H₅PW₁₀V₂O₄₀@VO_x/SBA-15-NH₂ catalyst for the solventless synthesis of 3-substituted indoles

Functionalization of mesoporous SBA-15 frameworks by transition metal oxides offers a flexible route to fabricate new heterogeneous catalysts. Here, an inorganic-organic hybrid nanoporous catalyst H₅PW₁₀V₂O₄₀@VO_x/SBA-15-NH₂, was prepared and utilized as an efficient, eco-friendly, and recyclable catalyst for the one-pot, multi-component synthesis of 3-substituted indoles by indole substitution with aldehydes and malononitrile under solvent-free conditions. Catalysts were prepared by the non-covalent attachment of H₅PW₁₀V₂O₄₀ to a 3 wt%VO_x/SBA-15 nanoporous support through a 3-(triethoxysilyl)propylamine linker. VO_x/SBA-15 was prepared by a one-pot hydrothermal synthesis from TEOS and vanadium(V) oxytri-tert-butoxide [VO(O^-tBu)3]. The resulting H₅PW₁₀V₂O₄₀@VO_x/SBA-15-NH₂ material was characterized by bulk and surface analysis including N2 porosimetry, FE-SEM, XRD, XPS, FT-IR, TGA-DTA, UV–Vis and ICP-OES, evidencing retention of the heteropolyacid Keggin structure. H₅PW₁₀V₂O₄₀@VO_x/SBA-15-NH₂ exhibits high activity and excellent yields (70–95%) of 3-substituted indoles under mild conditions, with negligible deactivation.