Ligands L1 Research Articles

Octadentate Bispidine Chelators for Tb(III) Complexation: Pyridine Carboxylate versus Pyridine Phosphonate Donors.

With their rigid and preorganized skeleton, bispidine (3,7-diazabicyclo[3.3.1]nonane) chelators are very appealing for the preparation of metal complexes with high kinetic inertness. With the aim to develop new Tb(III)-based medical imaging probes, this study describes the synthesis and physicochemical properties of two novel terbium(III) complexes with octadentate bispidine-based ligands substituted with either pyridine-phosphonate (H6L1) or picolinate (H4L2) subunits. Thermodynamic stability constants of the corresponding Tb(III) complexes have been determined by potentiometric, UV-visible absorption spectrophotometric and spectrofluorimetric methods. Despite their apparent similarity, these two octadentate ligands differ in their most stable conformation: chair-chair conformation for H4L2 and boat-chair conformation for H6L1, as confirmed by 1H NMR studies and suggested by physicochemical investigations. This conformational change induces different protonation schemes for the two ligands. The kinetic inertness of the Tb complexes has been studied in various media and assessed by transmetalation and transchelation experiments. In particular, Tb(L2) displayed a remarkable kinetic inertness with no measurable dissociation over two months in mouse serum at 10-5 M concentration. The complex was also very inert in the presence of a 50-fold excess of Zn(II) in H2O at pH = 7.4 (7% of dissociation over two months). The complexes with ligand L1 are significantly less inert, emphasizing the influence of the ligand conformation on the kinetic inertness of the Ln(III) complexes. Finally, the luminescence properties of the isolated complexes have also been investigated. A bright green luminescence was observed, especially for Tb(L2), which displays a high quantum yield value of 50% in H2O (60% in D2O; λexc = 263 nm). In addition, luminescence lifetimes of 1.9(2) and 1.7(2) ms have been measured for Tb(L1) and Tb(L2), respectively, hence confirming the formation of nona-coordinated complexes with one inner-sphere water molecule. These data on a bispidine scaffold pave the way for developing bright, inert luminescent probes for bioimaging and for radiolabeling applications with Tb(III) radioisotopes.

RECo-containing metal-organic frameworks based on 3-hydroxyisonicotinic acid: Proton conduction and magnetism

Three heterometallic metal-organic frameworks, namely, {RE2Co3L6(H2O)6}n (RE = Gd (1), Dy (2), Y(3)), have been hydrothermally synthesized based on rare-earth (RE) and transition metal ions and the organic ligand of 3-hydroxyisonicotinic acid (H2L). Single-crystal X-ray diffraction reveals that compounds 1‒3 are isomorphic and features three-dimensional (3D) porous structure. In compound 1, the Gd3+ ion is located in the C3 axis, and every two propeller-like {GdCo3} units are capped up and down to a {Gd6Co6} ring through twelve L2‒ ligands, giving rise to the formation of the cavities. Notably, three compounds display high thermal stability determined by thermogravimetric analysis (TGA), and good water stability proved by the well-matched of PXRD curves before and after soaked three samples in water for three days. AC impedance measurements exhibit the proton conductivities of compounds 1‒3 with powder samples are distinctly temperature and humidity dependent, and the values can reach 3.38×10‒5, 1.91×10‒5, and 2.23×10‒5 S cm‒1 at 98% RH and 338 K, respectively. Moreover, compounds 1‒3 display antiferromagnetic behaviours, and the magnetocaloric effect (MCE) study indicates that the entropy change (−ΔSm) of compound 1 is 7.1 J kg−1 K−1 at 7 K and 7 T. Compound 2 exhibits the slow magnetic relaxation behaviour.

Synthesis and Characterization of Cobalt (II) And Zinc (II) Complexes with Diphenylcarbazone and Dimethylsulfoxide: Exploring Antifungal Properties

This study investigates the synthesis of cobalt (II) and zinc (II) complexes with ligands L1 (diphenylcarbazone) and L2 (dimethylsulfoxide), specifically [CoL2(H2O)2]2H2O, [CoL2L1(H2O)2], [ZnL2(H2O)2]2H2O and [ZnL2L1(H2O)2] . The composition of the resulting complexes is shown to depend on the ratios of the starting materials. Characterization of the complexes was conducted using elemental analysis, X-ray phase analysis, UV-VIS spectroscopy, IR spectroscopy, and thermogravimetric analysis. UV spectroscopy revealed d-d transitions in the cobalt (II) complexes at wavelengths between 460-540 nm, while the zinc (II) complex showed a peak at 238 nm. Thermogravimetric analysis indicated that the final products of thermal decomposition for all compounds are metal oxides. Additionally, the effects of these complexes on the growth of selected fungi, specifically Candida, were examined.

