Development of a General and Selective Nanostructured Cobalt Catalyst for the Hydrogenation of Benzofurans, Indoles and Benzothiophenes

Improving the Hydrogenation Performance of Nano-Catalysts by Constructing a Cavity-Constrained Fluidized System

Nano-catalysts demonstrate exceptional performance in heterogeneous reactions, yet their potential is often underutilized due to a lack of attention to engineering design. In this study, an innovative encapsulated structure is presented for nano-catalysts and a corresponding catalytic system. Using an oil-in-water droplet strategy, millimeter-sized hollow spherical alumina (Al2O3-HS) is fabricated with an average diameter of ≈3 mm and a hollow void size of ≈1 mm. This approach enables the one-step encapsulation of nanoscale Pd/Al2O3 within the Al2O3-HS. The resulting assembly is immobilized within a tubular reactor for the hydrogenation of 2-ethylanthraquinone, with hydrogen introduced from the bottom of the reactor. Remarkably, the encapsulated catalyst achieved twice the H2O2 productivity of conventional supported catalysts. This enhancement is attributed to the cavity-constrained fluidization behavior of Pd/Al2O3 within the hollow alumina spheres. The design introduces a novel catalytic system that combines shell-immobilization with the fluidization of encapsulated nano-catalysts. As the gas velocity exceeds the minimum fluidization velocity, the Pd/Al2O3 particles remain highly accessible while allowing efficient gas and product flow. This hybrid approach integrates the advantages of fixed-bed and fluidized-bed systems, offering a promising solution to the technical challenges limiting the industrial application of nano-catalysts.

Reduction-Interrupted Tandem Reaction for General Synthesis of Functional Amino Acids by a Heterogeneous Cobalt Catalyst

Despite their significant importance in numerous fields, the challenges in direct and diverse synthesis of γ-amino-α-hydroxybutyric acids (AHBAs) pose substantial obstacles to explore their functions. Here, by preparation of a N-doped carbon-supported bifunctional cobalt catalyst (Co-DAPhen/C), it was applied to develop a reductive tandem reaction for general synthesis of AHBA derivatives from cheap and abundant nitroarenes, formaldehyde, and acrylates. This catalytic three-component reaction features broad substrate and functionality tolerance, an easily accessible and reusable catalyst, and high step and atom economy. The active Co sites of the catalyst are involved in the mild reduction processes with formic acid, whereas the N-doped carbon support enriches the HCHO and acrylates by physical adsorption, thus favoring the capture of hydroxylamine and nitrone intermediates via condensation and 1,3-dipolar cycloaddition, respectively. Such a metal-support synergy interrupts the conventional reduction of nitroarenes into anilines and results in a novel tandem reaction route. In this work, the concept merging mild reduction and effective intermediate transformations is anticipated to develop more useful tandem reactions by rational catalyst design.

Reductive Coupling of N-Heteroarenes and 1,2-Dicarbonyls for Direct Access to γ-Amino Acids, Esters, and Ketones Using a Heterogeneous Single-Atom Iridium Catalyst

Despite their significant importance, the challenges in direct and diverse synthesis of N-heterocyclic γ-amino acids/esters/ketones hamper exploration of their applications. Herein, by developing a multifunctional heterogeneous iridium single-atom catalyst composed of silica-confined iridium species and a boron-doped ZrO2 support (Ir-SAs@B-ZrO2/SiO2), we describe its utility in establishing a new reductive coupling reaction of N-heteroarenes and 1,2-dicarbonyls for selective and diverse construction of the as-described compounds in a straightforward manner. The striking features, including good substrate and functionality tolerance, high step and atom economy, exceptional catalyst reusability, and diversified product post-transformations, highlight the practicality of the developed chemistry. Mechanistic studies reveal that the synergy between the active Ir sites and acidic support favors a chemoselective reduction of the more inert N-heteroarenes and affords requisite enamine intermediates. In this work, the concept on precise transformation of reductive intermediates will open a door to further develop useful tandem reactions by rational catalyst design.

Reductive Amination of Aldehyde and Ketone with Ammonia and H2 by an In Situ-Generated Cobalt Catalyst under Mild Conditions

Herein, we present the simplest approach for the synthesis of primary amines via reductive amination using H2 as a reductant and aqueous ammonia as a nitrogen source, catalyzed by amorphous Co particles. The highly active Co particles were prepared in situ by simply mixing commercially available CoCl2 and NaBH4/NaHBEt3 without any ligand or support. This reaction system features mild conditions (80 °C, 1-10 bar), high selectivity (99%), a wide substrate scope, simple operation, and easy separation of the catalyst. The successful large-scale application of this reaction in the production of primary amines suggests its potential industrial interest.

