Ligands L1 Research Articles

Development of Immobilized Carreira (Phosphoramidite, Olefin) Ligands and Application in Iridium-Catalyzed Asymmetric Allylic Amination

A family of polystyrene-supported (phosphoramidite, olefin) ligands L1-L4, based on the original design by Defieber and Carreira, has been developed and applied in iridium-catalyzed asymmetric allylic amination of unmasked allylic alcohols (27 examples, up to 99% ee). Among them, functional resins L1 and L4 exhibit important advantages such as easy preparation, ligand recyclability, and easy handling for sequential use. As a distinctive advantage, the catalytic use of the iridium complexes of L1 and L4 allows the straightforward reuse of a high percentage of the expensive iridium metal involved in the complexes, which is not achievable under homogeneous conditions with the corresponding monomeric complexes.

Spin Crossover Behavior of FeII Complexes Bridged by Thiophene‐Functionalized Triazole Ligands with Different Sizes and Rigidities

AbstractFour thiophene functionalized triazole ligands (L1=4‐(thenyl)‐1,2,4‐triazole, L2=4‐(thiophene ethyl)‐1,2,4‐triazole, L3=N‐Thiophenylidene‐4H‐1,2,4‐triazole‐4‐amine, and L4=(4‐[(E)‐2‐(5‐sulfothiophene)vinyl]‐1,2,4‐triazole) were synthesized. These ligands have different lengths and rigidities, while ligand L4 has a sulfonic acid group that can form a hydrogen bond. Five 1D FeII chain complexes were synthesized: [Fe(L1)3](X)2 ⋅ nH2O [X=BF4−, n=1.5 (C1); X=ClO4−, n=1 (C2)], [Fe(L2)3](BF4)2 ⋅ 1.5H2O (C3); [Fe(L3)3](X)2 ⋅ nH2O [X=BF4−, n=2 (C4); X=ClO4−, n=2.5 (C5)]. The results of temperature‐dependent magnetic susceptibility reveal that complexes C1, C2, and C3 experienced the transition between two spin states. And C4 and C5 maintain high spin states at all temperature ranges. Binuclear complex [Fe2(L3)5(SCN)4] (C6) and mononuclear material [Fe(L4)2(H2O)4] ⋅ 2H2O (C7), these two zero‐dimensional molecules were also synthesized. They all display weak antiferromagnetic exchange coupling and a high spin state in the whole process.

N-Heterocyclic Carbene-Supported Nickel-Catalyzed Selective (Un)Symmetrical N-Alkylation of Aromatic Diamines with Alcohols

The "borrowing hydrogen" (BH) approach for the N-alkylation of phenylenediamines using alcohols as coupling partners is highly challenging due to the selectivity issue of the generated products. Furthermore, the development of base-metal systems that can potentially substitute precious metals with competitive activity is a major challenge in BH catalysis. We present herein an efficient protocol for the N,N'-di-alkylation of aromatic diamines using an in situ-generated Ni-NHC complex from NiCl2 and the ligand L1, which gave access to a wide range of N,N'-di-alkylated orthophenylene diamines (rather than the generally observed benzimidazole derivatives), meta- and para-phenylene diamines along with 2,6-diamino pyridine derivatives in good to excellent yields. Moreover, the catalyst system was also successful in the derivatization of a clinically important drug molecule, Dapsone. Notably, the present protocol could be applied effectively to synthesize unsymmetrically substituted N,N'-di-alkylated diamines via sequential alkylation and is the first report in the base-metal system to the best of our knowledge. Diverse control experiments including the deuterium incorporation studies suggest that the present protocol proceeds via a BH sequence.

