Nitrogen-Doped Carbon-Supported Nickel Nanoparticles: A Robust Catalyst to Bridge the Hydrogenation of Nitriles and the Reductive Amination of Carbonyl Compounds for the Synthesis of Primary Amines

Regulating the production distribution in Ni-Cu nanoparticle mediated nitrile hydrogenation

The selective hydrogenation of nitrile compounds represents a pivotal area of research within both industrial and academic catalysis. In this study, we prepared Ni-Cu bimetallic catalysts through a co-deposition-crystallization sequence, aimed at the efficient production of primary and secondary amines. The enhanced selectivity for primary amines is attributed to the downshift of the d-band center of Ni0.1Cu, which weakens the adsorption of key imine intermediates. Consequently, the synthesized Ni-Cu catalysts demonstrated exceptional catalytic performance in the selective hydrogenation of nitrile compounds, including those with reduction-sensitive functional groups such as -Cl and -Br, achieving 100 % conversion efficiency and significant yields ranging from 80 % to 99 %. The reaction conditions were comprehensively optimized, taking into account factors such as temperature, solvent, time, additives, and hydrogen pressure. Furthermore, the catalytic performance of Ni0.1Cu and Ni0.4Cu in the selective hydrogenation of nitriles was sustained over at least five reaction cycles. Temperature-programmed desorption results elucidated the structure-activity relationship, revealing that a strong interaction site prevails in Ni0.4Cu, while a weaker or moderate interaction site in Ni0.1Cu is responsible for the formation of primary amines. Theoretical calculations indicate that the reaction proceeds via an imine mechanism, with benzylideneimine serving as a key intermediate. This work may stimulate further research into the development of bimetallic nano-catalysts for selective nitrile hydrogenation in industrial catalytic processes.

Highly Selective Hydrogenation of Nitriles to Primary Amines without an Additive Using Nanoscale Ni0-NiII/III-bTiO2 Heterojunctions

Despite significant progress in the catalytic hydrogenation of nitriles, the persistent challenge of requiring additives to prevent condensation byproducts and achieve selectivity toward primary amines demands urgent attention. In this work, we present an integrated approach utilizing a ligand-bridged Ni-Ti bimetallic complex as a precursor to tune Ni0-NiO-NiO(OH) heterojunctions and phases of black titania (bTiO2) by controlling pyrolytic conditions. This tailored phase distribution and charge dynamics across heterojunctions create an effective balance of acidic and basic sites, enabling the direct hydrogenation of nitriles to primary amines without the need for additives. However, at elevated pyrolysis temperatures, this balanced composition begins to shift, with the loss of critical phases that alter the catalyst's structural and chemical properties. This shift reduces amphoteric behavior, resulting in decreased selectivity for primary amines and favoring the formation of condensation byproducts. The catalyst's structure, amphoteric nature, crystallinity, surface area, and active sites are comprehensively characterized using high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FT-IR), temperature programmed desorption of ammonia (NH3-TPD), temperature programmed desorption of carbon dioxide (CO2-TPD), and CO2 adsorption techniques. The magnetically retrievable catalyst exhibited excellent functional group tolerance, high selectivity, multiple reusability, broad substrate scope, and high activity for nitrile hydrogenation to primary amines, with the potential for advanced catalytic hydrogenation of other functional groups.

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.

Employing Ammonia for the Synthesis of Primary Amines: Recent Achievements over Heterogeneous Catalysts

Primary amines represent highly privileged chemicals for synthesis of polymers, pharmaceuticals, agrochemicals, coatings, etc. Consequently, the development of efficient and green methodologies for the production of primary amines are of great importance in chemical industry. Owing to the advantages of low cost and ease in availability, ammonia is considered as a feasible nitrogen source for synthesis of N-containing compounds. Thus, the efficient transformation of ammonia into primary amines has received much attention. In this review, the commonly applied synthetic routes to produce primary amines from ammonia were summarized, including the reductive amination of carbonyl compounds, the hydrogen transfer amination of alcohols, the hydroamination of olefins and the arylation with ammonia, in which the catalytic performance of the recent heterogeneous catalysts is discussed. Additionally, various strategies to modulate the surface properties of catalysts are outlined in conjunction with the analysis of reaction mechanism. Particularly, the amination of the biomass-derived substrates is highlighted, which could provide competitive advantages in chemical industry and stimulate the development of sustainable catalysis in the future. Ultimately, perspectives into the challenges and opportunities for synthesis of primary amines with ammonia as N-resource are discussed.

