Tetramethyl guanidinium chlorosulfonate as a highly efficient and recyclable organocatalyst for the preparation of bis(indolyl)methane derivatives

• Tetramethylguanidine ionic liquid (TMG IL) is synthesized and characterized.
• The TMG IL is an excellent organocatalyst for the synthesis of bisindolylmethanes.
• The products are quantitatively obtained at environmentally benign conditions.
• The TMG IL catalyst is recyclable without losing its catalytic activity.

The synthesis and characterization of a novel superbase ionic liquid, tetramethylguanidinium chlorosulfonate, are described. The guanidine ionic liquid (GIL) was characterized by FT-IR and NMR spectroscopies, and wide-angle X-ray scattering techniques, as well as thermogravimetric analysis. The GIL functions as an effective, environmentally benign, and recyclable catalyst for the synthesis of various bis(indolyl)methanes in outstanding yields (90–96%), within short reaction times; further, no chromatographic purification step for the product is required.

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