-OSO3H Functionalized Mesoporous MCM-41 Coated on Fe3O4 Nanoparticles: an Efficient and Recyclable Nano-Catalyst for Preparation of 3,2′-Bisindoles

Mesoporous MCM-41 was coated on Fe3O4 nanoparticles and then functionalized with sulfurochloridic acid to provide a core-shell solid acid nano-catalyst. The catalyst was characterized by transmission electron microscopy (TEM), infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TG), Brunauer-Emmet-Teller analysis (BET) and vibrating sample magnetometery (VSM). The obtained nano-sized magnetic catalyst was used in three-component reaction of indoles, phenylglyoxal monohydrate and N-arylenaminones to furnish the desired 3,2′- bisindoles in good yields under mild reaction conditions. In order to evaluate reusability of the catalyst, the reaction of indole, phenylglyoxal monohydrate and 5,5-dimethyl-3-(phenylamino)cyclohex-2-enone was carried out in the presence of the recycled catalyst in successive runs. From reaction run 1 to 5, the yields were 89%, 89%, 81%, 75% and 63%, respectively. Therefore after five runs, 26% decrease in the efficiency of the catalyst system was observed. In order to confirm heterogeneity of the catalyst, the amount of sulfonic acid loading was determined for the recycled catalyst of the 3rd run and a similar result (2.40 mmol SO3H/g) was obtained, which confirmed that no considerable leaching was occurred during the course of reaction.