Nitrogen Ligands Research Articles

Luminescent Cerium(III) Complexes with Poly(mercaptoimidazolyl)borate: A New Emitter Based on S-Coordinating Ligands.

Lanthanide ions are hard Lewis acids and usually form weak bonds with soft sulfur donors, which result in the supposed instability of their complexes with S-coordinating ligands. Compared with luminescent lanthanide complexes with hard nitrogen or oxygen donor ligands, the development of luminescent lanthanide complexes based on sulfur-donor ligands currently lags behind. In this work, two types of poly(mercaptoimidazolyl)borate ligands, one is tridentate and the other is tetradentate, were used for the design and synthesis of two series of novel S-coordinating cerium(III) (Ce(III)) complexes, which were found to be not only luminescent but also with moderate to surprisingly good stability in air. By tuning the ligand type and substituents, blue- and yellow-green-emitting Ce(III) complexes with different emission mechanisms of d-f transition, delayed d-f transition, and ligand-centered fluorescence/phosphorescence were obtained, among which the highest photoluminescence quantum yield (PLQY) was 97%, and the most stable one can still maintain 74% of the initial PLQY even after exposure to air for 1 month. Furthermore, we investigated the degradation mechanism of these complexes in air, revealing the oxidation of low-valence sulfur(II) to high-valence sulfur-containing S═O bonds. This work shows the potential of S-coordinating ligands in luminescent Ce(III) complexes and provides new perspectives for designing Ce(III) complexes with soft donors.

Expanding the scope of copper artificial metalloenzymes: A potential fluorinase?

Biocatalysts for fluorination are rare, and thus of great interest for artificial enzyme design. Biohybrid catalysts including Cu-based DNAzymes and dinucleotide catalysts can catalyse enantioselective electrophilic fluorination of β-ketoesters. Here we report the investigation of Cu-based artificial metalloenzymes as catalysts for electrophilic fluorination reactions. A library of artificial copper proteins was prepared by bioconjugation of bidentate and tridentate nitrogen ligands to cysteine variants of the Sterol Carrier Protein 2L (SCP-2L) and subsequent addition of Cu(II) salts. The resulting copper proteins were screened for activity for the fluorination of β-ketoesters using Selectfluor. Under aqueous acidic conditions it was observed that the designed catalysts did not outcompete the uncatalysed background reaction. This work highlights that careful consideration of substrate reactivity and background reactions is needed when considering potential reactions for artificial metalloenzyme catalysis.

Highly Efficient Degradation of Bisphenol A by Peroxymonosulfate Activation Using Bamboo Kraft Lignin Single-Atom Catalyst.

A nitrogen-coordinated Fe single-atom catalyst (SA Fe-N/C) is synthesized using a homogeneous ethanol-based dissolution system with bamboo kraft lignin serving as the carbon source. Uniformly dispersed Fe atoms with an interatomic distance of less than 2 Å throughout the SA Fe-N/C structure are revealed through X-ray absorption spectral analysis and HAADF-STEM images, which possessed a high Fe loading of 2.69%. The degradation rate of bisphenol A (BPA) approached 99% within 5 min, with the observed rate constant (kobs) of the catalysts markedly increasing from 0.070 to 0.615 min-1. The catalyst-mediated electron transfer pathway is identified as the predominant mechanism for BPA degradation. Both experimental data and DFT analysis of the nitrogen ligands demonstrated that pyridinic N-coordinated Fe single atoms are the principal active sites, attributed to the enhanced electron density and delocalization concentrated around the Fe sites. These findings significantly elucidate the role of nitrogen ligands in designing efficient lignin-derived carbon single-atom catalysts for environmental applications.

