Hybrid catalysts based on N-heterocyclic carbene anchored on hierarchical zeolites

Abstract

N-heterocyclic carbene has been grafted on hierarchical HZSM-5 and SAPO-5 to obtain hybrid catalysts, that are active in the benzoin condensation reaction.

First-Generation Organic Reaction Intermediates in Zeolite Chemistry and Catalysis

“…With a different approach, Gianotti and colleagues also prepared N-heterocyclic carbenes (NHC) anchored hierarchical HZSM-5 (MFI topology, 10 MR, 3D aluminosilicate) and hierarchical SAPO-5 (AFI topology, 12 MR, 1D silicoaluminophosphate) and tested these acid−base hybrid materials for the benzoin condensation reaction of furfural, which is a carbene catalyzed reaction at room temperature. 427 They confirmed the successful grafting with 1 H MAS NMR, 13 C CP MAS NMR, and FTIR spectroscopy; they found that silanol groups (Si−OH) anchor NHC moieties and Brønsted acid sites are free. Moreover, they stated that these hierarchical zeolites provide good dispersion for NHC, which results in high catalytic activity and recyclability.…”

“…In one of the recent studies, Buchmeiser et al showed the activity of confined cationic molybdenum imido alkylidene N -heterocyclic carbenes (NHC) complexes in SBA-15 (mesoporous silica) for olefin ring-closing metathesis reaction. With a different approach, Gianotti and colleagues also prepared N -heterocyclic carbenes (NHC) anchored hierarchical HZSM-5 (MFI topology, 10 MR, 3D aluminosilicate) and hierarchical SAPO-5 (AFI topology, 12 MR, 1D silicoaluminophosphate) and tested these acid–base hybrid materials for the benzoin condensation reaction of furfural, which is a carbene catalyzed reaction at room temperature . They confirmed the successful grafting with 1 H MAS NMR, 13 C CP MAS NMR, and FTIR spectroscopy; they found that silanol groups (Si–OH) anchor NHC moieties and Brønsted acid sites are free.…”

“…However, intrinsically stable N -heterocyclic carbenes (NHC) are widely used in heterogeneous catalysis as surface ligands. , [For those interested in applications of NHC as surface ligands in catalysis, we recommend refs , .] The NHC anchored-supported surfaces-particles vary from elemental metal allotrope species to bulk crystals, and also their applications vary from photo/electrocatalysis to thermalcatalysis. − In the early 2010s, Sanchez and his co-workers reported the immobilization of pincer-type NHC-metal (i.e., Ru, Rh, and Au) complexes in ordered mesoporous silica structures (MCM-41). , They studied the stability and structure of immobilized metal–carbene complexes via a battery of spectroscopic methods ( 13 C CP solid-state NMR, FTIR, UV–vis DRS) and tested the catalysts for hydrogenation of olefins and dehydrogenation of alcohols. In comparison to homogeneous catalysts, promising performance and recycling ability were observed with the hybrid mesoporous materials.…”

Influence of Pore Size in Benzoin Condensation of Furfural Using Heterogenized Benzimidazole Organocatalysts

“…Preparation of N-heterocyclic carbene (NHC) precursor and derived hybrids. [26] I-Alkylation of benzimidazole (compound 1 in Scheme 1): in a 50 mL round bottom flask kept under inert atmosphere, benzimidazole (8.5 mmol) was slowly added to a suspension of NaH (1 equiv.) in tetrahydrofuran (THF) (6 mL) at 0-5 °C under stirring; the solution was further stirred for 30 min at room temperature.…”

Predicting the Conformation of Organic Catalysts Grafted on Silica Surfaces with Different Numbers of Tethering Chains: The Silicopodality Concept

“…Hybrid catalysts, formed by organic moieties anchored onto inorganic matrices, are interesting for their capacity to combine enormous varieties of organic functional groups with a solid support with superior mechanical and thermal stabilities. − Such materials offer the advantages of homogeneous catalysis, as high yields, selectivities and possible stereoselectivity, along with those of heterogeneous catalysis, with easily separable products, reduced volume of solvents and so on. − Even more interesting is the possibility of using active inorganic surfaces, for instance silica with suitable concentrations of silanol groups, or silica–alumina surfaces with Brönsted and Lewis acid sites, which can in turn act as cocatalysts in cascade reactions. − …”