Fe₂O₃ Nanocatalysts Supported on Zeolite-Y for the Selective Synthesis of C2 Di-Indolyl Indolones and Isatins

Abstract

Iron-oxide (Fe 2 O 3 ) nanoparticles in the dimension of ∼2.3 nm supported on zeolite-Y appeared as an excellent, reusable heterogeneous catalyst for the chromatography-free selective synthesis of 2,2-di(3-indolyl)-3-indolones, a C2-trimerized product. The zeolite-Y-supported Fe-oxide nanocatalyst showed the catalytic activity better than the Pd-and Au-based catalysts in the synthesis of C2 di-indolyl indolones under the prevailing reaction conditions. Besides, this low-cost catalyst displayed the ability to synthesize the pharmaceutically significant isatin molecules with high selectivity. The nature of the solvent and oxidant played a crucial role in the regioselective trimerization of indoles. The selective formation of the C2-trimerized product was accomplished in acetonitrile with peroxymonosulfate (oxone) as the oxidant, while in a water/acetonitrile mixture, it led to the formation of isatin. Compared to many other high-cost catalysts, the cheaper zeolite-Y-supported iron oxide catalyst promoted the reaction at room temperature with high selectivity. The products were obtained within 15−30 min with ≤95% yield. Different pieces of spectroscopic and electrochemical evidence supported by density functional theory (DFT) studies provided strong evidence for the proposed reaction mechanism. The kinetics of the reaction was studied through UV−vis spectroscopy and found to follow first-order kinetics. The UV−vis spectrum of the C2-trimerized product was further evaluated through time-dependent DFT calculations. The CO 2temperature programmed desorption study indicated the presence of strong basic sites in the Fe 2 O 3 -Y catalyst, favoring the interaction of the acidic indole molecule with the catalyst surface.

Utilization of methanol and ethanol for 3,3′-bis(indolyl)methane synthesis through activation of peroxymonosulfate over a copper catalyst

“…At the same time, our previous study and various other studies reported that iron oxide can activate PMS. 6,15 Iron oxides are comparatively more environment friendly, highly abundant and hence cost-effective. Therefore, instead of using CuO, freshly prepared Fe 2 O 3 was used as the catalyst for the same reaction under the same reaction conditions.…”

“…5 At the same time, CuO is also known to activate peroxymonosulfate (PMS) which is used as an oxidant in the synthesis of C2/C3-trimerized indoles. 6 However, no literature is available on the application of the CuO-PMS system for the synthesis of 3,3′-BIMs through the dehydrogenation of CH 3 OH or C 2 H 5 OH. So in this work, an attempt was made to use the CuO-PMS system as an alternative to the known Ir and Ru catalysts for similar reactions.…”

Green Oxidation of Indoles Using Molecular Oxygen over a Copper Nitride Nanocube Catalyst

“…Several studies have been reported on the trimerization of indoles using homogeneous and heterogeneous catalysts (Scheme 1A‐I) [2] . However, these catalytic systems inevitably require organic and inorganic oxidants such as tert ‐butyl hydroperoxide (TBHP) [2a–c] and oxone, [2d,e] respectively, which produce large amounts of waste. From the atom efficiency and environmental viewpoint, molecular oxygen (O 2 ) has been considered an ideal oxidant.…”

Heterogeneous iron catalyst for C(1)–H functionalization of 2-naphthols with primary aromatic alcohols

“…10 During our recent studies on an iron oxide nanocatalyst supported on Na + -zeolite-Y, Fe 2 O 3 -Y was found to be a reusable and effective heterogeneous catalyst for the selective C-2 trimerization of indoles. 11 As these iron (Fe) catalysts are much cheaper and abundant in nature, so a similar Fe 2 O 3 catalyst is explored herewith to overcome the problems associated with the C(1)–H functionalization of 2-naphthol and its derivatives. Herein, we designed a Fe 2 O 3 nanocatalyst supported on potassium exchanged zeolite-Y (Fe 2 O 3 -KY).…”

“…However, the yield was significantly lower than in the case of our previously reported Fe 2 O 3 nanocatalyst supported on zeolite-NaY, halloysite nanotubes (HNT), alumina (Al 2 O 3 ), or silica (SiO 2 ). 11,16 Previous studies have reported that in such reactions, particularly those involving π-systems, the cation–π interactions play a significant role in the product formation. 9 We have also reported that during the oxidative coupling of 2-naphthols, the cation–π interactions played a vital role.…”