A Reusable FeCl3∙6H2O/Cationic 2,2′-Bipyridyl Catalytic System for Reduction of Nitroarenes in Water

The association of a commercially-available iron (III) chloride hexahydrate (FeCl3∙6H2O) with cationic 2,2′-bipyridyl in water was proven to be an operationally simple and reusable catalytic system for the highly-selective reduction of nitroarenes to anilines. This procedure was conducted under air using 1–2 mol% of catalyst in the presence of nitroarenes and 4 equiv of hydrazine monohydrate (H2NNH2∙H2O) in neat water at 100 °C for 12 h, and provided high to excellent yields of aniline derivatives. After separation of the aqueous catalytic system from the organic product, the residual aqueous solution could be applied for subsequent reuse, without any catalyst retreatment or regeneration, for several runs with only a slight decrease in activity, proving this process eco-friendly.

Tailored Inorganic-Organic Architectures via Metalloligands

This article discusses the design principles and strategies and the structural outcome of various supramolecular architectures constructed by utilizing well-defined coordination complexes as the metalloligands. We have included selected examples of metalloligands, offering either pyridyl or arylcarboxylic acid groups as the appended functional groups, for illustrating the construction of their supramolecular architectures. Both geometrical position and the number of the appended functional groups emerging from a metalloligand were found to critically regulate the structural aspects and dimensionality of the resultant material. The article concludes by delineating the structure-directing lessions as well as the potential applications of the metalloligand-based supramolecular architectures for the generation of next-level materials.

Selective Reduction of Nitroarenes to Arylamines by the Cooperative Action of Methylhydrazine and a Tris(N-heterocyclic thioamidate) Cobalt(III) Complex

We report an efficient catalytic protocol that chemoselectively reduces nitroarenes to arylamines, by using methylhydrazine as a reducing agent in combination with the easily synthesized and robust catalyst tris(N-heterocyclic thioamidate) Co(III) complex [Co(κS,N-tfmp2S)₃], tfmp2S = 4-(trifluoromethyl)-pyrimidine-2-thiolate. A series of arylamines and heterocyclic amines were formed in excellent yields and chemoselectivity. High conversion yields of nitroarenes into the corresponding amines were observed by using polar protic solvents, such as MeOH and ⁱPrOH. Among several hydrogen donors that were examined, methylhydrazine demonstrated the best performance. Preliminary mechanistic investigations, supported by UV-vis and NMR spectroscopy, cyclic voltammetry, and high-resolution mass spectrometry, suggest a cooperative action of methylhydrazine and [Co(κS,N-tfmp2S)₃] via a coordination activation pathway that leads to the formation of a reduced cobalt species, responsible for the catalytic transformation. In general, the corresponding N-arylhydroxylamines were identified as the sole intermediates. Nevertheless, the corresponding nitrosoarenes can also be formed as intermediates, which, however, are rapidly transformed into the desired arylamines in the presence of methylhydrazine through a noncatalytic path. On the basis of the observed high chemoselectivity and yields, and the fast and clean reaction processes, the present catalytic system [Co(κS,N-tfmp2S)₃]/MeNHNH₂ shows promise for the efficient synthesis of aromatic amines that could find various industrial applications.

Half-Sandwich Ruthenium Complexes of Amide-Phosphine Based Ligands: H-Bonding Cavity Assisted Binding and Reduction of Nitro-substrates

We present synthesis and characterization of two half-sandwich Ru(II) complexes supported with amide-phosphine based ligands. These complexes presented a pyridine-2,6-dicarboxamide based pincer cavity, decorated with hydrogen bonds, that participated in the binding of nitro-substrates closer to the Ru(II) centers, which is further supported with binding and docking studies. These ruthenium complexes functioned as the noteworthy catalysts for the borohydride mediated reduction of assorted nitro-substrates. Mechanistic studies not only confirmed the intermediacy of [Ru-H] in the reduction but also asserted the involvement of several organic intermediates during the course of the catalysis. A similar Ru(II) complex that lacked pyridine-2,6-dicarboxamide based pincer cavity substantiated its unique role both in the substrate binding and the subsequent catalysis.

Effect of pyridyl donors from organic ligands versus metalloligands on material design

This review illustrates designs and structures of various coordination frameworks constructed using assorted organic ligands and metalloligands offering pyridyl donors to evaluate the impact of flexibility versus rigidity on material design.

