Reactivity of a cationic N-heterocyclic carbene and its corresponding dicationic precursor

Detailed studies concerning the reactivity of the dicationic organometallic carbene precursor 1 and its related free cationic carbene 2 have been carried out. While dication 1 is stable in O-donor solvents like acetone, nitromethane and even water, it is degraded by softer nucleophiles like acetonitrile or electron rich aromatics. In contrast to the hydrolytic stability of dication 1, the cationic carbene 2a reacts readily with water to form the ring-opened formamide derivative 5a. The mechanism of the hydrolytic cleavage reaction was analysed by DFT calculations.

The dicationic (η6-RuCp*)benzimidazolium species 1 is stable in oxygen donor solvents like H3CNO2 or acetone – even in the presence of water – whereas the Cp*Ru+ fragment is cleaved off by acetonitrile or electron rich aromatics. The cationic carbene 2 reacts readily with water to afford the ring-opened formamide derivative 3. The mechanism of this hydrolytic cleavage reaction has been analysed by DFT calculations.Figure optionsDownload as PowerPoint slideHighlights
► A dicationic (η6-RuCp*)benzimidazolium is stable in water but degraded in acetonitrile.
► The corresponding cationic carbene is hydrolized under ring opening.
► A mechanism of the hydrolytic cleavage is suggested by DFT calculations.