The quest for the elusive carbodiimide ion HNCNH+ and its generation from ionized cyanamide by proton-transport catalysis

Tandem mass spectrometry based collision experiments and computational chemistry (CBS-QB3/APNO methods) indicate that the elusive carbodiimide ion HNCNH+ is a stable species in the gas-phase. The ion is the most stable of the family of CH2N2+ ions and a very high barrier (87 kcal mol−1) separates it from its tautomer ionized cyanamide, H2N−CN+.The computations also predict that, in the presence of a single H2O molecule as the catalyst, the cyanamide ion isomerizes into the carbodiimide ion. Experiments on the ion-molecule reaction of H2N−CN+ and H2O, a reaction of potential interest in astrochemistry, confirm this prediction.

The isomerization of the cyanamide ion (1) into its more stable carbodiimide tautomer (2) by an intramolecular 1,3-H shift is not feasible but a single H2O molecule catalyzes this reaction in a process termed proton-transport catalysis.