One-pot Reductive Amination of carbonyl Compounds with Nitro Compounds by Transfer Hydrogenation over Co-Nx as catalyst

Pd-catalyzed imine synthesis from nitroarenes via Fe-H2O under electromagnetic milling

This article introduces a novel, eco-friendly, one-pot method for synthesizing imines via mechanochemistry. Using water as a hydrogen donor and iron as a reducing agent, nitroaromatics react with aldehydes in the presence of a palladium catalyst to form imines efficiently.

Hydrogen-Bond-Mediated Formation of C-N or C=N Bond during Photocatalytic Reductive Coupling Reaction over CdS Nanosheets

Reductive amination of carbonyl compounds and nitro compounds represents a straightforward way to attain imines or secondary amines, but it is difficult to control the product selectivity. Herein, we report the selective formation of C-N or C=N bond readily manipulated through a solvent-induced hydrogen bond bridge, facilitating the swift photocatalytic reductive coupling process. The reductive-coupling of nitro compounds with carbonyl compounds using formic acid and sodium formate as the hydrogen donors over CdS nanosheets selectively generates imines with C=N bonds in acetonitrile solvent; while taking methanol as solvent, the C=N bonds are readily hydrogenated to the C-N bonds via hydrogen-bonding activation. Experimental and theoretical study reveals that the building of the hydrogen-bond bridge between the hydroxyl groups in methanol and the N atoms of the C=N motifs in imines facilitates the transfer of hydrogen atoms from CdS surface to the N atoms in imines upon illumination, resulting in the rapid hydrogenation of the C=N bonds to give rise to the secondary amines with C-N bonds. Our method provides a simple way to control product selectivity by altering the solvents in photocatalytic organic transformations.

Multicomponent Reductive Coupling for Selective Access to Functional γ-Lactams by a Single-Atom Cobalt Catalyst

Despite their significant importance to numerous fields, the difficulties in direct and diverse synthesis of α-hydroxy-γ-lactams pose substantial obstacles to their practical applications. Here, we designed a nitrogen and TiO2 co-doped graphitic carbon-supported material with atomically dispersed cobalt sites (CoSA-N/NC-TiO2), which was successfully applied as a multifunctional catalyst to establish a general method for direct construction of α-hydroxy-γ-lactams from cheap and abundant nitro(hetero)arenes, aldehydes, and H2O with alkynoates. The striking features of operational simplicity, broad substrate and functionality compatibility (>100 examples), high step and atom efficiency, good selectivity, and exceptional catalyst reusability highlight the practicality of this new catalytic transformation. Mechanistic studies reveal that the active CoN4 species and the dopants exhibit a synergistic effect on the formation of key acid-masked nitrones; their subsequent nucleophilic addition to the alkynoates followed by successive reduction, alkenyl hydration, and intramolecular ester ammonolysis delivers the desired products. In this work, the concept of reduction interruption leading to new reaction route will open a door to further develop useful transformations by rational catalyst design.

One-pot reductive amination of carbonyl compounds and nitro compounds via Ir-catalyzed transfer hydrogenation

The formation of C-N bond is a vital synthetic tool for establishing molecular diversity, which is highly sought after in a wide range of biologically active natural products and drugs. Herein, we present a new strategy for the synthesis of secondary amines via iridium-catalyzed one-pot reductive amination of carbonyl compounds with nitro compounds. This method is demonstrated for a variety of carbonyl compounds, including miscellaneous aldehydes and ketones, which are compatible with this catalytic system, and deliver the desired products in good yields under mild conditions. In this protocol, the reduction of nitro compounds occurs in situ first, followed by reductive amination to form amine products, providing a new one-pot procedure for amine synthesis.