Synthesis and Characterization of Chiral Iridium Complexes Bearing Carbohydrate Functionalized Pyridincarboxamide Ligands and Their Application as Catalysts in the Asymmetric Transfer Hydrogenation of α-Ketoacids in Water

[Cp*IrLnCl] complexes [L1 = (methyl-β-d-glucopyranosid-2-yl)picolinamide, 1; L2 = (methyl-3,4,6-tri-O-acetyl-β-d-glucopyranosid-2-yl)picolinamide, 2; L3 = (2,3,4,6-tetra-O-acetyl-β-d-glucopyranosid-1-yl)picolinamide, 3] have been synthesized and completely characterized in solution, by 1D- and 2D-NMR spectroscopy, and in the solid state, by X-ray single crystal diffractometry. Despite the chirality of the Ln-moiety and metal, a single diastereoisomer is observed for L1 (1) and L2 (2) having a (R)-iridium configuration: the pyranose moiety is oriented in a way to minimize the interactions of the axial protons, vicinal to the amide moiety, and Cp*, with the OMe-group pointing toward the Cp*-ligand and away from Ir–Cl. Such a diastereoisomer is also favored by the establishment of an O–H···Cl–Ir hydrogen bond (2.356 Å) and by the minimization of the steric repulsion between one acetyl moiety of L2 and Cp* and picolinamide ligands in 1 and 2, respectively. DFT calculations computed a stabilization by more than 5.9 and 3.1 kcal/mol of this diastereoisomer with respect to other possible ones. Two interconverting diastereoisomers with different chirality at iridium are instead observed in solution for complex 3 in which −CH2OAc [3a, 63%, (R)] and −OAc [3b, 37%, (S)] moieties, respectively, are oriented toward Cp* and N-arm of picolinamide ligands. Consistently, DFT calculations indicate that 3a and 3b have a comparable stability (ΔE = 1.2 kcal/mol). Complexes 1–3 catalyze the asymmetric transfer hydrogenation of RC(O)C(O)OH to RCH(OH)C(O)OH [R = Ph (PGA), CH2Ph (PPA), CH2(4-OH)C6H4 (HPPA)], using both HCOOH and H3PO3 as hydrogen donor, in water at pH 7 (by phosphate buffer), with excellent chemoselectivity and efficiency (conversion >99%) and moderate to good enantioselectivity (30–70% ee). Utilizing catalyst 3 instead of 2, bearing the pseudoenantiomeric L3 of L2 ligand, causes a reduction of the percentage of the major enantiomer (R) with PGA and an inversion of stereoselectivity from (R) to (S) with PPA and HPPA substrates.

Assessing the role of membrane lipids in the action of ruthenium(III) anticancer compounds.

This work addresses the possible role of the cell membrane in the molecular mechanism of action of two salan-type ruthenium complexes that were previously shown to be active against human tumor cells, namely [Ru(III)(L1)(PPh3)Cl] and [Ru(III)(L2)(PPh3)Cl] (where L1 is 6,6'-(1R,2R)-cyclohexane-1,2-diylbis(azanediyl)bis(methylene)bis(3-methoxyphenol); and L2 is 2,2'-(1R,2R)-cyclohexane-1,2-diylbis(azanediyl)bis(methylene)bis(4-methoxyphenol)). One-component membrane models were first used, a disordered fluid bilayer of dioleoylphosphatodylcholine (DOPC), and an ordered rigid gel bilayer of dipalmitoylphosphatidylcholine. In addition, two quaternary mixtures of phosphatidylcholine, phosphatidylethanolamine, sphingomyelin and cholesterol were used to mimic the lipid composition either of mammalian plasma membrane (1:1:1:1mol ratio) or of a cancer cell line membrane (36.2:23.6:6.8:33.4mol ratio). The results show that both salan ligands L1 and L2 bind relatively strongly to DOPC bilayers, but without significantly affecting their structure. The ruthenium complexes have moderate affinity for DOPC. However, their impact on the membranes was notable, leading to a significant increase in the permeability of the lipid vesicles. None of the compounds compromised liposome integrity, as revealed by dynamic light scattering. Fluorescence spectroscopy studies revealed changes in the biophysical properties of all membrane models analyzed in the presence of the two complexes, which promoted an increased fluidity and water penetration into the lipid bilayer in the one-component systems. In the quaternary mixtures, one of the complexes had an analogous effect (increasing water penetration), whereas the other complex reorganized the liquid ordered and liquid disordered domains. Thus, small structural differences in the metal ligands may lead to different outcomes. To better understand the effect of these complexes in cancer cells, the membrane dipole potential was also measured. For both Ru complexes, an increase in the dipole potential was observed for the cancer cell membrane model, while no alteration was detected on the non-cancer plasma membrane model. Our results show that the action of the Ru(III) complexes tested involves changes in the biophysical properties of the plasma membrane, and that it also depends on membrane lipid composition, which is frequently altered in cancer cells when compared to their normal counterparts.

