Bimetallic Nickel and Cobalt nanoparticles supported on TiO2 as catalyst for the synthesis of 2-substituted benzimidazole by reductive amination-cyclization of 2-nitroaniline and aldehydes

Abstract

The benzimidazole nucleus finds respectable space and interest among nitrogen heterocycles, whether for its applications or the number of synthetic methodologies employed in their preparation. Recent trends show that interest in the scientific fraternity is now bending towards exploring the use of bimetallic NiCo-based heterogeneous catalysts for the synthesis of benzimidazoles. This work is aimed at the development of new catalytic systems obtained from the H₂-assisted reduction of Ni_xCo_1–xTiO₃ mixed oxides to produce bimetallic Ni_xCo_1–x/TiO₂ (x = 0.0, 0.1, 0.3, 0.5, and 1.0) catalysts for the tandem selective production of 2-substituted benzimidazole scaffolds from 2-nitroaniline and aldehydes. The physicochemical characterization displayed the formation of the NiCo alloy supported on TiO₂-rutile and the active phase are almost in the zero-valent state after the reduction treatment. The catalytic activity showed that all the catalysts are active in the tandem synthesis of 2-benzimidazole, and the selectivity to the target product is a function of the Ni content in the catalyst. The most efficient and selective system was Ni_0.1Co_0.9/TiO₂, which remained active after 10 consecutive cycles. The Ni_0.1Co_0.9 composition in the catalyst formulation affords optimal physicochemical properties for enhanced catalytic performance and enables the recyclability ability to produce the target product. Thus, our results provide a valuable and practical method by which aromatic N-heterocycles of pharmaceutical relevance can be obtained via catalytic tandem reaction using non-noble based catalysts.