Stereocontrol of Metal-Centred Chirality in Rhodium(III) and Ruthenium(II) Complexes with N2N'P Ligand.

Rh(III) and Ru(II) complexes, [RhCl2(κ4-N2N'P-L)][SbF6] (1) and [RuCl2(κ4-N2N'P-L)] (2), were synthesised using the tetradentate ligand L (L=N,N-bis[(pyridin-2-yl)methyl]-[2-(diphenylphosphino)phenyl]methanamine). In each case only one diastereomer is detected, featuring cis-disposed pyridine groups. The chloride ligand trans to pyridine can be selectively abstracted by AgSbF6, with the ruthenium complex (2) reacting more readily at room temperature compared to the rhodium complex (1) which requires elevated temperatures. Rhodium complexes avoid the second chloride abstraction, whereas ruthenium complexes can form the chiral bisacetonitrile complex [Ru(κ4-N2N'P-L)(NCMe)2][SbF6]2 (5) upon corresponding treatment with AgSbF6. The complex [RhCl2(κ4-N2N'P-L)][SbF6] (1) has also been used to synthesise polymetallic species, such as the tetrametallic complex [{RhCl2(κ4-N2N'P-L)}2(µ-Ag)2][SbF6]4 (6) which was formed with complete diastereoselectivity and chiral molecular self-recognition. In addition, a stable bimetallic mixed-valence complex [{Rh(κ4-N2N'P-L)}{Rh(COD)}(µ-Cl)2][SbF6]2 (7) (COD=cyclooctadiene) was synthesised. These results highlight the significant differences in chloride lability between Rh3+ and Ru2+ complexes and demonstrate the potential for complexes to act as catalyst precursors and ligands in further chemistry applications.

Blue Phosphorescent Pt(II) Compound Based on Tetradentate Carbazole/2,3'-Bipyridine Ligand and Its Application in Organic Light-Emitting Diodes.

The tetradentate ligand, merging a carbazole unit with high triplet energy and dimethoxy bipyridine, renowned for its exceptional quantum efficiency in coordination with metals like Pt, is expected to demonstrate remarkable luminescent properties. However, instances of tetradentate ligands such as bipyridine-based pyridylcarbazole derivatives remain exceptionally scarce in the current literature. In this study, we developed a tetradentate ligand based on carbazole and 2,3'-bipyridine and successfully complexed it with Pt(II) ions. This novel compound (1) serves as a sky-blue phosphorescent material for use in light-emitting diodes. Based on single-crystal X-ray analysis, compound 1 has a distorted square-planar geometry with a 5/6/6 backbone around the Pt(II) core. Bright sky-blue emissions were observed at 488 and 516 nm with photoluminescent quantum yields of 34% and a luminescent lifetime of 2.6 µs. TD-DFT calculations for 1 revealed that the electronic transition was mostly attributed to the ligand-centered (LC) charge transfer transition with a small contribution from the metal-to-ligand charge transfer transition (MLCT, ~14%). A phosphorescent organic light-emitting device was successfully fabricated using this material as a dopant, along with 3'-di(9H-carbazol-9-yl)-1,1'-biphenyl (mCBP) and 9-(3'-carbazol-9-yl-5-cyano-biphenyl-3-yl)-9H-carbazole-3-carbonitrile (CNmCBPCN) as mixed hosts. A maximum quantum efficiency of 5.2% and a current efficiency of 15.5 cd/A were obtained at a doping level of 5%.

Redox Activity of IrIII Complexes with Multidentate Ligands Based on Dipyrido-Annulated N-Heterocyclic Carbenes: Access to High Valent and High Spin State with Carbon Donors.

Synthetic strategies to access high-valent iridium complexes usually require use of π donating ligands bearing electronegative atoms (e. g. amide or oxide) or σ donating electropositive atoms (e. g. boryl or hydride). Besides the η5 -(methyl)cyclopentadienyl derivatives, high-valent η1 carbon-ligated iridium complexes are challenging to synthesize. To meet this challenge, this work reports the oxidation behavior of an all-carbon-ligated anionic bis(CCC-pincer) IrIII complex. Being both σ and π donating, the diaryl dipyrido-annulated N-heterocyclic carbene (dpa-NHC) IrIII complex allowed a stepwise 4e- oxidation sequence. The first 2e- oxidation led to an oxidative coupling of two adjacent aryl groups, resulting in formation of a cationic chiral IrIII complex bearing a CCCC-tetradentate ligand. A further 2e- oxidation allowed isolation of a high-valent tricationic complex with a triplet ground state. These results close a synthetic gap for carbon-ligated iridium complexes and demonstrate the electronic tuning potential of organic π ligands for unusual electronic properties.