Ultra‐High Metal‐Ion Selectivity Induced by Intramolecular Cation‐π Interactions for the One‐Pot Synthesis of Precise Heterometallic Architectures

AbstractHeterometallic supramolecules, known for their unique synergistic effects, have shown broad applications in photochemistry, host‐guest chemistry, and catalysis. However, there are great challenges to precisely construct heterometallic supramolecules rather than a statistical mixture, due to the limited metal‐ion selectivity of coordination units. In particular, heterometallic architectures precisely encoded with different metal ions usually fail to form in a one‐pot method when only one type of coordinated motif exists due to its poor metal‐ion selectivity. Herein, we propose an effective intramolecular cation‐π (ICπ) strategy and successfully constructed the heterometallic supramolecule Zn2Cu4L34 by the one‐pot self‐assembly of tritopic terpyridyl ligand L3 with Zn(II) and Cu(II), following a clear self‐assembly mechanism in which only thermodynamic dimers ZnL12 and Cu2L22 were constructed with model ligands L1, L2, Zn(II) and Cu(II) with perfect self‐sorting and an ultra‐high metal‐selectivity feature. The successful construction of the heterometallic supramolecule Zn2Cu4L34, in which the definite sequence of metal ions Zn(II) and Cu(II) is encoded in the one‐pot method, will offer a novel approach to precisely construct heterometallic architectures.

Ultra-High Metal-Ion Selectivity Induced by Intramolecular Cation-π Interactions for the One-Pot Synthesis of Precise Heterometallic Architectures.

Heterometallic supramolecules, known for their unique synergistic effects, have shown broad applications in photochemistry, host-guest chemistry, and catalysis. However, there are great challenges to precisely construct heterometallic supramolecules rather than a statistical mixture, due to the limited metal-ion selectivity of coordination units. In particular, heterometallic architectures precisely encoded with different metal ions usually fail to form in a one-pot method when only one type of coordinated motif exists due to its poor metal-ion selectivity. Herein, we propose an effective intramolecular cation-π (ICπ) strategy and successfully constructed the heterometallic supramolecule Zn2Cu4L34 by the one-pot self-assembly of tritopic terpyridyl ligand L3 with Zn(II) and Cu(II), following a clear self-assembly mechanism in which only thermodynamic dimers ZnL12 and Cu2L22 were constructed with model ligands L1, L2, Zn(II) and Cu(II) with perfect self-sorting and an ultra-high metal-selectivity feature. The successful construction of the heterometallic supramolecule Zn2Cu4L34, in which the definite sequence of metal ions Zn(II) and Cu(II) is encoded in the one-pot method, will offer a novel approach to precisely construct heterometallic architectures.

Unveiling the interaction, cytotoxicity and antibacterial potential of pyridine derivatives: an experimental and theoretical approach with bovine serum albumin.

The binding interactions between bovine serum albumin (BSA) and three pyridine derivatives, i.e., 2-(5-bromopyridin-3-yl) acetic acid (L1), 3-bromo-5-nitropyridine (L2) and 2-chloro-4-nitropyridine (L3), have been carried out using UV-Vis and fluorescence spectroscopic methods. Fluorescence intensity quenching is observed by adding L2 and L3 to the BSA solution. The quenched fluorescence emission is due to the static nature. An isothermal titration calorimetry (ITC) experiment shows the binding ability of L1 with BSA. The binding constants are found to be 7.23 ± 0.32 × 105 M-1 for L1. The thermodynamic parameters were calculated from ITC measurements (i.e., ∆H = -2.78 ± 0.08 kcal/mol, ∆G = -5.65 ± 0.25 kcal/mol, and -T∆S = -2.87 ± 0.11 kcal/mol), which indicated that the protein-ligand complex formation between L1 and BSA is mainly due to the hydrogen bonds and van der Waals interactions. Cyclic voltammetry (CV) and structure activity and relationship (SAR) studies have been carried out to establish the relationship between ligands and proteins. Additionally, we conducted an antibacterial assay with gram-positive Staphylococcus aureus, Enterococcus faecalis, and negative bacterial strains Acinetobacter baumannii and Escherichia coli against L1, L2, and L3, aiming to address the challenges posed by the co-existence of multidrug-resistant bacteria. Finally, drosophila is used to test the cytotoxicity of ligands L1, L2, and L3's in vitro.

