Reductive N-Formylation of Nitroarenes Mediated by Rongalite

Herein, we disclose a straightforward approach to access transition-metal-free reductive N-formylation of nitroarenes. This reaction integrates the dual role of rongalite, which acts as a reductant and a C1 building block concurrently. This provides an alternative method for the synthesis of N-aryl formamides from nitroarenes, including the construction of a C-N bond. The utility of this protocol was demonstrated by scale-up synthesis and late-stage functionalizations of complex molecules.

Nitrogen and Phosphorus Dual-Coordinated Single-Atom Mn: MnN2P Active Sites for Catalytic Transfer Hydrogenation of Nitroarenes

The coordination environment of atomically metal sites can modulate the electronic states and geometric structure of single-atom catalysts, which determine their catalytic performance. In this work, the porous carbon-supported N, P dual-coordinated Mn single-atom catalyst was successfully prepared via the phosphatization of zeolitic imidazolate frameworks and followed by pyrolysis at 900 °C. The optimal Mn₁-N/P-C catalyst with atomic MnN₂P structure has displayed better catalytic activity than the related catalyst with Mn-N_x structure in catalytic transfer hydrogenation of nitroarenes using formic acid as the hydrogen donor. We find that the doping of P source plays a crucial role in improving the catalytic performance, which affects the morphology and electronic properties of catalyst. This is the first Mn heterogeneous catalyst example for the reduction of nitroarenes, and it also revealed that the MnN₂P configuration is a more promising alternative in heterogeneous catalysis.

PdII on Guanidine-Functionalized Fe3O4 Nanoparticles as an Efficient Heterogeneous Catalyst for Suzuki-Miyaura Cross-Coupling and Reduction of Nitroarenes in Aqueous Media

This paper presents guanidine-functionalized Fe3O4 magnetic nanoparticle-supported palladium (II) (Fe3O4@Guanidine-Pd) as an effective catalyst for Suzuki-Miyaura cross-coupling of aryl halides using phenylboronic acids and also for selective reduction of nitroarenes to their corresponding amines. Fe3O4@Guanidine-Pd synthesized is well characterized using FT-IR spectroscopy, XRD, SEM, TEM, EDX, thermal gravimetric analysis, XPS, inductively coupled plasma-optical emission spectroscopy, and vibrating sample magnetometry analysis. The prepared Fe3O4@Guanidine-Pd showed effective catalytic performance in the Suzuki-Miyaura coupling reactions by converting aryl halides to their corresponding biaryl derivatives in an aqueous environment in a shorter reaction time and with a meagerly small amount of catalyst (0.22 mol %). Also, the prepared Fe3O4@Guanidine-Pd effectively reduced nitroarenes to their corresponding amino derivatives in aqueous media at room temperature with a high turnover number and turnover frequency with the least amount of catalyst (0.13 mol %). The most prominent feature of Fe3O4@Guanidine-Pd as a catalyst is the ease of separation of the catalyst from the reaction mixture after the reaction with the help of an external magnet with good recovery yield and also reuse of the recovered catalyst for a few cycles without significant loss in its catalytic activity.

Synergistic catalysis within core-shell Fe3O4@SiO2 functionalized with triethylene glycol (TEG)-imidazolium ionic liquid and tetramethylpiperidine N-oxyl (TEMPO) boosting selective aerobic oxidation of alcohols

HYPOTHESIS

It is expected that incorporation of 2, 2, 6, 6-tetra-methyl piperidine-N-oxyl radical (TEMPO) and an imidazolium bromide bearing hydrophilic triethylene glycol (TEG) groups on Fe₃O₄@SiO₂ core-shell may not only result in a novel highly water-dispersible/magnetically separable multi-functional catalyst system for metal-free aerobic oxidation of alcohols, which operates through a synergistic relay pathway, but it could potentially provide a strong platform for simultaneous separation and recycling of all components.

EXPERIMENTS

The catalyst was prepared by anchoring TEMPO moieties onto a magnetic core-shell Fe₃O₄@SiO₂ functionalized with an ionic liquid bearing TEG groups. The materials was characterized using transmission electron microscopy, Fourier transform infrared spectroscopy, nitrogen adsorption-desorption isotherms, thermal gravimetric analysis, and elemental analysis. The performance of the catalyst was evaluated and quantitatively measured in the aerobic oxidation of alcohols in water.

FINDINGS

The catalyst exhibited excellent and stable colloidal dispersion in water and high performance in the aerobic oxidation of various types of alcohols under metal- and halogen-free reaction conditions. As hypothesized, strong synergistic effect between functionalized components was seen in the described reaction. The catalyst displayed excellent dual-adjustable-selectivity in the oxidation of primary alcohols to either the corresponding aldehydes or carboxylic acids by tuning the reaction solvent and/or reaction time and excellent recycling behavior through a "double-separation-strategy".