Preorganized Polyaromatic Soft Terdentate Hosts for the Capture of [Ln(β-diketonate)3 ] Guests in Solution.

The concept of preorganization is famous in coordination chemistry for having transformed flexible bidentate 2,2'-bipyridine scaffolds into rigid 1,10-phenanthroline platforms. The resulting boosted affinities for d-block cations has successfully paved the way for the design of a wealth of functional complexes, devices and materials for analysis and optics. Its extension toward terdentate homologues adapted for the selective complexation of f-block cations with larger coordination numbers remains more overlooked. The resulting rigidification of 2,6-bis(1-methyl-1H-benzo[d]imidazol-2-yl)pyridine ligands (L1-L7) produces the highly preorganized and extended polyaromatic benzo[4',5']imidazo[1',2' : 1,2]pyrido[3,4-b]benzo[4,5]imidazo[1,2-h][1,7]naphthyridines (L8-L11) receptors, which offer some novel and rare opportunities for efficiently complexing trivalent lanthanides with polyaromatic soft terimine ligands. The crystal structures of the stable heteroleptic [LkLn(hfac)3 ] adducts (Lk=L1, L8, L9; Ln=La, Eu, Gd, Er, Yb, Y; H-hfac=1,1,1,5,5,5-hexafluoropentane-2,4-dione) show a drastic decrease in the Ln-N bond valences upon replacement of the flexible ligand L1 with its preorganized counterparts L8 and L9. This points to a limited match between the preorganized cavity and the entering [Ln(hfac)3 ] lanthanide containers. However, thermodynamic studies conducted in dichloromethane reach the opposite conclusion, with an improved affinity, by up to three orders of magnitude for catching Ln(hfac)3 when L1 is replaced by the preorganized L8-L9 receptors. The key to the enigma lies in the removal of the energy penalty which accompanies the formation of flexible [L1Ln(hfac)3 ] complexes in solution. This driving force overcomes the poor match between the preorganized terdentate N∩ N∩ N cavity in L8 and L9 and the size of trivalent lanthanides. As planned, the rigid, planar and extended π-conjugated system found in L8 and L9 shifts the ligand-centered absorption bands by about 5000 cm-1 toward lower energies, a crucial point if these stable [L8Ln(hfac)3 ] and [L9Ln(hfac)3 ] platforms have to be considered for the visible sensitization of luminescent lanthanides in metallopolymers.

Synthesis and reactivity of a uranium(iv) complex supported by a monoanionic nitrogen–phosphorus ligand

A monoanionic N–P ligand L3 with a pendant dimethylamino group was designed. Species with multiple U–C bonds—a rare example of a metallafluorene containing an actinide element—and clusters with multiple U–M bonds were isolated.

Solvatochromic behaviour of cyclic dithioether-functionalized triphenylamine ligands and their mechano-responsive Cu(I) coordination polymers.

