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Updated: Feb 23, 2026

Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
Published on: July 30, 2017
A convenient access to N-phosphonio-substituted NHC metal complexes [M = Ag(i), Rh(i), Pd(ii)]
Idir Benaissa1, Rachid Taakili1, Noël Lugan1
1LCC-CNRS, Université de Toulouse, INPT, UPS, 205 route de Narbonne, 31077 Toulouse Cedex 4, France. yves.canac@lcc-toulouse.fr.
Abstract:
A series of NHC pre-ligands featuring a pendant phosphonium moiety attached to N' position through a propyl linker was readily obtained upon quaternization of N-mesityl- and N-methyl-imidazole, or N-mesityl-imidazoline using (3-bromo-propyl)-triphenylphosphonium bromide. Reactions of the resulting dicationic salts with [PdCl(allyl)]2 in the presence of K2CO3 afforded the anticipated NHC-ligated Pd(ii) metal complexes in high yields. Further treatment of the latter complexes with tBuOK induced a deprotonation of the carbon atom adjacent to the phosphonium moiety and the formation of the corresponding C,C-chelating NHC-phosphonium ylide Pd(ii) complexes. Investigation of an alternative synthetic route involving a silver transmetallation reaction incidentally allowed isolation and full characterization of an unusual dimeric tetranuclear NHC Ag(i) complex of general formula [(NHC∼P+)2(Ag4Br6)2-].
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