Design, Synthesis, and Biological Insights of Half Sandwich Ruthenium–Arene Schiff Base Complexes: Molecular Docking and DFT

AbstractRuthenium complexes are gaining attention for their promising roles as chemotherapeutic and antimicrobial agents. In this study, three half sandwich organoruthenium(II) complexes, [(η6‐p‐cymene)Ru(L1)Cl]Cl [M1], [(η6‐p‐cymene)Ru(L2)Cl]Cl [M2], and [(η6‐p‐cymene)Ru(L3)Cl]Cl [M3], have been synthesized by reacting [{(η6‐p‐cymene)RuCl}2(μ‐Cl)2] with Schiff base ligands namely.N‐(Salicylidene)‐4‐toluidine (L1), N‐(Salicylidene)‐4‐aminobenzoic acid (L2), and N‐(Salicylidene)‐2‐hydroxyaniline (L3). These complexes have been characterized by elemental analysis, UV–vis., FTIR, multinuclear NMR and ESI‐MS spectroscopic methods. Computational analysis for these complex cations suggests distorted octahedral geometry around Ru(II) that is coordinated to azomethine nitrogen and phenoxide centers of the Schiff base ligand in bidentate mode, chloro and p‐cymene ligand in η6‐mode. Further, molecular electrostatic potential (MEP) values calculations have been performed to gain insights into the electronic properties and stability. Molecular docking studies reveal strong interaction between M1 and penicillin‐binding protein‐2 (PBP2), thereby highlighting its potential as an antibacterial agent against resistant bacteria. M1 exhibits over 90% inhibition against Mycobacterium tuberculosis at 12.5 µM and showcases potential anticancer activity against Human cervical cancer cells (SiHa). This study underscores the structural, computational, and biological significance of such class of ruthenium(II) complexes for biomedical applications.

Synthesis, Characterisation, and Catalytic Evaluation of Ru‐ONO Complexes featuring N‐ and P‐based ligands

Nine new ruthenium complexes featuring nitrogen and phosphorus donor ligands were synthesised from a Ru precursor featuring a rigid ONO‐pincer ligand. The choice of nitrogen‐ and phosphorous‐based ancillary ligands were guided by a careful evaluation of their different electronic and steric properties. This evaluation aimed to understand how these ligands, once coordinated could influence the structural, electronic, and catalytic activity of the corresponding complexes. The range of complexes showed moderate catalytic activity in the transfer hydrogenation of alcohols, where the best performing catalyst achieved 96% conversion in 1 hour (TON = 96, TOF = 96 h‐1). All complexes were characterised using 1H, 13C, 31P (where applicable) NMR spectroscopy, FT‐IR spectroscopy, CHN (microanalysis) and HR‐MS analyses. Single crystal structures were obtained for all the nine new complexes, as well two new polymorphs of the precursor complex. Complimentary electrochemical (cyclic voltammetry) and density functional theory (DFT) studies provided additional insight into the structural and electronic properties of the different complexes.

Multifunctional Heterogeneous Cobalt Catalyst for the One-Pot Synthesis of Benzimidazoles by Reductive Coupling of Dinitroarenes with Aldehydes in Water.

The endeavor of sustainable chemistry has led to significant advancements in green methodologies aimed at minimizing environmental impact while maximizing efficiency. Herein, a straightforward synthesis of benzimidazoles by reductive coupling of o-dinitroarenes with aldehydes is reported for the first time in aqueous media while using a non-noble metal catalyst. This work demonstrates that the combination of nitrogen and phosphorous ligands in the synthesis of supported heteroatom-incorporated Co nanoparticles is crucial for obtaining the desired benzimidazoles. The process achieves >99 % conversion, >99 % chemoselectivity and stability for the reduction of dinitroarenes using water as the solvent and hydrogen as the reductant under mild reaction conditions. The robustness of the catalyst has been investigated using several advanced techniques such as HRTEM, HAADF-STEM, XEDS, EELS, and NAP-XPS. In fact, we have shown that the introduction of N and P dopants prevents metal leaching and the sintering of the cobalt nanoparticles. Finally, to explore the general catalytic performance, a wide range of substituted dinitroarenes and benzaldehydes were evaluated, yielding benzimidazoles with competitive and scalable results, including MBIB (94 % yield), which is a compound of pharmaceutical interest.

