Nitrogen Ligands Research Articles

Dense pyridine nitrogen as surface decoration of interwoven Cu-MOFs for chloramphenicol-specific electrochemical sensor

The detection of chloramphenicol (CAP), a strictly prohibited antibiotic in veterinary drugs, remains challenging owing to its specific-sensing requirements. However, achieving a specific sensing strategy is crucial and requires the design of high-performance materials. In this study, a stable, double-interpenetrated dual-wall cage-in-cage metal–organic framework (MOF), SXNU-3-Cu ({[Cu2(INA)2(TATB)]·H2O}n), was designed using a mixed-linker strategy that incorporated the ligands of 4,4,4,-s-triazine-2,4,6-triyltribenzonic acid (H3TATB) and isonicotinic acid (HINA). Owing to their high connectivity and double-interpenetrated structure, the SXNU-3-Cu MOFs exhibited excellent thermal stability, as well as resistance to water and pH changes. The SXNU-3-Cu/ACET/GCE electrochemical sensor demonstrated a wide linearity range from 0.03 to 0.1 μM and 0.3–70 μM, with an impressive CAP detection limit of 9.51 nM. In particular, the interaction between –NO2 in CAP and dense pyridine nitrogen of HINA ligand enhanced the adsorption of CAP on the surface of the cage via Van der Waals forces. Subsequently, targeted oxidation–reduction catalytic reactions occurred inside accessible copper sites against nitro groups in the CAP molecules, resulting in high sensitivity and specific sensing towards CAP. Furthermore, we conducted comprehensive experimental and theoretical investigations to verify the sensing mechanism between the SXNU-3-Cu MOFs and CAP molecules. We determined that Cu-based MOFs have significant potential for drug monitoring and biochemical analyses.

Study of cobalamin adducts with cysteine and its oxidized sulfenic, sulfinic and sulfonic derivatives

In this paper, the reactivity of cobalamin towards S-oxidized cysteine derivatives (sulfenic, sulfinic, sulfonic and S-sulfate) is analyzed and compared to the reactivity towards related nitrogen, oxygen and sulfur-based ligands, focusing on the concept of linkage isomerism. UV-Vis spectra complemented by DFT and TD-DFT calculations show that cysteine and its oxidized derivatives do yield adducts, with a preference for binding to the cobalt through the sulfur.

Computational Methods Enable the Prediction of Improved Catalysts for Nickel-Catalyzed Cross-Electrophile Coupling.

Cross-electrophile coupling has emerged as an attractive and efficient method for the synthesis of C(sp2)-C(sp3) bonds. These reactions are most often catalyzed by nickel complexes of nitrogenous ligands, especially 2,2'-bipyridines. Precise prediction, selection, and design of optimal ligands remains challenging, despite significant increases in reaction scope and mechanistic understanding. Molecular parameterization and statistical modeling provide a path to the development of improved bipyridine ligands that will enhance the selectivity of existing reactions and broaden the scope of electrophiles that can be coupled. Herein, we describe the generation of a computational ligand library, correlation of observed reaction outcomes with features of the ligands, and the in silico design of improved bipyridine ligands for Ni-catalyzed cross-electrophile coupling. The new nitrogen-substituted ligands display a 5-fold increase in selectivity for product formation versus homodimerization when compared to the current state of the art. This increase in selectivity and yield was general for several cross-electrophile couplings, including the challenging coupling of an aryl chloride with an N-alkylpyridinium salt.