Tuning the Selectivity of Catalytic Nitrile Hydrogenation with Phase-Controlled Co Nanoparticles Prepared by Hydrosilane-Assisted Method

Cobalt (Co) is a promising candidate to replace noble metals in the hydrogenation process, which is widely employed in the chemical industry. Although the catalytic performance for this reaction has been considered to be significantly dependent on the Co crystal phase, no satisfactory systematic studies have been conducted, because it is difficult to synthesize metal nanoparticles that have different crystalline structures with similar sizes. Here we report a new method for the synthesis of cobalt nanoparticles using hydrosilane as a reducing agent (hydrosilane-assisted method). This new method uses 1,3-butanediol and propylene glycol to successfully prepare fcc and hcp cobalt nanoparticles, respectively. These two types of Co nanoparticles have similar sizes and surface areas. The hcp Co nanoparticles exhibit higher catalytic performance than fcc nanoparticles for the hydrogenation of benzonitrile under mild conditions. The present hcp Co catalyst is also effective for highly selective benzyl amine production from benzonitrile without ammonia addition, whereas many catalytic systems require ammonia addition for selective benzyl amine production. Mechanistic studies revealed that the fast formation of the primary amine and the prevention of condensation and secondary amine hydrogenation promote selective benzonitrile hydrogenation for benzylamine over hcp Co nanoparticles.

Nickel Carbide Nanoparticle Catalyst for Selective Hydrogenation of Nitriles to Primary Amines

Despite its unique physicochemical properties, the catalytic application of nickel carbide (Ni3 C) in organic synthesis is rare. In this study, we report well-defined nanocrystalline Ni3 C (nano-Ni3 C) as a highly active catalyst for the selective hydrogenation of nitriles to primary amines. The activity of the aluminum-oxide-supported nano-Ni3 C (nano-Ni3 C/Al2 O3 ) catalyst surpasses that of Ni nanoparticles. Various aromatic and aliphatic nitriles and dinitriles were successfully converted to the corresponding primary amines under mild conditions (1 bar H2 pressure). Furthermore, the nano-Ni3 C/Al2 O3 catalyst was reusable and applicable to gram-scale experiments. Density functional theory calculations suggest the formation of polar hydrogen species on the nano-Ni3 C surface, which were attributed to the high activity of nano-Ni3 C towards nitrile hydrogenation. This study demonstrates the utility of metal carbides as a new class of catalysts for liquid-phase organic reactions.

Air-Stable Ni Catalysts Prepared by Liquid-Phase Reduction Using Hydrosilanes for Reactions with Hydrogen

The liquid-phase reduction method for the preparation of metal nanoparticles (NPs) by the reduction of metal salts or metal complexes in a solvent with a reducing agent is widely used to prepare Ni NPs that exhibit high catalytic activity in various organic transformations. Intensive research has been conducted on control of the morphology and size of Ni NPs by the addition of polymers and long-chain compounds as protective agents; however, these agents typically cause a decrease in catalytic activity. Here, we report on the preparation of Ni NPs using hydrosilane (Ni-Si) as a reducing agent and a size-controlling agent. The substituents on silicon can control not only the size but also the crystal phase of the Ni NPs. The prepared Ni NPs exhibited high catalytic performance for the hydrogenation of unsaturated compounds, aromatics, and heteroaromatics to give the corresponding hydrogenated products in high yields. The unique feature of Ni catalysts prepared by the hydrosilane-assisted method is that the catalysts can be handled under air as opposed to conventional Ni catalysts such as Raney Ni. Characterization studies indicated that the surface hydroxide was reduced under the catalytic reaction conditions with H2 at around 100 °C and with the assistance of organosilicon compounds deposited on the catalyst surface. The hydrosilane-assisted method presented here could be applied to the preparation of supported Ni catalysts (Ni-Si/support). The interaction between the Ni NPs and a metal oxide support enabled the direct amination of alcohols with ammonia to afford the primary amine selectively.