Cu(I)-based coordination polymers (CPs) are known as efficient emissive materials providing an eco-friendly and cost-effective platform for the development of various functional materials and sensors. In addition to the nature of the metal center, organic ligands also play a crucial role in controlling the emissive properties of coordination polymers. Herein, we report on the synthesis of dithiane- and dithiolane-substituted triphenylamine ligands L1 and L2. These ligands were found to be emissive both in the solid state and in solution. In addition, these ligands exhibit solvatochromic behaviour due to the twisted intramolecular charge transfer (TICT) phenomenon. Next, coordination behaviour of these ligands was explored with Cu(I)X salts (X = Br and Cl) and four new 1D coordination polymers [{Cu(μ2-X)2Cu}(μ2-L)]n, CP1 (X = Br, L = L1), CP2 (X = Cl, L = L1), CP3 (X = Br, L = L2), and CP4 (X = Cl, L = L2) were synthesized and crystallographically characterized. The emission behaviour of all the CPs suggests ligand-centered transitions. On mechanical grinding, emission maxima (λem) for CP1 and CP2 were blue-shifted, whereas for CP3 and CP4 red-shifts were observed. All CPs were found to emit at 448 nm with increased intensity after grinding. It is supposed that grinding is responsible for a change in the spatial arrangement (dihedral angles) of the phenyl groups of triphenylamine, causing the observed emission shifts. Furthermore, the higher emission intensity after grinding suggests the occurrence of a similar phenomenon as an aggregation-induced quenching in these CPs.

Synthesis, DNA binding and biological evaluation of benzimidazole Schiff base ligands and their metal(ii) complexes.

Two novel benzimidazole ligands (E)-2-((4-(1H-benzo[d]imidazole-2-yl)phenylimino)methyl)-6-bromo-4-chlorophenol (L1) and (E)-1-((4-(1H-benzo[d]imidazole-2-yl)phenylimino)methyl)naphthalene-2-ol (L2) with their corresponding Cu(ii), Ni(ii), Pd(ii) and Zn(ii) complexes were designed and synthesized. The compounds were characterized by elemental, IR, and NMR (1H & 13C) spectral analyses. Molecular masses were determined by ESI-mass spectrometry, and the structure of ligand L1 was confirmed by single crystal X-ray diffraction analysis. Molecular docking was carried out for the theoretical investigation of DNA binding interactions. The results obtained were verified experimentally by UV/Visible absorption spectroscopy in conjunction with DNA thermal denaturation studies. It was observed that ligands (L1 and L2) and complexes (1-8) were moderate to strong DNA binders, as evident from the binding constants (K b). The value was found to be highest for complex 2 (3.27 × 105 M-1) and lowest for 5 (6.40 × 103 M-1). A cell line study revealed that breast cancer cells were less viable to the synthesized compounds compared to that of standard drugs, cisplatin and doxorubicin, at the same concentration. The compounds were also screened for in vitro antibacterial activity for which complex 2 showed a promising broad-spectrum effect against all tested strains of bacteria, almost in the proximity of the reference drug kanamycin, while the rest of the compounds displayed activity against selected strains.

Impact of the central atom and halido ligand on the structure, antiproliferative activity and selectivity of half-sandwich Ru(II) and Ir(III) complexes with a 1,3,4-thiadiazole-based ligand.

Half-sandwich complexes [Ru(η6-pcym)(L1)X]PF6 (1, 3) and [Ir(η5-Cp*)(L1)X]PF6 (2, 4) featuring a thiadiazole-based ligand L1 (2-(furan-2-yl)-5-(pyridin-2-yl)-1,3,4-thiadiazole) were synthesized and characterized by varied analytical methods, including single-crystal X-ray diffraction (X = Cl or I, pcym = p-cymene, Cp* = pentamethylcyclopentadienyl). The structures of the molecules were analysed and interpreted using computational methods such as Density Functional Theory (DFT) and Quantum Theory of Atoms in Molecules (QT-AIM). A 1H NMR spectroscopy study showed that complexes 1-3 exhibited hydrolytic stability while 4 underwent partial iodido/chlorido ligand exchange in phosphate-buffered saline. Moreover, 1-4 demonstrated the ability to oxidize NADH (reduced nicotinamide adenine dinucleotide) to NAD+ with Ir(III) complexes 2 and 4 displaying higher catalytic activity compared to their Ru(II) analogues. None of the complexes interacted with reduced glutathione (GSH). Additionally, 1-4 exhibited greater lipophilicity than cisplatin. In vitro biological analyses were performed in healthy cell lines (CCD-18Co colon and CCD-1072Sk foreskin fibroblasts) as well as in cisplatin-sensitive (A2780) and -resistant (A2780cis) ovarian cancer cell lines. The results indicated that Ir(III) complexes 2 and 4 had no effect on human fibroblasts, demonstrating their selectivity. In contrast, complexes 1 and 4 exhibited moderate inhibitory effects on the metabolic and proliferation activities of the cancer cells tested (selectivity index SI > 3.4 for 4 and 2.6 for cisplatin; SI = IC50(A2780)/IC50(CCD-18Co)), including the cisplatin-resistant cancer cell line. Based on these findings, it is possible to emphasize that mainly complex 4 could represent a further step in the development of selective and highly effective anticancer agents, particularly against resistant tumour types.

