Diruthenium complexes with bridging diethynyl polyaromatic ligands: synthesis, spectroelectrochemistry, and theoretical calculations

This work describes syntheses and electrochemical, spectroscopic, and bonding properties in a new series of dinuclear ruthenium(II) complexes bridged by polyaromatic (biphenyl, fluorene, phenanthrene, and pyrene) alkynyl ligands. Longitudinal expansion of the π-conjugated polyaromatic core of the bridging ligands caused a reduced potential difference between the anodic steps and reinforced their bridge-localized nature, as evidenced by UV/vis/near-IR and IR spectroelectrochemical data combined with DFT and TDDFT calculations. Importantly, the intricate multiple IR ν(CC) absorption bands for the singly oxidized states imply a thermal population of a range of conformers (rotamers) with distinct electronic character. This behavior was demonstrated with more accurate DFT calculations of selected nontruncated 1e− oxidized complexes in three different conformations. The combined experimental and theoretical data reveal that thermally populated rotamers featuring various mutual orientations of the ligated metal termini and the bridging diethynyl polyaromatic moieties have a significant impact on the electronic absorption and ν(CC) wavenumbers of the singly oxidized systems.

Role of ligands in catalytic water oxidation by mononuclear ruthenium complexes

Since first reported in 2005, mononuclear ruthenium water oxidation catalysts have attracted a great deal of attention due to their catalytic performance and synthetic flexibility. In particular, ligands coordinated to a Ru metal centre play an important role in the catalytic mechanisms, exhibiting significant impact on catalyst efficiency, stability and activity towards water oxidation. This review focuses on finding possible correlations between the ligand effects and activity of mononuclear Ru aqua and non-aqua complexes as water oxidation catalysts. The ligand effects highlighted in the text include the electronic nature of core ligands and their substituents, the trans–cis effect, steric hindrance and the strain effect, the net charge effect, the geometric arrangement of the aqua ligand and the supramolecular effects, e.g., hydrogen bonding and influence of a pendant base. The outcome is not always obvious at the present knowledge level. Deeper understanding of the ligand effects, based on new input data, is mandatory for further progress towards a rational development of novel catalysts featuring enhanced activity in water oxidation.

Asymmetric oxidation of vinyl- and ethynyl terthiophene ligands in triruthenium complexes

A series of ruthenium(II) complexes [{RuCl(CO)(PMe3)3(–CHvCH–)}nX], 1a–1c (1a: n = 3, X = 3,3’’- dimethyl-2,2’:3’,2’’-terthiophene; 1b: n = 2, X = 2,2’-bithiophene; 1c: n = 2, X = 2,3-bis(3-methylthiophen- 2-yl)benzothiophene) and [{Cp*(dppe)2Ru(–CuC–)}3X], 1d (X = 3,3’’-dimethyl-2,2’:3’,2’’- terthiophene), were prepared and characterized by 1H, 13C and 31P NMR. Their redox, spectroscopic and bonding properties were studied with a range of spectro-electrochemical methods in combination with density functional theory calculations. The first two anodic steps observed for 1a and 1d are largely localized on the lateral frameworks of the molecular triangle, the direct conjugation between them being precluded due to the photostable open form of the dithienyl ethene moiety. The third anodic step is then mainly localized on the centerpiece of the triangular structure, affecting both bithiophene laterals. The experimental IR and UV-vis-NIR spectroelectrochemical data and, largely, also DFT calculations account for this explanation, being further supported by direct comparison with the anodic behavior of reference diruthenium complexes 1b and 1c.

Rapid selective separation of americium/curium from simulated nuclear forensic matrices using triazine ligands

In analysis of complex nuclear forensic samples containing lanthanides, actinides and matrix elements, rapid selective extraction of Am/Cm for quantification is challenging, in particular due the difficult separation of Am/Cm from lanthanides. Here we present a separation process for Am/Cm(III) which is achieved using a combination of AG1-X8 chromatography followed by Am/Cm extraction with a triazine ligand. The ligands tested in our process were CyMe4-BTPhen, CyMe4- BTBP, CA-BTP and CA-BTPhen. Our process allows for purification and quantification of Am and Cm (recoveries 80%–100%) and other major actinides in < 2d without the use of multiple columns or thiocyanate. The process is unaffected by high level Ca(II)/Fe(III)/Al(III) (10mg mL−1) and thus requires little pre-treatment of samples.