3D Porous MoS2-Decorated Reduced Graphene Oxide Aerogel as a Heterogeneous Catalyst for Reductive Transformation Reactions

The MoS2-based reduced graphene oxide aerogel (MoS2-rGOA)-assisted organic transformation reactions are presented. MoS2-rGOA is used as a heterogeneous catalyst for the reduction of benzene derivatives such as benzaldehyde, nitrobenzene, and benzonitrile to benzyl alcohol, aniline, and benzamide and their derivatives, respectively, in green solvents (water/methanol) and green reducing agents (hydrazine hydrate having N2 and H2 as byproducts). The mechanistic features of the reduction pathway, substrate scope, and the best suitable conditions by varying the temperature, solvent, reducing agent, catalyst loading, time, etc. are optimized. All of the synthesized products are obtained in quantitative yield with purity and well characterized based on nuclear magnetic resonance analysis. Further, it is also observed that our catalyst is efficiently recyclable and works well checked up to 5 cycles.

General Construction of Amine via Reduction of N=X (X = C, O, H) Bonds Mediated by Supported Nickel Boride Nanoclusters

Amines play an important role in synthesizing drugs, pesticides, dyes, etc. Herein, we report on an efficient catalyst for the general construction of amine mediated by nickel boride nanoclusters supported by a TS-1 molecular sieve. Efficient production of amines was achieved via catalytic hydrogenation of N=X (X = C, O, H) bonds. In addition, the catalyst maintains excellent performance upon recycling. Compared with the previous reports, the high activity, simple preparation and reusability of the Ni-B catalyst in this work make it promising for industrial application in the production of amines.

Hydrogenation of nitriles to primary amines catalyzed by an unsupported nanoporous palladium catalyst: understanding the essential reason for the high activity and selectivity of the catalyst

An efficient and highly selective heterogeneous catalyst system for nitrile hydrogenation was developed using unsupported palladium nanopores (PdNPore). The PdNPore-catalyzed selective hydrogenation of nitriles proceeded smoothly, without any additives, under mild conditions (low H₂ pressure and low temperature) to yield primary amines with satisfactory to excellent yields. Systematic studies demonstrated that the high activity and excellent selectivity of the PdNPore originated from its good Lewis acidity and porous structure. No palladium leached from the PdNPore during the hydrogenation reaction. Moreover, the catalyst was easily recovered and reused without any loss of catalytic activity. A deuterium-hydrogen exchange reaction clearly indicated that the present hydrogenation involves heterolytic H₂ splitting on the surface of the PdNPore catalyst.

Advances in the Catalytic Reductive Amination of Furfural to Furfural Amine: The Momentous Role of Active Metal Sites

One-pot synthesis of sustainable primary amines by catalytic reductive amination of bio-based carbonyl compounds with NH₃ and H₂ is emerging as a promising and robust approach. The primary amines, especially furfuryl amine (FUA) derived from furfural (FUR), with a wide range of applications from pharmaceuticals to agrochemicals, have attracted much attention due to their versatility. This Review is majorly comprised of two segments on the reductive amination of FUR to FUA, one with precious (Ru, Pd, Rh) and the other with non-precious (Co, Ni) metals on different supports and in various solvent systems in the presence of NH₃ and H₂ . The active metal sites generated on multiple supports are accentuated with experimental evidence based on CO-diffuse reflectance infrared Fourier-transform spectroscopy, H₂ temperature-programmed reduction, X-ray photoelectron spectroscopy, and calorimetry. Moreover, this Review comprehensively describes the role of acidic and basic support for the metal on the yield of FUA. Overall, this Review provides an insight into how to design and develop an efficiently robust catalyst for the selective reductive amination of a broad spectrum of carbonyl compounds to corresponding amines.

Synthesis and application of CdS nanoparticles-decorated core-shell Ag@Ni nanohybrids for visible-light spectrophotometric assay of sulfide in aqueous sample

Novel Ag@Ni nanosphere decorated with CdS NPs (Ag@Ni-CdS NCs) was synthesized by one step chemical synthesis method. The fabricated NCs were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), fourier transfer infra-red spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), zeta sizer and particle size analyzer. TEM and XRD confirmed the Ag in core and Ni in shell for the effective formation of Ag@Ni core shell nanosphere. EDAX and XPS spectra of NCs confirms the formation of Ag@Ni-CdS NCs. Zeta potential and particle size of the NCs was found to be 29.5 ± 1.5 mV and 24 ± 1 nm respectively. The complete loss in the peak intensity of Ag@Ni-CdS NCs (localized surface plasmon resonance (LSPR)) at ∼410 nm in presence of S^2- ions was observed which indicates its selective detection towards S^2- ions. The sulfide ion sensing by Ag@Ni-CdS NCs was due to the successive oxidation of Ag results in the formulation of Ag²⁺ ions in the system, which causes the diminishing of LSPR band of NCs. The limit of detection (LOD) of S^2- ions by Ag@Ni-CdS NCs was calculated to be of 2.66 nM. The combination of CdS NPs with core-shell Ag@Ni nanosphere guides a promising strategy for S^2- ions detection from environmental polluted samples.