Synthesis and photophysical properties of rare earth (La, Nd, Gd, Y, Ho) complexes with silanediamido ligands bearing a chelating phenylbenzothiazole chromophore

A new silanediamine ligand L2− bearing planar Ph-benzothiazole groups gives complexes [LnL2]− with larger Ln cations (La, Nd, Gd, Y), and [HoLCl2Li(thf)2]. Their luminescence was investigated, and the triplet state energy of the ligand was estimated.

A lanthanide luminescent sensor for the detection of 4-nitrophenol in aqueous media.

The development of facile luminescent sensors for detecting nitrophenols in aqueous media is of great necessity for the safety of the environment and human health, as they are a class of widespread toxic organic pollutants that cause serious adverse effects upon consumption. Based on a new multidentate asymmetric ligand (H2L) in which salicylamide and 4-nitryl-salicylaldimine are spaced by 1,2-bis(2-ethoxy)ethyl, a new hydrostable lanthanide intercycle, [Tb2L2(NO3)2]·CH3CN (Tb-[2]c), was prepared to act as a new luminescent sensor for 4-NP in water media. Structural analysis indicated that two fully deprotonated L2- ligands in cis-configuration and μ2-L-κ2O1:κO2:κO4:κN2:κO5 coordination mode were interlocked by two TbIII ions to render the emitted TbIII encapsulated by L2- for lessening non-radiative transitions. The excellent sensitizing capability of the ligand L2- to TbIII was ascertained by both experimental methods and theoretical calculations. The sensing exploration indicated that Tb-[2]c exhibited highly sensitive and selective recognition of 4-NP against other nitroaromatics in aqueous media. The recognition mechanism could be attributed to the internal filtration effect (IFE) mechanism when DFT calculations and accumulating experimental evidence were combined.

Zinc(II) and copper(II) complexes with N-substituted imines derived from 4-amino-1,2,4-triazole: Synthesis, crystal structure, and biological activity

Reactions of copper(II) and zinc(II) acetates with polynitrogen Schiff bases, namely 4-(pyridin-2-yl)methyleneamino-1,2,4-triazole (L1), 4-(pyridin-3-yl)methyleneamino-1,2,4-triazole (L2) and 4-(pyridin-4-yl)methyleneamino-1,2,4-triazole (L3), were studied. The reaction of Zn(OAc)2·2H2O and L1 gave crystals of trinuclear complex [Zn3(OAc)6(L1)2] (1). A similar reaction of Zn(OAc)2·2H2O and L2 resulted in 1D coordination polymer [Zn(OAc)2(L2)]n (2). The reactions of Cu(OAc)2·H2O with L2 or L3 gave crystals of 1D coordination polymer {[Cu2(OAc)4(L2)]·2MeCN}n (3) and binuclear complex [Cu2(OAc)2(L3)2]·2MeCN (4), respectively. The structures of the coordination compounds thus obtained were determined by single-crystal X-ray diffraction analysis. Complexes 1–4 demonstrated better antibacterial and antifungal activities in comparison with free L1, L2, and L3 ligands: the strongest antimicrobial activity was observed against E. coli for 2 and 3, and the highest antifungal activity was found for 1 and 2.

