An Abnormal N-Heterocyclic Carbene-Carbon Dioxide Adduct from Imidazolium Acetate Ionic Liquids: The Importance of Basicity

Kelemen, Zsolt and Péter-Szabó, Barbara and Székely, Edit and Hollóczki, Oldamur and Firaha, Dzmitry S. and Kirchner, Barbara and Nagy, József and Nyulászi, László (2014) An Abnormal N-Heterocyclic Carbene-Carbon Dioxide Adduct from Imidazolium Acetate Ionic Liquids: The Importance of Basicity. CHEMISTRY-A EUROPEAN JOURNAL, 20 (40). pp. 13002-13008. ISSN 0947-6539

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Abstract

In the reaction of 1-ethyl-3-methylimidazolium acetate [C2C1Im][OAc] ionic liquid with carbon dioxide at 125 8C and 10 MPa, not only the known N-heterocyclic carbene (NHC)–CO2 adduct I, but also isomeric aNHC-CO2 adducts II and III were obtained. The abnormal NHC-O2 adducts are stabilized by the presence of the polarizing basic acetate anion, according to static DFT calculations and ab initio molecular dynamics studies. A further possible reaction pathway is facilitated by the high basicity of the system, deprotonating of the initially formed NHC-CO2 adduct I, which can then be converted in the presence of the excess of CO2 to the more stable 2-deprotonated anionic abnormal NHC–CO2 adduct via the anionic imidazolium-2,4-dicarboxylate according to DFT calculations on model compounds, suggesting a generalizable pathway to abnormal NHC complex formation.

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