Redox Activity and Potentials of Bidentate N-Ligands Commonly Applied in Nickel-Catalyzed Cross-Coupling Reactions.

Bidentate N-ligands are paramount to recent advances in nickel-catalyzed cross-coupling reactions. Through comprehensive organometallic, spectroscopic, and computational studies on bi-oxazoline and imidazoline ligands, we reveal that a square planar geometry enables redox activity of these ligands in stabilizing nickel radical species. This finding contrasts with the prior assumption that bi-oxazoline lacks redox activity due to strong mesomeric donation. Moreover, we conducted systematic cyclic voltammetry (CV) analyses of bidentate pyridyl, oxazoline, and imidazoline nitrogen ligands, along with their corresponding nickel complexes. Complexation with nickel shifts the reduction potentials to a more positive region and narrows the differences in redox potentials among the ligands. Additionally, various ligands led to different degrees of bromide dissociation from singly reduced (L)Ni(Ar)(Br) complexes, reflecting varying reactivity in the subsequent activation of alkyl halides, a crucial step in cross-electrophile coupling. These insights highlight the significant electronic effects of ligands on the stability of metalloradical species and their redox potentials, which interplay with coordination geometry. Quantifying the electron-donating, π-accepting properties of these ligands, as well as their effect on catalyst speciation, provides crucial benchmarks for controlling catalytic activity and enhancing catalyst stability.

Palladium (II) pyridylidene sulfonamides (PYSAs) for electrocatalytic reduction of CO2

Palladium (II) pyridylidene sulfonamides (PYSAs) for electrocatalytic reduction of CO2

Fpa (YlaN) is an iron(II) binding protein that functions to relieve Fur-mediated repression of gene expression in Staphylococcus aureus.

Iron (Fe) is a trace nutrient required by nearly all organisms. As a result of the demand for Fe and the toxicity of non-chelated cytosolic ionic Fe, regulatory systems have evolved to tightly balance Fe acquisition and usage while limiting overload. In most bacteria, including the mammalian pathogen Staphylococcus aureus, the ferric uptake regulator (Fur) is the primary transcriptional regulator controlling the transcription of genes that code for Fe uptake and utilization proteins. Fpa (formerly YlaN) was demonstrated to be essential in Bacillus subtilis unless excess Fe is added to the growth medium, suggesting a role in Fe homeostasis. Here, we demonstrate that Fpa is essential in S. aureus upon Fe deprivation. Null fur alleles bypassed the essentiality of Fpa. The absence of Fpa abolished the derepression of Fur-regulated genes during Fe limitation. Bioinformatic analyses suggest that fpa was recruited to Gram-positive bacteria and, once acquired, was maintained in the genome as it co-evolved with Fur. Consistent with a role for Fpa in alleviating Fur-dependent repression, Fpa and Fur interacted in vivo, and Fpa decreased the DNA-binding ability of Fur in vitro. Fpa bound Fe(II) in vitro using oxygen or nitrogen ligands with an association constant that is consistent with a physiological role in Fe homeostasis. These findings have led to a model wherein Fpa is an Fe(II) binding protein that influences Fur-dependent regulation through direct interaction.IMPORTANCEIron (Fe) is an essential nutrient for nearly all organisms. If Fe homeostasis is not maintained, Fe may accumulate in the cytosol, which can be toxic. Questions remain about how cells efficiently balance Fe uptake and usage to prevent overload. Iron uptake and proper metalation of proteins are essential processes in the mammalian bacterial pathogen Staphylococcus aureus. Understanding the gene products involved in the genetic regulation of Fe uptake and usage and the physiological adaptations that S. aureus uses to survive in Fe-depleted conditions provides insight into pathogenesis. Herein, we demonstrate that the DNA-binding activity of the ferric uptake regulator transcriptional repressor is alleviated under Fe limitation, but uniquely, in S. aureus, alleviation requires the presence of Fpa.