A Tetradentate Ligand Enables Iron-Catalyzed Asymmetric Hydrogenation of Ketones in a CO- or Isocyanide-Free Fashion.

We herein reported the design and synthesis of a ferrocene-based tetradentate ligand that is featured with modular synthesis and rigid skeleton. Its iron(II) complex facilitates asymmetric direct hydrogenation of ketones without the participation of extra strong-field ligand such as CO and isocyanide. Hydride donor lithium aluminum hydride (LAH) converted non-reactive Fe(II) species to reactive Fe(II) hydride species. With this catalyst, various chiral alcohols including the intermediate for montelukast could be prepared with satisfactory yields and enantioinduction.

Trading Symmetry for Stereoinduction in Tetradentate, non-C2 -Symmetric Fe(II)-Complexes for Asymmetric Catalysis.

A series of stereogenic-at-metal iron complexes comprising a non-C2 -symmetric chiral topology is introduced and applied to asymmetric 3d-transition metal catalysis. The chiral iron(II) complexes are built from chiral tetradentate N4-ligands containing a proline-derived amino pyrrolidinyl backbone which controls the relative (cis-α coordination) and absolute metal-centered configuration (Λ vs. Δ). Two chloride ligands complement the octahedral coordination sphere. The modular composition of the tetradentate ligands facilitates the straightforward incorporation of different terminal coordinating heteroaromatic groups into the scaffold. The influence of various combinations was evaluated in an asymmetric ring contraction of isoxazoles to 2H-azirines revealing that a decrease of symmetry is beneficial for the stereoinduction to obtain chiral products in up to 99 % yield and with up to 92 % ee. Conveniently, iron catalysis is feasible under open flask conditions with the bench-stable dichloro complexes exhibiting high robustness towards oxidative or hydrolytic decomposition. The versatility of non-racemic 2H-azirines was subsequently showcased with the conversion into a variety of quaternary α-amino acid derivatives.

Synthesis and structure of metal-TCPE (metal = Th, Ce) metal-organic frameworks based on 1,2,4,5-tetrakis(4-carboxyphenyl) ethylene.

Two new metal-organic frameworks (MOFs) (Th/ Ce -TCPE) based on 1,2,4,5-tetrakis(4-carboxyphenyl)ethylene were obtained using a straightforward reaction under moderate conditions. Th and Ce formed the central units of this MOF in the mononuclear and in the unusual trinuclear cluster configurations, respectively. The resulting MOFs were analysed by fluorescence spectroscopy to understand their luminescence. The obtained data revealed that benzene's electron cloud density and torsion angle on the ligand were affected by the acetic acid molecule and Th(IV), which caused Th-TCPE to irradiate stronger blue emission, but Ce-TCPE showed no fluorescence due to the self-quenching. Such a unique luminescence property could be used for fluorescence or radiopharmaceutical sensing.

Ultrapure Blue Phosphorescent Organic Light-Emitting Diodes Employing a Twisted Pt(II) Complex.

Described herein is a stable complex, Pt(mpzpyOczpy-mesi), embodying efficient, narrow blue emission. The highly twisted structure of the complex improves the stability and efficiency of photo- and electroluminescence by reducing the intermolecular interactions. The complex in solution shows high photoluminescence efficiency (>95%) and radiative decay rate (Kr = 2.9 × 105 s-1) with a narrow emission spectrum. The bottom-emitting phosphorescent device, BE1, exhibits durable deep blue emission with CIE coordinates of (0.145, 0.166) and 5.2 h of LT50 at an initial luminance of 685 cd/m2. Top-emitting devices, TE1 and TE2, achieve ultrapure blue color with CIEx,y values of (0.141, 0.068) and (0.140, 0.071), respectively. TE4 shows high brightness of 3405 cd m-2 at 50 mA m-2, EQE of 10.2% at 1000 cd/m2, and almost negligible color deviation around (0.135, 0.096) at viewing angles of 0°-60°.