Notable differences between oxidized diruthenium complexes bridged by four isomeric diethynyl benzodithiophene ligands

Four new diruthenium complexes [{(η5-C5Me5)Ru(dppe)}2(μ-CuC–L–CuC)] featuring different bridging isomeric diethynyl benzodithiophenes viz. L = benzo[1,2-b;4,5-b’]dithiophene (complex 1), benzo[2,1-b;4,5b’]dithiophene (complex 2), benzo[1,2-b;3,4-b’]dithiophene (complex 3) and benzo[1,2-b;4,3-b’]-dithiophene (complex 4), were synthesized and characterized by molecular spectroscopic and crystallographicmethods. The subtle changes in the molecular structure introduced by the diethynyl benzodithiophene isomers have a notable impact on the stability of the oxidized complexes and their absorption characteristics in the visible-NIR and IR spectral domains. Electronic properties of stable oxidized complexes[1]n+ and [4]n+ (n = 1, 2) were investigated by cyclic voltammetry, UV-vis-NIR and IR spectroelectrochemistry as well as DFT and TDDFT calculations. The results document the largely bridgelocalized character of the oxidation of parents 1 and 4. Cations [2]+ and [3]+ are too unstable at ambient temperature to afford their unambiguous characterization. UV-vis-NIR absorption spectral data combined with TDDFT calculations (BLYP35) reveal that the broad electronic absorption of [1]+ and [4]+ in the NIR region has a mixed intraligand π–π* and MLCT character, with similar contribution from their spin-delocalized trans and cis conformers. A spin-localized (mixed-valence) rotamer was only observed for [1]+ at ambient temperature as a minor component on the time scale of IR spectroscopy.

Synthesis, characterization and evaluation of antileishmanial activity of copper(II) with fluorinated alpha-hydroxycarboxylate ligands

In this study, Cu(II) complexes with fluorinated ligands were produced aiming at the development of new, less toxic antileishmanial metallodrugs. Complexes of the general formula CuL(2) (L = lactate, trifluorolactate, 2-hydroxyisobutyrate, trifluoro-2-hydroxyisobutyrate) were synthesized in methanolic medium, purified by crystallization and characterized by elemental analysis and electronic and infrared spectroscopies. In vitro experiments with Leishmania amazonensis promastigotes showed that the trifluorolactate derivative more active than its non-fluorinated counterpart. Our results indicate that fluorinated chelators may be interesting to increase metal toxicity and/or open new paths for metallodrug chemotherapy against leishmaniasis.

Differential effects of TR ligands on hormone dissociation rates: Evidence for multiple ligand entry/exit pathways

Some nuclear receptor (NR) ligands promote dissociation of radiolabeled bound hormone from the buried ligand binding cavity (LBC) more rapidly than excess unlabeled hormone itself This result was interpreted to mean that challenger ligands bind allosteric sites on the LBD to induce hormone dissociation, and recent findings indicate that ligands bind weakly to multiple sites on the LBD surface. Here we show, that a large fraction of thyroid hormone receptor (TR) ligands promote rapid dissociation (T(1/2) < 2 h) of , radiolabeled T(3) vs. T(3) (T(1/2), approximate to 5-7 h). We cannot discern relationships between this effect and ligand size, activity or affinity for TR beta. One ligand, GC-24, binds the TR LBC and (weakly) to the TR beta-LBD surface that mediates dimer/heterodimer interaction, but we cannot link this interaction to rapid T(3) dissociation. Instead, several lines of evidence suggest that the challenger ligand must interact with the buried LBC to promote rapid T(3) release. Since previous molecular dynamics simulations suggest that TR ligands leave the LBC by several routes, we propose that a subset of challenger ligands binds and stabilizes a partially unfolded intermediate state of TR that arises during T(3) release and that this effect enhances hormone dissociation. (C) 2009 Elsevier Ltd. All rights reserved.

