Ligands L1 Research Articles

Synthesis of block copolymer with cis-1,4-polybutadiene and isotactic-rich polystyrene using α-diimine nickel catalysts.

A series of styrene-butadiene di-block copolymers with high cis-1,4 unit content (greater than 92%) polybutadiene (PB) and isotactic-rich polystyrene (PS) (mmmm > 65%) was synthesized using α-diimine nickel catalysts (Ni-diimine). Four different Ni-diimine catalysts were synthesized via a complexing reaction between nickel (II) naphthenate and laboratory-made α-diimine ligands L1, L2, L3 and L4, which have different steric volume structures. The results indicate that the Ni-diimine catalyst prepared using the L4 ligand with a higher steric volume can effectively initiate the block polymerization of butadiene and styrene, and the resulting polymer has distinguished cis-1,4 structure unit PB and high isotactic-selective PS block. Differential scanning calorimetry and electrochemical performance tests show that these block copolymers with cis-1,4-regulated and isotactic-selective polymerization have advantages in terms of high-temperature and low-temperature resistance as well as corrosion resistance. Therefore, these copolymers are expected to be widely used in some harsh industrial environments.

Schiff Base Derivatives in Zinc(II) and Cadmium(II) Complexation with the closo-Dodecaborate Anion

A series of Schiff base derivatives, namely N-(4-methoxyphenyl)-1-(1-methylbenzimidazol-2-yl)methanimine (L1), 4-methoxy-N-[(1-methylbenzimidazol-2-yl)methyl]aniline (L2), and 2-[(E)-(1-propylbenzimidazol-2-yl)iminomethyl]phenol (L3), were synthesized. These compounds feature different linker groups, including –CH=N–, –CH2–NH–, and –N=CH–, respectively. During the process of zinc(II) and cadmium(II) complexation in the presence of the closo-dodecaborate [B12H12]2– anion, it was observed that ligand L3 underwent degradation. Consequently, two compounds were isolated, [Zn(Bz-NH2)2(CH3COO)2] and (HBz-NH2)2[B12H12]∙2CH3CN, both containing 1-propyl-2-aminobenzimidazole (Bz-NH2), which is a degraded fragment of the ligand. Several new zinc(II) and cadmium(II) coordination compounds were synthesized and characterized using various physicochemical analysis methods, including elemental analysis, IR, and UV spectroscopy. Additionally, X-ray diffraction and Hirshfeld surface analysis were performed for compounds [Cd(L2)2(CH3CN)(H2O)][B12H12], [Zn(Bz-NH2)2(CH3COO)2], and (HBz-NH2)2[B12H12]∙2CH3CN, as well as for ligand L2.

Coordination driven self-assembled 18-component molecular octahedron

Unsymmetric bidentate ligands offer multiple binding modes with respect to the orientations of the coordinating sites, the unsymmetric nature of ligand 3,5-bis(3-pyridyl)-1,2,4-oxadiazole, L1 arises because of orientations of 3-pyridyl groups with respect to central 1,24-oxadiazole ring. Ligand L1 forms a discrete molecular octahedron [Pd6(L1)12](NO3)12, 1 when combined with Pd(NO3)2 in DMSO where the bound ligands are in cisoid-up orientation. In cage 1, Pd(II) ions are present at the vertices of the octahedron whereas twelve ligands are present at its edges, the opposite Pd-Pd distance in compound 1 is 17.501 Å. 1H NMR and DLS study of compound 1 with different guests reveals that resorcinol has interaction with the cage.

