H₂ Activation with Co Nanoparticles Encapsulated in N‐Doped Carbon Nanotubes for Green Synthesis of Benzimidazoles

Abstract

Co nanoparticles (NPs) encapsulated in N‐doped carbon nanotubes (Co@NC900) are systematically investigated as a potential alternative to precious Pt‐group catalysts for hydrogenative heterocyclization reactions. Co@NC900 can efficiently catalyze hydrogenative coupling of 2‐nitroaniline to benzaldehyde for synthesis of 2‐phenyl‐1H‐benzo[d]imidazole with >99 % yield at ambient temperature in one step. The robust Co@NC900 catalyst can be easily recovered by an external magnetic field after the reaction and readily recycled for at least six times without any evident decrease in activity. Kinetic experiments indicate that Co@NC900‐promoted hydrogenation is the rate‐determining step with a total apparent activation energy of 41±1 kJ mol−1. Theoretical investigations further reveal that Co@NC900 can activate both H2 and the nitro group of 2‐nitroaniline. The observed energy barrier for H2 dissociation is only 2.70 eV in the rate‐determining step, owing to the presence of confined Co NPs in Co@NC900. Potential industrial application of the earth‐abundant and non‐noble transition metal catalysts is also explored for green and efficient synthesis of heterocyclic compounds.

Hydrogenative coupling of nitriles with diamines to benzimidazoles using lignin-derived Rh2P catalyst

“…13 C{ 1 H} NMR (101 MHz, 25°C, DMSO- d 6 ) δ 145.45, 144.61, 143.55, 134.19, 122.46, 121.81, 118.72, 112.30, 111.34, 110.44. The spectral data is consistent with the literature data ( Lin et al., 2021 ).…”

Sulfonated N-Doped Carbon Nanotubes as Magnetic Solid Acid Catalysts for the Synthesis of Diphenolic Acid

“…Preparation of the Catalyst. The preparation of Co@NC was based on the previous work 29 with some modifications. Briefly, 2.25 g of melamine, 1.5 g of P123, and 1.0 g of cobalt acetate tetrahydrate [Co(CH 3 COO) 2 •4H 2 O] were dissolved in 80 mL of deionized water and stirred at room temperature for 2 h. Subsequently, it was stirred at 80 °C for 30 min.…”

Tandem Reduction, Ammonolysis, Condensation, and Deamination Reaction for Synthesis of Benzothiadiazines and 1-(Phenylsulfonyl)-1H-benzimidazoles

“…In view of their remarkable significance, enormous efforts have been devoted toward efficient and convenient strategies for the construction of the benzimidazole and quinazolin-4-(3 H )-one skeletons, especially 1-(phenylsulfonyl)-1 H -benzimidazole and benzothiazine, as summarized in Scheme − and Scheme . ,− Considering all of these facts, we have next focused on the design of a cascade reaction which uses nitrile and 2-nitro- N -phenylbenzenesulfonamide or N -(2-nitrophenyl)­benzenesulfonamide to access benzothiazine or 1-(phenylsulfonyl)-1 H -benzimidazole. Herein, we report the use of nitriles and 2-nitro- N -phenylbenzenesulfonamide as coupling partners, promoted by isopropyl alcohol and stannous chloride to synthesis of benzothiazines, which are cost-effective and easily available.…”