Half-Sandwich Ruthenium Complexes with Schiff-Base Ligands: Syntheses, Characterization, and Catalytic Activities for the Reduction of Nitroarenes

Ruthenium complexes with triazenide ligands bearing an N-heterocyclic moiety, and their catalytic properties in the reduction of nitroarenes

A series of ruthenium complexes of formulae [RuCl(triazenide)(p-cymene)] have been synthesized using as ligand a triazenide monofunctionalized with an N-heterocyclic moiety. Nuclear magnetic resonance, high resolution mass spectrometry and X-ray diffraction were used to characterize the triazenide ligands and their complexes. In addition, these ruthenium complexes catalyzed the reduction of nitrobenzene to aniline in the presence of sodium borohydride and ethanol as solvent at room temperature. Notably, complex 5 was especially active in the reduction of nitroarenes substituted at the aromatic ring with electron-withdrawing or electron-donating fuctional groups affording the desired arylamines in good to excellent yields (80-100%). The role of the N-heterocyclic moiety on catalysis was explored.

Design and synthesis of ruthenium complexes and their studies on the inhibition of amyloid β (1-42) peptide aggregation

Misfolding and protein aggregation have been linked to numerous human neurodegenerative disorders such as Alzheimer's, prions, and Parkinson's. Due to their interesting photophysical properties, ruthenium (Ru) complexes have received considerable attention in studying protein aggregation. In this study, we synthesized the novel Ru complexes ([Ru(p-cymene)Cl(L-1)][PF₆](Ru-1), and [Ru(p-cymene)Cl(L-2)][PF₆](Ru-2)) and investigated their inhibitory activity against the bovine serum albumin (BSA) aggregation and the Aβ_1-42 peptides amyloid formation. Several spectroscopic methods were used to characterize the complexes, and the molecular structure was determined by X-ray crystallography. Amyloid aggregation and inhibition activity were examined using the Thioflavin-T (ThT) assay, and secondary structures were analyzed by circular dichroism (CD) spectroscopy and transmission electron microscopy (TEM). The cell viability assay was carried out on the neuroblastoma cell line, revealing that the Ru-2 complex showed better protective effects against Aβ_1-42 peptide toxicity on neuro-2a cells than the Ru-1 complex. Molecular docking studies elucidate binding sites and interactions between the Ru-complexes and the Aβ_1-42 fibrils. The experimental studies revealed that these complexes significantly inhibited BSA aggregation and Aβ_1-42 amyloid fibril formation at 1:3 and 1:1 equimolar concentrations, respectively. Antioxidant assays demonstrated that these complexes act as antioxidants, protecting from amyloid-induced oxidative stress. Molecular docking studies with the monomeric Aβ_1-42 (PDB: 1IYT) show hydrophobic interaction, and both complexes bind preferably in the central region of the peptide and coordinate with two binding sites of the peptide. Hence, we suggest that the Ru-based complexes could be applied as a potential agent in metallopharmaceutical research against Alzheimer's disease.

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.

DNA binding, antitubercular, antibacterial and anticancer studies of newly designed piano-stool ruthenium(ii) complexes

The chemotherapeutic potential of ruthenium(ii) complexes as DNA binding, antitubercular, antibacterial, and anticancer agents.

Efficient Catalytic Reduction of 4-Nitrophenol Using Copper(II) Complexes with N,O-Chelating Schiff Base Ligands

The reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride was used as a model to test the catalytic activity of copper(II) complexes containing N,O-chelating Schiff base ligands. In this study, a series of copper(II) complexes containing respective Schiff base ligands, N'-salicylidene-2-aminophenol (1), N'-salicylidene-2-aminothiazole (2), and N,N'-bis(salicylidene)-o-phenylenediamine (3), were synthesized and characterized by elemental analysis, Fourier transform infrared (FT-IR), UV-Visible (UV-Vis) and electron paramagnetic resonance (EPR) spectroscopies. The results from the 4-nitrophenol reduction showed that 3 has the highest catalytic activities with 97.5% conversion, followed by 2 and 1 with 95.2% and 90.8% conversions, respectively. The optimization of the catalyst amount revealed that 1.0 mol% of the catalyst was the most optimized amount with the highest conversion compared to the other doses, 0.5 mol% and 1.5 mol%. Recyclability and reproducibility tests confirmed that all three complexes were active, efficient, and possess excellent reproducibility with consistent catalytic performances and could be used again without a major decrease in the catalytic activity.