Syntheses, crystal structure and theoretical investigation of novel heteroleptic complexes of nickel(II) with N-R-sulfonyldithiocarbimate and phosphine ligands

Five new complexes of general formula: [Ni(RSO(2)N=CS(2))(dppe)], where R = C(6)H(5) (1), 4-ClC(6)H(4) (2), 4-BrC(6)H(4) (3), 4-IC(6)H(4) (4) and dppe = 1,2-bis(diphenylphosphino) ethane and [Ni(4-IC(6)H(4)SO(2)N=CS(2))(PPh(3))(2)] (5), where PPh3 = triphenylphosphine, were obtained in crystalline form by the reaction of the appropriate potassium N-R-sulfonyldithiocarbimate K(2)(RSO(2)N=CS(2)) and dppe or PPh(3) with nickel(II) chloride in ethanol/water. The elemental analyses and the IR, (1)H NMR, (13)C NMR and (31)P NMR spectra are consistent with the formation of the square planar nickel(II) complexes with mixed ligands. All complexes were also characterized by X-ray diffraction techniques and present a distorted cis-NiS(2)P(2) square-planar configuration around the Ni atom. Quantum chemical calculations reproduced the crystallographic structures and are in accord with the spectroscopic data. Rare C-H center dot center dot center dot Ni intramolecular short contact interactions were observed in the complexes 1-5. (C) 2011 Elsevier B. V. All rights reserved.

Two-dimensional QSAR studies on arylpiperazines as high-affinity 5-HT(1A) receptor ligands

5-HT(1A) receptor plays an important role in the delayed onset of antidepressant action of a class of selective serotonin reuptake inhibitors. Moreover, 5-HT(1A) receptor levels have been shown to be altered in patients suffering from major depression. In this work, hologram quantitative structure-activity relationship (HQSAR) studies were performed on a series of arylpiperazine compounds presenting affinity to the 5-HT(1A) receptor. The models were constructed with a training set of 70 compounds. The most significant HQSAR model (q(2) = 0.81, r(2) = 0.96) was generated using atoms, bonds, connections, chirality, and donor and acceptor as fragment distinction, with fragment size of 6-9. Predictions for an external test set containing 20 compounds are in good agreement with experimental results showing the robustness of the model. Additionally, useful information can be obtained from the 2D contribution maps.

Ruthenium(II) complexes containing N(4)-tolyl-2-acetylpyridine thiosemicarbazones and phosphine ligands: NMR and electrochemical studies of cis-trans isomerization

[Ru(HL)(PPh3)(2)Cl]Cl complexes have been obtained in which HL = N(4)-ortho (complex 1), N(4)-meta (complex 2) and N(4) pctratolyl 2-acetylpyridine thiosemicarbazone (complex 3). NMR and electrochemical studies indicate that both cis and trans isomers exist in solution, and that the cis isomers are converted into the trans isomers with time. Crystal structure determination of (1) reveals that the traps isomer is formed in the solid state. (c) 2007 Elsevier B.V. All rights reserved.

New insights on the Lewis acidity of diorganolead(IV) compounds: Diphenyllead(IV) complexes with N,O,S-chelating ligands

The reactions of PbPh2(OAC)(2) with alkylglyoxylate thiosemicarbazones (HRGTSC, R = Et, Bu) afforded complexes of the type [PbPh2(GTSC)] center dot H2O, [PbPh2(RGTSC)(2)] and [PbPh2Cl(BUGTSC)]. The structures of HRGTSC (R = Me, Et, Bu), [PbPh2(OAc)(RGTSC)](R = Me, Et, Bu), [PbPh2Cl(BuGTSC)] and [PbPh2(GTSC)] center dot H2O have been studied by X-ray diffraction. [PbPh2(OAc)(RGTSC)] and [PbPh2(GTSC)] center dot H2O have [PbC2NO3S] kernels and the coordination sphere of the metal is pentagonal bipyramidal. [PbPh2Cl(BuGTSC)] has a [PbC2NOSCI] kernel and the coordination geometry around lead is pentagonal bipyramidal with one vacant site. Analysis of the bond distances in [PbPh2(GTSC)] center dot H2O suggests a significant affinity between diphenyllead(IV) and carboxylate donor groups, supporting a borderline acidic character for this organometallic cation. H-1 and C-13 NMR spectra in DMSO-d(6) suggest the partial dissociation of the acetate in [PbPh2(OAc)(RGTSC)] solutions and indicate some differences in the coordination mode of the two RGTSC(-) ligands in [PbPh2(RGTSC)(2)] complexes. (C) 2007 Elsevier Ltd. All rights reserved.