Rational design, synthesis, and applications of carbon-assisted dispersive Ni-based composites

Herein, we review recent developments in the rational design and engineering of various carbon-assisted dispersive nickel-based composites, and boosted properties for protein adsorption and nitroaromatics reduction.

Primary amine synthesis by hydrogen-involving reactions over heterogeneous cobalt catalysts

Co/SiO2 exhibited high selectivity for primary amines in hydrogenation of nitriles and reductive amination of carbonyl compounds.

Tuning the selectivity of catalytic nitriles hydrogenation by structure regulation in atomically dispersed Pd catalysts

The product selectivity in catalytic hydrogenation of nitriles is strongly correlated with the structure of the catalyst. In this work, two types of atomically dispersed Pd species stabilized on the defect-rich nanodiamond-graphene (ND@G) hybrid support: single Pd atoms (Pd₁/ND@G) and fully exposed Pd clusters with average three Pd atoms (Pd_n/ND@G), were fabricated. The two catalysts show distinct difference in the catalytic transfer hydrogenation of nitriles. The Pd₁/ND@G catalyst preferentially generates secondary amines (Turnover frequency (TOF@333 K 709 h⁻¹, selectivity >98%), while the Pd_n/ND@G catalyst exhibits high selectivity towards primary amines (TOF@313 K 543 h⁻¹, selectivity >98%) under mild reaction conditions. Detailed characterizations and density functional theory (DFT) calculations show that the structure of atomically dispersed Pd catalysts governs the dissociative adsorption pattern of H₂ and also the hydrogenation pathway of the benzylideneimine (BI) intermediate, resulting in different product selectivity over Pd₁/ND@G and Pd_n/ND@G, respectively. The structure-performance relationship established over atomically dispersed Pd catalysts provides valuable insights for designing catalysts with tunable selectivity.

The selective hydrogenation of nitriles to prepare corresponding amines is highly desired in chemistry industry. Here, the authors selectively obtained secondary amines and primary amines over two types of atomically dispersed Pd catalysts supported on the nanodiamond-graphene hybrid support.

Highly Dispersed CoNi Alloy Embedded in N-doped Graphitic Carbon for Catalytic Transfer Hydrogenation of Biomass-derived Furfural

The development of efficient, stable, and cost-effective heterogeneous catalysts for catalytic transfer hydrogenation (CTH) of biomass-derived furfural (FAL) is highly desired. Herein, series of N-doped graphitic carbon embedded CoNi bimetallic alloy nanoparticles were fabricated and used for the CTH of FAL to value-added furfuryl alcohol (FOL) with renewable isopropanol as hydrogen donor. Intrinsic catalytic activity examination indicated the catalytic performance of Ni_x Co_y @NGC (x:y=1 : 3, 1 : 1, 3 : 1) nanocatalysts were sensitive to their chemical compositions. The optimal Ni₁ Co₁ @NGC nanocatalyst with Ni/Co mole ratio of 1 : 1 afforded a largest FOL yield of 89.3% with nearly full conversion of FAL. The synergistic effect enabled by bimetallic alloys and the abundant N-based Lewis base sites and surface Co-N active species were revealed based on systematic structural characterization, responsible for the excellent catalytic efficiency of bimetallic Ni₁ Co₁ @NGC nanocatalyst for CTH of FAL.