Organoselenium functionalized oxacycles as ligands in some trans-palladium(II) complexes: biological evaluation and interaction with small biomolecules

In this article, the biological evaluation and interaction of three selenium-based trans-palladium complexes (Pd–Se1, Pd–Se2, and Pd–Se3) with small biomolecules were performed. The UV–Vis kinetic studies on substitution reaction of synthesized complexes with selected biologically important N- and S-bonding ligands (L-Cys, GSH, L-Met, 5′-GMP, L-His) has emphasized greater affinity of sulphur-based ligands for complex-binding, while the general order of the reactivity was L-Cys > GSH > L-Met > 5′-GMP > L-His. The complex reactivity toward small biomolecules is influenced by ligand flexibility, i.e. the steric hindrances of their corresponding ligands near the coordination site (Se–Pd) during the substitution process. The in vitro cytotoxicity of the investigated complexes against colorectal carcinoma HCT-116 and healthy fibroblast MRC-5 cells exhibited moderate prooxidative and significant cytotoxic character against HCT-116 cells, while such effect on MRC-5 was much weaker. Antioxidant activity (DPPH assay) indicated that all three complexes and their ligands have significant antioxidant activity, with Pd–Se2 being significantly stronger than its ligand L2 or the other complexes. Molecular docking simulations on tyrosinase (Tyr) singled out Pd–Se1 as the most compatible to bind to the cavity of Tyr. At all concentrations, the tested compounds demonstrated genotoxic effects (comet assay) compared to negative control.

Exploring novel coral reef-like RuO2 oxides: Synthesis and physicochemical characterizations of gatifloxacin-based Ru(III) complexes

ABSTRACT. Two mixed-ligand complexes of Ru(III) ions were synthesized and used to generate nanostructured RuO2 oxide. Complex A contains gatifloxacin (L1), the amino acid glycine (L2), and Ru(III) ions in a 1:1:1 ratio. Complex B contains gatifloxacin (L1), the amino acid alanine (L3), and Ru(III) ions in a 1:1:1 ratio. The synthesized complexes were characterized using UV-Visible and IR spectroscopies, molar conductance, elemental analyses, thermogravimetry, XRD, and SEM-EDX techniques. In both complexes, the L1 ligand acts as a bidentate and uses the nitrogen atoms of the piperazine ring to capture the Ru(III) ions, while the L2 and L3 ligands capture the Ru(III) ions using their oxygen atom of the carboxylate group and the nitrogen atom of the amino group. The atmosphere around the Ru(III) ion is octahedral, and the complexes were formulated as [RuL1L2(H2O)2]Cl2 and [RuL1L3(H2O)2]Cl2 for Complex A and Complex B, respectively. Complex A was directly decomposed in air at 600 °C for 3 h to produce RuO2 oxide (Oxide A), and complex B was decomposed under the same conditions to produce RuO2 oxide (Oxide B). Morphologically, oxide A and oxide B have a coral reef-like texture with large holes and cavities.
 KEY WORDS: Gatifloxacin, Ru(III) ion, Glycine, Alanine, Morphology, RuO2 oxide
 Bull. Chem. Soc. Ethiop. 2023, 37(6), 1443-1457. DOI: https://dx.doi.org/10.4314/bcse.v37i6.12

Binding studies of potential amyloid-β inhibiting chalcone derivative with bovine serum albumin

Chalcones (α-phenyl-β-benzoylethylene) and their natural-source derivatives have been investigated for their remarkable biological activities, like neuroprotective, anti-inflammatory, and anti-tumor properties. A triazole chalcone ligand (E)-3-(4-(dimethylamino)phenyl)-1-(4-((1-(2-(4-((E)-3-(4(dimethylamino)phenyl)acryloyl)phenoxy)ethyl)-1H-1,2,3-triazol-4-yl)methoxy)phenyl)prop-2-en-1-one (L1) was synthesized by Cu(I)- catalysed click reaction. The mechanistic properties of L1 for therapy were evaluated by analyzing the binding interactions between L1 and bovine serum albumin (BSA) through photophysical and computational studies. The structural elucidation of ligand L1 was carried out by NMR and mass spectrometry. The Aβ inhibitory activity of L1 was studied by thioflavin T assay and transmission electron microscopy. The biomolecular interaction of L1 with bovine serum albumin was examined through multi-spectroscopic techniques in combination with in silico studies. UV–Visible absorption, fluorescence spectroscopy, circular dichroism, Förster resonance energy transfer, and three-dimensional fluorescence studies confirmed the formation of a BSA-L1 complex. The potential binding sites, mechanism of interactions, and variations in the environment of tyrosine and tryptophan amino acid residues of BSA were assessed at different temperatures. The binding constant for the Static quenching mechanism of intrinsic fluorescence of BSA was of the order of 105 M−1. The esterase enzyme activity assay in the presence of L1 revealed an increase in the protein enzyme activity. Molecular docking studies suggested L1 was predominantly bound to BSA by hydrogen bonds and Van der Waals forces.

