Symmetric Ligand Research Articles

Naphthyridine–2NO, a new C2-symmetric rigid tetradentate bimetallic ligand and its application in asymmetric Friedel–Crafts alkylation

The development of a series of novel and easily accessed chiral naphthyridine-type binucleating ligands for asymmetric catalysis.

A solution-processable benzothiazole-substituted formazanate zinc(II) complex designed for a robust resistive memory device.

A novel mononuclear bis(formazanate)zinc complex (1) based on a redox-active 1-(benzothiazol-2-yl)-5-(2-benzoyl-4-chlorophenyl)-3-phenyl formazan ligand has been synthesized and characterized. Complex 1 was prepared by reacting one equivalent of Zn(OCOCH3)·2H2O with two equivalents of the corresponding formazan derivative. X-ray crystallography was employed to ascertain the solid-state structure of compound 1, and the analysis revealed a distorted octahedral geometry for the complex where the symmetrical ligands exhibit a preference for coordinating with the zinc center in the 'open' form, generating five-membered chelate rings. Moreover, cyclic voltammetry analysis reveals that complex 1 exhibits the capacity for electrochemical reduction as well as oxidation, resulting in the formation of radical anionic (L2Zn-) and dianionic (L2Zn2-) states as well as the oxidation state of 1. Additionally, the developed solution-processable complex 1 was employed as the fundamental building material for resistive switching memory applications. The [FTO/ZnIIL2(1)]/Ag RRAM device demonstrates exceptional resistive memory switching properties, with a substantial ION/IOFF ratio (103), low operational VSET and VRESET (0.9 V and -0.75 V) voltages, excellent endurance stability (100 cycles), and decent retention time (more than 2000 seconds). The findings presented in this study underscore the importance of redox-active formazanate metal complexes for creating promising memory storage devices.

Modular symmetric ligands for selective recognition of cancer-relevant G-quadruplexes

New G-quadruplex-interactive and selective ligands are strongly required to evolve innovative, effective and minimally toxic anticancer agents. With this purpose, we have here synthesized and evaluated a mini-library of organic molecules featured by aromatic cores of different rigidity (naphthalene or bioxazole), decorated with pendant groups including positively charged moieties and/or H-bond donors/acceptors. By exploiting different biophysical techniques, we proved the ability of the bioxazole-based derivatives to strongly and selectively interact with telomeric and oncogenic G-quadruplexes, while the compound featured by a naphthalene core did not emerge as a good G-quadruplex ligand. Molecular docking studies demonstrated the ability of the bioxazole-based ligands to preferentially target the outer G-tetrads of both telomeric and oncogenic G-quadruplexes, by positioning their cores on the G-tetrads in a symmetrical or asymmetrical way respectively, with the pendant groups pointing towards or away from the grooves. All bioxazole-based ligands showed anticancer activity in the low micromolar range. Particularly, the bioxazole derivative bearing piperazine groups was the most active compound of the investigated series, whereas the derivatives bearing morpholine groups were the most selective ones on cancer cells, in full agreement with their ability to act as the strongest and most selective G-quadruplex ligands, respectively.

Direct synthesis of polyethylene thermoplastic elastomers with high molecular weight and excellent elastic recovery via a hybrid steric bulky strategy

Recently, α-diimine nickel-catalyzed ethylene chain walking polymerization has enabled the direct preparation of polyethylene thermoplastic elastomers using ethylene as a single feedstock. In this study, a series of hybrid bulky butyl-based α-diimine nickel complexes constructed with o-aryl and -diarylmethyl anilines were synthesized and employed for the ethylene polymerization. All the nickel complexes showed high activities (level of 106 g mol-1h−1) and high molecular weight (Mn up to 1230.9 kg/mol) polyethylene with high branching density (82–118/1000C) were yielded in ethylene polymerization. The polyethylene obtained by Ni1-3 showed distinguished elastic properties (SR = 72–91 %) and the sample obtained by Ni1 at 50 °C exhibited optimal elastic recovery values (91 %), which is also the best reported so far in polyethylene elastomers. Compared to the corresponding nickel complexes with symmetrical ligand substituents, the complexes with unsymmetrical substituents (hybrid) in this study facilitate the synthesis of significantly higher branched polyethylene with much better elastic recovery. The hybrid cationic nickel catalysts are also capable of catalyzing the copolymerization of ethylene with methyl 10-undecenoate.