Hydrogenative coupling of nitriles with diamines to benzimidazoles using lignin-derived Rh2P catalyst

Nitrile (C≡N bond) activation for direct organic synthesis has been less explored so far due to a high redox potential of nitrile and its low dissociation energy of C−CN bond. Herein, we demonstrate a direct reductive coupling of nitriles and 1,2-phenylenediamines to yield various benzimidazoles in excellent yields (95%–99%) by using rhodium phosphide (Rh₂P) catalyst supported on lignin-derived carbon (LC) using H₂ (or hydrazine hydrate) as a hydrogen source. The high catalytic performance of Rh₂P/LC is attributed to enhanced charge transfer to Rh and strong P−Rh interactions. Our isotope trace experiment confirms the presence of H/D exchange between H₂ and the inert –CD₃ group of CD₃CN via an intramolecular D-shift. Reusability of Rh₂P/LC is further demonstrated by a seven-time recycling without evident loss of activity. This research thus highlights a great potential in organic transformation with nitrile as a synthetic building block.

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Nitrile was developed as synthetic building block for organic synthesis

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Reductive coupling of nitriles to 1,2-phenylenediamines yielded benzimidazoles

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Strong P−Rh interaction and charge transfer to Rh enhanced Rh₂P activity

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H/D exchange between H₂ and –CD₃ in CD₃CN occurred via intramolecular D-shift

Recent Advances on Heteroatom-Doped Porous Carbon/Metal Materials: Fascinating Heterogeneous Catalysts for Organic Transformations

Design and preparation of low-cost, effective, and novel catalysts are important topics in the field of heterogeneous catalysis from academic and industrial perspectives. Recently, heteroatom-doped porous carbon/metal materials have received significant attention as promising catalysts in divergent organic reactions. Incorporation of heteroatom into the carbon framework can tailor the properties of carbon, providing suitable interaction between support and metal, resulting in superior catalytic performance compared with those of traditional pure carbon/metal catalytic systems. In this review, we try to underscore the recent advances in the design, preparation, and application of heteroatom-doped porous carbon/metal catalysts towards various organic transformations.

Earth-abundant Metal-catalyzed Reductive Amination: Recent Advances and Prospect for Future Catalysis

Nitrogen-containing compounds, as an important class of chemicals, have been used widely in pharmaceuticals, materials synthesis. Transition metal-catalyzed reductive amination of an aldehyde or a ketone with ammonia or an amine has been proved to be an efficient and practical method for the preparation of nitrogen-containing compounds in academia and industry for a century. Given the above, several effective methods using transition metals have been developed in recent years. Noble transition metals like Pd, Pt, and Au-based catalysts have been predominately used in reductive amination. Because of their high prices, strict official regulations of residues in pharmaceuticals, and deleterious effects on the biological system, their industrial applications are severely hampered. With the increasing sustainable and environmental problems, the Earth-abundant transition metals including Ti, Fe, Co, Ni, and Zr have also been investigated for the reductive amination reaction and showed great potential to the advancement of sustainable and cost-effective reductive amination processes. This critical review will mainly summarize the work using Earth-abundant metals. The effects of different transition metals used in catalytic reduction amination were discussed and compared, and some suggestions were given. The last section highlights the catalytic activities of bi- and tri-metallic catalysts. Indeed, this latter family is very promising and simultaneously benefits from increased stability, and selectivity, compared to monometallic NPs, due to synergistic substrate activation. Few comprehensive reviews focusing on Earth-abundant transition metals catalyst has been published since 1948, although several authors reported some summaries dealing with one or the other part of this aspect. It is hoped that this critical review will inspire researchers to develop new efficient and selective earth-abundant metal catalysts for highly, environmentally sustainable reductive amination methods, as well as improve the pharmaceutical industry and related chemical synthesis company traditional method with the utilization of the green method widely.

Synthesis of Pyrazole-Carboxamides and Pyrazole-Carboxylic Acids Derivatives: Simple Methods to Access Powerful Building Blocks

Abstract:

Hybrid systems containing pyrazole moiety show a wide spectrum of biological activities. To access novel hybrids with pyrazole ring, in this work we synthesized twenty pyrazole-carboxylic acids and twenty pyrazole-carboxamides, using simple synthetic methods, to be used as building blocks in the development of new structures.