Benzotriazole/indazole-appended phenanthroline-based NNN-tridentate ligand-supported Ru(II) complexes and their application in catalytic transfer hydrogenation

Two discrete Ru(II) complexes [Ru(L1)(bpy)Cl]Cl (Ru-1) and [Ru(L2)(bpy)Cl]Cl (Ru-2) bearing benzotriazole/indazole-appended phenanthroline-based NNN-tridentate ligands L1 and L2 respectively, with one bipyridine and one chloride as co-ligands, were synthesized and characterized fully via spectroscopic and crystallographic techniques. The crystal structures of the complexes revealed the discrete monomeric structures. Both the complexes exhibited MLCT bands in the range of 400–500 nm. The RuII/III redox potential of Ru-1 was found to be more positive (by 155 mV) than that of Ru-2, indicating the stronger π-acceptor property of the ligand L1 than L2. Both the complexes have been found to be efficient precatalysts in transfer hydrogenation of aldehydes and ketones.

Design of new Zn(II) pyrazine and pyridine derivatives based complexes as potential anticancer agents: from synthesis to structure

The newly synthesized ligands based on pyrazine and pyridine derivatives and its Zn (II) complexes were reported. Elemental analysis (EA), flame atomic absorption spectroscopy (F-AAS), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), single-crystal X-ray and electron diffraction were used for the characterisation. The antimicrobial and antifungal activity of all the synthesized compounds was tested against Gram-positive bacteria, Gram-negative bacteria, and yeasts. Besides that, the anticancer nature of the studied compounds was also evaluated. The MTT test showed different results on the cytotoxicity of the ligands. Ligand L3 did not show toxicity after 24-hour incubation but its complex had some toxic effects on both glioblastoma cell lines. Although the obtained Zn(L3)Cl2 did not show the same activity against cancer cells as cisplatin, the studied complex proved to be less toxic against normal cells than the standard drug. Due to this, the further biological studies, such as cell apoptosis assay and DNA double-strand breaks (DSBs) were performed on this pair of compounds.

New thiosemicarbazones and their palladium(II) complexes: Synthesis, spectroscopic characterization, X-ray structure and anticancer evaluation

Thiosemicarbazones (TSCs) have proven to be an important group of NS donor Schiff base ligands. Their biological activities, structural and donor diversities are often improved after coordination to a metal ion. In this work, novel thiophene-based thiosemicarbazone ligands; (E)-N,N’-dimethyl-2-((5′-methyl-[2,2′-bithiophen]-5-yl)methylene)hydrazine-1-carbothioamide (L1), (E)-N-ethyl-2-((5-phenylthiophen-2-yl)methylene)hydrazine-1-carbothioamide (L2) and (E)-2-((5′methyl)-[2,2′-bithiophen]-5-yl)methylene)-N-phenylhydrazine-1-carbothioamide (L3) were synthesized via condensation reaction. The corresponding complexes (C1, C2 and C3) were synthesized by reacting the ligands with Pd(cod)Cl2 under inert nitrogen environment. All the prepared ligands and complexes were characterized by using the FTIR, UV–Vis, 1H and 13C NMR, elemental analysis and single crystal X-ray crystallography on ligand L2. The anticancer activities of the complexes were investigated against human the Caco-2, HT-29, HeLa and non-cancerous KMST-6 cell lines. In the preliminary studies, unexpectedly of all ligands and complexes, L1 showed the best anti-tumor activities at 100 µg/mL with cell viabilities < 31% in all the cell lines. In general, cell lines were more susceptible to complexes than free ligands except for C1. Complex C2 had the highest activity among complexes; HeLa (8.4%), HT-29 (8.8%), Caco-2 (16.1%) and KMST-6 (24.5%) cell viabilities at a concentration of 100 µg/mL. The C3 complex demonstrated appreciable selectivity since it had minimal effect on non-cancerous KMST-6 cell line (76%) with relatively reduced cytotoxicity in other cells except in HeLa (0.0%). All the complexes prepared inhibited proliferation of HeLa cells.