Metal-binding amino acid ligands commonly found in metalloproteins differentially fractionate copper isotopes

Copper (Cu) is a cofactor in numerous key proteins and, thus, an essential element for life. In biological systems, Cu isotope abundances shift with metabolic and homeostatic state. However, the mechanisms underpinning these isotopic shifts remain poorly understood, hampering use of Cu isotopes as biomarkers. Computational predictions suggest that isotope fractionation occurs when proteins bind Cu, with the magnitude of this effect dependent on the identity and arrangement of the coordinating amino acids. This study sought to constrain equilibrium isotope fractionation values for Cu bound by common amino acids at protein metal-binding sites. Free and bound metal ions were separated via Donnan dialysis using a cation-permeable membrane. Isotope ratios of pre- and post-dialysis solutions were measured by MC-ICP-MS following purification. Sulfur ligands (cysteine) preferentially bound the light isotope (63Cu) relative to water (Δ65Cucomplex-free = − 0.48 ± 0.18‰) while oxygen ligands favored the heavy isotope (65Cu; + 0.26 ± 0.04‰ for glutamate and + 0.16 ± 0.10‰ for aspartate). Binding by nitrogen ligands (histidine) imparted no isotope effect (− 0.01 ± 0.04‰). This experimental work unequivocally demonstrates that amino acids differentially fractionate Cu isotopes and supports the hypothesis that metalloprotein biosynthesis affects the distribution of transition metal isotopes in biological systems.

Local Environment of Sc and Y Dopant Ions in Aluminum Nitride Thin Films.

The local environments of Sc and Y in predominantly ⟨002⟩ textured, Al1-xDoxN (Do = Sc, x = 0.25, 0.30 or Y, x = 0.25) sputtered thin films with wurtzite symmetry were investigated using X-ray absorption (XAS) and photoelectron (XPS) spectroscopies. We present evidence from the X-ray absorption fine structure (XAFS) spectra that, when x = 0.25, both Sc3+ and Y3+ ions are able to substitute for Al3+, thereby acquiring four tetrahedrally coordinated nitrogen ligands, i.e., coordination number (CN) of 4. On this basis, the crystal radius of the dopant species in the wurtzite lattice, not available heretofore, could be calculated. By modeling the scandium local environment, extended XAFS (EXAFS) analysis suggests that when x increases from 0.25 to 0.30, CN for a fraction of the Sc ions increases from 4 to 6, signaling octahedral coordination. This change occurs at a dopant concentration significantly lower than the reported maximum concentration of Sc (42 mol % Sc) in wurtzite (Al, Sc)N. XPS spectra provide support for our observation that the local environment of Sc in (Al, Sc)N may include more than one type of coordination.

Benchtop Nickel Catalysis Invigorated by Electron-Deficient Diene Ligands.

ConspectusDue to the rarity of precious metals like palladium, nickel catalysis is becoming an increasingly important player in organic synthesis, especially for the formation of bonds with sp3-hybridized carbon centers. Traditionally, catalytic processes involving active Ni(0) species have relied on Ni(COD)2 or in situ reduction of Ni(II) salts. However, Ni(COD)2 is an air- and temperature-sensitive material that requires use in an inert-atmosphere glovebox, and in situ reduction protocols of Ni(II) salts using metallic or organometallic reductants add additional complications to reaction development.This Account chronicles the development of air-stable Ni(0) precursors as replacements for Ni(COD)2 or in situ reduction. Based on Schrauzer's seminal discovery of Ni(COD)(DQ) as an air-stable zerovalent organonickel complex, our research laboratories at Scripps Research and Bristol Myers Squibb have developed a class of precatalysts based on the Ni(COD)(EDD) (EDD = electron-deficient diene) framework, relying on the steric and electronic properties of the supporting diene to render the metal center stable to air, moisture, and even silica gel but reactive to ligand substitution and redox changes.The stable Ni(0) complexes can be accessed through ligand exchange with Ni(COD)2, through reduction of Ni(acac)2 using DIBAL-H, or electrochemically via cathodic reduction of Ni(acac)2 to Ni(COD)2, followed by addition of an EDD ligand in one pot. As a toolkit, the complexes demonstrate reactivity that is equivalent or enhanced compared to Ni(COD)2, catalyzing C-C and C-N cross-couplings, Miyaura borylations, C-H activations, and other transformations. Since the initial report on Ni(COD)(DQ), its reactivity in C(sp2)-CN activation, metallophotoredox, and electric field-induced cross-coupling have also been demonstrated.By incorporating the precatalyst toolkit into reaction discovery campaigns, our laboratories have been able to perform C(sp3)-S(alkyl) couplings and metallonitrenoid carboamination, both of which represent challenging transformations that were inaccessible with traditional phosphine, nitrogen, or electron-deficient olefin ligands. Computational and experimental studies demonstrate how the quinone ligands are hemilabile, adopting η1(O)-bound geometries to relieve steric strain or stabilize transition states and intermediates; redox-active, able to transiently oxidize the metal center; and electron-withdrawing or -donating, depending on metal oxidation state and coordination geometry. These studies show how the ligands enable key steps in catalysis beyond imparting air-stability.Since our report documenting the catalytic activity of Ni(COD)(DQ), many other laboratories have also observed unique reactivity with this precatalyst. Ni(COD)(DQ) was found to offer superior reactivity to Ni(COD)2 in C-N cross coupling to form N,N-diaryl sulfonamides and in preparation of biaryls from aryl halides and benzene through a Ni-mediated, base-assisted homolytic aromatic substitution.