Single-Crystal Cobalt Phosphide Nanorods as a High-Performance Catalyst for Reductive Amination of Carbonyl Compounds

The development of metal phosphide catalysts for organic synthesis is still in its early stages. Herein, we report the successful synthesis of single-crystal cobalt phosphide nanorods (Co₂P NRs) containing coordinatively unsaturated Co-Co active sites, which serve as a new class of air-stable, highly active, and reusable heterogeneous catalysts for the reductive amination of carbonyl compounds. The Co₂P NR catalyst showed high activity for the transformation of a broad range of carbonyl compounds to their corresponding primary amines using an aqueous ammonia solution or ammonium acetate as a green amination reagent at 1 bar of H₂ pressure; these conditions are far milder than previously reported. The air stability and high activity of the Co₂P NRs is noteworthy, as conventional Co catalysts are air-sensitive (pyrophorous) and show no activity for this transformation under mild conditions. P-alloying is therefore of considerable importance for nanoengineering air-stable and highly active non-noble-metal catalysts for organic synthesis.

Ni2 P Nanoalloy as an Air-Stable and Versatile Hydrogenation Catalyst in Water: P-Alloying Strategy for Designing Smart Catalysts

Non-noble metal-based hydrogenation catalysts have limited practical applications because they exhibit low activity, require harsh reaction conditions, and are unstable in air. To overcome these limitations, herein we propose the alloying of non-noble metal nanoparticles with phosphorus as a promising strategy for developing smart catalysts that exhibit both excellent activity and air stability. We synthesized a novel nickel phosphide nanoalloy (nano-Ni₂ P) with coordinatively unsaturated Ni active sites. Unlike conventional air-unstable non-noble metal catalysts, nano-Ni₂ P retained its metallic nature in air, and exhibited a high activity for the hydrogenation of various substrates with polar functional groups, such as aldehydes, ketones, nitriles, and nitroarenes to the desired products in excellent yields in water. Furthermore, the used nano-Ni₂ P catalyst was easy to handle in air and could be reused without pretreatment, providing a simple and clean catalyst system for general hydrogenation reactions.

Highly selective production of benzylamine from benzonitrile on metal-supported catalysts

Ni/SiO2 yields 92% of benzylamine from benzonitrile hydrogenation in methanol without the addition of additives.

Reductive amination of bio-based 2-hydroxytetrahydropyran to 5-Amino-1-pentanol over nano-Ni–Al2O3 catalysts

5-Amino-1-pentanol was efficiently synthesized by reductive amination of bio-based 2-hydroxytetrahydropyran with a high yield over stable nano-Ni–Al₂O₃ catalysts.

Transition-Metal-Catalyzed Reductive Amination Employing Hydrogen

The reductive amination, the reaction of an aldehyde or a ketone with ammonia or an amine in the presence of a reducing agent and often a catalyst, is an important amine synthesis and has been intensively investigated in academia and industry for a century. Besides aldehydes, ketones, or amines, starting materials have been used that can be converted into an aldehyde or ketone (for instance, carboxylic acids or organic carbonate or nitriles) or into an amine (for instance, a nitro compound) in the presence of the same reducing agent and catalyst. Mechanistically, the reaction starts with a condensation step during which the carbonyl compound reacts with ammonia or an amine, forming the corresponding imine followed by the reduction of the imine to the alkyl amine product. Many of these reduction steps require the presence of a catalyst to activate the reducing agent. The reductive amination is impressive with regard to the product scope since primary, secondary, and tertiary alkyl amines are accessible and hydrogen is the most attractive reducing agent, especially if large-scale product formation is an issue, since hydrogen is inexpensive and abundantly available. Alkyl amines are intensively produced and use fine and bulk chemicals. They are key functional groups in many pharmaceuticals, agro chemicals, or materials. In this review, we summarize the work published on reductive amination employing hydrogen as the reducing agent. No comprehensive review focusing on this subject has been published since 1948, albeit many interesting summaries dealing with one or the other aspect of reductive amination have appeared. Impressive progress in using catalysts based on earth-abundant metals, especially nanostructured heterogeneous catalysts, has been made during the early development of the field and in recent years.

The Synthesis of Primary Amines through Reductive Amination Employing an Iron Catalyst

The reductive amination of ketones and aldehydes by ammonia is a highly attractive method for the synthesis of primary amines. The use of catalysts, especially reusable catalysts, based on earth-abundant metals is similarly appealing. Here, the iron-catalyzed synthesis of primary amines through reductive amination was realized. A broad scope and a very good tolerance of functional groups were observed. Ketones, including purely aliphatic ones, aryl-alkyl, dialkyl, and heterocyclic, as well as aldehydes could be converted smoothly into their corresponding primary amines. In addition, the amination of pharmaceuticals, bioactive compounds, and natural products was demonstrated. Many functional groups, such as hydroxy, methoxy, dioxol, sulfonyl, and boronate ester substituents, were tolerated. The catalyst is easy to handle, selective, and reusable and ammonia dissolved in water could be employed as the nitrogen source. The key is the use of a specific Fe complex for the catalyst synthesis and an N-doped SiC material as catalyst support.

