The First Example of ortho-Arylation of Benzamides over Pd/Mesoporous Silica: A Novel Approach for Direct sp² C–H Bond Activation

Abstract

Three-dimensional mesoporous silica with a highly dispersed palladium nanoparticles composite (PS-3) catalyst has been prepared and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, nitrogen sorption, and high resolution transmission electron microscopy. The PS-3 catalyst utilized for the first time as an efficient and reusable catalyst in the ortho-arylation of benzamides by aryl iodides has been demonstrated with the simplest amide CONH2 as a directing group. It can be successfully applied to various benzamides and aryl iodides with both electron donating and withdrawing groups. The catalyst can be simply recovered and reused several times without significant loss in catalytic activity.

Sustainable protocols for direct C–H bond arylation of (hetero)arenes

“…In 2014, Srinivasu et al reported the first orthoarylation of benzamides 3 using a supported Pd catalyst: threedimensional mesoporous silica with highly dispersed palladium nanoparticles composite (named PS-3). 18 Direct C-H arylations were successfully performed between functionalized benzamides and aryl iodides with different stereo-electronic properties, in acetic acid as the solvent and silver acetate as the base, affording the ortho-arylated products 4 in reasonable yields, 36-76% (Scheme 3). Recyclability of PS-3 catalyst was also tested over five different cycles without significant loss of its activity.…”

“…The protocol looks highly attractive from a Scheme 3 Direct C-H ortho-arylation of benzamides 3 with aryl iodides catalysed by Pd nanoparticles supported on three-dimensional mesoporous silica (PS-3), developed by Srinivasu et al in 2014. 18 Scheme 2 Direct C-H bond arylation of naphthalene 1 with aryliodonium salts catalysed by recoverable Pd/C catalyst, developed by Glorius and co-workers in 2015. 17 Green Chemistry point of view, since the supported palladium catalyst was used in combination with γ-valerolactone (GVL) as a sustainable and environmentally benign reaction medium (see section 3.3.4).…”

Catalytic C–H bond functionalisation chemistry: the case for quasi-heterogeneous catalysis

“…106 The PS-3 catalyst contains particles of approximately 7-8 nm which display well resolved (111), (200) and (220) planes, indicating face-centered cubic structures. 106 The PS-3 catalyst contains particles of approximately 7-8 nm which display well resolved (111), (200) and (220) planes, indicating face-centered cubic structures.…”

Heterogeneous catalytic approaches in C–H activation reactions

“…Srinivasu and coworkers prepared a mesoporous silica with a highly dispersed palladium nanoparticle composite catalyst (PS-3) and tested it for the direct C-H arylation of benzamides 20 with aryl iodides 8 (Scheme 13). 29 The reaction occurred with excellent site-selectivity towards ortho-functionalization and was tolerant to the presence of functional groups, such as halides, ketones and ethers. Both electron-rich and electronpoor benzamides were competent substrates for the process.…”