Copper(II) trimethylacetate complexes with 3,5-dimethylpyrazole

Specific features of the chemical behavior and structure of copper(II) trimethylacetate complexes with 3,5-dimethylpyrazole have been considered based on X-ray crystallographic data.     

Rhenium(IV) and rhenium(V) complexes with 3,5-dimethylpyrazole

Mono-and dinuclear Re^IV and Re^V complexes with 3,5-dimethylpyrazole (Me₂pzH) were synthesized. The cis-[Re₂O₃Cl₄(3,5-Me₂pzH)₄] complex (cis-1) was prepared by the reaction of NH₄ReO₄ with K[HB(Me₂pz)₃] in concentrated HCl or by refluxing of [ReCl₃(MeCN)(PPh₃)₂] with Me₂pzH in air. The bromide complex trans-[Re₂O₃Br₄(3,5-Me₂pzH)₄] (trans-2) was synthesized by passing dry HBr through a solution of [Re₂O₃Br₂(μ-3,5-Me₂pz)₂(3,5-Me₂pzH)₂] (4) in chloroform. The pyrazolate-bridged complex [Re₂O₃Cl₂(μ-3,5-Me₂pz)₂(3,5-Me₂pzH)₂] (3) was prepared from (Et₄N)₂[ReOCl₅] or Cs₂[ReOCl₅] and Me₂pzH. The corresponding bromide and iodide complexes [Re₂O₃X₂(3,5-Me₂pz)₂(3,5-Me₂pzH)₂] · C₆H₆ (X = Br (4) or I (5)) were synthesized by the reactions of (NH₄)₂[ReBr₆] or K₂[ReI₆], respectively, with Me₂pzH. The [ReO(OMe)(3,5-Me₂pzH)₄]Br₂ · · 3,5-Me₂pzH · 4H₂O complex (6) was obtained as a by-product in the synthesis of complex 4. The reaction of [ReNCl₂(PPh₃)₂] with Me₂pzH was accompanied by hydrolytic denitration giving rise to the mixed-ligand complex [Re₂O₃Cl₂(μ-3,5-Me₂pz)₂(3,5-Me₂pzH)(PPh₃)] (7). The reaction of (NH₄)₂[ReBr₆] with a Me₂pzH melt gave the trans-[ReBr₄(3,5-Me₂pzH)₂] · · Me₂CO complex (8). The structures of complexes 2 and 4–8 were established by X-ray diffraction. All compounds were characterized by elemental analysis, electronic absorption spectroscopy, ¹H NMR and IR spectroscopy, mass spectrometry, and cyclic voltammetry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 52–59, January, 2006.     

The influence of solvent polarity on the tetrahedral-octahedral equilibrium of Co(II)complexes with 3,5-dimethylpyrazole

The configuration equilibrium:

(where DMPz = 3,5-dimethylpyrazole), has been studied spectrophotometrically in various non-aqueous polar solvents. The influence of solvent polarity on the K value has been investigated. Solvation studies have also been carried out on the tetrahedral species Co(SCN)₂(DMPz)₂, and the results are interpreted in terms of the polarity of the various solvents.     

Synthesis and structural characterization of new polynuclear complexes of 1-hydroxymethyl-3,5-dimethylpyrazole with Ni(II) and Fe(II)

The complexation of the simple 1-hydroxymethyl-3,5-dimethylpyrazole (HL) ligand with Fe and Ni salts leads to interesting polynuclear complexes in good yield. X-ray diffraction reveals that the resulting complexes (μ₄-L)₄Ni₄Cl₄(H₂O)₄ and (μ₂-L)₄(μ₃-L)₂Fe₈Cl₁₆(μ₄-O)₆ adopt cubane-type and open-cubane-type structures in the solid state.     

Nitric oxide reactivity of fluorophore coordinated carboxylate-bridged diiron(II) and dicobalt(II) complexes

The synthesis, structural characterization, and NO reactivity of carboxylate-bridged dimetallic complexes were investigated. The diiron(II) complex [Fe(2)(mu-O(2)CAr(Tol))(4)(Ds-pip)(2)] (1), where O(2)CAr(Tol) = 2,6-di(p-tolyl)benzoate and Ds-pip = dansyl-piperazine, was prepared and determined by X-ray crystallography to have a paddlewheel geometry. This complex reacts with NO within 1 min with a concomitant 4-fold increase in fluorescence emission intensity ascribed to displacement of Ds-pip. Although the diiron complex reacts with NO, as revealed by infrared spectroscopic studies, its sensitivity to dioxygen renders it unsuitable as an atmospheric NO sensor. The air-stable dicobalt(II) analogue was also synthesized and its reactivity investigated. In solution, the dicobalt(II) complex exists as an equilibrium between paddlewheel [Co(2)(mu-O(2)CAr(Tol))(4)(Ds-pip)(2)] (2) and windmill [Co(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(Ds-pip)(2)] (3) geometric isomers. Conditions for crystallizing pure samples of each of these isomers are described. Reaction of 2 with excess NO proceeds by reductive nitrosylation giving [Co(mu-O(2)CAr(Tol))(2)(NO)(4)] (5), which is accompanied by release of the Ds-pip fluorophore that is N-nitrosated in the process. This reaction affords an overall 9.6-fold increase in fluorescence emission intensity, further demonstrating the potential utility of ligand dissociation as a strategy for designing fluorescence-based sensors to detect nitric oxide in a variety of contexts.     

