Imidazol-2-ylidene-4-olate: an anionic N-heterocyclic carbene pre-programmed for further derivatization.

The 4-hydroxyimidazolium salt, readily prepared in two steps by acylation of a formamidine and quaternization of the second nitrogen, affords, after deprotonation, the anionic imidazol-2-ylidene-4-olate, which can be complexed to a transition metal and still be subsequently functionalized at O or C backbone atom in the outer coordination sphere of the metal.