Construction of Indium(III)-Organic Framework Based on a Flexible Cyclotriphosphazene-Derived Hexacarboxylate as a Reusable Green Catalyst for the Synthesis of Bioactive Aza-Heterocycles

The constant demand for eco-friendly methods of synthesizing complex organic compounds inspired researchers to design and develop modern, highly efficient heterogeneous catalytic systems. Herein, In-HCPCP metal-organic framework (SRMIST-1), a heterogeneous Lewis acid catalyst containing less toxic indium and eco-friendly robust cyclotriphosphazene and exhibiting notable chemical and thermal stability, durable catalytic activity, and exceptional reusability was produced through the reaction between indium(III) nitrate hydrate and hexakis(4-carboxylatophenoxy)-cyclotriphosphazene. In the SRMIST-1 structure, secondary building units {InO7} are assembled by a connection of η2- and η1-carboxylic oxo atoms from different HCPCP ligands, forming a three-dimensional network. The occurrence of regularly distributed In(III) sites in SRMIST-1 confers superior reactivity on the catalyst toward the synthesis of 2,3-dihydroquinazolin-4(1H)-ones and 3,4-dihydro-2H-1,2,4-benzothiadiazine-1,1-dioxides by the cyclization reaction of 2-aminobenzamides and 2-aminobenzenesulphonamides with aldehydes under optimized reaction conditions, respectively. The notable features of this method include broad functional group compatibility, low catalyst loading (1-5 mol %), mild reaction conditions, easy workup procedures, good to excellent reaction yields, ethanol as a green solvent, reusability of the catalyst (five cycles), and economic attractiveness, which is mainly due to sustainability of SRMIST-1 as a reusable green catalyst. Our findings demonstrate that the highly reactive and reusable green catalyst finds widespread applications in medicinal chemistry.

Copper(I)-Catalyzed Dearomatization of Benzofurans with 2-(Chloromethyl)anilines through Radical Addition and Cyclization Cascade

Herein, we described a copper(I)-catalyzed dearomatization of benzofurans with 2-(chloromethyl)anilines to prepare various tetrahydrobenzofuro[3,2-b]quinolines and 2-(quinolin-2-yl)phenols in good to excellent yields through radical addition and an intramolecular cyclization process. Mechanistic studies revealed that 2-(chloromethyl)anilines served as radical precursors. The present method features broad substrate scope, good functional group tolerance, quinoline scaffold diversity, and radical addition dearomatization of benzofurans.

A general and robust Ni-based nanocatalyst for selective hydrogenation reactions at low temperature and pressure

Catalytic hydrogenations are important and widely applied processes for the reduction of organic compounds both in academic laboratories and in industry. To perform these reactions in sustainable and practical manner, the development and applicability of non-noble metal-based heterogeneous catalysts is crucial. Here, we report highly active and air-stable nickel nanoparticles supported on mesoporous silica (MCM-41) as a general and selective hydrogenation catalyst. This catalytic system allows for the hydrogenation of carbonyl compounds, nitroarenes, N-heterocycles, and unsaturated carbon─carbon bonds in good to excellent selectivity under very mild conditions (room temperature to 80°C, 2 to 10 bar H2). Furthermore, the optimal nickel/meso-silicon dioxide catalyst is reusable (4 cycles) without loss of its catalytic activity.

Reductive Coupling of Nitroarenes and HCHO for General Synthesis of Functional Ethane-1,2-diamines by a Cobalt Single-Atom Catalyst

Despite the extensive applications, selective and diverse access to N,N'-diarylethane-1,2-diamines remains, to date, a challenge. Here, by developing a bifunctional cobalt single-atom catalyst (CoSA-N/NC), we present a general method for direct synthesis of such compounds via selective reductive coupling of cheap and abundant nitroarenes and formaldehyde, featuring good substrate and functionality compatibility, an easily accessible base metal catalyst with excellent reusability, and high step and atom efficiency. Mechanistic studies reveal that the N-anchored cobalt single atoms (CoN4) serve as the catalytically active sites for the reduction processes, the N-doped carbon support enriches the HCHO to timely trap the in situ formed hydroxyamines and affords the requisite nitrones under weak alkaline conditions, and the subsequent inverse electron demand 1,3-dipolar cycloaddition of the nitrones and imines followed by hydrodeoxygenation of the cycloadducts furnishes the products. In this work, the concept of catalyst-controlled nitroarene reduction to in situ create specific building blocks is anticipated to develop more useful chemical transformations.