Comparison of the immobilization of chiral bis(oxazoline)-copper complexes onto anionic solids and in ionic liquids

Chiral bis(oxazoline)-copper complexes can be easily immobilized onto anionic solids or in ionic liquids and used as catalysts in cyclopropanation reactions. The efficiency and recovery of the catalysts are strongly dependent on the stability of the complex. In the case of a highly stable bis(oxazoline)-copper complex, both solid supports and ionic liquids allow efficient recovery of the catalyst with results quite similar to those obtained in molecular solvents. However, ionic liquids are clearly better when the complex is not so stable. In this case, the nature of both the anion and cation, the presence of water and the method used to synthesize the ionic liquid have a noticeable influence on both catalytic performance and catalyst recovery. Enantioselectivity is also influenced by the ionic liquid/catalyst molar ratio.