Influence of oxophilic behavior of UiO‐66(Ce) metal–organic framework with superior catalytic performance in Friedel‐Crafts alkylation reaction

Abstract

In recent years, one of the analogous metal organic frameworks (MOFs) with UiO‐66(Zr) topology receiving wider attention is UiO‐66(Ce), which exhibits interesting properties and high thermal and chemical stability. Hence, in the present work, UiO‐66(Ce) is synthesized by adopting an earlier procedure and characterized by series of spectroscopic techniques like UV‐visible (UV‐Vis), Fourier transform infrared (FT‐IR), Raman and scanning electron microscope (SEM) to confirm its structural features and crystallinity using powder X‐ray diffraction (XRD) and these results are in close agreement with other reports. The catalytic performance of UiO‐66(Ce) was evaluated in the Friedel–Crafts alkylation reaction between β‐nitrostyrene and indole to obtain heterocyclic compounds with biological activity. A series of control experiments indicate that Ce4+ located within the framework plays an important role in promoting this reaction and its activity is found to be much superior to that of UiO‐66(Zr). This enhanced activity with Ce4+ compared to Zr4+ is attributed due to the higher oxophilicity of Ce4+, which can readily bind with an oxygen‐containing substrate such as β‐nitrostyrene. The leaching test confirms the heterogeneity of the reaction and the catalyst can be reused three times with identical activity to the fresh solid. UiO‐66(Ce) shows wide substrate scope with high yields of the desired product. A proposed mechanism is also discussed.

Excellent Catalytic Performance of Ce–MOF with Abundant Oxygen Vacancies Supported Noble Metal Pt in the Oxidation of Toluene

“…In addition, the out-of-plane vibration of C-H groups was observed at 793 cm −1 . The spectrum of UiO-66 was identical to previous study [51] and the peaks at 1607, 1417, 1136, and 852 cm −1 correspond to the C=C, COO, C-C, and C-H vibration, respectively. Compared to MOF-808, there was a weak peak at 415 cm −1 corresponding to the vibration band of Ce-O.…”

Exploring novel heterojunctions based on the cerium metal–organic framework family and CAU-1, as dissimilar structures, for the sake of photocatalytic activity enhancement

“…All synthesized MOFs are based on carboxylic acids, and so the charge transfer from the linker to the metal is a common phenomenon that results in broad peaks. 61–64…”

“…All synthesized MOFs are based on carboxylic acids, and so the charge transfer from the linker to the metal is a common phenomenon that results in broad peaks. [61][62][63][64] Analyzing the Tauc plots by applying the formula (ahv) 2 = B(hv − E g ) led to the bandgap energy values (E g ) of MOFs and composites. In the formula, hv, a, B, and v are the photo energy, absorption coefficient, proportionality constant, and the light frequency.…”

Friedel–Crafts alkylation of indoles with β-nitroalkenes using ammonium niobium oxalate as a recyclable catalyst

“…[9][10][11] Owing to the low nucleophilicity of indole, its Friedel-Crafts alkylation is slow compared with that of N-alkylated indoles. [12][13][14] Over the past few years, many appreciable efforts have been made to overcome this barrier employing different kinds of catalysts, such as Lewis acid catalysts, [15][16][17][18] ionic liquids, 19 organocatalysts, 12,20,21 photocatalysts, 22,23 heterogeneous catalysts including metal-organic frameworks, [24][25][26][27][28][29][30] and others. Even though several catalytic systems have been used for the alkylation of indoles with nitroalkenes, only a handful of these have employed 'green' solvents and possess recyclability.…”

“…Even though several catalytic systems have been used for the alkylation of indoles with nitroalkenes, only a handful of these have employed 'green' solvents and possess recyclability. 31,32 In the past decade, a good number of heterogeneous catalysts have been reported for this reaction; [24][25][26]29,33,34 although recyclable, however, most of these catalytic systems used pure organic solvents, required high catalyst loadings and involved tedious catalyst synthesis. In this context, it is highly desirable to develop an efficient, atom economical, low toxic, recyclable and environmentally friendly platform for synthesizing alkylated indole derivatives.…”