Recent Advances in Schiff Base Ruthenium Metal Complexes: Synthesis and Applications

This review concentrates on recent developments in ruthenium Schiff bases, whose steric and electronic characteristics can be manipulated easily by selecting suitable condensing aldehydes or ketones and primary amines, and their metal complexes. Ruthenium metal-based complexes and Schiff base ligands are rapidly becoming conventionally considered for biological applications (antioxidant, anticancer, antimicrobial), in catalysis, in functional materials, in sensors, and as pigments for dyes. Ruthenium complexes exhibit a broad variety of activities concerning simple Schiff base ligands. This may be due to the octahedral bonding of both Ru(II) and Ru(III) complexes, which acquire an extended reservoir of a three-dimensional framework, providing the potential for an elevated degree of site selectivity for binding to their biological targets. This review provides an overview of this field, and intends to highlight both ligand design and synthetic methodology development, as well as significant applications of these metal complexes. In this review, we summarize our work on the development of ruthenium complexes, which was performed over the last few years.

Synthesis, characterization and anticancer activity of Fe(II) and Fe(III) complexes containing N-(8-quinolyl)salicylaldimine Schiff base ligands

A series of Fe(II) complexes (1-4) and Fe(III) complexes (5-8) from Fe(II)/(III) chloride and N-(8-quinolyl)-X-salicylaldimine Schiff base ligands (Hqsal-X2/X: X = Br, Cl) were successfully synthesized and characterized by spectroscopic (FT-IR, 1H-NMR), mass spectrometry, thermogravimetric analysis (TGA), and single crystal X-ray crystallographic techniques. The interaction of complexes 1-8 with calf thymus DNA (CT-DNA) was determined by UV-Vis and fluorescence spectroscopy. The complexes exhibited good DNA-binding activity via intercalation. The molecular docking between a selected complex and DNA was also investigated. The in vitro anticancer activity of the Schiff base ligands and their complexes were screened against the A549 human lung adenocarcinoma cell line. The complexes showed anticancer activity toward A549 cancer cells while the free ligands and iron chloride salts showed no inhibitory effects at 100 µM. In this series, complex [Fe(qsal-Cl2)2]Cl 6 showed the highest anticancer activity aginst A549 cells (IC50 = 10 µM). This is better than two well-known anticancer agents (Etoposide and Cisplatin). Furthermore, the possible mechanism for complexes 1-8 penetrating A549 cells through intracellular ROS generation was investigated. The complexes containing dihalogen substituents 1, 2, 5, and 6 can increase ROS in A549 cells, leading to DNA or macromolecular damage and cell-death induction.

Postsynthetic Modification of Half-Sandwich Ruthenium Complexes by Mechanochemical Synthesis

A mild and environmentally friendly method to synthesize half-sandwich ruthenium complexes through the Wittig reaction between an aldehyde-tagged half-sandwich ruthenium complex and phosphorus ylide mechanochemically is reported herein. The mechanochemical synthesis of valuable half-sandwich ruthenium complexes resulted in a fast reaction, good yield with simple workup, and the avoidance of harsh reaction conditions and organic solvents. The synthesized half-sandwich ruthenium complexes exhibited high catalytic activity for transfer hydrogenation of ketones using 2-propanol as the hydrogen source and solvent. Density functional theory was carried out to propose a mechanism for the transfer hydrogenation process. The modeling suggests the importance of the labile p-cymene ligand in modulating the reactivity of the catalyst.

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.

Nickel hydroxide nanoparticles decorated napthalene sulfonic acid-doped polyaniline nanotubes as efficient catalysts for nitroarene reduction

Nanosize nickel hydroxide decorated 2-napthalene sulfonic acid-doped polyaniline nanotubes nanocomposites (Ni(OH)₂@NSA-PANI NCs) were successfully developed for the catalytic reduction of aromatic nitro compounds. The Ni(OH)₂@NSA-PANI NCs were synthesised by depositing Ni(OH)₂ nanoparticles onto 2-napthalene sulfonic acid doped PANI nanotubes surface. The resulting material was characterized using field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), powder X-ray diffraction (P-XRD), Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The prepared nanocomposite showed a remarkable ability to catalytically hydrogenate aromatic nitro compounds using sodium borohydride (NaBH₄) as hydrogen source in aqueous medium at room temperature. Kinetic studies were performed using 4-nitrophenol (4-NP) as the model substrate, using the Langmuir-Hinshelwood model. The catalyst showed pseudo-first-order kinetics, with rate constants estimated between 0.08287 and 0.3649 min^-1. Catalyst recyclability without reduced activity was demonstrated over 10 successive cycles. The optimised nanocomposite catalyst demonstrated a low activation energy barrier towards 4-NP reduction.

