1. Anionic N-heterocyclic carbenes by decarboxylation of sydnone-4-carboxylates
- Author
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Ana-Luiza Lücke, Tamás Földes, Sascha Wiechmann, Arnold Adam, Martin Nieger, Mimoza Gjikaj, Andreas Schmidt, Imre Pápai, Tyll Freese, and Department of Chemistry
- Subjects
Thermogravimetric analysis ,RING ,Decarboxylation ,116 Chemical sciences ,chemistry.chemical_element ,Infrared spectroscopy ,Protonation ,Sydnone ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Medicinal chemistry ,chemistry.chemical_compound ,HYDROGEN-BOND ,CHEMISTRY ,Drug Discovery ,NUCLEOPHILIC CARBENES ,YLIDES ,010405 organic chemistry ,Hydrogen bond ,Organic Chemistry ,Mesoionic ,article ,CONJUGATED MESOMERIC BETAINES ,Mesoionic compound ,BORANE ADDUCTS ,LEWIS PAIR ,0104 chemical sciences ,chemistry ,13. Climate action ,IR spectroscopy ,ddc:540 ,CYCLOADDITION REACTIONS ,Lithium ,Mesoionic compound -- N-heterocyclic carbene -- Sydnone -- Decarboxylation -- IR spectroscopy ,SIGMA-SYDNONYL COMPLEXES ,N-heterocyclic carbene - Abstract
Unstable N-heterocyclic carbenes can be masked and stabilized as pseudo-cross-conjugated hetarenium-carboxylates which decarboxylate on warming. This study deals with the decarboxylation of carboxylates of mesoionic compounds to generate anionic N-heterocyclic carbenes. Lithium sydnone-4-carboxylates were therefore prepared via 4-bromosydnones by halogen-lithium exchange with nBuLi and subsequent treatment with carbon dioxide. Protonation gave the corresponding sydnone-4-carboxylic acids. Thermogravimetric measurements in addition to temperature dependent IR spectroscopy proved the decarboxylation of lithium sydnone-4-carboxylates and formation of the corresponding sydnone anions which can be represented as anionic N-heterocyclic carbenes. In DMSO-d6 solution, water favors the decarboxylation. Calculations have been performed to elucidate the mechanism of the decarboxylation in the absence and presence of water. (C) 2018 Elsevier Ltd. All rights reserved.
- Published
- 2018