1T-MoS2 catalysed reduction of nitroarenes and a one-pot synthesis of imines

Abstract

Earth-abundant transition metal dichalcogenides (TMDs) have emerged as an effective catalyst to improve the catalytic performance of heterogeneous catalysis, especially in organic functional group conversion chemistry. The layered structural feature and metallic (1T) phase availability are advantages of molybdenum disulfide (MoS₂) for their significant catalytic performance over other TMDs. To date, the exfoliation of alkali metal was considered the most embraced technique to obtain 1T-MoS₂. The main difficulty of this technique is the usage of pyrophoric alkali metal ions and undesirable organic media. On the other hand, the lack of reproducibility and the lesser extent of the 1T phase is the problem associated with the synthesis of 1T-MoS₂ in an aqueous medium. In contrast, herein, 84% of 1T phase enrichment has been achieved in the SBA-15 silica template assisted synthesis of 1T-MoS₂. This is a very significant amount of 1T phase enrichment in MoS₂, especially in the aqueous medium, which certifies the methodology for industrial scale applications. To the best of our knowledge, 1T-MoS₂ has not yet been exploited as a heterogeneous catalyst for organic functional group transformations. In this context, we reported the hydrogenation of nitroaromatics with the assistance of 1T-MoS₂ catalyst in a green solvent (water) and a sequential one-pot synthesis of Schiff bases from nitroaromatics and aldehydes. This synthetic transformation requires hydrazine hydrate as a hydrogen source at ambient pressure and base-free conditions. However, such a conversion is unable to be performed without the help of a 1T-MoS₂ catalyst. Notable features of this method include high recyclability, retaining of catalytic activity after six successive cycles, and highly efficient, stable, and short reaction times. Hence, it is worth mentioning that, here, a new catalytic behavior of 1T-MoS₂ (84% phase enrichment) in organic functional group transformation, i.e. reduction of the aromatic nitro compound into an aromatic amine, has been realized with high reproducibility. In this reduction process, the conversion and selectivity are >99% and 97%, respectively, when the solvent is water, whereas both are >99% when toluene was employed as a solvent. Thus, for the industrial viability of this reduction process, the applicability of the catalytic reduction behavior of 1T-MoS₂ in other organic framework compounds with the nitro group will be studied in the near future.