Dinuclear ruthenium complexes containing tripodal dithiophosphonate ligands

Treatment of [(η⁶-p-cymene)RuCl(μ-Cl)]₂ with Lawesson’s reagent [ArP(S)(μ-S)]₂ (Ar = p-C₆H₄OMe) in the presence of ammonium hydroxide afforded the dinuclear complex [(η⁶-p-cymene)Ru{μ-η¹(S),η²(S,S′)-ArP(O)S₂}]₂ (1) in which the tripodal [ArP(O)S₂]²⁻ ligands bind to the ruthenium atom in both bridging and chelating modes with two non-coordinating PO groups. Interaction of [RuHCl(CO)(PPh₃)₃] with [ArP(S)(μ-S)]₂ and bis(diphenylphosphino)methane (dppm) in the presence of ammonium hydroxide gave the dinuclear complex [Ru(CO){μ₃-η¹(O),η²(S,S′)-ArP(O)S₂}(dppm)]₂ (2) in which the tripodal [ArPOS₂]²⁻ ligands bind the two Ru atoms via both sulfur and oxygen atoms. Treatment of [Ru(PPh₃)₃Cl₂] with [ArP(S)(μ-S)]₂ at reflux in the presence of ammonium hydroxide led to the formation of the dinuclear mixed valence complex [Ru₂Cl₂(μ-S){μ₃-η¹(O),η¹(S),-η²(S,S′)-ArP(O)S₂}(PPh₃)₃] (3), which contains a [Ru^II(PPh₃)₂Cl]⁺ and [Ru^IV(PPh₃)Cl]³⁺ moieties by the tripodal [ArPOS₂]²⁻ ligand in a μ₃-η¹(O),η¹(S),η²(S,S′) coordination mode and the μ-S²⁻ anion. The crystal structures of 1, 2, and 3·CH₂Cl₂ along with their spectroscopic and electrochemical properties are reported.     

Synthesis,structure analysis,solution chemistry,and in vitro insulinomimetic activity of novel oxovanadium(IV) complexes with tripodal ligands containing an imidazole group derived from amino acids

Structures, chemical properties, and in vitro insulinomimetic activities of new vanadyl [oxovanadium(IV), VO(2+)] complexes with five tripodal ligands containing an imidazole functionality were examined. The ligands, N-(carboxymethyl)- N-(4-imidazolylmethyl)amino acids, contain glycine, ( S)- and ( R)-alanine, and ( S)- and ( R)-leucine residues. The molecular structures of the latter four alanine- and leucine-containing complexes were determined by X-ray analysis. The coordination geometry around each vanadium center was octahedral, where an imino nitrogen occupied the apical site and two carboxylate oxygens, an imidazole nitrogen, and a water molecule coordinated in the equatorial plane. The spectroscopic properties of the complexes were characterized by means of IR, electronic absorption, and CD spectra. Acid dissociation constants (p K(a)) and protonation sites of the ligands were determined by a combination of potentiometric titrations and (1)H NMR spectra. The potentiometric study demonstrated that stability constants (log beta) were not so different among the present complexes (14.0-14.9) and a species of molecular complex with a 1:1 metal:ligand ratio existed predominantly at physiological pH 7.4. EPR parameters indicated that the species at pH 7.4 had an octahedral structure similar to the complex in the solid state. On the other hand, an EPR study in phosphate buffer (pH 7.4) suggested that inorganic phosphate coordinated to the vanadium center instead of the imidazole group in the presence of excess phosphate ion. Cyclic voltammograms in the phosphate buffer showed chemically reversible oxidation waves, whereas irreversible oxidation waves were observed in non-coordinating HEPES buffer. Moreover, the oxidation potential of each complex in phosphate buffer was more positive than that in HEPES buffer. Partition coefficients of the present complexes in a n-octanol/saline system were very low, probably due to hydrophilicity of the imidazole group. The in vitro insulinomimetic activities were estimated on the basis of the ability of the complexes to inhibit epinephrine-stimulated free fatty acid release from isolated rat adipocytes. The achiral glycine-derivative complex exhibited the highest insulinomimetic activity, which was higher than that of VOSO(4) as a positive control. Putting our previous observations together, it was found that the vanadyl complexes with tetradentate amino acid derivatives having no alkyl side chain tend to have high in vitro insulinomimetic activity.     

