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Updated: May 29, 2026

Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
Published on: July 30, 2017
Imidazolidene carboxylate bound MBPh4 complexes (M = Li, Na) and their relevance in transcarboxylation reactions
Bret R Van Ausdall1, Nils F Poth, Virginia A Kincaid
1Department of Chemistry, Henry Eyring Building, University of Utah, 315 S. 1400 E, Salt Lake City, Utah 84112-0850, United States.
Abstract:
Combination of 1,3-bis(2,6-diisopropylphenyl)imidazolum-2-carboxylate (IPrCO(2)) with the Lewis acids MBPh(4), where M = Li or Na, provided two separate complexes. The crystal structures of these complexes revealed that coordination to NaBPh(4) yielded a dimeric species, yet coordination of IPrCO(2) with LiBPh(4) yielded a monomeric species. Combination of 1,3-bis(2,4,6-trimethylphenyl)imidazolum-2-carboxylate (IMesCO(2)) with LiBPh(4) also afforded a dimeric species that was similar in global structure to that of the IPrCO(2)+NaBPh(4) dimer. In all three cases, the cation of the organic salt was coordinated to the oxyanion of the zwitterionic carboxylate. Thermogravimetric analysis of the crystals demonstrated that decarboxylation occurred at lower temperatures than the decarboxylation temperature of the parent NHC·CO(2) (NHC = N-heterocyclic carbene). Kinetic analysis of the transcarboxylation of IPrCO(2) to acetophenone with NaBPh(4) to yield sodium benzoylacetate was performed. First-order dependences were observed for IPrCO(2) and acetophenone, whereas zero -order dependence was observed for NaBPh(4). Direct dicarboxylation was observed when I(t)BuCO(2) was added to MeCN in the absence of added MBPh(4).
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