Mechanism of formic acid dehydrogenation catalysed by Cp*Co(III) and Cp*Rh(III) complexes with N,N’-bidentate imidazoline-based ligands: A DFT exploration

Homogenous formic acid dehydrogenation (FAD) is largely accomplished with the aid of Ir and Rh based catalysts. The use of earth-abundant transition-metal based catalysts for FAD are rather scarcely reported. This work computationally explores the mechanistic aspects of FAD catalysed by Cp*Co(III) and Cp*Rh(III) -based catalysts with pyridyl-imidazoline (L1) and 2,2’-biimidazoline (L2) ligand architectures. The computed free energy profiles substantiate that the β-hydride elimination is the slowest step in the FAD process. Further mechanistic analysis revealed that H3O+ is the energetically favoured proton source compared to formic acid (FA) for generating H2. NBO analysis signified that the proton from H3O+ ion is relatively more electrophilic than FA and that the metal-hydride bond in the transition state is more negatively charged in the transition state involving H3O+ ion. These factors make the protonation process easier and decreases the barrier for hydronium ion mediated protonation process. All the four designed catalysts were found to possess a moderate range of computed activation barrier (13.5 kcal/mol to 16.2 kcal/mol) at the rate-determining step which are comparable with their corresponding iridium analogues reported in the earlier studies. The Co and Rh catalysts designed in the present work with L1 ligand system were found to be relatively better candidates than L2. Particularly, the Co catalysts and the mechanistic details derived there in would help in the development of efficient earth-abundant transition metal-based catalysts for FAD.

Anticancer and antimicrobial activity of new copper (II) complexes

In this study, three new organic ligands N′-(benzylidene)-6-chloropyrazine-2-carbohydrazonamide (L1), 6-chloro-N′-(4-nitrobenzylidene)picolinohydrazonamide(L2), and N′-(benzylidene)-4-chloropicolinohydrazonamide (L3) and three copper coordination compounds (Cu(L1)Cl2, Cu(L2)Cl2 and Cu(L3)Cl2) based on them were synthesized. All obtained compounds were characterized using appropriate analytical techniques: elemental analysis (EA), thermogravimetric analysis (TG–DTG), Fourier transform infrared spectroscopy (FTIR) and flame-atomic absorption spectrometry (F-AAS). These methods of physicochemical analyses helped to assume that the complexation in three cases proceeds in a bidentate manner. The X-ray investigation confirmed the synthesis pathway and molecular structures for L1 and L3 ligands. The antimicrobial activity of the obtained compounds was then comprehensively investigated, where Cu(L3)Cl2 showed the strongest antibacterial properties against all tested bacteria (Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli). LN229 human glioma cells and BJ human normal fibroblasts cells were treated with tested compounds and their cytotoxicity was evaluated with MTT test. The effect of complexing on antitumor activity has been investigated. The ligand L1 and its complex showed similar activity against normal cells while complexation increases toxicity against cancer cells in concentrations of 50 and 100 μM. For the one pair of ligand/complex compounds the apoptosis detection, cell cycle analysis and gene expression analysis (qRT-PCR) were performed. Cu(L1)Cl2 showed the stronger toxic effect in comparison with L1 due to the population of early apoptotic cells which revealed metabolic activity in MTT assay.