Synthesis of Nickel(II) Complexes Based on Dialkylphosphorylpyridines and Their Cytotoxic Activity

Bis-chelate nickel complex of composition [L2Ni(H2O)2](BF4)2 (4), where L = 1,3-dibenzhydryl-5-(pyridin-2-yl)-5-oxo-1,3,5-diazaphosphorinane, and tris-chelate complexes 5 and 6 of composition [L3Ni](BF4)2, where L = 2-diethylphosphorylpyridine and 2-diisopropylphosphorylpyridine, based on 1,4-N,O ligands L2–L4 with phosphoryl groups of acyclic and cyclic structure have been prepared. The structure and composition of complexes 4–6 were confirmed by mass-spectrometry, IR spectroscopy, thermogravimetric and elemental analysis. The structure of complexes 4-EtOH and 5 in crystals has been established by X-ray diffraction study. Cytotoxic properties toward M-HeLa and HuTu80 cancer cells and Chang Liver normal cell lines for the previously prepared nickel(II) complexes 1–3 based on 2-(oxophospholane)pyridines and the nickel(II) complexes obtained in this work have been studied. It has been found that the complexes with ligands containing cyclic phosphoryl groups show higher cytotoxicity toward cancer cells as compared with the complexes with their acyclic analogs.

Photophysical, electrochemical and electrochromic behavior of transition metal complexes with 1,10-phenanthroline ligands

A series of non-noble transition metal complexes were synthesized by coordinating Fe2+, Co2+, and Ni2+ with ligands having a parent structure of 4,7-diphenyl-1,10-phenanthroline (L1 and L2) and dipyrido[3,2-a:2′,3′-c]phenazine (L3–L5), and their photophysical, electrochemical, and electrochromic properties were studied. Both transition metal ions and ligands produce more or less influence on these properties. Electrochromic properties such as color, optical contrast, response time, coloration efficiency and switching stabilities can be tuned by selecting proper metal ions, parent structure of ligands, and substituent groups. Theory calculation results indicate that electrons flow from the metallic center to the ligands. The UV–vis spectra of all five Fe(II) complexes showed a broad and strong MLCT band at ca. 530 nm. The UV–vis spectra of Fe(II), Co(II) and Ni(II) complexes with L2 ligand showed a strong LC (π–π*) band at ca. 325 nm. Electrochromic process caused a change in the intensity of LC and MLCT absorption. The ligands produced little effect on the bleached and colored states of Fe(II) complexes, all of them showed a bleached state of red and a colored state of purple-red probably due to the reversible Fe(II)/Fe(III) transition. Both Co(II) and Ni(II) complexes showed a bleached state of pale yellow, however, the ligands produced significant effect on their colored states probably due to the partially electron density displacement between the metal ions and the ligands. When the parent structure of ligand is 4,7-diphenyl-1,10-phenanthroline, electron-donating substituent such as –OCH3 is beneficial to electrochromic properties, and Fe(II) complexes have higher optical contrast and coloration efficiency compared to Co(II) and Ni(II) complexes. When the parent structure of ligand is dipyrido[3,2-a:2′,3′-c]phenazine, –CN substituent markedly enhances the optical contrast and coloration efficiency of Fe(II), Co(II) and Ni(II) complexes.