Engineering of Local Coordination Microenvironment in Single-Atom Catalysts Enabling Sustainable Conversion of Biomass into a Broad Range of Amines

Utilizing renewable biomass as a substitute for fossil resources to produce high-value chemicals with a low carbon footprint is an effective strategy for achieving a carbon-neutral society. Production of chemicals via single-atom catalysis is an attractive proposition due to its remarkable selectivity and high atomic efficiency. In this work, a supramolecular-controlled pyrolysis strategy is employed to fabricate a palladium single-atom (Pd1 /BNC) catalyst with B-doped Pd-Nx atomic configuration. Owing to the meticulously tailored local coordination microenvironment, the as-synthesized Pd1 /BNC catalyst exhibits remarkable conversion capability for a wide range of biomass-derived aldehydes/ketones. Thorough characterizations and density functional theory calculations reveal that the highly polar metal-N-B site, formed between the central Pd single atom and its adjacent N and B atoms, promotes hydrogen activation from the donor (reductants) and hydrogen transfer to the acceptor (C═O group), consequently leading to exceptional selectivity. This system can be further extended to directly synthesize various aromatic and furonic amines from renewable lignocellulosic biomass, with their greenhouse gas emission potentials being negative in comparison to those of fossil-fuel resource-based amines. This research presents a highly effective and sustainable methodology for constructing C─N bonds, enabling the production of a diverse array of amines from carbon-neutral biomass resources.

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

An expedient synthesis of aromatic amines and imines via the reduction of nitroaromatics using 1T-MoS2 as a heterogeneous catalyst.

Pd Anchored on a Phytic Acid/Thiourea Polymer as a Highly Active and Stable Catalyst for the Reduction of Nitroarene

A kind of N, P, C, O-containing polymer was easily prepared via microwave heating of phytic acid and thiourea just for 90 s. After impregnation and reduction of H₂PdCl₄, highly dispersed Pd single atoms/sub-nano clusters loaded on the phytic acid/thiourea polymer (Pd-CNSP) were successfully obtained. Owing to the synergetic effect of the polymer support and Pd, the catalyst Pd-CNSP achieves a great atomic efficiency of Pd species and exhibits an outstanding catalytic ability in the reduction of 4-nitrophenol. The k value of the catalyst Pd-CNSP (2.17 min^-1 mg^-1) is about 19 times higher than that of the commercial Pd/C (5 wt %) catalyst. The turnover frequency value is as high as 848 min^-1, which is the highest value reported so far. Pd-CNSP also has good selectivity for the reduction of halogen-substituted (Cl and Br) nitroaromatics. It is expected to be mass-produced and used in other industrial hydrogenation reactions.

Metal-based Heterogeneous Catalysts for One-Pot Synthesis of Secondary Anilines from Nitroarenes and Aldehydes

Recently, N-substituted anilines have been the object of increasing research interest in the field of organic chemistry due to their role as key intermediates for the synthesis of important compounds such as polymers, dyes, drugs, agrochemicals and pharmaceutical products. Among the various methods reported in literature for the formation of C-N bonds to access secondary anilines, the one-pot reductive amination of aldehydes with nitroarenes is the most interesting procedure, because it allows to obtain diverse N-substituted aryl amines by simple reduction of nitro compounds followed by condensation with aldehydes and subsequent reduction of the imine intermediates. These kinds of tandem reactions are generally catalyzed by transition metal-based catalysts, mainly potentially reusable metal nanoparticles. The rapid growth in the last years in the field of metal-based heterogeneous catalysts for the one-pot reductive amination of aldehydes with nitroarenes demands for a review on the state of the art with a special emphasis on the different kinds of metals used as catalysts and their recyclability features.

