present report discloses a modular synthetic route to a new type of anionic N-heterocyclic carbene ligand incorporating an enolate group as a reactive backbone component of its heterocyclic framework. The presence of such a reactive unit facilitates further tailoring of the ligand, even after its complexation to transition metals, with concomitant tuning of the electronic donor properties of the carbene
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.