Development of new cobalt, copper, and zinc complexes of Schiff-base ligands as prospective chemotherapeutic agents

Fluorobenzaldehyde was converted into new, bidentate Schiff-base ligands with nitrogen and sulphur donor sites in two steps. The first step proceeds via Knoevenagel condensation; the product obtained was treated with thiosemicarbazide to yield the ligand L1. The Schiff-base ligand, L2, was synthesized by treating L1 with 4-chlorobenzylchloride in a basic medium. Co (II), Cu (II), and Zn (II) complexes were synthesized with the ligands L1 and L2. All these complexes were characterized by FTIR, UV–Vis, NMR spectroscopy, ESI-mass spectral analysis, magnetic moment, molar conductance, thermal, powder XRD, and electrochemical studies. From these studies, the molecular formulae of the complexes were found to be [M(L)2Cl2], where M = Co (II), Cu (II) and Zn (II) and L = L1 or L2 based on the ligand used in the synthesis. The synthesized complexes were observed to have a high spin and distorted octahedral geometry and were non-electrolytic. The UV absorption titrimetric analysis confirmed that these complexes would bind strongly to CT-DNA through the intercalative mode. The electrophorograms supported the statement that Cu (II) complexes could effectively catalyze the hydrolytic cleavage of CT-DNA and can be considered potent metallonuclease agents. The DPPH assay determined the antioxidant properties of these complexes, and the cupric complexes were observed to possess better antioxidant properties than the standard used ascorbic acid. The cell viability analysis of these complexes showed an elevated control of proliferation against a human breast adenocarcinoma (MCF-7) cancer cell line compared to a human cervical carcinoma (HeLa) cell line. The results exhibited by these compounds were compared with the standard drug, cisplatin. The binding affinity of the Cu (II) metal ion complex towards CT-DNA was high when compared to Co (II) and Zn (II) metal ions. These results are in line with the cytotoxicity studies. Molecular docking studies also hold up the experimental data. Cu (II) complexes using ligand L2 show higher efficiency than those with ligand L1 in all biological assays and can be considered a potent DNA-targeting drug.

Azide‐Alkyne Cycloaddition Reaction Catalyzed by Cu(II) Complexes: Studies on the effect of Different Ligand Systems

AbstractA series of bidentate ligands L1–L6 (where L1=2‐(2‐(diphenylmethylene)‐1‐phenylhydrazinyl)pyridine, L2=(E)‐2‐(2‐benzylidene‐1‐phenylhydrazinyl)pyridine, L3=(E)‐2‐(2‐(4‐methoxybenzylidene)‐1‐phenylhydrazinyl)pyridine, L4=(E)‐2‐(2‐(4‐chlorobenzylidene)‐1‐phenylhydrazinyl)pyridine, L5=(E)‐2‐(2‐(4‐nitrobenzylidene)‐1‐phenylhydrazinyl)pyridine, L6=(E)‐N,N‐dimethyl‐4‐((2‐phenyl‐2‐(pyridin‐2‐yl)hydrazono)methyl)aniline) were synthesized and characterized using reported literature.[1–4] Ligands were reacted with Cu(NO3)2 metal salt to synthesize metal complexes [Cu(L1‐6)(ONO2)(H2O)]NO3 i. e., (C1–C6). Metal complexes were characterized by IR, UV‐Visible, TGA and ESI‐MS spectral methods. The molecular structure of complex C2 was analyzed by single crystal X‐ray technique. Complexes were employed as catalysts to perform click reaction. The catalytic reaction was also observed in situ by reacting ligands with Cu(NO3)2 metal salt in presence of sodium ascorbate. The role of substituents present in the ligand frame of metal complexes were studied, and a probable mechanism was proposed.