Synthesis of Functionalized Heteroleptic Germylene Alkoxides

AbstractN‐coordinated Ge(II) alkoxides L1(tBuO)Ge (1), L2(tBuO)Ge (2) and [L2(OtBu)Ge ⋅ BH3] (4) were prepared. Effect of either chelating ligands L1 and L2 or Ge→B interaction on strength of the Ge−OtBu bond was studied by insertion reaction of PhNCO. As a result, the Ge(II) carbamate L2{[(tBuO)OC](Ph)N}Ge (3) was isolated. Alcoholysis exchange reactions of 1 and 2 with substituted phenols were studied to find an easy synthetic protocol for a synthesis of functionalized Ge(II) alkoxides. Reactions yielded Ge(II) alkoxides L1,2(2‐Br−C6H4O)Ge (5 for L1, 8 for L2), L1,2(2‐MeNH−C6H4O)Ge (6 for L1, 9 for L2), L1,2(2‐Ph2P−C6H4O)Ge (7 for L1, 10 for L2), L2(2‐Br‐3‐OH−C6H3O)Ge (11) and L2(2‐NC5H4O)Ge (12) containing the additional polar groups Y (Y=Br, MeNH, PPh2, OH or N). Finally, phosphane decorated Ge(II) alkoxides 7 and 10 were tested as suitable ligands in reactions with (COD)W(CO)4 and BH3. As a consequence, new complexes [(κ2‐7)W(CO)4] (13) and [L1(2‐Ph2P ⋅ {BH3}‐C6H4O)Ge ⋅ {BH3}] (14) were isolated. All compounds were characterized by NMR and IR spectroscopy, and compounds 3, 4, 9 and 11 were additionally characterized by X‐ray diffraction analysis.

Synthesis and crystal structures of copper complexes with N,N,N-tridentate chelating ligands containing o-phenanthroline-appended benz-fused polyazoles and their catalytic application in A3 coupling reaction

Design of two new N-enriched N,N,N-tridentate chelating ligands comprising of benz-fused polyazole-based heterocyclic scaffolds in combination with 1,10-phenanthroline motif, has been presented in this work for exploring their Cu-complexes as structurally well-defined precatalysts for A3 coupling reactions. With the two different tridentate N-donor ligands L1 and L2, two monomeric Cu(II) complexes, [Cu(L1)2(OClO3)][ClO4] (Cu-1) and [Cu(L2)(OClO3)(OH2)2][ClO4] (Cu-2) have been synthesized in good yield and characterized well with spectroscopic and crystallographic techniques. In spite of similar type of ligands, structures of the complexes are quite different which can be attributed to the electronic effect of the ligands. Crystal structure of Cu-1 reveals that the central copper ion is in octahedral geometry where one ligand is ligated in tridentate mode and the other is coordinated in a bidentate mode. In case of complex Cu-2, it is observed that only one ligand has been coordinated in tridentate mode. The N-heterocyclic backbone possesses key electronic properties such as good π-accepting/σ-donating property, and efficient charge sinks due to the presence of the extended π-conjugation, Accordingly, both the complexes have been found to be efficient precatalysts in A3 coupling of aldehydes, amines, and alkynes for the synthesis of propargylamines.

Ni(II), Co(II), Fe(III), and Zn(II) mixed ligand complexes of indoline-dione and naphthalene-dione: Synthesis, characterization, thermal, antimicrobial, and molecular modeling studies

New mixed ligand complexes with metal ions (Ni(II), Co(II), Zn(II), and Fe(III)) of the type [ML1L2] (where L1 = indoline-2,3-dione and L2 = naphthalene-1,2-dione) were synthesized and characterized using elemental analyses, molar conductivity, spectroscopic (IR, UV–visible, diffused reflectance), magnetic moment, and thermal studies. Mass spectra for [Co(L1L2)(H2O)2]Cl2, [Ni(L1L2)(H2O)2]Cl2, [Fe(L1L2) (H2O)2]Cl3 and [Zn(L1L2)(H2O)2]Cl2 complexes were studied. The IR spectral data revealed that L1 and L2 ligands behaved as neutral bidentate ligands with OO donation sites (indoline O and naphthalene-dione O for L1 and L2). An octahedral geometry for the complexes was proposed based on spectroscopic data. The thermogravimetric study was used to look into the metal complexes temperature stability and deterioration. The Co(II), Zn(II), Ni(II), and Fe(III) complexes' SEM and XRD spectra were also obtained. Theoretical investigation of Zn(II) complex was performed with the DFT-B3LYP computational method. DFT calculations better understand molecular mechanisms that could not be elucidated experimentally where the energy gaps and other key theoretical parameters were calculated. The vina dock mechanisms and affinities of Zn(II) complexes for E. coli (PDB ID: 3 t88), S. aureus (PDB ID: 3ty7), B. subtilis (PDB ID: 5 h67), and P. aeruginosa (PDB ID: 5i39) receptors were also investigated. The mixed ligand complexes were evaluated for antibacterial efficacy against two species of Gram-positive and Gram-negative bacteria and fungi. All the complexes inferred antimicrobials activity against the studied organisms which make them promising drugs.

