Green Approach for the Domino Reduction/Reductive Amination of Nitroarenes and Chemoselective Reduction of Aldehydes Using Fe/aq. Citric Acid/Montmorillonite K10

Preparation of core-shell catalyst for the tandem reaction of amino compounds with aldehydes

Heterogeneous noble metal-based catalysts with stable, precise structures and high catalytic performance are of great research interest for sustainable catalysis. In this article, we designed a novel core-shell catalyst, Pd@UiO-66-NH₂@mSiO₂, with Pd@UiO-66-NH₂ as the core and mesoporous SiO₂ (mSiO₂) as the shell. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) measurement results demonstrated that the obtained catalyst has an excellent core-shell structure. It can significantly prevent the aggregation of Pd nanoparticles (NPs), as well as the leaching of Pd NPs during the reaction process, owing to the protective effect of mSiO₂. During the tandem reaction of aniline and benzaldehyde to generate secondary amines, the prepared Pd@UiO-66-NH₂@mSiO₂ is highly efficient, due to the strong acid sites provided by UiO-66-NH₂ and the hydrogenation reduction sites provided by Pd NPs. Meanwhile, the Pd@UiO-66-NH₂@mSiO₂ with porous structure can also enhance the mass transfer of reactants to improve the reaction efficiency. Additionally, the prepared catalyst was used to catalyze the series reaction of amino compounds and aldehydes, and the results showed that just 5 mg of the catalyst can convert more than 99% of the reactants within 60 minutes in the presence of 1 atm H₂ at room temperature. Finally, the selectivity and stability of the as-prepared catalyst were also confirmed.

Molecularly Engineering Defective Basal Planes in Molybdenum Sulfide for the Direct Synthesis of Benzimidazoles by Reductive Coupling of Dinitroarenes with Aldehydes

Developing more sustainable catalytic processes for preparing N-heterocyclic compounds in a less costly, compact, and greener manner from cheap and readily available reagents is highly desirable in modern synthetic chemistry. Herein, we report a straightforward synthesis of benzimidazoles by reductive coupling of o-dinitroarenes with aldehydes in the presence of molecular hydrogen. An innovative molecular cluster-based synthetic strategy that employs Mo₃S₄ complexes as precursors have been used to engineer a sulfur-deficient molybdenum disulfide (MoS₂)-type material displaying structural defects on both the naturally occurring edge positions and along the typically inactive basal planes. By applying this catalyst, a broad range of functionalized 2-substituted benzimidazoles, including bioactive compounds, can be selectively synthesized by such a direct hydrogenative coupling protocol even in the presence of hydrogenation-sensitive functional groups, such as double and triple carbon-carbon bonds, nitrile and ester groups, and halogens as well as diverse types of heteroarenes.

Construction of a sandwich-like UiO-66-NH2@Pt@mSiO2 catalyst for one-pot cascade reductive amination of nitrobenzene with benzaldehyde

Heterogeneous noble metal-based catalysts with stable, precise structures and high catalytic performance are of great research interest for sustainable catalysis. Herein, we designed the novel sandwich-like metal-organic-framework composite nanocatalyst UiO-66-NH₂@Pt@mSiO₂ using UiO-66-NH₂@Pt as the core, and mesoporous SiO₂ as the shell. The obtained UiO-66-NH₂@Pt@mSiO₂ catalyst shows a well-defined structure and interface, and the protection of the mSiO₂ shell can efficiently prevent Pt NPs from aggregating and leaching in the reaction process. In the one-pot cascade reaction of nitroarenes and aromatic aldehydes to secondary amines, UiO-66-NH₂@Pt@mSiO₂ shows excellent catalytic performance due to acid catalytic sites provided by UiO-66-NH₂ and Pt hydrogenation catalytic sites. Furthermore, the porous structure of the UiO-66-NH₂@Pt@mSiO₂ catalyst also enhances reactant diffusion and improves the reaction efficiency. This work provides a new avenue to meticulously design well-defined nanocatalysts with superior catalytic performance and stability for challenging reactions.