Decarboxylative Cross-Electrophile Coupling of (Hetero)Aromatic Bromides and NHP Esters.

Aryl bromides are known to be challenging substrates in the decarboxylative cross-electrophile coupling with redox-active NHP esters-the majority of such processes utilize aryl iodides. Herein, we describe the development of conditions that are suitable for the decarboxylative cross-electrophile coupling of NHP esters and a wide range of (hetero)aryl bromides. The key advances that allowed for the use of aryl bromides in this reaction are (1) the identification of ligand L3 as an optimal ligand for the use of electron-neutral and deficient aryl bromides and (2) the significant improvement in yield that iodide salts and excess heterogenous zinc impart to this reaction. A wide variety of NHP esters perform well under the optimized conditions, including methyl, primary, secondary, and several strained tertiary systems. Likewise, a variety of aromatic and heteroaromatic bromides relevant to medicinal chemistry perform well in this transformation, including an aryl bromide precursor to the known drug dapagliflozin.

Preclinical Evaluation of a New Series of Albumin-Binding 177Lu-Labeled PSMA-Based Low-Molecular-Weight Radiotherapeutics.

Prostate-specific membrane antigen (PSMA)-based low-molecular-weight agents using beta(β)-particle-emitting radiopharmaceuticals is a new treatment paradigm for patients with metastatic castration-resistant prostate cancer. Although results have been encouraging, there is a need to improve the tumor residence time of current PSMA-based radiotherapeutics. Albumin-binding moieties have been used strategically to enhance the tumor uptake and retention of existing PSMA-based investigational agents. Previously, we developed a series of PSMA-based, β-particle-emitting, low-molecular-weight compounds. From this series, 177Lu-L1 was selected as the lead agent because of its reduced off-target radiotoxicity in preclinical studies. The ligand L1 contains a PSMA-targeting Lys-Glu urea moiety with an N-bromobenzyl substituent in the ε-amino group of Lys. Here, we structurally modified 177Lu-L1 to improve tumor targeting using two known albumin-binding moieties, 4-(p-iodophenyl) butyric acid moiety (IPBA) and ibuprofen (IBU), and evaluated the effects of linker length and composition. Six structurally related PSMA-targeting ligands (Alb-L1-Alb-L6) were synthesized based on the structure of 177Lu-L1. The ligands were assessed for in vitro binding affinity and were radiolabeled with 177Lu following standard protocols. All 177Lu-labeled analogs were studied in cell uptake and selected cell efficacy studies. In vivo pharmacokinetics were investigated by conducting tissue biodistribution studies for 177Lu-Alb-L2-177Lu-Alb-L6 (2 h, 24 h, 72 h, and 192 h) in male NSG mice bearing human PSMA+ PC3 PIP and PSMA- PC3 flu xenografts. Preliminary therapeutic ratios of the agents were estimated from the area under the curve (AUC0-192h) of the tumors, blood, and kidney uptake values. Compounds were obtained in >98% radiochemical yields and >99% purity. PSMA inhibition constants (Kis) of the ligands were in the ≤10 nM range. The long-linker-based agents, 177Lu-Alb-L4 and 177Lu-Alb-L5, displayed significantly higher tumor uptake and retention (p < 0.001) than the short-linker-bearing 177Lu-Alb-L2 and 177Lu-Alb-L3 and a long polyethylene glycol (PEG) linker-bearing agent, 177Lu-Alb-L6. The area under the curve (AUC0-192h) of the PSMA+ PC3 PIP tumor uptake of 177Lu-Alb-L4 and 177Lu-Alb-L5 were >4-fold higher than 177Lu-Alb-L2, 177Lu-Alb-L3, and 177Lu-Alb-L6, respectively. Also, the PSMA+ PIP tumor uptake (AUC0-192h) of 177Lu-Alb-L2 and 177Lu-Alb-L3 was ~1.5-fold higher than 177Lu-Alb-L6. However, the lowest blood AUC0-192h and kidney AUC0-192h were associated with 177Lu-Alb-L6 from the series. Consequently, 177Lu-Alb-L6 displayed the highest ratios of AUC(tumor)-to-AUC(blood) and AUC(tumor)-to-AUC(kidney) values from the series. Among the other agents, 177Lu-Alb-L4 demonstrated a nearly similar ratio of AUC(tumor)-to-AUC(blood) as 177Lu-Alb-L6. The tumor-to-blood ratio was the dose-limiting therapeutic ratio for all of the compounds. Conclusions: 177Lu-Alb-L4 and 177Lu-Alb-L6 showed high tumor uptake in PSMA+ tumors and tumor-to-blood ratios. The data suggest that linker length and composition can be modulated to generate an optimized therapeutic agent.