An unprecedented iron(III) complex supported by an asymmetric N-capped tripodal ligand incorporating the NO2S donor set

The synthesis of an iron(III) complex [Fe(L)(1-Meim)] (1-Meim = 1-methylimidazole) coordinated by an asymmetric N-capped tripodal tetradentate ligand (L) equipped with three aromatic arms is described. X-ray crystallographic analysis shows that the complex adopts a distorted bipyramidal geometry with a new type of N₂O₂S coordination environment around the iron centre.     

Structure and spectroscopic studies of cis-bis(bipyridine) ruthenium(II) complexes of phenylcyanamide ligands

New ruthenium(II) complexes with cyanamide ligands, cis-[Ru(bpy)₂(Ipcyd)₂] (1) and [Ru(bpy)₂(OHpcyd)₂] (2) (bpy = 2,2′-bipyridine, Ipcyd = 4-iodophenylcyanamide anion, OHpcyd = 4-(3-hydroxy-3-methylbut-1-ynil)phenylcyanamide), have been prepared and characterized by UV-Vis, IR and ¹H NMR spectroscopies as well as electrochemical technique (CV). The complex cis-[Ru(bpy)₂(Ipcyd)₂] (1) crystallized with empirical formula of C₃₄H₂₄I₂N₈Ru in a monoclinic crystal system and space group of P2₁/c with a = 11.769(7) Å, b = 24.188(12) Å, c = 11.623(2) Å, β = 91.63(3)°, V = 3308(3) ų and Z = 4.     

A new tripodal poly-imine indole-containing ligand: Synthesis, complexation, spectroscopic and theoretical studies

A novel flexible tripodal ligand derived from 3-methylindole, (“InTREN” L), and its mononuclear Zn(II), Cu(II), Ni(II), Hg(II) and Pd(II) complexes are described. All compounds gave analytically pure solid samples. Characterisation of the compounds was accomplished by ¹H NMR, IR and absorption spectroscopies, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and elemental analysis and their geometry optimized using density functional theory (DFT).Time-dependent-density functional theory (TD-DFT) calculations have been used to assign the lowest energy absorption bands of the free ligand and the Zn(II) complex. The system is a very good candidate for in situ recognition/coordination effects by MALDI-TOF-MS spectrometry and absorption spectroscopy. The presence of three indole groups in InTREN opens up the possibility to synthesize new three-dimensional self-assembly supramolecular structures.     

The use of the borocaptate anion as a ligand. Synthesis and X-ray crystal structure of pentaammine (1-thiolato-closo-undecahydrododecaborane)ruthenium(III) dihydrate

The complex [Ru(SB₁₂H₁₁)(NH₃)₅]·2H₂O has been prepared by the reaction of Cs₂B₁₂H₁₁SH with [RuCl(NH₃)₅]Cl₂ in aqueous solution. The complex represents the first reported example of the borocaptate anion acting as a ligand. The structure of the complex has been determined by single crystal X-ray diffraction analysis. The crystal parameters are monoclinic, space group P2₁/c, A = 8.056(1), B = 14.240(2), C = 15.172(2) Å, β=98.48° and Z = 4. The ruthenium atom has a distorted octahedral coordination. The distortion is probably due to the high (3⁻) charge and the large bulk of the borocaptate ligand. These features can also be observed in the spectroscopic properties of the complex.     