Synthesis and Evaluation of Cytotoxicity and Molecular Docking of New Symmetrical Macroacyclic Schiff Base Ligands and Their Ni(II) and Zn(II) Complexes

To synthesize new symmetrical macroacyclic Schiff base ligands (L1 and L2), polyamine (A) was condensed with 2-formylpyridine and salicylaldehyde. Furthermore, Ni(ClO4)2.6H2O and Zn(ClO4)2.6H2O in methanol were reacted with the ligands to prepare corresponding metal complexes. The cytotoxicity of the synthesized complexes against MCF-7 and A549 adenocarcinoma cells was evaluated, where Zn-complexes displayed greater cytotoxic effects than Ni-complexes. Conductivity measurements, ESI-MS, UV-Vis, molar conductivity, IR, 1H, and 13C NMR spectra were used to characterize the products. Furthermore, molecular docking was performed to assess the biological activity of the complexes, and it was observed that Zn-complexes exhibited the highest inhibition effect against cytotoxic receptors.

Synthesis, Crystal Structure Determination and Magnetic Study of a New [2 × 2] Grid Tetranuclear Fe(II) and Ni(II) Complexes Derived from the Ligand 1, 5-Bis(1-(Pyridin-2-Yl) Ethylidene) Carbonohydrazide)

Complexes of nickel (II) and iron (III) are easily synthetized using the symmetrical ligand 1,5-bis(1-(pyridin-2-yl)ethylidene)carbonohydrazide) (H2L) and metal nitrate salts. Square [2x2] grids structure of one tetranuclear iron and one tetranuclear nickel complex were isolated. X ray diffraction analysis reveals that the crystal structures of the two complexes are similar. The asymmetric unit of each complex consists of four cationic ligand molecules and four metal ions. Each ligand acts in its monodeprotonated form through five coordination sites such as two pyridine nitrogen atoms, two azomethine nitrogen atoms and one oxygen atom. Each of the four ligand molecules acts as a bridge between two metal ions yielding a square 2 x 2 grid structure. Each of the metal ion is hexacoordinated and is situated in a N4O2 core and the environment is best described as a severely distorted square bipyramidal geometry. Electrochemical studies show two electrons process for complex 1 and one electron process for complex 2. Variable temperature magnetic study shows that antiferromagnetic coupling is stronger in the nickel(II) than in the iron(II) complex. Perfect correlation between the magnetic properties and the crystallographic data are observed in both complexes.

Statement of Retraction: Indium(III)-coordination polymer based on a C3- symmetric ligand: crystal structure and anticancer activity on neuroblastoma

Statement of Retraction: Indium(III)-coordination polymer based on a C3- symmetric ligand: crystal structure and anticancer activity on neuroblastoma

Metal‐Organic Gels of Tris‐tetrazole‐tri‐amido Molecule with Co(II) and Ni(II) as Effective Electrocatalysts for Oxygen Evolution Reaction: Effect of Metal Ion, Porosity and Morphology on the Catalytic Activity of MOGs

AbstractDevelopment of efficient and low cost electrocatalysts has been an important area of research in the field of materials chemistry. In this regard metal‐organic gels (MOGs) are one of the promising materials and they are being utilized for various materials applications including energy conversion and storage. Electrochemical applications of the MOGs are still in its infancy and further studies are required for exploration of structure‐property correlation that is crucial for targeted and efficient materials design. Herein we report multi stimuli responsive MOGs containing a tris‐tetrazole‐tri‐amido based organic ligand. The self‐assembly of the threefold symmetric ligand with Co(II)/Ni(II) acetates results in the MOGs with distinct morphological and structural characteristics, regardless of containing the same organic ligand. These MOGs were synthesized by direct mixing of the precursors under ambient conditions. The xerogels of these MOGs (Co‐MOG′ and Ni‐MOG′) exhibit excellent OER performance as the Co‐MOG′ and Ni‐MOG′ shows the overpotential of 312 mV and 418 mV at 10 mA/cm2 in an alkaline electrolyte. Electrocatalytic performance of the xerogels were correlated to their structural features like distinct morphology and porosity of the material that facilitates the mass transfer and maximum exposure to the electrochemical active sites. Importantly, this work demonstrates the functional application of MOGs as electrocatalysts for OER and the effect of metal ion, porosity and morphology on their overall performance.

A Click Chemistry-Based Artificial Metallo-Nuclease.