Purine-based Schiff base Co(II), Cu(II), and Zn(II) complexes: Synthesis, characterization, DFT calculations, DNA binding study, and molecular docking

A series of metal complexes of Co(II), Zn(II), and Cu(II) of purine base Schiff base ligand L1 6,6′-((1E,1′E)-((7H-purine-2,6-diyl)bis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol) and L2 3,3′-((1E,1′E)-((7H-purine-2,6-diyl)bis(azanylylidene))bis (methanylylidene))bis(4H-chromen-4-one) were synthesized. The characterization of synthesized compounds was investigated through elemental analysis, UV–vis, FT-IR, NMR, and mass spectrometry. The spectroscopic and DFT studies validate the coordination of ligand to the metal centers along with their structural details. In complexes of L1 and L2, the N and O atoms coordinate to metal centers of zinc, cobalt, and copper. However, in the case of L1 complexes the binding mode of oxygen is through phenolic –OH of vanillin moiety. In contrast, complexes of L2 the binding mode of oxygen source is carbonyl oxygen of chromone carboxaldehyde moiety. The stability order follow- ZnL1 < CoL1 < CuL1 < CuL2 < CoL2 < ZnL2. The CT-DNA binding activity of all synthesized complexes with the help of UV–vis absorption titration, fluorescence titration, and viscosity measurement was studied. In both cases, cobalt complexes of L1 and L2 showed high DNA binding activity. The binding constant values are in the order of 105 via intercalation mode of binding. The molecular docking study was performed to speculate on the active binding site between metal complexes and CT-DNA.

A new potential ONO Schiff-Base ligand and its Cu(II), Zn(II) and Cd(II) Complexes: Synthesis, structural Elucidation, theoretical and bioactivity studies

• Cu(II), Zn(II), and Cd(II) complexes of a new ONO donor Schiff base ligand were synthesized. • Single-Crystal XRD data of ligand L1 showed that ligand is in zwitterionic form. • Interaction with calf thymus DNA (CT-DNA) was studied for all the synthesized compounds. • The in-vitro Antibacterial study was performed for all the compounds. • Molecular docking experiment was also carried out. A series of Cu(II), Zn(II), and Cd(II) complexes coordinated with a new Schiff base ligand (L1) were synthesized. The ligand L1 constituting of ONO donor site was synthesized by the condensation of 5-bromo-3-methoxysalicylaldehyde and 3-aminobenzoic acid and characterized by various analytical and spectroscopic methods. SCXRD data confirmed that the ligand exists as zwitterion possessing E-configuration along the C=N bond. The optimization of ligand and complexes were performed using DFT method. The geometry of the Cu(II) complex was acquired to be distorted square planar, whereas Zn(II) and Cd(II) complexes were obtained to be distorted tetrahedral. The DNA binding study was examined for all the synthesized compounds through electronic absorption titration method. The results suggested that ligand exhibited more DNA binding ability which follows the order: CuL1<ZnL1<CdL1<L1. The in-vitro antibacterial study was also performed by employing the micro-broth dilution technique. The result showed that Cd(II) complex depicts better antibacterial properties, in comparison to others. The calculation by TD-DFT was carried out to validate the experimental result of UV-Vis spectra with the simulated one. Moreover, molecular docking simulation was also done to confirm the experimental results as well as to better understand the binding mode and nature of compounds with CT-DNA.