An Efficient Reusable Mesoporous Solid-Based Pd Catalyst for Selective C2 Arylation of Indoles in Water

Abstract

The completely C2-selective arylation of N-methylindole was achieved by using a reusable solid Pd catalyst and water as a solvent without any other ligands or additives or exclusion of air. The catalysts possess well-dispersed Pd nanoparticles (~ 1.5 nm), N-containing functional groups (~ 11 wt%), and uniform mesopores (~ 5 nm). The turnover frequency (TOF) is calculated to be 82 h -1 .Arylations of both N-H indoles and N-protected indoles with diaryliodonium salts were achieved to give the desired products in high to excellent isolated yields in water.Mercapto-functionalized silica as a selective trapping agent, together with hot infiltration, confirms the undetected leaching of Pd. The catalyst samples can be reused at least 8 times without any additional activation treatment. The catalytic performance of the Pd catalyst is also compared with the performance of other mesoporous Pd catalysts on silica, carbon, and resins. The catalytic activity and stability of the present catalyst may be related to the well-dispersed Pd nanoparticles, the electron-rich environment stabilized by the N-containing functional groups, and the large, uniform mesopores.

Palladium‐Catalyzed O‐Arylation Reaction Using Different Heterogeneous Catalyst Systems: The Role of Support

“…Furthermore, a broad band at about 1654 cm −1 is due to the O–H bending vibration of the water adsorbed on the surface . Modification of the solid support by 3‐aminopropyl groups results in the appearance of new bands at 2900–3000 cm −1 which are assigned to C−H stretching vibrations (Figure b) . The FT‐IR spectrum of P,N‐MCM‐41 shows a peak at 1652 cm −1 due to the stretching vibration of C=N bond (Figure c) .…”

Environmentally Benign Arylations of 5‐Membered Ring Heteroarenes by Pd‐Catalyzed C−H Bonds Activations

“…[50] In 2011 and 2016, Hierso et al employed palladium nanoparticles of 2 nm size highly dispersed on a polypyrrole support (35 Pd wt%) for the C5-arylation of thiophenes, furans, pyrroles and imidazoles (Scheme 31, b). [51,52] The catalyst could be recovered and reused. According to the authors, the active species of this catalytic system likely come from the releasing of molecular or colloidal soluble palladium species.…”

A Self‐Assembly Process for the Immobilization of N‐Modified Au Nanoparticles in Ordered Mesoporous Carbon with Large Pores

“…Further impregnation or deposition‐precipitation of metal precursors results in well‐dispersed Pd nanoparticles . Recently we reported the loading of Pd nanoparticles in a N‐doped ordered mesoporous carbonaceous matrix for the direct arylation of indoles . Because of the ordered mesopores and the strong bonding between Pd and N‐containing groups, the migration and agglomeration of palladium nanoparticles (approximately 1.5 nm in size) are limited.…”

“…[15] Recently we reported the loading of Pd nanoparticles in a Ndoped ordered mesoporous carbonaceous matrix for the direct arylation of indoles. [16] Because of the ordered mesopores and the strong bonding between Pd and N-containing groups, the migration and agglomeration of palladium nanoparticles (approximately 1.5 nm in size) are limited. This catalyst shows a maximum 98 % yield of 2-phenyl-indole at 60°C in the absence of ligands and additives.…”