Bridge-Dependent Donor-Metal-Acceptor-Metal-Donor (D-M-A-M-D) Systems: From Charge Transfer to Electron Transfer in Dioxolene-Ge-Diimine Complexes.

Synthesis and structural characterization of a family of germanium-dioxolene complexes with ditopic N-donor ligands (L1-L5) (L1=1,2-bis(pyridin-2-ylmethylene)hydrazine L2=1,6-bis-(pyridin-2-yl)-2,5-diaza-1,5-hexadiene, L3=N,N-bis(pyridin-2-ylmethylene)-1,4-benzenediamine, L4=N,N-bis(pyridin-2-ylmethylene)-(biphenyl)-4,4-diamine, L5=2,2'-azopyridine) is reported. The reaction of germanium bis-catecholate with bridging ligands L1 - L4, differing by the nature of the linker between pyridine sites gives rise to dinuclear digermanium complexes (36Cat2Ge)2L1-4 (36Cat=dianion of 3,6-di-tert-butylcatechol) 1-4 of DMAMD type (donor-metal-acceptor-metal-donor) with a charge transfer in the UV-Vis region. In opposite, the interaction of the 36Cat2Ge with 2,2'-azopyridine (L5) results in the two-electron transfer from the donor 36Cat2- ligands to the azopyridine bridge forming stable open-shell complex 5 [(36SQ)(36CatGe)]2(L5)2- (36SQ=radical-anionic semiquinonate ligand). Molecular structures of compounds 3 and 5 were determined by single crystal X-ray diffraction analysis. Electronic structures of complexes 1-5 were studied by means of DFT calculations.

Bioactivity Modulation: Anionic Influence on Cu(II) Schiff Base Complexes

ABSTRACTThis article explains the synthesis of three Schiff base Cu(II) complexes derived from 3‐hydroxybenzaldehyde and ethylenediamine using three distinct copper anionic salts, and it explores the effects of those salts on the properties of the complexes. Elemental analysis, electronic spectra, FT‐IR, ESR, molar conductance, magnetic measurement, thermogravimetric analysis and PXRD were used to characterize the compounds. The anionic salt has been demonstrated to exhibit distinctive characteristics on Gram‐positive and Gram‐negative bacteria in terms of structure, DNA binding, cell viability, DNA breakage and activity. Furthermore, this ligand L1 and its derivatives indicated positive antifungal efficacy against Aspergillus niger and Trichophyton tonsurans. The study elucidates the manner in which distinct anion salts impacted the properties of complexes and their antifungal, anticancer and antibacterial outcomes.

Electrocatalytic Applications in Hydrogen Evolution of Two Nitrogen Heterocyclic Cu(I) Coordination Polymer Modified Electrodes

ABSTRACTThe development of low‐cost, high‐efficiency, stable, and structurally adjustable electrocatalysts for hydrogen evolution reaction (HER) is of great significance for energy conversion. In this study, two new Cu(I) coordination polymers (CPs), formulated as {[Cu(L1)](PF6)·CH2Cl2}n (1) and {[Cu2(L2)1.5(PPh3)](PF6)2}n (2) (L1 = 1,3‐bis[1‐(pyridin‐3‐ylmethyl) ‐1H‐benzimidazol‐2‐yl]propane, L2 = 1,4‐bis[1‐(3‐pyridylmethyl)‐1H‐benzimidazol‐2‐yl]butane), were synthesized by interfacial diffusion method and characterized by single‐crystal x‐ray diffraction and IR and UV–Vis spectra. Structural analysis shows that the CP‐1 is a one‐dimensional chain structure, whereas the CP‐2 is a two‐dimensional layered structure, which is due to the different coordination modes of ligands L1 (bridging chelation) and L2 (bridging). The electrocatalytic activity for HER of Cu(I) CPs was studied by preparing modified glassy carbon electrodes (CP‐1/GCE and CP‐2/GCE). Electrochemical HER studies manifest that in 0.5 M H2SO4, the overpotential (η10298K) and Tafel slope (b 298K) are −769 mV and 173 mV dec−1 for CP‐1/GCE, −933 mV and 301 mV dec−1 for CP‐2/GCE, and −930 mV and 298 mV dec−1 for bare/GCE, respectively. The η10298K and b298K of CP‐1/GCE were significantly positive shifted and decreased compared with the bare/GCE, indicating that CP‐1/GCE has significant electrocatalytic activity and electrocatalytic HER activity order is CP‐1/GCE > CP‐2/GCE ≈ bare/GCE. This work provides an important reference for the application of non‐noble metal CPs in the field of electrocatalysis.

