Lewis acidic ionic liquids of crown ether complex cations: preparation and applications in organic reactions

Abstract

A range of Lewis acidic ionic liquids composed of crown ether complex cations were designed, synthesised and characterised by Raman, MS, FT-IR, thermogravimetric differential thermal analysis (TGA-DSC) and elemental analysis. These Lewis acidic ionic liquids were utilized as catalysts to prepare 2-phenyl-1H-benzo[d]imidazole using the same amount of aldehyde and o-phenylenediamine under air atmosphere and 1-benzyl-2-phenyl-1H-benzo[d]imidazole using two equivalents of aldehyde and one equivalent of o-phenylenediamine in argon. These ionic liquids were also found to be good catalysts to synthesize bis(indolyl)methane derivatives under mild conditions. In addition, the plausible mechanisms of the above reactions in the presence of ionic liquids as catalysts are suggested and discussed.