Artificial metallo-nucleases (AMNs) are promising DNA damaging drug candidates. Here, we demonstrate how the 1,2,3-triazole linker produced by the Cu-catalysed azide-alkyne cycloaddition (CuAAC) reaction can be directed to build Cu-binding AMN scaffolds. We selected biologically inert reaction partners tris(azidomethyl)mesitylene and ethynyl-thiophene to develop TC-Thio, a bioactive C3 -symmetric ligand in which three thiophene-triazole moieties are positioned around a central mesitylene core. The ligand was characterised by X-ray crystallography and forms multinuclear CuII and CuI complexes identified by mass spectrometry and rationalised by density functional theory (DFT). Upon Cu coordination, CuII -TC-Thio becomes a potent DNA binding and cleaving agent. Mechanistic studies reveal DNA recognition occurs exclusively at the minor groove with subsequent oxidative damage promoted through a superoxide- and peroxide-dependent pathway. Single molecule imaging of DNA isolated from peripheral blood mononuclear cells shows that the complex has comparable activity to the clinical drug temozolomide, causing DNA damage that is recognised by a combination of base excision repair (BER) enzymes.

Au(III) complexes of symmetrical tetradentate Schiff base ligands: Synthesis, characterization, anticancer/antioxidant potency, in silico prediction, and catalase binding properties

Two new gold(III) complexes, [AuL1]Cl3, A, and [AuL2]Cl3, B, were synthesized and characterized. DFT calculations showed square planar geometry for both complexes. Antioxidant results showed that the ability of compounds to inhibit DPPH• is as follows: A > B > L2 > L1. The anticancer assay showed that both complexes have the ability to inhibit the growth of HCT116 colon cancer cell lines, but B shows a relatively better effect than cisplatin. The interaction effects of A and B on the activity and structure of the bovine liver catalase (BLC) were investigated by spectroscopic techniques and molecular docking. Both complexes were able to change the performance and structure of BLC; B has a greater effect on BLC activity, so at concentration of 2 μM, A and B inhibit initial BLC activity by 92.2% and 55.6%, respectively. The interaction mechanism of A and B with BLC was also different; A interacted mostly with van der Waals interactions and hydrogen bonds, but the most important forces for B was hydrophobic interactions. According to docking results, both complexes prefer the domain III of BLC, but B has higher affinity toward BLC than A, which supports the results of spectroscopic and FMO analysis.

Near IR Bandgap Semiconducting 2D Conjugated Metal-Organic Framework with Rhombic Lattice and High Mobility.

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) are emerging as a unique class of electronic materials. However, 2D c-MOFs with band gaps in the Vis-NIR and high charge carrier mobility are rare. Most of the reported conducting 2D c-MOFs are metallic (i.e. gapless), which largely limits their use in logic devices. Herein, we design a phenanthrotriphenylene-based, D2h -symmetric π-extended ligand (OHPTP), and synthesize the first rhombic 2D c-MOF single crystals (Cu2 (OHPTP)). The continuous rotation electron diffraction (cRED) analysis unveils the orthorhombic crystal structure at the atomic level with a unique slipped AA stacking. The Cu2 (OHPTP) is a p-type semiconductor with an indirect band gap of ≈0.50 eV and exhibits high electrical conductivity of 0.10 S cm-1 and high charge carrier mobility of ≈10.0 cm2 V-1 s-1 . Theoretical calculations underline the predominant role of the out-of-plane charge transport in this semiquinone-based 2D c-MOF.

A general method for metallocluster site-differentiation.

The deployment of metalloclusters in applications such as catalysis and materials synthesis requires robust methods for site-differentiation: the conversion of clusters with symmetric ligand spheres to those with unsymmetrical ligand spheres. However, imparting precise patterns of site-differentiation is challenging because, compared with mononuclear complexes, the ligands bound to clusters exert limited spatial and electronic influence on one another. Here, we report a method that employs sterically encumbering ligands to bind to only a subset of a cluster's coordination sites. Specifically, we show that homoleptic, phosphine-ligated Fe-S clusters undergo ligand substitution with N-heterocyclic carbenes (NHCs) to give heteroleptic clusters in which the resultant clusters' site-differentiation patterns are encoded by the steric profile of the incoming NHC. This method affords access to every site-differentiation pattern for cuboidal [Fe4S4] clusters and can be extended to other cluster types, particularly in the stereoselective synthesis of site-differentiated Chevrel-type [Fe6S8] clusters.