Architectural and catalytic aspects of designer materials built using metalloligands of pyridine-2,6-dicarboxamide based ligands

This perspective presents the design, synthesis and crystal structures of a large number of architectures constructed using assorted metalloligands of pyridine-2,6-dicarboxamide based ligands. The metalloligands offered various appended functional groups, whereas design strategies included varying both their position and number. A combination of these parameters resulted in the development of assorted architectures including discrete trinuclear and tetranuclear complexes as well as 1D/2D/3D coordination polymers. The metalloligand strategy not only assisted in the construction of ordered crystalline materials with varied dimensionalities but also judiciously allowed the incorporation of Lewis acidic and redox-active secondary metals in the resultant architectures. As a result, such designer architectures illustrated their noteworthy role both as homogenous and heterogeneous catalysts in different organic transformation reactions.

Rice husk-SiO2 supported bimetallic Fe-Ni nanoparticles: as a new, powerful magnetic nanocomposite for the aqueous reduction of nitro compounds to amines

This paper reports a novel green procedure for immobilization of bimetallic Fe/Ni on amorphous silica nanoparticles extracted from rice husk (RH-SiO₂). The heterogeneous nanocomposite (Fe/Ni@RH-SiO₂) was identified using SEM, EDX, TEM, BET, H₂-TPR, TGA, XRD, VSM, ICP-OES, and FT-IR analyses. The Fe/Ni@RH-SiO₂ nanocomposite was applied as a powerful catalyst for the reduction of structurally diverse nitro compounds with sodium borohydride (NaBH₄) in green conditions. This procedure suggests some benefits such as green chemistry-based properties, short reaction times, non-explosive materials, easy to handle, fast separation and simple work-up method. The catalyst was separated by an external magnet from the reaction mixture and was reused for 9 successive cycles with no detectable changes of its catalytic efficiency.

This paper reports a novel green procedure for immobilization of bimetallic Fe/Ni on amorphous silica nanoparticles extracted from rice husk (RH-SiO₂).

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.

A metalloligand appended with benzimidazole rings: tetranuclear [CoZn3] and [CoCd3] complexes and their catalytic applications

A novel Co³⁺-based metalloligand, offering appended benzimidazole rings, has been utilized for the synthesis of catalytically active tetranuclear [CoZn₃] and [CoCd₃] heterometallic coordination complexes.

Cobalt complexes of pyrrolecarboxamide ligands as catalysts in nitro reduction reactions: influence of electronic substituents on catalysis and mechanistic insights

Square-planar Co³⁺ complexes, displaying substrate binding abilities and facile Co^3+/2+ redox potentials, function as efficient catalysts for hydrazine-mediated reduction of aromatic, heterocyclic, as well as aliphatic nitro substrates.

A ternary Cu2O-Cu-CuO nanocomposite: a catalyst with intriguing activity

In this work, the syntheses of Cu2O as well as Cu(0) nanoparticle catalysts are presented. Copper acetate monohydrate produced two distinctly different catalyst particles with varying concentrations of hydrazine hydrate at room temperature without using any surfactant or support. Then both of them were employed separately for 4-nitrophenol reduction in aqueous solution in the presence of sodium borohydride at room temperature. To our surprise, it was noticed that the catalytic activity of Cu2O was much higher than that of the metal Cu(0) nanoparticles. We have confirmed the reason for the exceptionally high catalytic activity of cuprous oxide nanoparticles over other noble metal nanoparticles for 4-nitrophenol reduction. A plausible mechanism has been reported. The unusual activity of Cu2O nanoparticles in the reduction reaction has been observed because of the in situ generated ternary nanocomposite, Cu2O-Cu-CuO, which rapidly relays electrons and acts as a better catalyst. In this ternary composite, highly active in situ generated Cu(0) is proved to be responsible for the hydride transfer reaction. The mechanism of 4-nitrophenol reduction has been established from supporting TEM studies. To further support our proposition, we have prepared a compositionally similar Cu2O-Cu-CuO nanocomposite using Cu2O and sodium borohydride which however displayed lower rate of reduction than that of the in situ produced ternary nanocomposite. The evolution of isolated Cu(0) nanoparticles for 4-nitrophenol reduction from Cu2O under surfactant-free condition has also been taken into consideration. The synthetic procedures of cuprous oxide as well as its catalytic activity in the reduction of 4-nitrophenol are very convenient, fast, cost-effective, and easily operable in aqueous medium and were followed spectrophotometrically. Additionally, the Cu2O-catalyzed 4-nitrophenol reduction methodology was extended further to the reduction of electronically diverse nitroarenes. This concise catalytic process in aqueous medium at room temperature revealed an unprecedented catalytic performance which would draw attention across the whole research community.

Lanthanide-based coordination polymers as promising heterogeneous catalysts for ring-opening reactions

Eu and Tb based coordination polymers function as reusable heterogeneous catalysts for ring-opening reactions with amines, alcohols, thiols, and azides as nucleophiles.