Facile access to N-formyl imide as an N-formylating agent for the direct synthesis of N-formamides, benzimidazoles and quinazolinones

N-Formamide synthesis using N-formyl imide with primary and secondary amines with catalytic amounts of p-toluenesulfonic acid monohydrate (TsOH·H₂O) is described. This reaction is performed in water without the use of surfactants. Moreover, N-formyl imide is efficiently synthesized using acylamidines with TsOH·H₂O in water. In addition, N-formyl imide was successfully used as a carbonyl source in the synthesis of benzimidazole and quinazolinone derivatives. Notable features of N-formylation of amines by using N-formyl imide include operational simplicity, oxidant- and metal-free conditions, structurally diverse products, and easy applicability to gram-scale operation.

Palladium Nanoparticles on a Creatine-Modified Bentonite Support: An Efficient and Sustainable Catalyst for Nitroarene Reduction

Creatine as the nitrogen-rich, green and cheap compound is used for modification of natural bentonite and the resulting material is employed for the stabilization of Palladium nanoparticles having an average diameter of 3 nm. This new material bento-crt@Pd is characterized using different techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), solid state UV-vis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and energy-dispersive X-ray spectroscopy (EDX). This green catalyst promotes efficient reduction of aromatic nitro compounds in aqueous media. By using this catalyst nitroarenes having electron donating as well as electron withdrawing groups were reduced efficiently to their corresponding amines at room temperature. The catalyst can be recycled seven times and the reused catalyst was characterized by TEM and XPS.

A Co–Cu bimetallic magnetic nanocatalyst with synergistic and bifunctional performance for the base-free Suzuki, Sonogashira, and C–N cross-coupling reactions in water

A novel bimetallic catalytic system based on Cu/Co has been developed and used as an efficient, eco-friendly, and recyclable catalyst for base- and Pd-free Sonogashira, Suzuki and C–N cross-coupling reactions in mild reaction conditions.

On the catalytic transfer hydrogenation of nitroarenes by a cubane-type Mo3S4 cluster hydride: disentangling the nature of the reaction mechanism

Cubane-type Mo₃S₄ cluster hydrides decorated with phosphine ligands are active catalysts for the transfer hydrogenation of nitroarenes to aniline derivatives in the presence of formic acid (HCOOH) and triethylamine (Et₃N). The process is highly selective and most of the cluster species involved in the catalytic cycle have been identified through reaction monitoring. Formation of a dihydrogen cluster intermediate has also been postulated based on previous kinetic and theoretical studies. However, the different steps involved in the transfer hydrogenation from the cluster to the nitroarene to finally produce aniline remain unclear. Herein, we report an in-depth computational investigation into this mechanism. Et₃N reduces the activation barrier associated with the formation of Mo-HHOOCH dihydrogen species. The global catalytic process is highly exergonic and occurs in three consecutive steps with nitrosobenzene and N-phenylhydroxylamine as reaction intermediates. Our computational findings explain how hydrogen is transferred from these Mo-HHOOCH dihydrogen adducts to nitrobenzene with the concomitant formation of nitrosobenzene and the formate substituted cluster. Then, a β-hydride elimination reaction accompanied by CO₂ release regenerates the cluster hydride. Two additional steps are needed for hydrogen transfer from the dihydrogen cluster to nitrosobenzene and N-phenylhydroxylamine to finally produce aniline. Our results show that the three metal centres in the Mo₃S₄ unit act independently, so the cluster can exist in up to ten different forms that are capable of opening a wide range of reaction paths. This behaviour reveals the outstanding catalytic possibilities of this kind of cluster complexes, which work as highly efficient catalytic machines.

Highly efficient nitrobenzene and alkyl/aryl azide reduction in stainless steel jars without catalyst addition

Mechanochemically promoted reduction of nitro and azido derivatives may be successfully performed in stainless steel jars without catalyst addition.

One-pot selective N-formylation of nitroarenes to formamides catalyzed by core–shell structured cobalt nanoparticles

A first heterogeneous non-noble cobalt catalyst for one-pot direct N-formylation of nitroarenes exhibiting high activity with a broad substrate scope under mild conditions is synthesised. It is easily separated with good recyclability.

Simple and Practical Synthesis of Various New Nickel Boride-Based Nanocomposites and their Applications for the Green and Expeditious Reduction of Nitroarenes to Arylamines under Wet-Solvent-Free Mechanochemical Grinding

In this paper, we report a simple synthesis of four new nickel boride-based nanocomposites, namely Ni2B@ZrCl4, Ni2B@Cu2O, Ni2B@CuCl2 and Ni2B@FeCl3, from commercially available and cheap starting materials. All of the new Ni2B-based nanocomposites were well characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Further, the catalytic applications of these new nanocomposites were successfully evaluated in the wet-solvent-free reduction of aromatic nitro compounds to arylamines with sodium borohydride (NaBH4) at room temperature by a mechanochemical grinding technique. All the introduced catalytic systems provide excellent yields of arylamines in very short reaction times for a wide range of substrates. Also, recoverability and reusability of the new nanocomposites were investigated.

PdCl2 immobilized on metal–organic framework CuBTC with the aid of ionic liquids: enhanced catalytic performance in selective oxidation of cyclohexene

PdCl₂ immobilized on CuBTC with the aid of ILs shows an enhanced catalytic performance in cyclohexene oxidation due to Pd–Cu cooperative catalysis and stabilization of Pd(ii).