Magnetic inorganic–organic hybrid nanomaterial for the catalytic preparation of bis(indolyl)arylmethanes under solvent-free conditions: Preparation and characterization of H5PW10V2O40/pyridino-Fe3O4 nanoparticles

• Preparation of a new magnetic inorganic–organic nanohybrid material.
• Introducing a new and efficient protocol for the synthesis of substituted bis(indolyl)phenylmethanes.
• Using a highly reusable nanocatalyst without significant loss of catalytic activity.
• The heteropolyacid catalyst was covalently linked to the modified magnetite.

Magnetically separable inorganic–organic hybrid material H5PW10V2O40/pyridino-Fe3O4 (HPA/TPI-Fe3O4) nanoparticles provide an efficient and economic route for the synthesis of substituted bis(indolyl)methanes by the electrophilic substitution of indole with various aldehydes and ketones under solvent-free conditions with excellent yields in <30 min. This catalyst was prepared by the chemically anchoring H5PW10V2O40 onto Fe3O4 nanoparticles via the use of N-[3-(triethoxysilyl)propyl]isonicotinamide (TPI) linker. High catalytic activity and ease of recovery using an external magnetic field are additional eco-friendly attributes of this new catalytic system. The catalyst was recycled at least eight times without significant loss of catalytic activity. Characterization techniques such as XRD, SEM, and FTIR for HPA/TPI-Fe3O4 verified that the Keggin structure of tungsto-vanadophosphoric acid on the surface of pyridine modified Fe3O4 nanoparticles is retained.

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