text: A third method involves decarboxylation of NHC-carboxylates.  In this approach, N-methylimidazoles react with methyl formate to give zwitterionic N,N-dimethylimidazolium-2-carboxylate.  This zwitterion decarboxylates in the presence of metal ions to give N,Ndimethylimidazolidene-based NHC complexes.