Synthesis and characterization of phenoxy-bridged copper(II) complexes: Structural features, magnetic, thermal and redox properties, and theoretical studies

Three phenoxy-bridged Cu(II) complexes, atrinuclear partial cubane type Cu(II) complex [Cu3(L1)3(µ3-OH)](ClO4)2 (1) (where L1H = (E)-2-(((2-aminoethyl)imino)methyl)-5-(diethylamino) phenol) and two dinuclear Cu(II) complexes, [Cu(L2)(MeOH)(OMe)]2 (2)and [Cu(sal)(bipy)(ClO4)]2 (3) (where L2H = (E)-N'-(5-bromo-2-hydroxybenzylidene) benzohydrazide), sal = 5-Bromo salicylaldehyde, bipy = 2,2-Bipyridine) were synthesized via in-situ reaction and have been successfully characterized both experimentally and computationally. In an in-situ reaction, the Schiff base formed (L1H/L2H) behaves as tridentate ligands having ONO donor sites. The structures of Cu(II) complexes(1)-(3)were established by X-ray crystallography. In the trinuclear Cu(II) complex(1), the three phenoxy oxygen atoms of ligand L1 bridge the Cu(II) center ions in µ3-fashion, while in dinuclear Cu(II) complexes (2)and(3), the phenoxy oxygen bridges the Cu(II) center ionsin µ2-fashion. The temperature dependence magnetic susceptibility, thermal gravimetric analysis (TGA) and cyclic voltammetry analysis were performed for Cu(II) complexes(1)-(3). Hirshfeld surface analysis and 2D fingerprint plots have also been explored in the crystal structure of complexes.

Self-Assembly and Photothermal Conversion of MetallaRussian Doll and Metalla[2]catenanes Induced via Multiple Stacking Interactions.

A variety of organometallic supramolecular architectures have been constructed over the past decades and their properties were also explored via different strategies. However, the synthesis of metalla-Russian doll is still a fascinating challenge. Herein, a series of new coordination supramolecular complexes, including a metalla-Russian doll, metalla[2]catenanes, and metallarectangles, were synthesized by using meticulously selected Cp*Rh (Cp* = η5-C5Me5) building units (E1, E2, and E3) and three rigid anthracylpyridine ligands (L1, L2, and L3) via a self-assembly strategy. While the combination of the short ligand L1 and E1 or E2 generated two metallarectangles, the longer ligand L2 containing an alkynyl group resulted in two new [2]catenanes, most likely due to which the strong electron-donating effect of alkynyl groups causes self-accumulation. Interestingly, an unusual Russian doll assembly was obtained through the reaction of L3 and E3 based on sextuple π···π stacking interactions. Furthermore, the dynamic structural conversion between [2]catenanes and the corresponding metallarectangles could be observed through concentration-, solvent-, and guest-induced effects. The [2]catenane complexes 4b displayed efficient photothermal conversion efficiency in solution (20.2%), in comparison with other organometallic macrocycles. We believe that π···π stacking interactions generate active nonradiative pathways and promote radiative photodeactivation pathways. This study proves the versatility of half-sandwich building units, not only to build complicated supramolecular topologies but also in effective functional materials for various appealing applications.

