1, 3-Dialkylimidazolium salts are one of the most popular and investigated classes of the vast family of roomtemperature ionic liquids (RTILs). In particular, those resulting from the association of the 1-n-butyl-3-methylimidazolium (bmim) cation with relatively weakly coordinating anions such as tetrafluoroborate, hexafluorophosphate,[1] and trifluoromethanesulfonate display unique physical-chemical properties: they are liquids over a large range of temperatures (down to À808C), possess high thermal and chemical stability, a large electrochemical window, high density, relatively low viscosity, and negligible vapor pressure. These materials are very popular and have been used in various domains of physical sciences such as fluids in synthesis, catalysis, spectroscopy, electrochemistry, nanomaterials, extraction and separation processes.[2] It is usually assumed that these liquids are entirely innocent and noncoordinating solvents. However, in older and more recent examples such innocuous behavior was not always observed, and a certain degree of caution should be exercised when ionic liquids are chosen as solvents.

There is no doubt that most 1, 3-dialkylimidazolium ILs are stable towards many organic and inorganic substances, but under certain reaction conditions both the cation and anion can undergo “undesirable” transformations. In some cases the anions of imidazolium ILs can easily undergo hydrolysis, particularly those containing AlCl4 and PF6 anions. In the case of the hexafluorophosphate anion, phosphate and HF are formed, and 1, 3-dialkylimidazolium phosphates and transition-metal fluorides have been isolated during reactions and purification procedures.[3] The hydrolysis of the PF6 anion may be more pronounced in reactions involving metals, which can catalyze this decomposition. Cation metathesis was also observed with highly negatively charged complexes such as Na3 [Co (CN) 5] and Na2 [{(UO2)(NO3) 2} 2 (μ4-C2O4)] dissolved in ionic liquids, and the the respective coordination complexes associated with the imidazolium cation precipitated.[4] The reactivity of imidazolium cations mainly stems from the relatively high acidity (pKa= 21–23) of the H2 hydrogen of the imidazolium nucleus, which has been found to be roughly intermediate between the acidities of acetone (pKa= 19.3) and ethyl acetate (pKa= 25.6).[5] It is well known from the seminal work of Arduengo that deprotonation at the C2 position of the imidazolium salt generates N-heterocyclic carbene ligands.[6] Not surprisingly, the formation of metal–carbene complexes has been observed in Pd-catalyzed Heck-type reactions performed in ionic liquids. In these cases the side reaction has a beneficial effect since the carbenes most probably stabilize the catalytically active species.[7] For exam-