Synthesis, spectral characterization, DFT calculations, pharmacological studies, CT-DNA binding and molecular docking of potential N, O-multidentate chelating ligand and its VO(II), Zn(II) and ZrO(II) chelates.

The pharmacological efficacy of the variety tetradentate ligands encouraged us to design attractive compounds through effective synthetic procedure. The prepared Schiff base ligand 6,6'-((1E,1'E)-((4-chloro-1,2-phenylene)bis(azaneylylidene))bis(methaneylylidene))bis(2-ethoxy phenol (H2L), which derived from 4-chloro-o-phenylenediamine and 3-ethoxy-salicylaldehyde and its VO(II), Zn(II) and ZrO(II) metal chelates, have been synthesized and characterized with aim of that it may struggle the invasion of drug resistance. The chemical structural of studied compounds were discussed by TGA, elemental analysis, UV-Vis., 1H NMR, 13C NMR, FTIR, mass spectral, PXRD, molar conductance, magnetic susceptibility measurements and density functional theory. The results assigned square pyramid geometries for [VOL] and [ZrOL].2H2O chelates and an octahedral geometry for [ZnL(H2O)2].2H2O chelate. Powder XRD data showed that the complexes are monoclinic with polycrystalline nature. The results of CT-DNA interaction with the titled chelates showed that the binding between CT-DNA and the metal complexes occurs through intercalation mode. Their CT-DNA binding efficiency estimated in terms of their binding constants (Kb), which gave the order: VOL (6.9 × 105) > ZrOL (6.3 × 105) > ZnL(H2O)2 (5.5 × 105). The antimicrobial activities of the synthesized compounds were tested against selected fungal and bacterial strains using well diffusion technique. The obtained chelates showed higher antifungal and antibacterial activities than their corresponding ligand. Furthermore, the M-complexes showed higher potent cytotoxic effect toward HEK-293, human colorectal HepG-2, HCT-116 and MCF-7 adenocarcinoma cell lines compared to the free H2L ligand. Investigation of antioxidant property represented that all the prepared complexes have better radical scavenging potencies against DPPH radicals than the free H2L ligand. To study the molecular docking of proposed compounds versus Tyrosine kinases receptor (TKR), we used AutoDock1.5.6rc3® suite. The current compounds (H2L, VOL, ZrOL and ZnL(H2O)2) and STI were found to bind with C-kit of TKR with HBs at ILE789.A, ILE808.A, ASP810.A, GLU640.A and TYR846 amino acid residue and the binding energies were - 8.9, -8.93, -8.83, -1.48 and -10.39 kcal/mol respectively.

Antitumor activity via apoptotic cell death pathway of water soluble copper(II) complexes: effect of the diamino unit on selectivity against lung cancer NCI-H460 cell line.

The cytotoxicity against five human tumor cell lines (THP-1, U937, Molt-4, Colo-205 and NCI-H460) of three water soluble copper(II) coordination compounds containing the ligands 3,3'-(ethane-1,2-diylbis(azanediyl))dipropanamide (BCEN), 3,3'-(piperazine-1,4-diyl)dipropanamide (BPAP) or 3,3'-and (1,4-diazepane-1,4-diyl)dipropanamide (BPAH) are reported in this work. The ligands contain different diamine units (ethylenediamine, piperazine or homopiperazine) and two propanamide units attached to the diamine centers, resulting in N2O2 donor sets. The complex containing homopiperazine unit presented the best antiproliferative effect and selectivity against lung cancer cell line NCI-H460, showing inhibitory concentration (IC50) of 58 µmol dm-3 and Selectivity Index (SI) > 3.4. The mechanism of cell death promoted by the complex was investigated by Sub-G1 cell population analysis and annexin V and propidium iodide (PI) labeling techniques, suggesting that the complex promotes death by apoptosis. Transmission electron microscopy investigations are in agreement with the results presented by mitochondrial membrane potential analysis and also show the impairment of other organelles, including endoplasmic reticulum.

Synthesis of cool white light emitting novel dysprosium (Dy3+ ) complexes with tetradentate ß-ketoamide and heterocyclic auxiliary ligands.