Osmium(II) and ruthenium(II) arene maltolato complexes: rapid hydrolysis and nucleobase binding

Density functional calculations show that aquation of [Os(eta6-arene)(XY)Cl]n+ complexes is more facile for complexes in which XY=an anionic O,O-chelated ligand compared to a neutral N,N-chelated ligand, and the mechanism more dissociative in character. The O,O-chelated XY=maltolato (mal) [M(eta6-p-cym)(mal)Cl] complexes, in which p-cym=p-cymene, M=OsII (1) and RuII (2), were synthesised and the X-ray crystal structures of 1 and 22 H2O determined. Their hydrolysis rates were rapid (too fast to follow by NMR spectroscopy). The aqua adduct of the OsII complex 1 was 1.6 pKa units more acidic than that of the RuII complex 2. Dynamic NMR studies suggested that O,O-chelate ring opening occurs on a millisecond timescale in coordinating proton-donor solvents, and loss of chelated mal in aqueous solution led to the formation of the hydroxo-bridged dimers [(eta6-p-cym)M(mu-OH)3M(eta6-p-cym)]+. The proportion of this dimer in solutions of the OsII complex 1 increased with dilution and it predominated at micromolar concentrations, even in the presence of 0.1 M NaCl (conditions close to those used for cytotoxicity testing). Although 9-ethylguanine (9-EtG) binds rapidly to Os(II) in 1 and more strongly (log K=4.4) than to RuII in 2 (log K=3.9), the OsII adduct [Os(eta6-p-cym)(mal)(9EtG)]+ was unstable with respect to formation of the hydroxo-bridged dimer at micromolar concentrations. Such insights into the aqueous solution chemistry of metal-arene complexes under biologically relevant conditions will aid the rational design of organometallic anticancer agents.     

Anion binding and luminescent sensing using cationic ruthenium(II) aminopyridine complexes

The synthesis of a series of ruthenium(II) based anion sensors of the type [Ru(eta(6)-C(6)H(4)MeCHMe(2))Cl(L)(2)][BF(4)] (2) is reported in which ligand L represents a series of substituted pyridinylmethyl-amine derivatives. The carbazole based ligand L(3) exhibits a fluorescent intraligand charge-transfer (ILCT) state that is quenched by ligand-to-metal charge transfer (LMCT) upon coordination to ruthenium in the 1:1 complex [Ru(eta(6)-C(6)H(4)MeCHMe(2))Cl(2)(L(3))] (1 c). The 1:2 complex 2 c is fluorescent, however, and acts as a fluorescent anion sensor because of the mixing of an anion-dependent charge-transfer component into the excited state. The 1:2 complexes of type 2 all exhibit interesting low symmetry (1)H NMR spectra that also are a useful handle on anion complexation. The electronic structures of L(3), 1 c and 2 c have been probed by time-dependent DFT calculations.     

DNA binding and topoisomerase II inhibitory activity of water-soluble ruthenium(II) and rhodium(III) complexes

Water-soluble piano-stool arene ruthenium complexes based on 1-(4-cyanophenyl)imidazole (CPI) and 4-cyanopyridine (CNPy) with the formulas [(eta6-arene)RuCl2(L)] (L = CPI, eta6-arene = benzene (1), p-cymene (2), hexamethylbenzene (3); L = CNPy, eta6-arene = benzene (4), p-cymene (5), hexamethylbenzene (6)) have been prepared by our earlier methods. The molecular structure of [(eta6-C6Me6)RuCl2(CNPy)] (6) has been determined crystallographically. Analogous rhodium(III) complex [(eta5-C5Me5)RhCl2(CPI)] (7) has also been prepared and characterized. DNA interaction with the arene ruthenium complexes and the rhodium complex has been examined by spectroscopic and gel mobility shift assay; condensation of DNA and B-->Z transition have also been described. Arene ruthenium(II) and EPh3 (E = P, As)-containing arene ruthenium(II) complexes exhibited strong binding behavior, however, rhodium(III) complexes were found to be Topo II inhibitors with an inhibition percentage of 70% (7) and 30% (7a). Furthermore, arene ruthenium complexes containing polypyridyl ligands also act as mild Topo II inhibitors (10%, 3c and 40%, 3d) in contrast to their precursor complexes. Complexes 4-6 also show significant inhibition of beta-hematin/hemozoin formation activity.     