New Tailored RNA-Targeted Organometallic Drug Candidates against Huh7 (Liver) and Du145 (Prostate) Cancer Cell Lines

New organometallic drug candidates [Ph2Sn(HL)], 1, and [Ru(η6--p-cymene)(HL)Cl], 2, were designed and synthesized by in situ reaction of a Schiff base ligand (HL) and diphenyltin dichloride and [RuCl2(p-cymene)]2, respectively. The drug candidates 1 and 2 have been characterized by spectroscopic methods (Fourier-transform infrared spectroscopy, UV-vis, and 1H/13C NMR), elemental analysis, and single X-ray crystallographic studies (in case of 1). The ground-state geometry optimization of 1 and 2 was performed by density functional theory calculations. The interaction of 1 and 2 with tRNA was assessed by absorption spectroscopy, cyclic voltammetry, circular dichroism, and ethidium bromide displacement assay using fluorescence emission spectroscopy to determine their potential to act as antitumor agents. The cytotoxicity of 1 and 2 was screened against human liver carcinoma (Huh7), prostate cancer (Du145), and the normal prostate cell line (PNT 2). The results implicated a dose-dependent growth inhibition of the two cancer cells at concentrations (2.5-15 μM) of 1 and 2 with the treatment after 48 h. Interestingly, 1 revealed good selective activity toward the liver cancer cell line (Huh7). Furthermore, both the drug candidates 1 and 2 were found to be nontoxic toward the PNT 2 normal cell line. These studies lay a paradigm for rational efficacious drug design for chemotherapeutic intervention in cancers using new tailored organometallic drug entities; organotin(IV) and organoruthenium(II) have been demonstrated to be viable for the safe administration and specific targeted drug uptake by the resistant cancerous cell lines at low intracellular concentrations.

Biomolecule-Mediated Generation of Ru Nanocatalyst for Sustainable Reduction of Nitrobenzene

A mild and sustainable synthetic route was followed for the generation of biomolecule-assisted Ru nanocatalyst under open as well as inert atmosphere using the polyphenol morin. The nanocatalyst was characterized thoroughly by powder X-ray diffraction, N₂ adsorption-desorption, high-resolution transmission electron microscopy, dynamic light scattering, X-ray photoelectron spectroscopy, absorption spectroscopy, Fourier transform infrared spectroscopy, fluorescence spectroscopy, thermogravimetric analysis, and inductively coupled plasma optical emission spectrometry. The nanocatalyst reveals excellent catalytic activity for the reduction of several substituted nitrobenzene to aniline derivatives under simple, mild, and environment-friendly conditions. The catalyst can be reused for four consecutive cycles without significant loss in its catalytic activity.

Reduction of nitroarenes catalyzed by microgel-stabilized silver nanoparticles

Poly(N-isopropylacrylamide-co-acrylamide) (PNA-BIS-2) microgels were synthesized by free radical precipitation polymerization in aqueous medium. Spherical Ag nanoparticles with diameter of 10-20 nm were fabricated inside the PNA-BIS-2 microgels by in-situ reduction of silver nitrate using sodium borohydride as reducing agent. The Ag nanoparticles- loaded hybrid microgels were characterized by Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Energy dispersive X-ray (EDX), Scanning transmission electron microscopy (STEM), Ultraviolet visible spectroscopy (UV Visible), Thermogravimetric analysis (TGA) and X-ray diffraction (XRD). Ag contents in the hybrid system were determined by inductively coupled plasma - optical emission spectrometry (ICP-OES). Various nitroarenes were successfully converted into their respective aromatic amines with good to excellent yields (ranging from 75% to 97%) under mild reaction conditions. The catalyst has ability to successfully convert substituted nitroarenes into desired products keeping many functionalities intact. The catalyst can be stored for long time without any sign of aggregation and can be used multiple times without any significant loss in its catalytic activity.

Catalytic hydrogenation of carbonyl and nitro compounds using an [N,O]-chelate half-sandwich ruthenium catalyst

A series of N,O-chelate half-sandwich ruthenium complexes have been synthesized, which exhibited high activity for the catalytic hydrogenation of carbonyl and nitro compounds in aqueous solution.

Exploring the hidden potential of a benzothiazole-based Schiff-base exhibiting AIE and ESIPT and its activity in pH sensing, intracellular imaging and ultrasensitive & selective detection of aluminium (Al3+)

The hidden potential of an AIE-ESIPT active, simple substituted benzothiazole compound has been explored.

An Efficient Method for Reduction of Nitroaromatic Compounds to the Corresponding Aromatic Amines with NH2NH2·H2O Catalysed by H2O2-Treated Activated Carbon

An efficient and green protocol for the reduction of nitroaromatic compounds to the corresponding amines has been developed. The reduction catalyst system includes NH2NH2·H2O and H2O2-treated activated carbon. Without adding additional metals, the H2O2-treated activated carbon could be reused for many cycles without decreasing catalytic efficiency. The aromatic amines could be obtained in good to excellent yields.