Charge‐Tagged N‐Heterocyclic Carbenes (NHCs): Revealing the Hidden Side of NHC‐Catalysed Reactions through Electrospray Ionization Mass Spectrometry

Abstract

N-heterocyclic carbenes (NHCs) are key intermediates in a variety of chemical reactions. Owing to their transient nature, the interception and characterization of these reactive species have always been challenging. Similarly, the study of reaction mechanisms in which carbenes act as catalysts is still an active research field. This Minireview describes the contribution of electrospray ionization mass spectrometry (ESI-MS) to the detection of charge-tagged NHCs resulting from the insertion of an ionic group into the molecular scaffold. The use of different mass spectrometric techniques, combined with the chargetagging strategy, allowed clarification of the involvement of NHCs in archetypal reactions and the study of their intrinsic chemistry.

Free N‐heterocyclic carbenes from Brønsted acidic ionic liquids: Direct detection by electrospray ionization mass spectrometry

“…[17][18][19] In this context, the coupling of MS with soft ionization techniques, such as electrospray ionization (ESI), allows one to intercept elusive intermediates, and gently transfer them from solution to the gas-phase environment for structural and reactivity investigations. [20][21][22] Therefore, the chemistry of NHCs has been assessed in the gas phase, [23][24][25][26][27] also in the view of knowing their detailed reaction mechanism to gain desirable benefits for solution chemistry. Free NHCs can be obtained in the gas phase, as well as in solution, by adding strong bases 28,29 or eventually forcing a hydrogen transfer reaction by collisionally dissociating the ion pair of the parent IL.…”

Kinetic Study of the Maillard Reaction in Thin Film Generated by Microdroplets Deposition

“…The electrospray ionization (ESI) source of a mass spectrometer operating under ambient conditions can be considered as a miniaturized laboratory by which the reactions taking place at the liquid-gas interface can be easily studied [1][2][3][4][5][6][7]. The charged microdroplets generated in the ESI process represent confined reaction volumes where the rate of the chemical reactions can be accelerated hundreds of times with respect to the same processes performed in bulk [8][9][10][11][12][13][14][15].…”