Tridentate Nitrogen Ligand as a Tool for the Construction of Well-Defined Rare Earth Trichloride Complexes.

LnCl3(THF)3 (Ln = Y, La ÷ Nd, Sm ÷ Lu) readily react with the tridentate 1,3,5-trimethyl-1,3,5-triazacyclohexane (Me3tach) ligand to form mono- or binuclear lanthanide trichloride complexes, depending on the stoichiometry of the reaction and the ionic radius of the metal: mononuclear pseudosandwich [LnCl3(Me3tach)2], (Ln = Y, La ÷ Ho) or binuclear complexes [Ln2Cl6(Me3tach)3], or [LnCl3(Me3tach)(THF)]2 (Ln = Sm, Tb). Detailed analysis of the NMR data of [LnCl3(Me3tach)2] complexes with paramagnetic lanthanide ions showed that their structures remained unchanged in the toluene solution. A series of isomorphous complexes [LnCl3(Me3tach)(Py)2] (Ln = La, Sm, Tb, Er, Lu; Py = pyridine) have been obtained by the recrystallization of either mononuclear or binuclear complexes from pyridine. Complexes of terbium and europium ions with the Me3tach ligand exhibit relatively high quantum yields of metal-centered luminescence (0.39 and 0.32, respectively).

Spin crossover iron complexes with spin transition near room temperature based on nitrogen ligands containing aromatic rings: from molecular design to functional devices.

During last decades, significant advances have been made in iron-based spin crossover (SCO) complexes, with a particular emphasis on achieving reversible and reproducible thermal hysteresis at room temperature (RT). This pursuit represents a pivotal goal within the field of molecular magnetism, aiming to create molecular devices capable of operating in ambient conditions. Here, we summarize the recent progress of iron complexes with spin transition near RT based on nitrogen ligands containing aromatic rings from molecular design to functional devices. Specifically, we discuss the various factors, including supramolecular interactions, crystal packing, guest molecules and pressure effects, that could influence its cooperativity and the spin transition temperature. Furthermore, the most recent advances in their implementation as mechanical actuators, switching/memories, sensors, and other devices, have been introduced as well. Finally, we give a perspective on current challenges and future directions in SCO community.

F-Element heavy pnictogen chemistry.

The coordination and organometallic chemistry of the f-elements, that is group 3, lanthanide, and actinide ions, supported by nitrogen ligands, e.g. amides, imides, and nitrides, has become well developed over many decades. In contrast, the corresponding f-element chemisty with the heavier pnictogen analogues phosphorus, arsenic, antimony, and bismuth has remained significantly underdeveloped, due largely to a lack of suitable synthetic methodologies and also the inherent hard(f-element)-soft(heavier pnictogen) acid-base mismatch, but has begun to flourish in recent years. Here, we review complexes containing chemical bonds between the f-elements and heavy pnictogens from phosphorus to bismuth that spans five decades of endeavour. We focus on complexes whose identity has been unambiguously established by structural authentication by single-crystal X-ray diffraction with respect to their synthesis, characterisation, bonding, and reactivity, in order to provide a representative overview of this burgeoning area. By highlighting that much has been achieved but that there is still much to do this review aims to inspire, focus and guide future efforts in this area.