ATH434, a promising iron-targeting compound for treating iron regulation disorders.

Cytotoxic accumulation of loosely bound mitochondrial Fe2+ is a hallmark of Friedreich's Ataxia (FA), a rare and fatal neuromuscular disorder with limited therapeutic options. There are no clinically approved medications targeting excess Fe2+ associated with FA or the neurological disorders Parkinson's disease and Multiple System Atrophy. Traditional iron-chelating drugs clinically approved for systemic iron overload that target ferritin-stored Fe3+ for urinary excretion demonstrated limited efficacy in FA and exacerbated ataxia. Poor treatment outcomes reflect inadequate binding to excess toxic Fe2+ or exceptionally high affinities (i.e. ≤10-31) for non-pathologic Fe3+ that disrupts intrinsic iron homeostasis. To understand previous treatment failures and identify beneficial factors for Fe2+-targeted therapeutics, we compared traditional Fe3+ chelators deferiprone (DFP) and deferasirox (DFX) with additional iron-binding compounds including ATH434, DMOG, and IOX3. ATH434 and DFX had moderate Fe2+ binding affinities (Kd's of 1-4 µM), similar to endogenous iron chaperones, while the remaining had weaker divalent metal interactions. These compounds had low/moderate affinities for Fe3+(0.46-9.59µM) relative to DFX and DFP. While all compounds coordinated iron using molecular oxygen and/or nitrogen ligands, thermodynamic analyses suggest ATH434 completes Fe2+ coordination using H2O. ATH434 significantly stabilized bound Fe2+ from ligand-induced autooxidation, reducing reactive oxygen species (ROS) production, whereas DFP and DFX promoted production. The comparable affinity of ATH434 for Fe2+ and Fe3+ position it to sequester excess Fe2+ and facilitate drug-to-protein iron metal exchange, mimicking natural endogenous iron binding proteins, at a reduced risk of autooxidation-induced ROS generation or perturbation of cellular iron stores.

Evaluation of Cobalt, Nickel, and Palladium Complexes as Catalysts for the Hydrogenation and Improvement of Oxidative Stability of Biodiesel

Developing effective catalysts that can selectively hydrogenate C=C bonds in biodiesel samples is vital as it tackles the major problem of oxidative stability, which greatly limits the utilization of biodiesel as an alternative fuel. In this work, Co, Ni, and Pd catalysts stabilized with the bidentate nitrogen ligands N-(3-(triethoxysilyl)propyl)pyridin-2-ylmethylimine and N-(3-(triethoxysilyl)propyl)picolinamide were synthesized, characterized, and used as pre-catalysts in the transfer hydrogenation of C=C bonds in fatty acid methyl esters. The active catalysts from the Co, Ni, and Pd complexes sequentially hydrogenate the C18:2 chains to C18:1, which is further converted to C18:0 in the FAMEs of both methyl linoleate and jatropha biodiesel. The hydrogenation process was kinetically controlled, and after 3 h it yielded a biodiesel sample that contained 25.83% C16:0, 12.52% C18:2, 41.54% C18:1, 14.47% C18:0 and 3.0% C18:2 isomers. The un-hydrogenated jatropha diesel, hydrogenated jatropha diesel, and a B20 blend of jatropha were tested for susceptibility to oxidation reactions using the Rancimat method and FTIR spectroscopy, and the partial hydrogenation had improved the induction period by 3 h.

Synthesis, crystal structure, and thermal properties of energetic complex Cu(II) and Ag(I) based on 3-amino-4-(4,5-diamino-1,2,4-triazole-3yl)-furazan

Synthesis, crystal structure, and thermal properties of energetic complex Cu(II) and Ag(I) based on 3-amino-4-(4,5-diamino-1,2,4-triazole-3yl)-furazan

Ligand‐Tailored Divergence of Copper‐Catalyzed Aerobic Oxidation of Cyclopropanols. Application to the Practical Synthesis of β‐Aminoketones and β‐Enaminones