Synthesis, characterization, and cytotoxicity studies of diimine derivatives and their ruthenium(II)-p-cymene complexes

The reaction of five di-imines obtained by condensation of etilendiamine with 4-hydroxybenzaldehyde (L1), 2,4-dihydroxibenzaldehyde (L2) and 1-(2,4-dihydroxyphenyl)ethan-1-one (L3) or, condensations of glyoxal with 4-aminophenol (L4) and 4-amino-3-fluorphenol (L5) with [Ru2(Cl)4(η6-p-cymene)2] was studied. In absence of silver salts, four cationic complexes of formula [RuCl(η6-p-cymene)(Ln)]X where n = 1, 3, 4 and X = Cl and, n = 5 and X = PF6 could be isolated as pure solid materials. The complexes were characterized by different spectroscopic techniques and the X-ray structures of the L1 hydrate and its complex [RuCl(η6-p-cymene)(L1)]Cl were also determined. These studies confirm the N,N’-bidentate nature of the ligand L1 and the pseudo-octahedral geometry of the ruthenium coordination environment in the complex. Furthermore, the complex derived from L3, shows a potent cytotoxic activity against tumor cell line A549.

A Lead(II) Substituted Triplet Carbene.

Reaction of the pincer-type ligand L3 supported complex [L3PbBr][BArF24] (1) with Li[(C(═N2)TMS)] furnishes [L3Pb(C(═N2)TMS)][BArF24] (2). Diazo-compound 2 eliminates dinitrogen upon irradiation affording formal plumba-alkyne 3, which persists in cold fluoroarene solutions. Variable temperature UV/Vis and NMR spectroscopies in combination with quantum-chemical calculations identify 3 as a metal-substituted triplet carbene. In-crystallo irradiation of [L3Pb(C(═N2)TMS)(tol)][BArF24] (2·tol) provides a snapshot of intermolecular C-H bond insertion with toluene (4).

Pd-Catalyzed C(sp2)-C(sp3) Suzuki Coupling and Synthesis of Lumacaftor Using Designed Monophosphine Ligands.

Novel monophosphine ligands L1 and L2 with a C-P ring were designed and synthesized for the efficient Pd-catalyzed C(sp2)-C(sp3) Suzuki coupling. With 0.5 mol % Pd2dba3 and 2 mol % L1, aryl halides coupled with alkylboronic acids to give the products in up to 99% yield. The aryl thianthrene salt was further applied for late-stage methylation in 97% yield. The active pharmaceutical ingredient lumacaftor was synthesized by aryl-alkyl and aryl-aryl Suzuki coupling reactions using L1 and L2.

Experimental and theoretical studies of carbacylamidophosphate-La (III) complexes: Synthesis, crystal structure, antibacterial activity, electronic and morphology properties

The present study tries to contribute to the body of knowledge concerning the effects of O-donor ligands based on carbacylamidophosphate on the topology, geometry, and dimensions of relevant metal complexes. Accordingly, the octa-coordinated lanthanum (III) complex with formula, [La(L1)4Cl2]Cl (C1) (L1 = 4-NC5H4C(O)NHP(O)(NC6H12)2), has been synthesized and its crystal structure has been determined. In the crystal structure, C1 is C2-symmetrical, and there are separate [La(L1)4Cl2]+ cations and Cl- anions. In the complex molecule, the four L1 ligands adopt two anti- and two syn-chelating conformations. Moreover, two other carbacylamidophosphate-based lanthanide complexes La(L2)2(NO3)3 (C2) (L2 = PhC(O)NHP(O)(NH(tert‑C4H9))2)2(NO3) and La(L3)2(NO3)3(H2O)[(CH3)2CO] (C3) (L3 = (4-NO2C6H4CONHPO(NC4H8O)2) were considered and density functional theory computations, at the B3PW91 level, were performed to gain a deeper understanding of the structural and electronic properties in complexes (C1 - C3). Nano and micro-structures of (C’1 - C’3) were prepared by means of a sonochemical process to study how the reaction condition and non-covalent forces function in terms of the form as well as the size of the particles in these complexes. Thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) were performed on compounds C’1- C’3. The Hirshfeld surface analysis and NCI method were used to show the effects of non-covalent interactions on the compounds’ morphologies. The antimicrobial activity of all selected compounds has been screened against two Gram-positive (Bacillus subtilis, Staphylococcus aureus) and one Gram-negative (Escherichia coli) bacteria by well diffusion method. The results indicated that all selected compounds did not show any antibacterial activity against bacteria as compared to standard drugs.