Template Synthesis of Ni(II) and Zn(II) Complexes Derived from N2O2 Donor Symmetrical Tetradentate Ligands System: Comparative Antioxidant, Xanthine inhibitory, and Computational Studies

Four mononuclear symmetric coordination compounds of Ni(II) and Zn(II) (C1–C4), obtained from N2O2 donor Schiff base ligand systems were synthesized in-situ and characterized with a variety of analytical and spectroscopic techniques such as elemental CHN-analysis, 1H-NMR, 13C{H}NMR, UV-Visible, Infrared, powder X-ray diffraction, scanning electron, and high-resolution mass spectroscopies. These analyses revealed that the ligands chelate the metal ions through the oxygen and nitrogen (N2O2) atoms of the phenolate and azomethine functional groups, resulting in distorted and perfect square planar geometry around Zn(II) and Ni(II) ions, respectively. The 2,2-diphenylpicrylhydrazyl (DPPH) radical scavenging and xanthine oxidase activity of the complexes were investigated using in vitro assay techniques. The studies revealed that the complexes possess moderate radical scavenging activity with no or very weak xanthine oxidase activity, in which the controls show better activity than the complexes in both assays. However, C3 and C1 demonstrated some level of activity at higher concentrations but not commensurate with the controls. The DFT calculation of the complexes using the M06- 2X/B3LYP-311G9d.p) level of the theory presented electronic properties that supported the experimental findings on the complexes

Self-Assembly Heterometallic Cu-Ln Complexes: Synthesis, Crystal Structures and Magnetic Characterization

Using N2O4 donor symmetric ligand H2L and dca co-ligand, two new isostructural dinuclear CuII–LnIII complexes [Cu(Cl)(L)Ln(NO3)(CH3OH)(H2O)(dca)] [Ln=Ho (1CuHo), Gd (2CuGd)] [H2L = 6,6′-((1E,1′E)-(ethane-1,2-diylbis(azaneylylidene))bis(methaneylylidene))bis(2-methoxyphenol); dca=dicyanamide] were designed, synthesized and studied. In the two isostructural compounds, the geometric environment around the nine-coordinated Ln(III) ions is muffin, whereas the geometry of the penta-coordinated Cu(II) ions is square pyramid. The magnetic properties of both complexes were also studied. Direct current magnetic susceptibility measurements indicate ferromagnetic interactions between the Cu(II) ion and Gd(III) ion in complex 2CuGd. Alternating current (ac) magnetic measurements indicate that complex 1CuHo displays slow magnetic relaxation behaviour.

A pyrazolone-based dinuclear Cu(II) Schiff-base complex: DFT studies on the rate-determining steps of the tautomerism in the ligand and molecular docking modelling with COVID-19 main protease (6LU7)

A new dinuclear Schiff-base complex, [Cu2L'2(μ-OAc)2], was synthesized and characterized by various spectroscopic methods and single-crystal X-ray diffraction (SCXRD). The symmetrical H2L ligand was synthesized from the reaction between 4-acetyl-3-methyl-1-phenyl-2-pyrazoline-5-one (or acylpyrazolone) with 1,3-propanediamine, but upon reaction with a metal salt, it gave the unsymmetrical HL'. The transition states and rates of interconversion between different tautomeric forms of HL' were studied by DFT computations. The imine-one (Z) in the gas phase and imine-ol (Z) in the solution were the most stable forms, most probably due to better hydrogen bonding. We also applied molecular docking modeling on the various tautomeric forms of the ligand as well as the complex with the main protease (6LU7) of the SARS-CoV-2 virus. Based on the obtained results, the complex had better interactions with the receptor. The order of the interactions was [Cu2L2(μ-OAc)2] > amine-one (Z) > imine-one (E) > imine-ol (Z) > amine-one (E) > imine-one (Z) > imine-ol (E).

Fe(II)-Based Metallo-Supramolecular Polymer Film for Electrochemical Detection of Nitrite: Studies of Kinetics and Reaction Mechanisms

Here, a monometallic supramolecular polymer (SMP) was synthesized for the fabrication of an electrochemical nitrite sensor, and a mechanism for nitrite detection was proposed based on the experimental findings. The SMP (polyFe) was synthesized using a symmetrical ligand containing terpyridine moieties [4′,4′′′′-(1,4- Phenylene) bis(2,2′:6′,2′′-terpyridine)] and ferrous acetate. Various analytical methods, such as ultraviolet/visible (UV/Vis) titration, field-emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and energy dispersive X-ray spectroscopy (EDS), were used to characterize polyFe. The molecular weight of polyFe was calculated from the intrinsic viscosity measurement using the Mark-Houwink-Sakurada equation. The electrochemical behavior of the fabricated sensor was investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The variation in scan rate from CV was used to investigate the kinetics of nitrite oxidation. A possible reaction mechanism was proposed based on the kinetic studies. The proposed sensor showed a good linear range of 2.49 μM to 1.23 mM and a limit of detection of 0.17 μM. Stability, interference, and reproducibility of the proposed sensor were also investigated. The CV technique was used to demonstrate the applicability of the nitrite sensor for real sample analysis. A satisfactory recovery with a low relative standard deviation was achieved.

