Development of Brönsted–Lewis acidic solid catalytic system of 3-methyl-1-sulfonic acid imidazolium transition metal chlorides for the preparation of bis(indolyl)methanes

•Brönsted and Lewis acidic three heterogeneous 3-methyl-1-sulfonic acid imidazolium transition metal chlorides were synthesized.•All compounds were characterized by NMR, FT-IR, RAMAN, XRD, SEM-EDX, BET, AAS, powder XRD and elemental analysis techniques.•Acidity of these compounds was measured by Hammett function.•Higher catalytic activity was observed in solution for the preparation of bis(indolyl)methane at room temperature.•All compounds were recycled for three consecutive runs without reactivation.

Three new heterogeneous catalysts of 3-methyl-1-sulfonic acid imidazolium transition metal chlorides [Msim][X] (where X = [FeCl4]−, [ZnCl3]−, [CuCl2]−) were synthesized containing both Lewis and Brönsted acidic sites. These solid acids were fully characterized by various analytical tools such as FT-IR, Raman, 1H NMR, 13C NMR, SEM-EDX, TGA, Powder XRD, AAS, BET, UV–vis and elemental analysis. All of them were efficiently utilized as reusable catalysts (5–10 mol%) for the selective synthesis of bis(indolyl)methane derivatives in ethylacetate at room temperature within short time with excellent yields.

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