In silico evaluation of favipiravir-associated potential new drugs against polymerase enzyme of SARS-CoV-2

Millions of lives have been lost to the deadly SARS-CoV-2 virus. Vaccines and antiviral drugs are essential scientific tools in combating viral infections. This in silico study focused on the RdRp inhibitor favipiravir, exploring new analogs by substituting the fluorine atom on the pyrazine ring with both homocyclic and heterocyclic moieties. Initially, ADME and toxicity properties were assessed using SwissADME and ProTox-II online tools. Ligands L6 and L7 exhibited high bioavailability and drug-likeness compared to favipiravir. Subsequently, all new analogs were docked into the RdRp active site using AutoDock Vina, demonstrating high affinity compared to favipiravir. Based on optimal ADMET profiles and docking scores, ligands L4, L6, and L7 underwent 200 ns MDS using the CHAARM 36 force field in NAMD software to validate docking results. Various trajectory analyses, including RMSD, RMSF, histograms, total number of contacts, and ligand properties, were conducted to gain insights into the interaction patterns between ligands and RdRp. All protein-ligand complexes exhibited greater stability than favipiravir throughout simulations period. This theoretical study suggests that ligands L6 and L7 could serve as lead candidates for RdRp inhibition. Cell-Based SARS-CoV-2 RdRp Activity Assay is recommended to validate these in silico findings.

Synthesis of Dinuclear Cobalt Silylene Complexes and Their Catalytic Activity for Alkene Hydrosilylation Reactions.

A novel dinuclear silylene cobalt complex [((Me3P)2Co)(PMe2)(CoCl(PMe3))(Si(NCH2PPh2)2C6H4)] (1) supported by the [PSi(silylene)P] ligand was prepared through the reaction of N-heterocyclic [PSiP] pincer ligand L1 (HSiCl(NCH2PPh2)2C6H4) with Co(PMe3)4. Complex [((Me3P)2Co)2(Si(NCH2PPh2)2C6H4)] (2) was formed through the reaction of complex 1 with MeLi. To the best of our knowledge, complexes 1 and 2 are the first examples of dinuclear silylene cobalt complexes supported by the [PSi(silylene)P] ligand. A new preligand L2 (SiCl2(NCH2PPh2)2C6H4) was synthesized, and the reaction of preligand L2 with Co(PMe3)4 afforded silyl cobalt complex [((Me3P)2Co)(SiCl(NCH2PPh2)2C6H4)] (3). The reaction of 3 with CO delivered cobalt carbonyl complex [((Me3P)(CO)Co)(Si(NCH2PPh2)2C6H4)]2O (4). The catalytic activity of cobalt complexes 1-4 on the hydrosilylation of alkenes was explored. Among the four complexes, complex 1 has the best catalytic activity. The catalytic process could be promoted with NaBHEt3 as an additive, and a complete conversion with an excellent selectivity of 98:2 (b/l) could be reached at 120 °C within 8 min for aryl alkenes. A possible catalytic cycle was proposed on the basis of the experimental results and literature reports, with a cobalt hydride complex as an active intermediate. The molecular structure of complexes 1-4 was determined by single-crystal X-ray diffraction analysis.

Synthesis and Biological Evaluation of Novel Imidazolone - Thiabendazole-Based Metal Complexes.