To improve current multiphase white light emitting diodes (WLEDs), a novel series of five complexes consisting of one binary and four ternary complexes that emitted cool white light was successfully synthesized using a chelating tetradentate ligand and auxiliary ligands, i.e. 5,6-dimethyl-1,10-phenanthroline, 1,10-phenanthroline, 4,4'-dimethyl-2,2'-bipyridyl, and 2,2'-bipyridyl. The series was examined structurally using elemental analysis, Fourier transform infrared spectroscopy, energy dispersive X-ray analysis, ultraviolet-visible spectroscopy, and proton nuclear magnetic resonance spectroscopy. These complexes had the appropriate thermal stability required for the generation of white organic LEDs (WOLEDs). Dysprosium (III) (Dy3+ ) ion complexes demonstrated the characteristic emission peaks of blue colour at 482 nm and yellow colour at 572 nm, respectively, when excited using near ultraviolet light. Band gap, refractive index, and decay lifetime of the optimized samples were recorded as 2.68 eV, 2.12, and 1.601 ms, respectively. Correlated colour temperature value (7875 K), Commission International de l'Eclairage coordinates (0.300, 0.294), and colour purity (21.04 × 10-2 ) of the optimized complex were near to those of white illuminants as defined by the National Television System Committee. These complexes had promise as commercial LEDs for the advanced optoelectronics devices, especially as WOLEDs for illumination applications.

Enantioselectivity-Evaluation of Chiral Copper(II) Complexes Coordinated by Novel Chiral Tetradentate Ligands for Free Amino Acids by Mass Spectrometry Coupled With the Isotopically Labeled Enantiomer Method.

A series of copper(II) complexes with chiral tetradentate ligands, N,N'-ethylene- bis(S-amino acid methyl amide or methyl ester) prepared from S-alanine, S-phenylalanine, S-valine or S-proline, was generated in methanol. The copper complexes provided three component complexes in the presence of a free chiral amino acid. The enantioselectivity for the amino acid was evaluated by electrospray ionization-mass spectrometry coupled with the deuterium-labeled enantiomer method and these copper complexes were found to exhibit high enantioselectivity for free amino acids having bulky side chains. This result suggests that steric interaction between the tetradentate ligand and free amino acid was a major factor in chiral recognition. The copper complex with a chiral tetradentate ligand prepared from S-proline showed opposite enantioselectivity to copper complexes consisting of tetradentate ligands prepared from other S-amino acids. The conformational difference of the tetradentate ligand in the copper complex was found to be significant for enantioselectivity.

Multiresponsive Tetradentate Phosphorescent Metal Complexes as Highly Sensitive and Robust Luminescent Oxygen Sensors: Pd(II) Versus Pt(II) and 1,2,3-Triazolyl Versus 1,2,4-Triazolyl.

Two Pd(II) complexes based on tetradentate chelate ligands with either a 1,2,4-triazolyl (Pd1) or 1,2,3-triazolyl (Pd2) unit were synthesized, and their structure-property relationships were studied. Both Pd1 and Pd2 are rare bright deep blue Pd(II) phosphors with contrasting properties. Pd1 displays stimuli-responsive luminescence in response to UV irradiation, concentration, or temperature change, which is ascribed to the facile switching of monomer to excimer emission. In contrast, a similar stimuli-responsive luminescence was not observed for Pd2. Crystal structures and time-dependent density functional theory computational studies established that the excimer formation of Pd1 is caused by electronically favored intermolecular π-π interactions and less steric protection of the Pd core because of the position of its alkyl chains, compared to Pd2. In solution, the excimer emission of Pd1 shows a much greater sensitivity toward oxygen than the monomer emission with a very large Stern-Volmer constant ( Ksv) that is more than twice that of the monomer emission. Both Pd(II) complexes are found to be outstanding oxygen sensors in ethyl cellulose films with superior sensitivity ( Ksvapp = 0.228-0.346 Torr-1) over their Pt(II) equivalents ( Ksvapp = 0.00674-0.0110 Torr-1), owing to their long phosphorescence decay lifetimes. Furthermore, Pd1 shows an excellent photostability, compared to the Pt(II) analogue, making it one of the best and highly robust oxygen sensors based on cyclometalated metal complexes.

Reagent-Less and Robust Biosensor for Direct Determination of Lactate in Food Samples.

