In recent years, task-specific Brønsted acidic ionic liquids (BAILs) have become increasingly popular and widely used in industrial processes since, as non-volatile materials, they are considered less harmful and corrosive than traditional liquid acids.1 The presence of carboxylic acid groups into the cation scaffold of BAILs represents indeed an important opportunity for the discovery of novel applications and new materials. In situ formation of free N-heterocyclic carbenes (NHC) from Brønsted acidic ionic liquids will be studied, highlighting the crucial role of the anion basicity in promoting the C2-H proton abstraction from imidazolium cations with a carboxylic side chain. The question of the presence of free NHC in the reaction medium is current and of utmost importance being related to the interest in NHC in synthetic chemistry and catalysis, which remains as high as ever.2 The acidic carboxylic group inserted on the N-side chains of the cation can act as a “charge tag” for the direct detection of NHCs in ILs by mass spectrometry (MS). The coupling of MS techniques with soft ionization methods, such as electrospray ionization (ESI), allows one to intercept elusive intermediates, and gently transfer them from the solution to the gas-phase environment for structural and reactivity investigations.3 This experimental study can prove the possibility of using BAILs to furnish proper amounts of stable NHCs. The results can pave the way to the use of the novel compounds as MAIAc (see Fig. 1) and other customized BAILs as catalysts in carbene-mediated reactions, avoiding the use of other bases, generally added to the reaction bulk, with high benefits for organic synthesis. References [1] a) Sarma, P., Dutta, A. K., Borah, R. Catal. Surv. Asia, 2017, 21, 70-93; b) J. S. Wilkes, J. Mol. Catal. A: Chem., 2004, 214, 11-17. [2] Chiarotto, I., Mattiello, L., Pandolfi, F., Rocco, D., Feroci, M. Front. Chem., 2018, 6, 355. [3] a) Troiani, A., de Petris, G., Pepi, F., Garzoli, S., Salvitti, C., Rosi, M. Ricci, A. ChemistryOpen, 2019, 8, 1190-1198; b) Salvitti, C., Chiarotto,I., Pepi, F., Troiani, A. ChemPlusChem, 2021, 86, 209-223.
Free N-heterocyclic carbenes from Bronsted Acidic Ionic Liquids: Direct detection by electrospray ionization mass spectrometry and study of their speciation / Chiarotto, Isabella; Troiani, Anna; Salvitti, Chiara; DE PETRIS, Giulia. - (2022). (Intervento presentato al convegno 1° Congresso nazionale divisione di Chimica per le Tecnologie tenutosi a Napoli).
Free N-heterocyclic carbenes from Bronsted Acidic Ionic Liquids: Direct detection by electrospray ionization mass spectrometry and study of their speciation
Isabella Chiarotto
;Anna Troiani;Chiara Salvitti;Giulia de Petris
2022
Abstract
In recent years, task-specific Brønsted acidic ionic liquids (BAILs) have become increasingly popular and widely used in industrial processes since, as non-volatile materials, they are considered less harmful and corrosive than traditional liquid acids.1 The presence of carboxylic acid groups into the cation scaffold of BAILs represents indeed an important opportunity for the discovery of novel applications and new materials. In situ formation of free N-heterocyclic carbenes (NHC) from Brønsted acidic ionic liquids will be studied, highlighting the crucial role of the anion basicity in promoting the C2-H proton abstraction from imidazolium cations with a carboxylic side chain. The question of the presence of free NHC in the reaction medium is current and of utmost importance being related to the interest in NHC in synthetic chemistry and catalysis, which remains as high as ever.2 The acidic carboxylic group inserted on the N-side chains of the cation can act as a “charge tag” for the direct detection of NHCs in ILs by mass spectrometry (MS). The coupling of MS techniques with soft ionization methods, such as electrospray ionization (ESI), allows one to intercept elusive intermediates, and gently transfer them from the solution to the gas-phase environment for structural and reactivity investigations.3 This experimental study can prove the possibility of using BAILs to furnish proper amounts of stable NHCs. The results can pave the way to the use of the novel compounds as MAIAc (see Fig. 1) and other customized BAILs as catalysts in carbene-mediated reactions, avoiding the use of other bases, generally added to the reaction bulk, with high benefits for organic synthesis. References [1] a) Sarma, P., Dutta, A. K., Borah, R. Catal. Surv. Asia, 2017, 21, 70-93; b) J. S. Wilkes, J. Mol. Catal. A: Chem., 2004, 214, 11-17. [2] Chiarotto, I., Mattiello, L., Pandolfi, F., Rocco, D., Feroci, M. Front. Chem., 2018, 6, 355. [3] a) Troiani, A., de Petris, G., Pepi, F., Garzoli, S., Salvitti, C., Rosi, M. Ricci, A. ChemistryOpen, 2019, 8, 1190-1198; b) Salvitti, C., Chiarotto,I., Pepi, F., Troiani, A. ChemPlusChem, 2021, 86, 209-223.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