Thiabendazole-based metal complexes are attracting interest due to their special antimicrobial activities. The current investigation describes the preparation of ligand L1 and its metal complexes [M (C26H17N5OS) Cl2] M = Co, Ni, Cu and Zn. Mass, 1 H-NMR, IR, and UV were used to characterize these compounds. L1 exhibited the highest potency towards many bacteria. It shows the maximum zone of inhibition as compared to any other ligand. Thus, the antibacterial potency of L1 is better as compared to standard drugs. Imidazolone-TBZ ligands L1 are also more susceptible to some bacteria and also show antifungal potency against Pseudomonas aeruginosa. The significance of such work triggered the possibility that these ligands L1 and metal complexes can be efficacious drugs against bacterial and fungal species that could be advantageous in designing powerful antibacterial and antifungal compounds for medicinal use. All these synthesized compounds are in addition to the library of heterocyclic compounds.

Copper(II) and Zinc(II) complexes of new water-soluble Schiff base ligands and their antiproliferative properties towards mesothelioma cell line

In this work, three Schiff base ligands (HL1-HL3) containing a triphenyl phosphonium cation and their Cu(II) and Zn(II) complexes with the general formulae of [M(L)Cl2] were synthesized and their structures were characterized by spectroscopic and analytical methods. Crystal structure of complex [Zn(L1)Cl2] was determined. In the structure of the complex, each Zn(II) ion is four coordinated binding to phenolate oxygen and imine nitrogen atoms of the ligand L1 and two chloride atoms in approximately tetrahedral geometry. The equilibrium geometry of three Schiff base ligands (HL1-HL3) and their Cu(II) and Zn(II) complexes were calculated using the density functional theory (DFT/B3LYP) method with the 6–31++G(d,p) basis set for the C, H, Cl, N, O, P atoms and LANL2DZ for the I atom. Frontier molecular orbitals (HOMO, LUMO) analyses were conducted for the optimized geometries of the compounds, and chemical reactivity descriptors such as hardness, softness, electrophilicity, and electronegativity were examined. Additionally, the molecular electrostatic potential (MEP) of all compounds was modeled using DFT calculations. These calculations were thoroughly examined, and their implications were discussed. The ligands and their metal complexes were investigated for their DNA binding properties. The compounds showed comparable DNA binding properties to ethidium bromide (EB) and 5-fluorouracyl (5-Fu) with DNA binding constant (Kb) 1.5–6.25 × 105 M−1. The cytotoxic properties of the compounds towards HUVEC and H2452 (mesothelioma cell line) cells were investigated using an MTS assay. The IC50 values determined for HUVEC cells were found to range between 27.28 µg/mL ([Cu(L2)Cl2]) and 273.1 µg/mL ([Zn(L2)Cl2]), while in H2452 cells, they varied from 39.48 µg/mL ([Cu(L2)Cl2]) to 319.3 µg/mL ([Zn(L3)Cl2]). The compounds HL1, HL3, and [Zn(L3)Cl2] exhibited antioxidant activity at the highest concentration (750 µg/mL) only, while [Zn(L1)Cl2], HL2, [Zn(L2)Cl2], [Cu(L2)Cl2], and [Cu(L3)Cl2] showed antioxidant activity at 250 µg/mL.

C–H bond activation over chitosan based Fe(III) and Ni(II) catalysts

Chitosan (Cs) supported heterogeneous catalysts of Fe(III) and Ni(II) is developed by the equimolar reaction of two schiff base ligands, L1 [Cs-HACP] and L2 [ANI-HACP] and Metal salts {where Metal = Fe(III) and Ni(II)}with chitosan. The L1 ligand is prepared by the reaction of chitosan (Cs) and ortho hydroxyl (HACP) acetophenone in methanol and L2 ligand is prepared by the condensation of aniline (ANI) and ortho hydroxyl acetophenone (HACP) in solvent free condition. The prepared catalysts {M-[Cs-L1-L2]Cl2} are characterized by different analytical techniques viz. scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), powder X-ray diffraction (XRD), Thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), Raman, UV-VIS-NIR, X-ray photoelectron spectroscopy (XPS) and computational studies. The catalytic behavior of newly synthesized catalysts are tested for the C–H activation using 70 % tert-butyl hydroperoxide (TBHP). The best results are obtained for tetralin oxidation. The order of catalytic reactivity of {M-[Cs-L1-L2]Cl2}catalyst is in decreasing order: {Fe(III)-[Cs-L1-L2]Cl2} > {Ni(II)-[Cs-L1-L2]Cl2}. The {Fe(III)-[Cs-L1-L2]Cl2} gives maximum conversion 81.99 % of tetralin with 84.50 % selectivity of tetralone (T-lone) and 6.47 % selectivity of tetralol (T-lol) after 5 h of reaction at 80 °C temperature. The chitosan based heterogeneous catalyst is easy to separate and recover. It can be recycled seven times.