Ru/g-C3N4 as an efficient catalyst for selective hydrogenation of aromatic diamines to alicyclic diamines

A series of Ru/g-C3N4 materials with highly dispersed Ru were firstly prepared by an ultrasonic impregnation method using carbon nitride as a support. The catalysts were characterized by various techniques including BET and elemental analysis, ICP-AES, XPS, XRD, CO2-TPD and TEM. The results demonstrated that Ru/g-C3N4 materials with a mesoporous structure and highly dispersed Ru were successfully prepared. The chemo-selective hydrogenation of p-phenylenediamine (PPDA) to 1,4-cyclohexanediamine (CHDA) over Ru/g-C3N4 as a model reaction was investigated in detail. PPDA conversion of 100% with a CHDA selectivity of more than 86% could be achieved under mild conditions. It can be inferred that the carbon nitride support possessed abundant basic sites and the Ru/g-C3N4-T catalysts provided suitable basicity for the aromatic ring hydrogenation. Compared to the N-free Ru/C catalyst, the involvement of nitrogen species in Ru/g-C3N4 remarkably improved the catalytic performance. In addition, the recyclability of the catalyst demonstrated that the aggregation of Ru nanoparticles was responsible for the decrease of the catalytic activity. Furthermore, this strategy also could be expanded to the selective hydrogenation of other aromatic diamines to alicyclic diamines.

Ultrafine bimetallic Ag-doped Ni nanoparticles embedded in cage-type mesoporous silica SBA-16 as superior catalysts for conversion of toxic nitroaromatic compounds

Highly active Ag-doped Ni nanoparticles are successfully fabricated within carboxylic acid (-COOH) functionalized mesoporous silica SBA-16 by a facile wet incipient technique for catalytic conversion of toxic nitroaromatics. The -COOH groups on SBA-16 play a crucial role by enhancing the electrostatic interactions with Ag(I)/Ni(II) cations, that control the crystal growth during the thermal reduction. Systematic characterizations of SBA-16C and Ag_x%Ni@SBA-16C are performed by different techniques including solid state ¹³C and ²⁹Si nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), N₂ sorption, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and superconducting quantum interference device (SQUID). The highly dispersed ultrafine Ag-doped Ni NPs (∼3 nm) are well-confined within SBA-16C and exhibit magnetic properties that are extremely beneficial for recycling. The bimetallic Ag_2.4%Ni@SBA-16C shows exceptionally high catalytic activity during catalytic conversion of toxic nitroaromatics to environmentally friendly amino-aromatics. The enhanced catalytic activity could be ascribed to the combined effects of unique electronic properties, synergistic effects of Ag-doped Ni, ultra-small size, metal loading, and favorable textural properties. These magnetically separable nanocatalysts show excellent durability.

Facile Fabrication of Glycosylpyridyl-Triazole@Nickel Nanoparticles as Recyclable Nanocatalyst for Acylation of Amines in Water

In this report, novel glycosylpyridyl-triazole@nickel nanoparticles (GPT-Ni) were successfully prepared via click chemistry and were fully characterized by various spectroscopy measurements. The as-prepared catalysts could be used as a recyclable catalyst for the catalytic acylation of amines by employing N,N-dimethylacetamide (DMA), N,N-dimethylpropionamide (DMP), and N,N-dimethylformamide (DMF) as acylation reagents in water, providing the corresponding amides in good yields. The practicability of this methodology is highlighted by the good recyclability of the catalyst. A unique mechanism was proposed for the catalytic process.