Lactic acid is a relevant analyte in the food industry, since it affects the flavor, freshness, and storage quality of several products, such as milk and dairy products, juices, or wines. It is the product of lactose or malo-lactic fermentation. In this work, we developed a lactate biosensor based on the immobilization of lactate oxidase (LOx) onto N,N'-Bis(3,4-dihydroxybenzylidene) -1,2-diaminobenzene Schiff base tetradentate ligand-modified gold nanoparticles (3,4DHS-AuNPs) deposited onto screen-printed carbon electrodes, which exhibit a potent electrocatalytic effect towards hydrogen peroxide oxidation/reduction. 3,4DHS-AuNPs were synthesized within a unique reaction step, in which 3,4DHS acts as reducing/capping/modifier agent for the generation of stable colloidal suspensions of Schiff base ligand-AuNPs assemblies of controlled size. The ligand-in addition to its reduction action-provides a robust coating to gold nanoparticles and a catalytic function. Lactate oxidase (LOx) catalyzes the conversion of l-lactate to pyruvate in the presence of oxygen, producing hydrogen peroxide, which is catalytically oxidized at 3,4DHS-AuNPs modified screen-printed carbon electrodes at +0.2 V. The measured electrocatalytic current is directly proportional to the concentration of peroxide, which is related to the amount of lactate present in the sample. The developed biosensor shows a detection limit of 2.6 µM lactate and a sensitivity of 5.1 ± 0.1 µA·mM-1. The utility of the device has been demonstrated by the determination of the lactate content in different matrixes (white wine, beer, and yogurt). The obtained results compare well to those obtained using a standard enzymatic-spectrophotometric assay kit.

New 3 D Tubular Porous Structure of an Organic-Zincophosphite Framework with Interesting Gas Adsorption and Luminescence Properties.

A new 3D tubular zinc phosphite, Zn2 (C22 H22 N8 )0.5 (HPO3 )2 ⋅H2 O (1), incorporating a tetradentate organic ligand was synthesized under hydro(solvo)thermal conditions and structurally characterized by single-crystal X-ray diffraction. Compound 1 is the first example of inorganic zincophosphite chains being interlinked through 1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene to form a tubular porous framework with unusual organic-inorganic hybrid channels. The thermal and chemical stabilities, high capacity for CO2 adsorption compared to that for N2 adsorption, and interesting optical properties of LED devices fabricated using this compound were also studied.

Multi-tasking Schiff base ligand: a new concept of AuNPs synthesis.

Multi-tasking 3,4-dihydroxysalophen Schiff base tetradentate ligand (3,4-DHS) as reductant, stabilizer, and catalyst in a new concept of gold nanoparticles (AuNPs) synthesis is demonstrated. 3,4-DHS is able to reduce HAuCl4 in water, acting also as capping agent for the generation of stable colloidal suspensions of Schiff base ligand-AuNPs assemblies of controlled size by providing a robust coating to AuNPs, within a unique reaction step. Once deposited on carbon electrodes, 3,4-DHS-AuNPs assemblies show a potent electrocatalytic effect towards hydrazine oxidation and hydrogen peroxide oxidation/reduction.

Spectroscopic, thermal analysis and DFT computational studies of salen-type Schiff base complexes.

A new series of metal(II) complexes of Co(II), Ni(II), Cu(II), Zn(II), and Pb(II) have been synthesized from a salen-type Schiff base ligand derived from o-vanillin and 4-methyl-1,2-phenylenediamine and characterized by elemental analysis, spectral (IR, UV-Vis, (1)H NMR, (13)C NMR and EI-mass), molar conductance measurements and thermal analysis techniques. Coats-Redfern method has been utilized to calculate the kinetic and thermodynamic parameters of the metal complexes. The molecular geometry, Mulliken atomic charges of the studied compounds were investigated theoretically by performing density functional theory (DFT) to access reliable results to the experimental values. The theoretical (13)C chemical shift results of the studied compounds have been calculated at the B3LYP, PBEPBE and PW91PW91 methods and standard 6-311+G(d,p) basis set starting from optimized geometry. The comparison of the results indicates that B3LYP/6-311+G(d,p) yields good agreement with the observed chemical shifts. The measured low molar conductance values in DMF indicate that the metal complexes are non-electrolytes. The spectral and thermal analysis reveals that all complexes have octahedral geometry except Cu(II) complex which can attain the square planner arrangement. The presence of lattice and coordinated water molecules are indicated by thermograms of the complexes. The thermogravimetric (TG/DTG) analyses confirm high stability for all complexes followed by thermal decomposition in different steps.