Catalytic Reductive Amination of Aldehydes and Ketones With Nitro Compounds: New Light on an Old Reaction

Reductive amination of carbonyl compounds with primary amines is a well-established synthetic methodology for the selective production of unsymmetrically substituted secondary and tertiary amines. From the industrial and green chemistry perspective, it is attractive to combine reductive amination with the synthesis of primary amines in a single one-pot catalytic process. In this regard, nitro compounds, which are readily available and inexpensive feedstocks, received much attention as convenient precursors to primary amines in such processes. Although the direct reductive coupling of nitro compounds with aldehydes/ketones to give secondary and tertiary amines has been known since the 1940's, due to the development of highly efficient and selective non-noble metal-based catalysts a breakthrough in this area was made in the last decade. In this short overview, recent progress in the methodology of the reductive amination with nitro compounds is summarized together with applications to the synthesis of bioactive amines and heterocycles. Remaining challenges in this field are also analyzed.

Sustainable route for the synthesis of flower-like Ni@N-doped carbon nanosheets from bagasse and its catalytic activity towards reductive amination of nitroarenes with bio-derived aldehydes

Waste derived N-doped carbon for one pot domino catalytic transformation starting from nitroarenes and carbonyl compounds directed towards the preparation of imines and benzimidazole products.

One-pot reductive amination of carbonyl compounds with nitro compounds over a Ni/NiO composite

Easy-to-prepare Ni/NiO acts as an efficient heterogeneous catalyst for one-pot reductive amination of carbonyl compounds with nitroarenes.

Hydrogenation of Functionalized Nitroarenes Catalyzed by Single-Phase Pyrite FeS2 Nanoparticles on N,S-Codoped Porous Carbon

Catalytic hydrogenation of nitroarenes is an industrially very important and environmentally friendly process for the production of anilines; however, highly chemoselective reduction of nitroarenes decorated with one or more reducible groups in a nitroarene molecule remains a challenge. Herein, a novel hybrid non-noble iron-based nanocatalyst (named as FeS₂ /NSC) was developed, which was prepared from biomass as C and N source together with inexpensive Fe(NO₃ )₃ as Fe source through high-temperature pyrolysis in a straightforward and cost-effective procedure. Comprehensive characterization revealed that single-phase pyrite FeS₂ nanoparticles with precisely defined composition and uniform size were homogeneously dispersed on N,S-codoped porous carbon with large specific surface area, hierarchical porous channels, and high pore volume. The resultant catalyst FeS₂ /NSC demonstrated good catalytic activity for hydrogenation of functionalized nitroarenes with good tolerance of various functional groups in water as a sustainable and green solvent. Compared with bulk pyrite FeS₂ and other non-noble metal-based heterogeneous catalysts reported in the literature, a remarkably enhanced activity was observed under mild reaction conditions. More importantly, FeS₂ /NSC displayed exclusive chemoselectivity for the reduction of nitro groups for nitroarenes bearing varying readily reducible groups.

Efficient Transfer Hydrogenation of Nitro Compounds to Amines Enabled by Mesoporous N-Stabilized Co-Zn/C

N-doped metal materials with enhanced stability and abundant porosity have attracted tremendous attention in catalytic reactions. Herein, a simple solvothermal approach was demonstrated to significantly enlarge the pore dimension of conventional microporous zeolitic imidazolate framework (ZIF) incorporated with two kinds of central metals (Co, Zn), while maintaining the original ZIF crystal morphology. Upon further pyrolysis, the resulting mesoporous Co-Zn/N-C material could possess the highly dispersed metal particle on the N-doped carbon, with satisfactory pore volume and surface area. The partial vaporization of Zn and the stabilizing effect of N, illustrated by XRD, HRTEM, HAADF-STEM with mapping, SEM, Raman Spectrum, BET, and TGA, were able to remarkably increase the accessibility of substrate toward active sites and prevent the aggregation of metal particles, respectively. Under mild reaction conditions, the N-stabilized Co-Zn/N-C exhibited good activity and selectivity in transfer hydrogenation of various nitro compounds to corresponding amines, where a synergistic role among Co, Zn, and N was responsible for its superior performance to other tested catalysts. In addition, the N-doped non-noble metal/carbon heterogeneous catalyst was fairly stable and could be reused several times without obvious deactivation.