Nickel Hollow Spheres Concatenated by Nitrogen-Doped Carbon Fibers for Enhancing Electrochemical Kinetics of Sodium-Sulfur Batteries

The high energy density of room temperature (RT) sodium-sulfur batteries (Na-S) usually rely on the efficient conversion of polysulfide to sodium sulfide during discharging and sulfur recovery during charging, which is the rate-determining step in the electrochemical reaction process of Na-S batteries. In this work, a 3D network (Ni-NCFs) host composed by nitrogen-doped carbon fibers (NCFs) and Ni hollow spheres is synthesized by electrospinning. In this novel design, each Ni hollow unit not only can buffer the volume fluctuation of S during cycling, but also can improve the conductivity of the cathode along the carbon fibers. Meanwhile, the result reveals that a small amount of Ni is polarized during the sulfur-loading process forming a polar Ni-S bond. Furthermore, combining with the nitrogen-doped carbon fibers, the Ni-NCFs composite can effectively adsorb soluble polysulfide intermediate, which further facilitates the catalysis of the Ni unit for the redox of sodium polysulfide. In addition, the in situ Raman is employed to supervise the variation of polysulfide during the charging and discharging process. As expected, the freestanding S@Ni-NCFs cathode exhibits outstanding rate capability and excellent cycle performance.

Halloysite nanotubes based heterogeneous solid acid catalysts

Taking into account the excellent catalytic performance of halloysite nanotubes, the main focus of this review article is to unveil the research on halloysite nanotubes for the preparation of solid acids and their applications in acid catalysis.

Mild and selective hydrogenation of nitriles into primary amines over a supported Ni catalyst

The mesoporous Al₂O₃ supported Ni catalyst demonstrated a high activity and selectivity for the hydrogenation of nitriles into primary amines under the mild conditions (60–80 °C and 2.5 bar H₂) with ammonia as the additive.

Catalytic reductive aminations using molecular hydrogen for synthesis of different kinds of amines

Catalytic reductive aminations using molecular hydrogen represent an essential and widely used methodology for the synthesis of different kinds of amines.

Biomass-derived carbon-supported Ni catalyst: an effective heterogeneous non-noble metal catalyst for the hydrogenation of nitro compounds

The biomass-derived carbon material supported Ni catalysts (Ni/C) demonstrated a high catalytic activity for the hydrogenation of nitro compounds into primary amines at room temperature.

Nickel(ii) and nickel(0) complexes as precursors of nickel nanoparticles for the catalytic hydrogenation of benzonitrile

The use of nickel(ii) and nickel(0) complexes as precursors of nickel nanoparticles with catalytic activity in the hydrogenation of benzonitrile is reported.

Chitosan-derived N-doped carbon catalysts with a metallic core for the oxidative dehydrogenation of NH-NH bonds

Sustainable metal-encased (Ni-Co/Fe/Cu)@N-doped-C catalysts were prepared from bio-waste and used for the oxidative dehydrogenation reaction. A unique combination of bimetals, in situ N doping, and porous carbon surfaces resulted in the formation of the effective "three-in-one" catalysts. These N-doped graphene-like carbon shells with bimetals were synthesized via the complexation of metal salts with chitosan and the subsequent pyrolysis at 700 °C. A well-developed thin-layer structure with large lateral dimensions could be obtained by using Ni-Fe as the precursor. Importantly, the Ni-Fe@N-doped-C catalyst was found to be superior for the dehydrogenation of hydrazobenzene under additive/oxidant-free conditions compared to the conventional and other synthesized catalysts. Characterizations by TEM and XPS accompanied by BET analysis revealed that the enhanced catalytic properties of the catalysts arose from their bimetals and could be attributed to the graphitic shell structure and graphitic N species, respectively.

Synergistic catalysis on Fe-N x sites and Fe nanoparticles for efficient synthesis of quinolines and quinazolinones via oxidative coupling of amines and aldehydes

In this paper, we developed a reusable heterogeneous non-precious iron nanocomposite comprising metallic Fe-Fe3C nanoparticles and Fe-N x sites on N-doped porous carbon, which allows for highly efficient synthesis of quinolines and quinazolinones via oxidative coupling of amines and aldehydes using H2O2 as the oxidant in aqueous solution under mild conditions. A set of quinazolines and quinazolinones were synthesized in high yields with a broad substrate scope and good tolerance of functional groups. Characterization and control experiments disclose that a synergistic effect between the metallic Fe nanoparticles and built-in Fe-N x sites is primarily responsible for the outstanding catalytic performance. Furthermore, the iron nanocomposite could be readily recovered for successive use without appreciable loss in catalytic activity and selectivity. This work provides an expedient and sustainable method to access pharmaceutically relevant N-heterocycles.