Electronic Transition and Magnetic Coupling Regulation in Trimetallic Complexes Featuring a New Bridging Ligand Obtained by Oxidative Addition.

A series of trimetallic complexes [FeIII(μ-L)(py)]2MII(py)n (n = 2, MII = MnII, 1; FeII, 2; CoII, 3; ZnII, 4; n = 3, MII = CdII, 5) with a new bridging ligand L4- (deprotonated 1,2-N1,N2-bis(2-mercaptoanil) oxalimidic acid) were synthesized and fully characterized by elemental analysis, single-crystal X-ray crystallography, IR, and Mössbauer spectra. Interestingly, the bridging ligand was obtained by oxidative addition of the (gma•)3- ligand from the mononuclear precursor Fe(gma)py (gma = glyoxal-bis(2-mercaptoanil)). In the obtained complexes, the bridging ligand L4- coordinates to the terminal FeIII ions (intermediate-spin with SFe = 3/2) by the N, S atoms, and coordinate to the central metal MII ion by the four O atoms. The resonance structure of the bridging ligand can be described as the two 4π-electron delocalized systems connected by one single-bond (C1-C2), which is different from the electronic structure of the precursor Fe(gma)py. Remarkably, the magnetic coupling interaction can be regulated through the central metal. The ferromagnetic coupling constant J gradually decreases as MII changes from FeII to CoII and MnII, while the paramagnetic behaviors are presented when MII = ZnII and CdII, confirmed by the magnetic susceptibility measurements and further supported by using the PHI program. Furthermore, the bridging ligand to the terminal FeIII charge transfer (LMCT) transitions emerged in all complexes but the central FeII to terminal FeIII charge transfer (MMCT) only presented in complex 2, strongly supported by the UV/vis-NIR electronic spectra and TDDFT calculations.

Iridium-Catalyzed Intramolecular Asymmetric Allylic Etherification of Pyrimidinemethanols: Enantioselective Construction of Multifunctionalized Pyrimidine-Fused Oxazepines.

An iridium-catalyzed intramolecular asymmetric allylic etherification of pyrimidinemethanols is described. In the presence of chiral-bridged biphenyl phosphoramidite ligand L3 and triethylborane, this process provided a class of novel pyrimidine-fused oxazepanes in up to 99% yield with 99.5% enantiomeric excess. The work addresses the challenge of insufficient nucleophilicity of aliphatic alcohols for allyl substitution and indicates the vital value of chiral-bridged biphenyl phosphoramidites. Various multifunctionalized transformations of the products further demonstrate the robust synthetic utility of this methodology.

Pd(II)-complexes of telluro-substituted Schiff base ligands: Effect of the pendant alkyl group on Suzuki and Heck coupling through in situ generated palladium nanoparticles

Two telluro-substituted Schiff bases L1/L2 having different pendant carbon chains (−Me in L1 and − C10H21 in L2) and their corresponding square planar Pd(II)-complexes (1/2) have been synthesized and their structural characterization has been carried out using multinuclear NMR and elemental analysis. The ligand L2 showed a Smectic liquid crystalline phase and melts at 81 °C into isotropic liquid whereas L1 and complexes (1/2) did not show any liquid crystalline property. The square planar Pd(II)-complexes (1/2) have been formed through the coordination of ligands (L1/L2) respectively in mono-anionic tridentate mode (Te,N,O−) and the fourth coordination sphere at the palladium center is occupied with chloride ion. Both complexes 1/2 (1 to 2 mol%) have beenexamined as a catalyst for Suzuki and Heck coupling reactions and their activity depends significantly on the length pendant alkyl chain. The results obtained from Hg-/PPh3-poisoning and three phase test on Suzuki-Miyaura coupling indicate the participation of both homogeneous as well as heterogeneous palladium species protected with the ligand or its fragment.