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Free N‐heterocyclic carbenes from Brønsted acidic ionic liquids: Direct detection by electrospray ionization mass spectrometry
RATIONALE: The occurrence of N‐heterocyclic carbenes in imidazolium‐based ionic liquids has long been discussed, but no spectroscopic evidence has been reported yet due to their transient nature. The insertion of an ionizable acid group into the cation scaffold of an ionic liquid which acts as a cha...
Autores principales: | , , , , , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
John Wiley and Sons Inc.
2022
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9542177/ https://www.ncbi.nlm.nih.gov/pubmed/35729083 http://dx.doi.org/10.1002/rcm.9338 |
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author | Salvitti, Chiara Pepi, Federico Managò, Marta Bortolami, Martina Michenzi, Cinzia Chiarotto, Isabella Troiani, Anna de Petris, Giulia |
author_facet | Salvitti, Chiara Pepi, Federico Managò, Marta Bortolami, Martina Michenzi, Cinzia Chiarotto, Isabella Troiani, Anna de Petris, Giulia |
author_sort | Salvitti, Chiara |
collection | PubMed |
description | RATIONALE: The occurrence of N‐heterocyclic carbenes in imidazolium‐based ionic liquids has long been discussed, but no spectroscopic evidence has been reported yet due to their transient nature. The insertion of an ionizable acid group into the cation scaffold of an ionic liquid which acts as a charge tag allows for the direct detection of free carbenes by mass spectrometry. METHODS: Three different Brønsted acidic ionic liquids were synthesized: 1‐methyl‐3‐carboxymethylimidazolium chloride (MAICl), 1‐methyl‐3‐carboxymethylimidazolium acetate (MAIAc) and the corresponding 2‐(3‐methyl‐1H‐imidazol‐3‐ium‐1‐yl)acetate zwitterion (MAI − H). The speciation of these compounds was then analysed by electrospray ionization ion‐trap mass spectrometry in the negative ion mode. RESULTS: The C2‐H deprotonation of the imidazolium cation leading to the formation of the corresponding carbene is highly affected by the basic properties of the counter‐anion. In the case of MAICl and MAI − H ionic liquids, no charged species corresponding to the free N‐heterocyclic carbene was detected. On the contrary, in the presence of a sufficiently basic anion, such as acetate of MAIAc ionic liquid, an intense signal related to the free carbenic species was observed without the addition of an external base. CONCLUSIONS: In situ formation of free N‐heterocyclic carbenes from Brønsted acidic ionic liquids was demonstrated, highlighting the crucial role of anion basicity in promoting the C2‐H proton abstraction from imidazolium cations with a carboxylic side chain. |
format | Online Article Text |
id | pubmed-9542177 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2022 |
publisher | John Wiley and Sons Inc. |
record_format | MEDLINE/PubMed |
spelling | pubmed-95421772022-10-14 Free N‐heterocyclic carbenes from Brønsted acidic ionic liquids: Direct detection by electrospray ionization mass spectrometry Salvitti, Chiara Pepi, Federico Managò, Marta Bortolami, Martina Michenzi, Cinzia Chiarotto, Isabella Troiani, Anna de Petris, Giulia Rapid Commun Mass Spectrom Research Articles RATIONALE: The occurrence of N‐heterocyclic carbenes in imidazolium‐based ionic liquids has long been discussed, but no spectroscopic evidence has been reported yet due to their transient nature. The insertion of an ionizable acid group into the cation scaffold of an ionic liquid which acts as a charge tag allows for the direct detection of free carbenes by mass spectrometry. METHODS: Three different Brønsted acidic ionic liquids were synthesized: 1‐methyl‐3‐carboxymethylimidazolium chloride (MAICl), 1‐methyl‐3‐carboxymethylimidazolium acetate (MAIAc) and the corresponding 2‐(3‐methyl‐1H‐imidazol‐3‐ium‐1‐yl)acetate zwitterion (MAI − H). The speciation of these compounds was then analysed by electrospray ionization ion‐trap mass spectrometry in the negative ion mode. RESULTS: The C2‐H deprotonation of the imidazolium cation leading to the formation of the corresponding carbene is highly affected by the basic properties of the counter‐anion. In the case of MAICl and MAI − H ionic liquids, no charged species corresponding to the free N‐heterocyclic carbene was detected. On the contrary, in the presence of a sufficiently basic anion, such as acetate of MAIAc ionic liquid, an intense signal related to the free carbenic species was observed without the addition of an external base. CONCLUSIONS: In situ formation of free N‐heterocyclic carbenes from Brønsted acidic ionic liquids was demonstrated, highlighting the crucial role of anion basicity in promoting the C2‐H proton abstraction from imidazolium cations with a carboxylic side chain. John Wiley and Sons Inc. 2022-07-07 2022-09-15 /pmc/articles/PMC9542177/ /pubmed/35729083 http://dx.doi.org/10.1002/rcm.9338 Text en © 2022 The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd. https://creativecommons.org/licenses/by/4.0/This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ (https://creativecommons.org/licenses/by/4.0/) License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. |
spellingShingle | Research Articles Salvitti, Chiara Pepi, Federico Managò, Marta Bortolami, Martina Michenzi, Cinzia Chiarotto, Isabella Troiani, Anna de Petris, Giulia Free N‐heterocyclic carbenes from Brønsted acidic ionic liquids: Direct detection by electrospray ionization mass spectrometry |
title | Free N‐heterocyclic carbenes from Brønsted acidic ionic liquids: Direct detection by electrospray ionization mass spectrometry |
title_full | Free N‐heterocyclic carbenes from Brønsted acidic ionic liquids: Direct detection by electrospray ionization mass spectrometry |
title_fullStr | Free N‐heterocyclic carbenes from Brønsted acidic ionic liquids: Direct detection by electrospray ionization mass spectrometry |
title_full_unstemmed | Free N‐heterocyclic carbenes from Brønsted acidic ionic liquids: Direct detection by electrospray ionization mass spectrometry |
title_short | Free N‐heterocyclic carbenes from Brønsted acidic ionic liquids: Direct detection by electrospray ionization mass spectrometry |
title_sort | free n‐heterocyclic carbenes from brønsted acidic ionic liquids: direct detection by electrospray ionization mass spectrometry |
topic | Research Articles |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9542177/ https://www.ncbi.nlm.nih.gov/pubmed/35729083 http://dx.doi.org/10.1002/rcm.9338 |
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