A Cobalt Catalyst Permits the Direct Hydrogenative Synthesis of 1H-Perimidines from a Dinitroarene and an Aldehyde

A new sustainable catalytic reaction, the synthesis of 1H- perimidines from a dinitroarene and an aldehyde in the presence of H₂ , was achieved. An earth-abundant metal catalyst was developed to permit the efficient, highly chemoselective, and consecutive hydrogenation of dinitroarenes. The catalyst was reusable and easy to handle. The use of a specific Co complex and its pyrolysis at a certain temperature was crucial to achieve high activity for the complex organic transformation. Benzylic and aliphatic aldehydes could undergo the hydrogenative condensation, and many functional groups, including hydrogenation-sensitive examples such as iodo aryl, nitrile, olefin, and alkyne groups, were tolerated.

Cobalt Entrapped in N,S-Codoped Porous Carbon: Catalysts for Transfer Hydrogenation with Formic Acid

Catalysts with Co nanoparticles (NPs) entrapped in N,S-codoped carbon shells were successfully fabricated by pyrolysis of porous organic polymers (POPs) with cobalt salts. The encapsulated structure consisting of Co NPs and N,S-codoped carbon layers was verified by TEM, XRD, and X-ray photoelectron spectroscopy. The catalysts displayed excellent activity and stability for the catalytic transfer hydrogenation (CTH) of nitrobenzene with formic acid under base-free conditions. Furthermore, the resultant catalysts allowed for highly efficient and selective transfer hydrogenation of various functionalized nitroarenes to the corresponding anilines. Through control experiments, the covered Co NPs were identified as active sites for CTH. The incorporation of S into the N-doped carbon lattice promoted the electron transfer from metallic cobalt NPs to their shells, which played a significant role in the acceleration of CTH. Moreover, the Co-NSPC-850 catalyst pyrolyzed at 850 °C showed excellent stability in the recycling experiments.

Reduction of Nitro Compounds Using 3d-Non-Noble Metal Catalysts

The reduction of nitro compounds to the corresponding amines is one of the most utilized catalytic processes in the fine and bulk chemical industry. The latest development of catalysts with cheap metals like Fe, Co, Ni, and Cu has led to their tremendous achievements over the last years prompting their greater application as "standard" catalysts. In this review, we will comprehensively discuss the use of homogeneous and heterogeneous catalysts based on non-noble 3d-metals for the reduction of nitro compounds using various reductants. The different systems will be revised considering both the catalytic performances and synthetic aspects highlighting also their advantages and disadvantages.

Direct Reductive N-Functionalization of Aliphatic Nitro Compounds

The first general protocol for the direct reductive N-functionalization of aliphatic nitro compounds is presented. The nitro group is partially reduced to a nitrenoid, with a mild and readily available combination of B₂ pin₂ and zinc organyls. Thereby, the formation of an unstable nitroso intermediate is avoided, which has so far severely limited reductive transformations of aliphatic nitro compounds. The reaction is concluded by an electrophilic amination of zinc organyls.

Nitrogen-doped mesoporous SiC materials with catalytically active cobalt nanoparticles for the efficient and selective hydrogenation of nitroarenes

Mesoporous nitrogen-doped silicon carbide catalysts with integrated cobalt nanoparticles (Co@N-SiC) were synthesized by the thermal decomposition of a microphase-separated block copolymer of polycarbosilane and polyethylene. The catalysts are highly active, reusable and offer selective hydrogenation of the nitro group in the presence of hydrogenation-sensitive functional groups.

A versatile, immobilized gold catalyst for the reductive amination of aldehydes in batch and flow

A process for the reductive amination of aldehydes in continuous flow catalyzed by gold nanoparticles immobilized onto mesoporous silica has been developed.

Flow synthesis of secondary amines over Ag/Al2O3 catalyst by one-pot reductive amination of aldehydes with nitroarenes

The reaction of aldehydes with nitroarenes over Ag/Al₂O₃ catalyst under H₂ in a flow reactor gives secondary amines in high yield.