottawa, 10 Marie Curie Street, Ottawa K1N 6H5, ON (Canada)

  3. 3

    Department of Chemistry, M. V. Lomonosov Moscow State University, Leninskie Gory 1/3, Moscow 119991 (Russia)

Publication History

  1. Issue published online: 13 JUL 2009
  2. Article first published online: 2 JUL 2009
  3. Manuscript Revised: 25 APR 2009
  4. Manuscript Received: 10 FEB 2009

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Keywords:

  • carbene ligands;
  • density functional calculations;
  • palladium;
  • transmetalation

Graphical Abstract

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Strong bonds easily broken: The reaction between a family of PdII–NHC complexes and aryl halides yields 2-arylimidazolium salts with complete selectivity. The mechanism of this intriguing reaction was investigated by kinetic experiments and DFT calculations. An autocatalytic ligand transfer mechanism is shown to operate and strong evidence was found for an unusual NHC exchange between two palladium complexes.

Abstract

A detailed experimental and DFT study (PBE level) of the reaction of [Pd(η3-C3H5)(tmiy)(PR3)]BF4 (tmiy=tetramethylimidazolin-2-ylidene, PR3=phosphane), precursors to monoligated Pd0 species, with aryl electrophiles yielding 2-arylimidazolium salt is reported. Experiments establish that an autocatalytic ligand transfer mechanism is preferred over PdIV and σ-bond metathesis pathways, and that transmetalation is the rate-determining step. Calculations indicate that the key step involves the concerted exchange of NHC and iodo ligands between two different PdII complexes. This is corroborated by experimental results showing the slower reaction of complexes containing the bulkier dipdmiy (dipdmiy = diisopropyldimethylimidazolin-2-ylidene).

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