Mesoporous silica supported ytterbium as catalyst for synthesis of 1,2‐disubstituted benzimidazoles and 2‐substituted benzimidazoles

Abstract

The benzimidazole ring is an important pharmacophore in contemporary drug discovery. Thus, effort to identifying new compounds containing benzimidazole scaffolds have gained much attention in recent years. In the present study, MCM‐41 type mesoporous silica with large pore (l‐MSN) supported ytterbium was successfully prepared by wet impregnation method. Among rare earth metal salts, ytterbium triflate has already been widely investigated as a catalyst in organic synthesis but less toxic ytterbium oxide has yet to be explored. Relatively high abundance and low cost of ytterbium with respect to many catalytically active metals (e.g. Pd, Au, Ru, Ir, Pt) offer an opportunity to develop sustainable catalysts for organic conversions. The catalyst has been characterized by various techniques including nitrogen adsorption, FT‐IR, TEM, SEM, EDX technique and elemental mapping. The obtained materials exhibit high surface area and a narrow distribution of mesoporosity. The catalytic performance of the Yb@l–MSNs was tested by synthesis of 1,2‐disubstituted benzimidazoles and 2‐substituted benzimidazoles through the coupling of aldehydes with o‐phenylenediamine. The catalyst resulted in excellent yields in short reaction times and the reaction showed tolerance toward both electron‐donating and electron‐withdrawing functional groups at room temperature. A particularly interesting finding was the solvent selectivity of this reaction; namely, 1,2‐disubstituted benzimidazoles generated as major product in water‐ethanol, while the 2‐substituted benzimidazoles was generated exclusively in non‐polar solvents like toluene.

Selective Synthesis of Benzimidazoles from o-Phenylenediamine and Aldehydes Promoted by Supported Gold Nanoparticles

“…To date, the emphasis is given to developing new, efficient, and "green" methods for the conversion of o-phenylenediamine and aldehydes to benzimidazole derivatives. Several heterogeneous catalytic systems that involve inorganic salts [31][32][33][34], zeolites [35][36][37], heterogeneous ionic liquid gel [38], micelles [39], and metal oxides [40][41][42][43][44][45][46][47][48][49] have been reported (Scheme S1). This transformation can be also achieved via photocatalytic processes in the presence of photosensitized molecules or semiconductor materials (Scheme S2) [50][51][52][53][54][55][56].…”

Copper(II) Oxide Nanoparticles Impregnated on Melamine‐Modified UiO‐66‐NH2 Metal–Organic Framework for C–N Cross‐Coupling Reaction and Synthesis of 2‐Substituted Benzimidazoles

“…The mechanism for the synthesis of 2‐substituted benzimidazole involves a primary activation of the carbonyl group (aldehyde) by CuO NPs and followed by a nucleophilic addition reaction to produce iminium by dehydration . An intramolecular nucleophilic addition of the second amine group to the carbon of the iminium by oxidative aromatization (i.e., dehydrogenation) leads to the formation of the benzimidazoles.…”

“…Magnetically recoverable ZnO supported catalyst on chitosan was reported by Tian and co‐workers for this synthesis . Numerous supported organic and metallic catalysts have been also introduced recently in the literature, for example, SiO 2 /Brønsted acidic ionic liquid gel , SiO 2 ‐dendrimer/Cu (II) , aluminum‐organic hybrid supramolecular material (Al‐ITQ‐HB) , Co 3 O 4 ‐Mo , Co 3 O 4 @Al 2 O 3 /SiO 2 , SiO 2 /Co@Fe 2 O 4 , Fe 3 O 4 ‐poly(melamine‐terephthaldehyde)/Cu , GO‐SO 3 H , activated carbon‐SO 3 H , Ir/N‐heterocyclic moieties , SiO 2 ‐Yb , P 2 O 7 ‐Sn , and Zeolite‐Y/Ni (II) . The reported methods had some drawbacks such as elevated temperature, longer reaction time, using organic solvent and high amount of catalyst, low yield, and use oxidant.…”

Sulfonated Graphitic Carbon Nitride (Sg-C3N4): A Highly Efficient Heterogeneous Organo-Catalyst for Condensation Reactions

“…Catalysts in condensation reactions can be acidic or basic. Heterogeneous catalysts such as mesoporous silica [4] are used in this reaction, but they suffer from low yields, long reaction time, and toxic reagents [5]. Herein, we applied graphitic carbon nitride nanosheets (g-C3N4) as a catalyst support, due to its promising chemical and physical properties such as electronic structure, large surface area, and high thermal stability.…”