AbstractThe aerobic ring‐opening oxidation of cyclopropanols catalyzed by copper complexes was systematically investigated, with a focus on the effect of nitrogen ligands on the distribution of oxidation products. This study led to the development of a new synthesis of β‐aminoketones and β‐enaminones from cyclopropanols, where product specificity is tuned through ligand and solvent selection. β‐Aminoketones were prepared in 34–99% yields by copper(II) acetate‐catalyzed aerobic oxidation of cyclopropanols in the presence of nucleophilic secondary aliphatic amines. In contrast, bipyridine‐ligated copper catalysts resulted in the generation of β‐enaminones in 36–86% yields, presumably via the Kornblum‐DeLaMare rearrangement of intermediate 1,2‐dioxolanes.

Mol-ecular structure of tris-[(6-bromo-pyridin-2-yl)meth-yl]amine.

Coordination compounds of polydentate nitro-gen ligands with metals are used extensively in research areas such as catalysis, and as models of complex active sites of enzymes in bioinorganic chemistry. Tris(2-pyridyl-meth-yl)amine (TPA) is a tripodal tetra-dentate ligand that is known to form coordination compounds with metals, including copper, iron and zinc. The related compound, tris-[(6-bromo-pyridin-2-yl)meth-yl]amine (TPABr3), C18H15Br3N4, which possesses a bromine atom on the 6-position of each of the three pyridyl moieties, is also known but has not been heavily investigated. The mol-ecular structure of TPABr3 as determined by X-ray diffraction is reported here. The TPABr3 molecule belongs to the triclinic, P space group and displays interesting intermolecular Br⋯Br interactions that provide a stabilizing influence within the molecule.

Nitrogen‐Containing Surface Ligands Lead to False Positives for Photofixation of N2 on Metal Oxide Nanocrystals: An Experimental and Theoretical Study

AbstractMany ligands commonly used to prepare nanoparticle catalysts with precise nanoscale features contain nitrogen (e.g., oleylamine); here, it is found that the use of nitrogen‐containing ligands during the synthesis of metal oxide nanoparticle catalysts substantially impacts product analysis during photocatalytic studies. These experimental results are confirmed via hybrid Density Functional Theory (DFT) computations of the materials’ electronic properties to evaluate their viability as photocatalysts for nitrogen reduction. This nitrogen ligand contamination, and subsequent interference in photocatalytic studies is avoidable through the careful design of synthetic pathways that exclude nitrogen‐containing constituents. This result highlights the urgent need for careful evaluation of catalyst synthesis protocols, as contamination by nitrogen‐containing ligands may go unnoticed since the presence of nitrogen is often not detected or probed.

Axial coordination engineering of atomic Co–N4 sites for exceptional aromatic nitroreduction

Axial coordination engineering of atomic Co–N4 sites for exceptional aromatic nitroreduction

Stable CAAC-Triazenes: A New Nitrogen Ligand System With Donor and Conformational Flexibility, and With Application in Olefin Activation Catalysis.

N-heterocyclic imines such as pyridylidene amines impart high catalytic activity when coordinated to a transition metal, largely imposed by their electronic flexibility. Here, this donor flexibility has been applied for the first time to CAAC-based systems through the synthesis of CAAC-triazenes. These new ligands offer a larger π-conjugation that extends from the N-heterocyclic carbene through three nitrogens rather than just one, as observed in N-heterocyclic imines. We demonstrate the straightforward synthesis of three new CAAC-triazenes containing different substituents on the terminal triazene nitrogen. These compounds are remarkably stable up to 120 °C without loss of N2 as typically observed with similar triazenes. E-to-Z isomerization within the triazene is instigated by UV light and is partially reversible dependent on the triazene substituent. The quinoline-substituted CAAC-triazene 1-Q has been applied as an L,L'-type ligand in the synthesis of [PdCl2(1-Q)], [PdCl(Me)(1-Q)] and [Pd(Me)(H2O(1-Q)]+. E-to-Z ligand isomerization also occurs when coordinated to PdCl2, providing access to on-metal manipulation. The cationic complex [PdMe(H2O)(1-Q)]+ is a precatalyst for oligomerization of ethylene to form initially 2-butene and subsequently linear and branched C8-C12 products from butene activation. Moreover, isomerization of 1-hexene takes place efficiently with exceptionally low catalyst loading (10 ppm) and up to 74,000 turnover numbers.

