Imidazol-2-yl complexes of Cp*Ir as bifunctional ambident reactants.

Loss of chloride ion from imidazol-2-yl complex 4a activates the H-H bond of dihydrogen or the C-H bond of acetylene, forming an Ir(III) N-heterocyclic carbene (NHC) complex (3b or 9). Deprotonation of Ir(III) hydride 4b gives one new species, formulated as Ir(I) carbene complex 5. Protonation or alkylation of 5 occurs at the metal, returning the Ir(III) core of 6a,b. Deprotonation of cationic NHC complex 3a gives neutral imidazol-2-yl analogue 4a; as seen by X-ray diffraction, the Ir-C bond in 3a is shorter than that in 4a. These and other comparisons and interconversions of NHC complexes with an NH function and related imidazol-2-yl species expand the potential of NHC complexes by showing their bifunctional character.