Synthesis and luminescent properties of three excellent yellow emissive Cu(i) complexes based on the diphosphine ligand and the diimine ligand

High quantum yield (72–88%) yellow-emitting Cu(i) complexes obtained by tuning the nitrogen ligands and anions.

Mechanistically guided development of homogenous nickel catalysis through rapid computational catalyst screening

Advances in understanding the mechanisms of homogeneous nickel catalysis has led to a remarkable progress in this field. However, the discovery of active catalysts is still largely based on trial and error, and the catalysts are mostly based on chelating (nitrogen) ligands. We report a combined theoretical and experimental study of nickel-catalyzed hydroarylation of vinylarenes, where experimental advances were complemented with a rapid computation catalyst screening. Once the mechanism is known and preliminary experimental data is available, the screening approach can predict other suitable ligands by assessing the electronic structure of the catalyst complex without the computationally intensive determination of the transition states. Using the approach described, we developed the reaction that proceeds under unusually mild conditions and is broadly applicable on a range of vinylarenes and (het)aryl halides, including previously inaccessible chlorides. The reaction was found to be highly dependent on the choice of ligand, with monodentate PPh3 proving optimal. Extensive quantum chemical simulations elucidated the reaction mechanism and identified Ni(PPh3)xClyH as the crucial active species.

Ligand Relay for Nickel-Catalyzed Decarbonylative Alkylation of Aroyl Chlorides.

Transition metal-catalyzed direct decarboxylative transformations of aromatic carboxylic acids usually require high temperatures, which limit the substrate's scope, especially for late-stage applications. The development of the selective decarbonylative of carboxylic acid derivatives, especially the most fundamental aroyl chlorides, with stable and cheap electrophiles under mild conditions is highly desirable and meaningful, but remains challenging. Herein, a strategy of nickel-catalyzed decarbonylative alkylation of aroyl chlorides via phosphine/nitrogen ligand relay is reported. The simple phosphine ligand is found essential for the decarbonylation step, while the nitrogen ligand promotes the cross-electrophile coupling. Such a ligand relay system can effectively and orderly carry out the catalytic process at room temperature, utilizing easily available aroyl chlorides as an aryl electrophile for reductive alkylation. This discovery provides a new strategy for direct decarbonylative coupling, features operationally simple, mild conditions, and excellent functional group tolerance. The mild approach is applied to the late-stage methylation of various pharmaceuticals. Extensive experiments are carried out to provide insights into the reaction pathway and support the ligand relay process.

Observing N in Co-Nx-C during cathodic reaction via operando X-ray spectroscopy

Single atom catalysts (SACs) anchored to N-carbon (M-Nx-C) have been extensively investigated owing to their impressive catalytic activity and relatively low cost. In contrast to the bulk catalysts, M-Nx-C almost maintain their oxidation states even under the cathodic potentials, displaying only minor adjustments in its pristine electronic structure. In this context, we have examined the electronic structure of nitrogen through in-situ/operando NEXAFS to unveil the origin of the distinct electronic configuration of M-Nx-C. We were able to observe the behavior of N, which significantly influences the state of SACs. When exposed to conditions resembling hydrogen evolution reactions, the electronic structure of cobalt exhibited slight changes, while the electronic configuration of the nitrogen ligands remained largely intact. Through a combination of in-situ/operando NEXAFS investigation and insights from prior literature, we hypothesized that the sustained electronic structure of M-Nx-C can be attributed to the inherent stability of the nitrogen ligands under the cathodic potentials. Moreover, any subtle shifts in the cobalt state appeared to result from chemical adsorption rather than modifications to the nitrogen ligands, such as protonation. Our study contributes valuable insights into the functional role of nitrogen ligands in M-Nx-C, thereby bolstering the findings of previous theoretical and experimental studies.