Multisite-assisted design of asymmetric silicon-bridged diphosphine ligands for selective ethylene tri-/tetramerization

A series of novel silicon-bridged asymmetric diphosphine ligands (PNSiP-type L1-L3 and PCSiP-type L4) and their corresponding Cr(Ⅲ) catalysts have been synthesized and evaluated for ethylene tri-/tetramerization. When DMAO/AlEt3 was used as a co-catalyst, catalyst 1 based on ligand L1, with a cyclopentyl group on the N atom and two methyl groups on the Si atom, showed the highest catalytic activity of 8.21 kg g-1 Cr/h with 90.45 % combined (60.53 % 1-C6= + 29.92 % 1-C8=) selectivity. Moreover, the catalytic system based on catalyst 1 achieved a remarkable selectivity for 1-C8= of 62.58 % at 15 °C, even though polymers were the main products. Catalyst 2 based on ligand L2, bearing a cyclopentyl group at N and one methyl and one phenyl group on the Si moiety, exhibited a catalytic activity of 8.09 kg g-1 Cr/h accompanied with 71.61 % 1-C6= and 14.12 % 1-C8=product selectivity. Catalyst 3 based on ligand L3 having an isopropyl group on the N atom and two methyl groups on the Si atom, displayed 6.95 kg g-1 Cr/h catalytic activity with 69.06 % 1-C6= and 17.88 % 1-C8=product selectivity. Catalyst 4 based on PCSiP-type ligand L4, showed poor catalytic activity and 79.15 % of high 1-C6= selectivity. Compared with the previously reported long-chain Cr(Ⅲ) catalysts based on silicon-bridged diphosphine ligands (PNSiCP-/PCSiCP-type), Cr(Ⅲ) catalysts based on short-chain PNSiP-type and PCSiP-type ligands designed in this work exhibited higher ethylene oligomerization performance. Among them, PNSiP-type ligands are more inclined to generate 1-C8= than PCSiP-type ligand, and reducing the steric bulk of substituents on the Si atom in PNSiP-type ligands is also beneficial for 1-C8= generation. Density functional theory (DFT) calculations also revealed that the PNSiP-type catalysts could exhibit excellent ethylene trimerization performance. The DFT calculations thus provide a theoretical foundation for a deeper understanding of the ethylene tri-/tetramerization mechanism and designing of new ligand structures.

Lanthanide complexes of related click tripodal 1,2,3-triazole-containing ligands on the Ph<sub>3</sub>P(O) platform. The N<sup>2</sup> and N<sup>3</sup> coordination of triazole fragments

The coordination and extraction properties of two related tripodal ligands differed by types of addition of the triazole fragment and linker length in the {2-[(4-Ph-1,2,3-triazol-1-yl)CH2CH2O]C6H4}3P(O) (L1) and {2-[(1-Ph-1,2,3-triazol-4-yl)CH2O]C6H4}3P(O) (L2) are compared. The structures of the complexes [Lа(NO3)3L1] (I) and [Lu(NO3)3L1] (II) are studied in the solid phase (elemental analysis, IR and Raman spectroscopy) and in solutions (IR and multinuclear1H,13C, and31P NMR spectroscopy). A normal coordinate analysis at the TPSS-D4/Def2-SVP level is performed for an isolated molecule of the model complex [La{P(O),N3,N2-L3}(O,O-NO3)3] (L3= {2-[(4-Me-1,2,3-triazol-1-yl)CH2CH2O]C6H4}3-P(O)). According to the set of spectral and quantum chemical data, ligand L1exhibits the tridentate P(O),N2,N2coordination in lanthanide complexes I and II. These are neutral complexes in the solid state and in CD3CN solutions, and the dynamic equilibrium of the neutral and ionic complexes is observed in CDCl3. Unlike ligand L1, ligand L2exhibits the tetradentate P(O),N3,N3,N3coordination in the [Ln(NO3)3L2] complexes with the same metals (Ln = La3+, Lu3+) in solutions. The efficiency of extraction of microquantities offelements from the aqueous phase to 1,2-dichloroethane by compounds L1and L2is discussed in comparison with the structures of the complexes of both ligands in solutions.