Stability and CO2 Capture Ability of Electrogenerated N-Heterocyclic carbene in the Parent 1-Butyl-3-methylimidazoliun ionic liquid (BMIm-X): the role of the anion X-

The electrochemical reduction of imidazolium based ionic liquids (BMIm-X) led to the formation of the corresponding N-heterocyclic carbene (NHC). Due to the peculiar reactivity of NHC, the solutions containing NHC in ionic liquid (IL) can be used in CO2 capture or in organocatalysed reactions. It is thus important to know the stability of the carbene in the parent IL. In fact, the NHC lifetime can be influenced by the nature of the anion X of the ionic liquid. To better understand the relationship between NHC lifetime (and reactivity towards CO2) and ionic liquid medium, the presence of electrogenerated NHC in the parent IL was studied by voltammetric, IR and thermogravimetric analyses and by isolation of the adduct between NHC and benzaldehyde. It was thus possible to estimate the actual NHC concentration and its lifetime by voltammetric peak current measurements. Moreover, NHC in BMIm-X is able to catch CO2 (yielding the adduct NHC-CO2) and, triggered by heating (60-150°C), to release CO2. It was proved that the half life of NHC and the rate of CO2 capture are both affected by the nature of anion X.