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

Abstract

In the reaction of 1-ethyl-3-methylimidazolium acetate [C2C1Im][OAc] ionic liquid with carbon dioxide at 125 °C 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-CO2 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 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. This suggests a generalizable pathway to abnormal NHC complex formation.

Calorimetric Studies and Structural Aspects of Ionic Liquids in Designing Sorption Materials for Thermal Energy Storage

“…The presence of hydrogen bonds involving the “abnormal” C−H can be observed for 12 , 13 , 25 , and 26 . Owing to the lack of structural information for ILs in general, this feature is difficult to judge, however, it is closely related to findings for abnormal hydrogen bonding in NHCs …”

Activation of CO2by ionic liquid EMIM–BF4in the electrochemical system: a theoretical study

“…They are too large, suggesting that they are unable to deprotonate even in the case after receiving electrons. 12 Although the existence of "abnormal" deprotonations at C4 and C5 positions of imidazolium cation in the presence of strong base acetate has been shown by experiments, 53 Gibbs free energy change of Eq. 10 was estimated to be -18.5 kcal/mol in aqueous solution in the B3LYP/6-31++G(d,p) level, confirming it is thermodynamically favourable.…”

Optical and XPS evidence for the electrochemical generation of an N-heterocyclic carbene and its CS2adduct from the ionic liquid [bmim][PF6]

“…For instance, in a study reported by Nyulászi and co-workers in 2011, 1-ethyl-3-methylimidazolium acetate was shown to be an effective organocatalytic ionic liquid for benzoin condensation and hydroacylation reaction. [67][68][69] This catalytic activity was attributed to the in situ formation of the corresponding N-heterocyclic carbene with the help of the basic acetate anion, which was supported by the lack of catalytic activity when non-basic anions were used. was mixed with CS 2 , no red color formation was observed.…”