Direct C-metallation of N-substituted triazoles promoted by mercury acetate. An alternative route to N-heterocyclic carbene complexes

Abstract

C-Metallation of neutral mono-substituted triazoles could be induced by Hg(OAc)₂ to give a near quantitative yield of C,N-bonded mercury complexes. Initial N-coordination to mercury(II) is confirmed by NMR spectroscopy. Subsequent acetate assisted deprotonation–metallation is a viable route to C-metallated products. Hg(OAc)₂ is unique for this reaction. Metal salts of Ag₂O, Ag(OAc), Pd(OAc)₂ or HgCl₂ in combination with bases of NaOH and K₂CO₃ did not yield triazolate complexes. Further reaction of one of these mercury(II)–C,N-triazolate complexes with a source of methyl cation yielded a monomeric N-heterocyclic carbene complex. Therefore the facile reaction of triazole with Hg(OAc)₂ followed by alkylation is a handy alternative way to prepare Hg–NHCs.