Charge-tagged N-heterocyclic carbenes

The interception, formation and characterization of the first stable, long lived charge-tagged N-heterocyclic carbenes of the general type 4(x+) (x = 1-3) and analogues is reported. Via ESI(+)-MS of solutions of bromine salts of doubly, triply and quadruply charged imidazolium ion IL (3. Br-n, n = 2-4), the isolated 4(x+) as well as charged aggregates [3.Br(n-x)](x+) likely to be participating in the [3.Br(n-x)](x+) reversible arrow 4(x+) + HBr solution equilibrium could be transferred and characterized in the gas phase. Mimicking the solution equilibrium, the gaseous [3.Br(n-x)](x+) were found to dissociate nearly exclusively via HBr loss during thermal activation via collisions to form gaseous 4(x+), which were found to add to acrolein and acetone.