Synthesis and Characterization of Copper (II) Soap Complexes Derived from Natural Edible Oils with Substituted Benzothiazoles

The aim of this research work is to present the fundamental chemical properties and new investigations of coordination compounds of some transition metal ions with an overview of medicinal applications. The primary purpose of this study is to understand the characteristic nature and biocidal properties of copper (II) soap complexes with nitrogen and sulphur donor ligands. Wide varieties of geometries and reactivity of transition metal complexes have been reported to possess several biocidal activities. Copper (II) soaps derived from natural edible oils like sesame and groundnut have a tendency of complexation with nitrogen and sulphur containing ligands. Synthesized copper (II) soap complexes may play a significant role in biological activities and have sufficient pharmaceutical, industrial and analytical applications. During last few decades, the use of macrocyclic nitrogen and sulphur containing six-membered heterocyclic ligands with transition metal complexes has been an interesting and fascinating area of research activity in scientific community all over the world due to its various applications.

Cobalt-Sulfur Coordination Chemistry Drives B12 Loading onto Methionine Synthase.

Cobalt-sulfur (Co-S) coordination is labile to both oxidation and reduction chemistry and is rarely seen in nature. Cobalamin (or vitamin B12) is an essential cobalt-containing organometallic cofactor in mammals and is escorted via an intricate network of chaperones to a single cytoplasmic target, methionine synthase. In this study, we report that the human cobalamin trafficking protein, MMADHC, exploits the chemical lability of Co-S coordination for cofactor off-loading onto methionine synthase. Cys-261 on MMADHC serves as the β-axial ligand to cobalamin. Complex formation between MMADHC and methionine synthase is signaled by loss of the lower axial nitrogen ligand, leading to five-coordinate thiolato-cobalamin. Nucleophilic displacement by the vicinal thiolate, Cys-262, completes cofactor transfer to methionine synthase and release of a cysteine disulfide-containing MMADHC. The physiological relevance of this mechanism is supported by clinical variants of MMADHC, which impair cofactor binding and off-loading, explaining the molecular basis of the associated homocystinuria.

Effect of ligand coordination on the mechanism and regioselectivity of cobalt-catalyzed hydroboration/cyclization of 1,6-enynes

The 3d transition metal-catalyzed cyclization of enynes provides a sustainable and useful strategy for the construction of cyclic compounds. Controlling the regioselectivity is a central challenge for the hydrofunctionalization of multiply unsaturated substrates such as 1,6-enynes. Herein, we report a computational mechanistic study of the cobalt-catalyzed hydroboration/cyclization of 1,6-enynes in the presence of three representative ligands including bidentate nitrogen ligand and phosphine ligand as well as tridentate nitrogen-based ligand. A detailed analysis is carried out on the ligand-substrate interactions to understand the effect of ligand coordination on the mechanism and regioselectivity. Our results indicate that although the initial catalyst-substrate complexes adopt the pseudo-trigonal bipyramidal geometries for the two nitrogen-based ligands, there is a remarkable difference in the free energy surfaces. The steric repulsions and hydrogen bonding interactions between the substrate and the ligand play important roles in regulating the competing migration insertion. Energy decomposition analyses are further performed for the subsequent σ-bond metathesis to illustrate the impacts of steric and electronic effects on the regioselectivity and the electrostatics and orbital interactions are disclosed to be the dominant factors. This work provides a deeper understanding of the specific structural and electronic properties of the cobalt complexes and their potential influences on the reactivity and selectivity.

Nitrogen‐containing Porous Organic Polymer Supported Rhodium Catalyst for Hydroformylation of Olefins

AbstractThe hydroformylation reaction of olefins with syngas (CO/H2) to manufacture aldehydes is one of the largest homogeneous catalytic processes. However, it is important to extend the use of Rh catalysts promoted by nitrogen ligands to heterogeneous system. In this study, a nitrogen‐containing porous organic polymer supported Rh catalyst (Rh/TImT‐TBPT) was successfully synthesized, as well as showed excellent catalytic activity (TOF=216 h−1) and selectivity of aldehydes (98 %) in the hydroformylation of 1‐octene. Furthermore, the catalytic performance of Rh/TImT‐TBPT in the hydroformylation of various olefins was also investigated, displaying outstanding results. The catalytic material was characterized by FT‐IR, XRD, XPS, TEM, SEM and TGA in detail. The characterization data showed that Rh species were highly dispersed on the support, leading to the good stability. More importantly, the Rh/TImT‐TBPT catalyst could be separated from the reaction system at the end of the hydroformylation, and then reused in the next cycle under optimized conditions.