Unique Use of Dibromo-L-Tyrosine Ligand in Building of Cu(II) Coordination Polymer-Experimental and Theoretical Investigations.

Although the crystals of coordination polymer {[CuCl(μ-O,O'-L-Br2Tyr)]}n (1) (L-Br2Tyr = 3,5-dibromo-L-tyrosine) were formed under basic conditions, crystallographic studies revealed that the OH group of the ligand remained protonated. Two adjacent [CuCl(L-Br2Tyr)] monomers, bridged by the carboxylate group of the ligand in the syn-anti bidentate bridging mode, are differently oriented to form a polymeric chain; this specific bridging was detected also by FT-IR and EPR spectroscopy. Each Cu(II) ion in polymeric compound 1 is coordinated in the xy plane by the amino nitrogen and carboxyl oxygen of the parent ligand and the oxygen of the carboxyl group from the symmetry related ligand of the adjacent [Cu(L-Br2Tyr)Cl] monomer, as well as an independent chlorine ion. In addition, the Cu(II) ion in the polymer chain participates in long-distance intermolecular contacts with the oxygen and bromine atoms of the ligands located in the adjacent chains; these intramolecular contacts were also supported by NCI and NBO quantum chemical calculations and Hirshfeld surface analysis. The resulting elongated octahedral geometry based on the [CuCl(L-Br2Tyr)] monomer has a lower than axial symmetry, which is also reflected in the symmetry of the calculated molecular EPR g tensor. Consequently, the components of the d-d band obtained by analysis of the NIR-VIS-UV spectrum were assigned to the corresponding electronic transitions.

Visible Light-Driven Hydrogen Evolution Catalysis by Heteroleptic Ni(II) Complexes with Chelating Nitrogen Ligands: Probing Ligand Substituent Position and Photosensitizer Effects

This study aims to advance the field of green chemistry and catalysis by exploring alternatives to conventional non-renewable energy sources. Emphasis is placed on hydrogen as a potential fuel, with a focus on the catalytic properties of Ni(II) complexes when coordinated with o-phenylenediamine and diimine ligands. We report the synthesis and comprehensive characterization, with various physical and spectroscopic techniques, of three heteroleptic Ni(II) complexes: [Ni(1,10-phenanthroline)(o-phenylene diamine)] (1), [Ni(2,2-dimethyl-2,2-bipyridine)(o-phenylene diamine)] (2), and [Ni(5,5-dimethyl-2,2-bipyridine)(o-phenylene diamine)] (3). The catalytic activity of these complexes for hydrogen evolution was assessed through photochemical studies utilizing visible light irradiation. Two distinct photosensitizers, fluorescein and quantum dots, were examined under diverse conditions. Additionally, their electrocatalytic behavior was investigated to elucidate the hydrogen evolution reaction (HER) mechanism, revealing a combined proton-coupled electron transfer (PCET)/electron-coupled proton transfer (ECPT) mechanism attributed to the chemical nature of the diamine ligand. The influence of ligand substituent position, ligand chemical nature, and photosensitizer type on catalytic performance was systematically studied. Among the complexes investigated, complex 2 demonstrated superior catalytic performance, achieving a turnover number (TON) of 3357 in photochemical experiments using fluorescein as a photosensitizer. Conversely, complex 1 exhibited the highest TON of 30,066 for HER when quantum dots were employed as the photosensitizer.

Synthesis and cytotoxicity of copper(II) semicarbazone complexes with lipophilic counter-anions

Synthesis and cytotoxicity of copper(II) semicarbazone complexes with lipophilic counter-anions