Dithiocarboxylate complexes of ruthenium(II) and osmium(II)

The ruthenium(II) complexes [Ru(R)(κ(2)-S(2)C·IPr)(CO)(PPh(3))(2)](+) (R = CH=CHBu(t), CH=CHC(6)H(4)Me-4, C(C≡CPh)=CHPh) are formed on reaction of IPr·CS(2) with [Ru(R)Cl(CO)(BTD)(PPh(3))(2)] (BTD = 2,1,3-benzothiadiazole) or [Ru(C(C≡CPh)=CHPh)Cl(CO)(PPh(3))(2)] in the presence of ammonium hexafluorophosphate. Similarly, the complexes [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)](+) and [Ru(C(C≡CPh)=CHPh)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)](+) are formed in the same manner when ICy·CS(2) is employed. The ligand IMes·CS(2) reacts with [Ru(R)Cl(CO)(BTD)(PPh(3))(2)] to form the compounds [Ru(R)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) (R = CH=CHBu(t), CH=CHC(6)H(4)Me-4, C(C≡CPh)=CHPh). Two osmium analogues, [Os(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) and [Os(C(C≡CPh)=CHPh)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) were also prepared. When the more bulky diisopropylphenyl derivative IDip·CS(2) is used, an unusual product, [Ru(κ(2)-SC(H)S(CH=CHC(6)H(4)Me-4)·IDip)Cl(CO)(PPh(3))(2)](+), with a migrated vinyl group, is obtained. Over extended reaction times, [Ru(CH=CHC(6)H(4)Me-4)Cl(BTD)(CO)(PPh(3))(2)] also reacts with IMes·CS(2) and NH(4)PF(6) to yield the analogous product [Ru{κ(2)-SC(H)S(CH=CHC(6)H(4)Me-4)·IMes}Cl(CO)(PPh(3))(2)](+)via the intermediate [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+). Structural studies are reported for [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IPr)(CO)(PPh(3))(2)]PF(6) and [Ru(C(C≡CPh)=CHPh)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)]PF(6).     

Electroluminescence in ruthenium(II) complexes

We have investigated the electrochemical, spectroscopic, and electroluminescent properties of a family of diimine complexes of Ru featuring various aliphatic side chains as well as a more extended pi-conjugated system. The performance of solid-state electroluminescent devices fabricated from these complexes using indium tin oxide (ITO) and gold contacts appears to be dominated by ionic space charge effects. Their electroluminescence efficiency was limited by the photoluminescence efficiency of the Ru films and not by charge injection from the contacts. The incorporation of di-tert-butyl side chains on the dipyridyl ligand was found to be the most beneficial substitution in terms of reducing self-quenching of luminescence.     

Cyanato-copper(II) complexes with organic ligands—XXIV. Diisocyanato-bis(3,5-dimethylpyrazole)copper(II)—the cyanate member of the coligand isomer

The title compound was prepared, and found to be isomeric with the known bis(1-carbamoyl-3,5-dimethylpyrazolato)copper(II). Its IR, far-IR, electronic     

Molecular wiring of LiMnPO4 (olivine) by ruthenium(II)-bipyridine complexes

LiMnPO₄ (olivine) was surface-modified by two different complexes: Ru-bis(4,4′-diethoxycarbonyl-2,2′-bipyridine)(4,4′-dicarboxylate-2,2′-bipyridine) and Ru-bis(4-carboxylic acid-4′-carboxylate-2,2′-bipyridine)(4,4′-dinonyl-2,2′bipyridine). These complexes have redox potentials of 4.45 and 4.25 V vs. Li/Li⁺, respectively, and are both active for molecular wiring of LiMnPO₄. The surface-confined Ru(II)/Ru(III) redox reaction propagates across the monolayer via hole-hopping, allowing a subsequent chemical delithiation of the underneath olivine towards MnPO₄. The activity of LiMnPO₄ is about half of that of LiFePO₄ (olivine) at similar experimental conditions.     