Modulating Metal‐Nitrogen Coupling in Anti‐Perovskite Nitride via Cation Doping for Efficient Reduction of Nitrate to Ammonia

AbstractThe complexes of metal center and nitrogen ligands are the most representative systems for catalyzing hydrogenation reactions in small molecule conversion. Developing heterogeneous catalysts with similar active metal‐nitrogen functional centers, nevertheless, still remains challenging. In this work, we demonstrate that the metal‐nitrogen coupling in anti‐perovskite Co4N can be effective modulated by Cu doping to form Co3CuN, leading to strongly promoted hydrogenation process during electrochemical reduction of nitrate (NO3−RR) to ammonia. The combination of advanced spectroscopic techniques and density functional theory calculations reveal that Cu dopants strengthen the Co−N bond and upshifted the metal d‐band towards the Fermi level, promoting the adsorption of NO3− and *H and facilitating the transition from *NO2/*NO to *NO2H/*NOH. Consequently, the Co3CuN delivers noticeably better NO3−RR activity than the pristine Co4N, with optimal Faradaic efficiency of 97 % and ammonia yield of 455.3 mmol h−1 cm−2 at −0.3 V vs. RHE. This work provides an effective strategy for developing high‐performance heterogeneous catalyst for electrochemical synthesis.

Modulating Metal-Nitrogen Coupling in Anti-Perovskite Nitride via Cation Doping for Efficient Reduction of Nitrate to Ammonia.

The complexes of metal center and nitrogen ligands are the most representative systems for catalyzing hydrogenation reactions in small molecule conversion. Developing heterogenous catalysts with similar active metal-nitrogen functional centers, nevertheless, still remains challenging. In this work, we demonstrate that the metal-nitrogen coupling in anti-perovskite Co4N can be effective modulated by Cu doping to form Co3CuN, leading to strongly promoted hydrogenation process during electrochemical reduction of nitrate (NO3-RR) to ammonia. The combination of advanced spectroscopic techniques and density functional theory calculations reveal that Cu dopants strengthen the Co-N bond and upshifted the metal d-band towards the Fermi level, promoting the adsorption of NO3- and *H and facilitating the transition from *NO2/*NO to *NO2H/*NOH. Consequently, the Co3CuN delivers noticeably better NO3-RR activity than the pristine Co4N, with optimal Faradaic efficiency of 97% and ammonia yield of 455.3 mmol h-1 cm-2 at -0.3 V vs. RHE. This work provides an effective strategy for developing high-performance heterogenous catalyst for electrochemical synthesis.

Oxa‐TriQuinoline: A New Entry to Aza‐Oxa‐Crown Architectures**

AbstractA new 15‐membered‐macrocyclic molecular entity, oxa‐TriQuinoline (o‐TQ), was designed and synthesized. In o‐TQ, three oxygen atoms were joined onto three quinoline units at the 2‐ and 8‐positions in a head‐to‐tail fashion by three‐fold SNAr reactions, giving rise to the characteristic N3O3 aza‐oxa‐crown architecture. o‐TQ can serve as a new tridentate nitrogen ligand to capture a CuI cation and adopt a bowl shape, before supramolecular complexation with corannulene and [12]cycloparaphenylene (CPP) occurs through π–π and CH–π interactions. In the presence of the CuI cation, the non‐emissive o‐TQ becomes a highly emissive material in the solid state, whereby the emission wavelengths depend on the ancillary ligand on the CuI cation. The o‐TQ/CuI complex is able to promote carbene catalysis to provide a range of enamines with a gem‐difluorinated terminus.