New Pd(II) and Pt(II) complexes with N,S-chelated pyrazolonate ligands: Molecular and supramolecular structure and preliminary study of their in vitro antitumoral activity

New Pd(II) and Pt(II) complexes [ML2] (HL = a substituted 2,5-dihydro-5-oxo-1H-pyrazolone-1-carbothioamide) have been synthesized by reacting K2MCl4 (M = Pd, Pt) or Pd(OAc)(2) with beta-ketoester thiosemicarbazones. The structures of seven of these complexes were determined by X-ray diffraction. Although all exhibit a distorted square-planar coordination with trans- or (in one case) cis-[MN2S2] kernels, their supramolecular arrangements vary widely from isolated molecules to 3D-networks. The in vitro antitumoral assays performed with two HL ligands and their metal complexes showed significant cytostatic activity for the latter, with the most active [ML2] derivative (a palladium complex) being about sixteen times more active than cis-DDP against the cis-platinum-resistant cell line A2780cisR. (c) 2007 Elsevier Inc. All rights reserved.

Catecholase and DNase activities of copper(II) complexes containing phenolate-type ligands

Three new homodinuclear complexes containing substituted phenolate-type ligands based on the N(5)O(2) donor (2-(N,N-Bis(2-pyridylmethyl)aminomethyl)-6-(N`,N`-(2-hydroxybenzyl)(2-pyridylmethyl))aminomethyl)-4-methylphenol (H(2)L-H) were synthesized and characterized by X-ray crystallography. Potentiometric titration studies in 70% (v/v) aqueous ethanol show that all three complexes exhibit a common {Cu(II)(mu-phenoxo)(mu-OH)Cu(II)(OH)} core in solution. Kinetic studies on the oxidation reaction of 3,5-di-tert-butylcatechol revealed that the catalytic activity of the metal complexes increases toward the ligand containing an electron-donating group. In addition, these complexes also carried out DNA cleavage by hydrolytic and oxidative pathways. Copyright (C) 2010 John Wiley & Sons, Ltd.

Pharmacophore-based 3D QSAR studies on a series of high affinity 5-HT(1A) receptor ligands

5-HT(1A) receptor antagonists have been employed to treat depression, but the lack of structural information on this receptor hampers the design of specific and selective ligands. In this study, we have performed CoMFA studies on a training set of arylpiperazines (high affinity 5-HT(1A) receptor ligands) and to produce an effective alignment of the data set, a pharmacophore model was produced using Galahad. A statistically significant model was obtained, indicating a good internal consistency and predictive ability for untested compounds. The information gathered from our receptor-independent pharmacophore hypothesis is in good agreement with results from independent studies using different approaches. Therefore, this work provides important insights on the chemical and structural basis involved in the molecular recognition of these compounds. (C) 2010 Elsevier Masson SAS. All rights reserved.

(1)H NMR spectroscopy as a tool to determine accurate photoisomerization quantum yields of stilbene-like ligands coordinated to rhenium(I) polypyridyl complexes

In this work, the use of proton nuclear magnetic resonance, (1)H NMR, was fully described as a powerful tool to follow a photoreaction and to determine accurate quantum yields, so called true quantum yields (Phi(true)), when a reactant and photoproduct absorption overlap. For this, Phi(true) for the trans-cis photoisomerization process were determined for rhenium(I) polypyridyl complexes, fac-[Re(CO)(3)(NN)(trans-L)](+) (NN = 1,10-phenanthroline, phen, or 4,7-diphenyl-1,10-phenanthroline, ph(2)phen, and L = 1,2-bis(4-pyridyl) ethylene, bpe, or 4-styrylpyridine, stpy). The true values determined at 365 nm irradiation (e. g. Phi(NMR) = 0.80 for fac-[Re(CO)(3)(phen)(trans-bpe)](+)) were much higher than those determined by absorption spectral changes (Phi(UV-Vis) = 0.39 for fac-[Re(CO)(3)(phen)(trans-bpe)](+)). Phi(NMR) are more accurate in these cases due to the distinct proton signals of trans and cis-isomers, which allow the actual determination of each component concentration under given irradiation time. Nevertheless when the photoproduct or reactant contribution at the probe wavelength is negligible, one can determine Phi(true) by regular absorption spectral changes. For instance, Phi(313) nm for free ligand photoisomerization determined both by absorption and (1)H NMR variation are equal within the experimental error (bpe: Phi(UV-Vis) = 0.27, Phi(NMR) = 0.26; stpy: Phi(UV-Vis) = 0.49, Phi(NMR) = 0.49). Moreover, (1)H NMR data combined with electronic spectra allowed molar absorptivity determination of difficult to isolate cis-complexes. (C) 2009 Elsevier B. V. All rights reserved.