Thin-film solid-state electroluminescent devices based on tris(2,2'-bipyridine)ruthenium(II) complexes

The behavior of light-emitting electrochemical cells (LEC) based on solid films ( approximately 100 nm) of tris(2,2'-bipyridine)ruthenium(II) between an ITO anode and a Ga-In cathode was investigated. The response times were strongly influenced by the nature of the counterion: small anions (BF(4)(-) and ClO(4)(-)) led to relatively fast transients, while large anions (PF(6)(-), AsF(6)(-)) produced a slow time-response. From comparative experiments of cells prepared and tested in a glovebox to those in ambient, mobility of the anions in these films appears to be related to the presence of traces of water from atmospheric moisture. An electrochemical model is proposed to describe the behavior of these LECs. The simulation results agreed well with experimental transients of current and light emission as a function of time and show that the charge injection is asymmetric at the two electrodes. At a small bias, electrons are the major carriers, while for a larger bias the conduction becomes bipolar.     

Nitric oxide photorelease from ruthenium salen complexes in aqueous and organic solutions

The complexes [Ru(salen)(NO)Cl] and [Ru(salen)(NO)(H(2)O)](+) were shown to release the nitrosyl ligand as nitric oxide upon exposure to visible light in organic and aqueous solutions respectively, by means of UV-visible, EPR, and FTIR spectroscopies. The former was prepared by a new synthetic route and had its structure determined by single-crystal X-ray diffraction. A crystal of the dichloromethane solvate is orthorhombic, space group Fdd2 (No. 43) and formula C(16)H(14)ClN(3)O(3)Ru.CH(2)Cl(2), with Z = 16 and cell parameters a = 25.489(4), b = 33.435(4), and c = 9.3716(9) A. The electronic absorption spectra of the complexes were calculated using the INDO/S method. The water-soluble complex is a potential drug for antitumoral phototreatment.     

Redox-switchable conjugated bimetallic ruthenium(II) complexes

The conjugated bimetallic ruthenium(II) complex composed of 1,4-phenylenediamine as a bridging ligand was synthesized by photo-irradiation to show redox-switching of the emission properties of the terminal Ru(II) units depending on the redox state of the π-conjugated bridging spacer.     

Nitric oxide reduction of copper(II) complexes: spectroscopic evidence of copper(II)-nitrosyl intermediate

Two copper(II) complexes, 1 and 2 with L(1) and L(2) [L(1) = 2- aminomethyl pyridine; L(2) = bis-(2-aminoethyl)amine], respectively, in degassed acetonitrile solvent, on exposure to NO gas, were found to form a thermally unstable [Cu(II)-NO] intermediate which then resulted in the reduction of the copper(II) centers. The formation of the [Cu(II)-NO] intermediate was evidenced by UV-visible, FT-IR, and EPR spectroscopic studies. The reduction of the copper(II) centers by nitric oxide afforded ligand transformation through diazotization at the primary amine coordination site, in both cases. The modified ligands, in each case, were isolated and characterized.     

Inert benzothiazole functionalised ruthenium(II) complexes; potential DNA hairpin binding agents

The two enantiomers of [Ru(bpy)2(bbtb)]2+{bpy = 2,2'-bipyridine; bbtb = 4,4'-bis(benzothiazol-2-yl)-2,2'-bipyridine} have been isolated and fully characterised. Both enantiomers have been shown to have a strong association with calf thymus DNA by UV/visible absorption, emission and CD spectroscopy, with the Lambda enantiomer having the greater affinity. The binding of both enantiomeric forms of [Ru(bpy)2(Me2bpy)]2+ and [Ru(bpy)2(bbtb)]2+{Me(2)bpy = 4,4'-dimethyl-2,2'-bipyridine} to a range of oligonucleotides, including an octadecanucleotide and an icosanucleotide which contain hairpin-sequences, have been studied using a fluorescent intercalator displacement (FID) assay. The complex [Ru(bpy)2(bbtb)]2+ exhibited an interesting association with hairpin oligonucleotides, again with the Lambda enantiomer binding more strongly. A (1)H NMR spectroscopic study of the binding of both enantiomers of [Ru(bpy)2(bbtb)]2+ to the icosanucleotide d(CACTGGTCTCTCTACCAGTG) was conducted. This sequence contains a seven-base-pair duplex stem and a six-base hairpin-loop. The investigation gave an indication of the relative binding of the complexes between the two different regions (duplex and secondary structure) of the oligonucleotide. The results suggest that both enantiomers bind at the hairpin, with the ruthenium centre located at the stem-loop interface. NOE studies indicate that one of the two benzothiazole substituents of the bbtb ligand projects into the loop-region. A simple model of the metal complex/oligonucleotide adduct was obtained by means of molecular modelling simulations. The results from this study suggest that benzothiazole complexes derived from inert polypyridine ruthenium(II) complexes could lead to the development of new fluorescent DNA hairpin binding agents.