Asymmetric epoxidation of alkenes using a mixed-ligand complex of ruthenium(III) containing a sugar-based ligand

A mixed-ligand ruthenium(III) catalyst complex, [Ru^III(TDL*)(bipy)(H₂O)]Cl (1) (TDL* = N-3,5-di-(t-butyl)salicylidine-d-glucosamine; bipy = 2,2′-bipyridine) exhibited catalytic activity toward enantioselective alkene epoxidation using tert-butyl hydroperoxide as terminal oxidant. Styrene, 4-chlorostyrene, 4-methylstyrene, 4-methoxystyrene, 1-methylcyclohexene and 1,2-dihydronaphthalene were effectively converted to their organic epoxides with moderate enantioselectivity (37-47% ee) at ambient temperature. A mechanism involving the formation of a high-valent Ru(V)-oxo species, and the subsequent oxo-transfer to the alkene through a metallaoxetane intermediate is proposed.     

An unsaturated half-sandwich ruthenium(II) complex containing a dithioimidodiphosphinate ligand

Treatment of [Cp*RuCl₂]_x (Cp* = η⁵-C₅Me₅) with K[N(Ph₂PS)₂] afforded [Cp*Ru{N(Ph₂PS)₂}Cl] (1). Reduction of 1 with Li[BEt₃H] gave the 16-electron half-sandwich Ru(II) complex [Cp*Ru{N(Ph₂PS)₂}] (2). Complexes 1 and 2 have been characterized by X-ray crystallography. The Ru-Cp*(centroid) and average Ru-S distances in 1 are 1.827 and 2.3833(5) Å, respectively. The corresponding bond distances in 2 are 1.739 and 2.379(1) Å. Treatment of 2 with 2-electron ligands L afforded the adducts [Cp*Ru{N(Ph₂PS)₂}L] (L = CO (3), 2,6-Me₂C₆H₄NC (4), MeCO₂CCCO₂Me (5)). Oxidation of 2 with tetramethylthiuram disulfide gave the Ru(IV) complex [Cp*Ru{S₂CNMe₂}₂][N(Ph₂PS)₂] (6). The Ru-Cp*(centroid) and average Ru-S distances in 6 are 1.897 and 2.387(1) Å, respectively.     

A new oxo-vanadium complex employing an imidazole-rich tripodal ligand: A bioinspired bromide and hydrocarbon oxidation catalyst

A vanadyl complex with the ligand (bis(1-methylimidazol-2-yl)methyl)(2-(pyridyl-2-yl)ethyl)amine was synthesized and fully characterized by X-ray crystallography, elemental analyses, cyclic voltammetry and infrared, electronic and electron paramagnetic resonance spectroscopies. This compound was designed under the so called hybrid concept. It shows to be able to promiscuously use hydrogen peroxide to oxidize bromide and to catalyze the oxidation of benzene and cyclohexane with very good selectivities.     

Synthesis, DNA-binding and photocleavage studies of ruthenium(II) complex with 2-(3'-phenoxyphenyl)imidazo[4,5-f][1,10]phenanthroline

A new polypyridyl ligand MPPIP {MPPIP=2-(3'-phenoxyphenyl)imidazo[4,5-f]-[1,10]phenanthroline} and its ruthenium(II) complexes, [Ru(bpy)(2)MPPIP](2+) (1) (bpy=2,2'-bipyridine) and [Ru(phen)(2)MPPIP](2+) (2) (phen=1,10-phenanthroline) have been synthesized and characterized. The binding of the two complexes to calf thymus DNA (CT-DNA) has been investigated with spectrophotometric methods, viscosity measurements, as well as equilibrium dialysis and circular dichroism spectroscopy. The results suggest that both complexes bind to CT-DNA through intercalation, and enantioselectively interact with CT-DNA in a way. However, complex 2 is a much better candidate as an enantioselective binder to CT-DNA than complex 1. When irradiated at 365nm, both complexes have also been found to promote the photocleavage of plasmid pBR322 DNA.     