Elucidating the Roles of Distinct Chemical Factors in the Hydrolytic Activities of Hetero- and Homonuclear Synthetic Analogues of Binuclear Metalloenzymes

In this study, hydrolytic activities of hetero- and homobinuclear metallovariants of an asymmetric (I) or symmetric (II) ligand with the FeIII-ZnII, ZnII-ZnII, and CuII-CuII cores (i.e., IFZ, IZZ, and ICC or IIFZ, IIZZ, and IICC, respectively) are investigated using DFT calculations through four distinct mechanisms: dissociative (DA), substrate-assisted (SA), water-assisted (WA), and associative (AS). Additionally, the effects of different nucleophiles (μ-OH, terminal-OH, and -O2H3), coordination numbers, para substituents (-CH3, -Cl, and -NO2) of the linker, and an external electric field on the energetics of these reactions are computed. The geometries, spin ground states, and substrate binding modes of the three metal centers for both asymmetric (I) and symmetric (II) ligands differ from each other. There is no Lewis acid activation of the bis(2,4-dinitrophenyl) phosphate (BDNPP) substrate, and hydrolysis is predominantly controlled by the nucleophilicity of the metal-bound hydroxyl ion. The electronic nature of the metal ions determines the activities of their complexes, and the homobinuclear IZZ is found to be the most active complex. However, complexes formed with ligand I are not more active than their ligand-II-containing counterparts for all metal ions. The DFT calculations suggest that the DA pathway is the energetically most feasible among the four pathways. The terminal hydroxyl group is the strongest nucleophile, and the electron-donating -CH3 group is the most suitable para substituent in the linker. Whereas the introduction of an external electric field along the reaction axis lowers the barrier for IFZ, it leaves that unchanged for IZZ and increases that for ICC. These combined results in this study highlight the influence of distinct critical chemical factors such as the electronic nature of the metal ions, the ligand environment, as well as the linker and nucleophile on phosphoester hydrolysis. Insights gained will guide the design of the next generation of versatile metal complexes for a wide range of reactions and applications.

Crossing the ortho-hurdle: Ionic stereocontrol enables atroposelective Suzuki-Miyaura coupling

Atropisomerism—a unique stereochemical phenomena arising from a rotationally restricted single bond—is ubiquitous in natural products, functional materials, and pharmaceuticals. As a direct approach to atropoenantiomers of biaryls, catalyst-controlled asymmetric cross-coupling relies exclusively on differentiation between substrates’ ortho-substituents. Here, we describe the development of ionic interaction-directed atroposelective Suzuki-Miyaura coupling. Unprecedented stereocontrol is attainable through catalyst-substrate interactions at not only the ortho- but also the meta-positions. In particular, our study surmounts a formidable hurdle of decoupling the asymmetric induction from the intrinsic influence of proximal ortho-groups and demonstrates that high atroposelectivity is achievable by engaging distal meta-substituents as the dominant stereocontrol elements. The general adaptability of the new ionic catalyst system is attributable to the unconventional approach that engages strong electrostatic steering of substrates by a sterically symmetrical ligand, which could serve as the design principle of novel catalysts to unleash the vast potential of ionic interactions in catalysis.

Effect of remote substituents and coordination anions on the magnetic properties of Co(ii) dimer complexes

Four related dinuclear Co(ii) complexes based on symmetric Schiff base ligands were synthesized and characterized. Magnetic studies indicate that remote substituents of the ligands and the coordination anions have no significant effect.

Synthesis and structures of homoleptic germylenes and stannylenes with sulfonimidamide ligands.

An unusual series of germylenes and stannylenes with homoleptic symmetric and unsymmetric N-substituted sulfonimidamide ligands PhSO(NiPr)(NHiPr) 1 and PhSO(NMes)(NHiPr) 2 have been prepared by protonolysis reaction of Lappert's metallylenes [M(HMDS)2] (M = Ge or Sn) with two equivalents of the appropriate sulfonimidamide. The homoleptic germylenes [PhSO(NiPr)2]2Ge 3 and [PhSO(NMes)(NiPr)]2Ge 4, and stannylenes [PhSO(NiPr)2]2Sn 5 and [PhSO(NMes)(NiPr)]2Sn 6 were fully characterized by NMR spectroscopy and by X-ray diffraction analysis. DFT calculations have been performed to understand the electronic properties brought by the sulfonimidamide ligand.