How does the presence of impurities change the performance of catalytic systems in ionic liquids? A case study: the Michael addition of acetylacetone to methyl vinyl ketone

The catalytic activity of several metal complexes in ionic liquids towards Michael addition of acetylacetone to methyl vinyl ketone is found to be strongly dependent on the presence of halogenide impurities of the solvent. The tested metal complexes are Ni(acac)2·2H2O, FeCl3·6H2O, Yb(TfO)3 (TfO = triflate) and Co(acac)2, and the ionic liquids used as solvents are [bmim]BF4 and [bmim]PF6 (bmim = 1-n-butyl-3-methylimidazolium). The rationalisation of the halogenide effect in terms of ligand exchange from the starting complex with the excess chloride of impure ionic liquids is demonstrated in the case of the cobalt based system where the formation of the poorly active CoCl42− species is detected by UV-Vis analysis.