A 2-quinolinecarboxylate-substituted ruthenium(II) complex as a new type of sensitizer for dye-sensitized solar cells

A new type of ruthenium(II) complex containing a 2-quinolinecarboxylate ligand was designed and synthesized as a sensitizer for dye-sensitized solar cells, and its photophysical and photochemical properties were characterized. The solar cells created with this complex exhibited efficient panchromatic sensitization over the entire visible wavelength range extending into the near-IR region. An overall conversion efficiency of 8.2% was attained under standard air mass 1.5 irradiation (100 mW cm⁻²) with the short-circuit photocurrent density of 18.2 mA cm⁻², the open-circuit photovoltage of 0.63 V and the fill factor of 0.72.     

Monoporphyrinate neodymium (III) complexes stabilized by tripodal ligand: synthesis, characterization and luminescence

A series of monoporphyrinate neodymium (III) complexes stabilized by anionic tripodal ligand (cyclopentadienyl)tris(dimethylphosphito)cobaltate(I) were prepared and characterized by IR, ESI-HRMS, UV-Vis and X-ray diffraction studies. Structural analyses revealed that the Nd³⁺ ion was seven-coordinate, surrounded by four nitrogen atoms from the porphyrinate dianion and three oxygen atoms from the anionic tripodal ligand. Photoluminescence studies showed that the porphyrinate dianion acting as a sensitizer absorbed the light and transferred the energy to the Nd³⁺ center, which then allowed the metal ion to emit efficiently at 885 and 1071 nm. The luminescent intensity of the complexes increases when there are strong electronic donating groups on the porphyrin rings but decreases with increasing polarity of the solvents.     

Substitution of chloride by nitrosyl ligand in a scorpionate ruthenium(III) compound: A theoretical study

A theoretical study of the ruthenium(III) complex [RuCl₂(pz₂CHSO₃)(en)] and of its nitrosyl-substituted product [Ru(NO)Cl(pz₂CHSO₃)(en)]⁺ is presented, based on density functional calculations. Several isomers of each compound differing in the position of the anionic tail of a bis(3,4-dimethyl-1-yl)methanesulfonate scorpionate ligand, pz₂CHSO₃⁻, relative to the monodentate ligands have been optimized. A two-step mechanism is proposed for the ligand substitution reaction that is consistent with the computational results and the weak coordination of the sulfonate group.     

Synthesis and characterization of Cu(II) and Ni(II) complexes of a tripodal ligand containing imidazoles

Two complexes of the formula [MH₃L](ClO₄)₂ [M = Cu(II) (1), Ni(II) (2)] have been prepared by the reaction of M(ClO₄)₂ · 6H₂O with the ligand (H₃L) formed by the Schiff base condensation of tris(2-aminoethyl)amine (tren) with three molar equivalents of 4-methyl-5-imidazolecarboxaldehyde and structurally and magnetically characterized. The structures of 1 and 2 are isomorphous with each other and with the iron(II) complex of H₃L which has been reported previously. The ligand, while potentially heptadentate, forms six coordinate complexes with both metal centers forming three M-N_imine and three M-N_imidazole bonds. The tren central N atom is at a nonbonded distance from M of 3.261 Å for 1 and 3.329 Å for 2. The neutral complex CuHL 3 was prepared by reaction of H₃L with Cu(OCH₃)₂ and the ionic complex Na[NiL] 4 was prepared by deprotonation of 2 with aqueous sodium hydroxide. Magnetic measurements of 1-3 are consistent with the spin-only values expected for S = 1/2 (d⁹, Cu(II)) and S = 1 (d⁸, Ni (II)) systems.     

Synthesis, spectral and structural studies of water soluble arene ruthenium (II) complexes containing 2,2′-dipyridyl-N-alkylimine ligand

A series of water soluble complexes of general formula [(η⁶-arene)Ru{(C₅H₄N)₂CNRi}Cl]PF₆ have been prepared by the reaction of [{(η⁶-arene)RuCl₂}₂] with appropriate 2,2′-dipyridyl-N-alkylimine ligands (dpNRi) in the presence of NH₄PF₆ (where; R = Me or Et; arene = p-cymene, C₆Me₆, C₆H₆). The 2,2′-dipyridyl-N-alkylimine ligands are prepared by reaction of 2,2′-dipyridyl ketone with the corresponding alkylamine. The complexes are readily obtained as air stable yellow to dark brown solids by simple stirring at room temperature. The complexes are isolated as their hexafluorophosphate salts and characterized on the basis of spectroscopic data. The molecular structure of representative complex [(η⁶-C₆Me₆)Ru{(C₅H₄N)₂CN-Me}Cl]PF₆ has been determined by single crystal X-ray diffraction studies.     

Synthesis, crystal structure and photoluminescent property of an iridium complex with coumarin derivative ligand

Novel iridium complex containing coumarin derivative as a cyclometalated ligand (L) and picolinate (pic) as the ancillary ligand, Ir(III)bis(3-(pyridin-2-yl)coumarinato N,C⁴)(picolinate) [Ir(L)₂(pic)], was synthesized and characterized. It was demonstrated that the iridium (III) ion in Ir(L)₂(pic) is hexacoordinated by two C atoms and two N atoms from 3-(pyridin-2-yl)coumarin ligands and one N atom and one O atom from picolinate ligand, displaying a distorted octahedral coordination geometry. The Ir(L)₂(pic) has very strong absorption and intensive emission at 532 nm. These results show the promising future of that Ir(L)₂(pic) in fabrication organic light-emitting diodes.     

DNA-binding and photocleavage studies of mixed polypyridyl ruthenium(II) complexes with calf thymus DNA

New mixed polypyridyl {NMIP = 2′-(2″-nitro-3″,4″-methylenedioxyphenyl)imidazo-[4′,5′-f][1,10]-phenanthroline, dmb = 4,4′-dimethyl-2,2′-bipyridine, bpy = 2,2′-bipyridine} ruthenium(II) complexes [Ru(dmb)₂(NMIP)]²⁺ (1) and [Ru(bpy)₂(NMIP)]²⁺ (2) have been synthesized and characterized. The binding of these complexes to calf thymus DNA (CT-DNA) has been investigated with spectroscopic methods, viscosity and electrophoresis measurements. The experimental results indicate that both complexes could bind to DNA via partial intercalation from the minor/major groove. In addition, both complexes have been found to promote the single-stranded cleavage of plasmid pBR 322 DNA upon irradiation. Under comparable experimental conditions compared with [Ru(phen)₂(NMIP)]²⁺, during the course of the dialysis at intervals of time, the CD signals of both complexes started from none, increased to the maximum magnitude, then no longer changed, and the activity of effective DNA cleavage dependence upon concentration degree lies in the following order: [Ru(phen)₂NMIP]²⁺ > complex 2 > complex 1.     

Synthesis, spectroscopic and X-ray characterization of a copper(II) complex with the Schiff base derived from pyridoxal and aminoguanidine: NMR spectral studies of the ligand

A copper(II) complex with the pyridoxal-aminoguanidine (PL-AG) Schiff base adduct, as an organic compound of the very potent biological activity and promising pharmacological importance in the treatment of diabetic complications, has been prepared and characterized. The X-ray structural analysis of the [CuCl2(PL-AG)] complex showed that it has a distorted pseudo-square-pyramidal (4+1) structure with the tridentate ONN Schiff base in the equatorial plane, with the Cu-O(1), Cu-N(1) and Cu-N(3) bond lengths of 1.917(2)A, 1.930(2)A and 1.984(2)A, respectively. The bond length of the equatorial Cu-Cl(1) is 2.279(1)A, while that of the apical Cu-Cl(2) is 2.792(1)A. Pyridoxal fragment is coordinated in its zwitterionic form. In addition to the X-ray structural analysis, the complex was characterized by IR spectrometric, conductometric and magnetic techniques, and the ligand itself by IR, 1H and 13C NMR spectra.     

Isolation of a singly oxo-bridged Fe(III) dinuclear complex: Synthesis, crystal structure, spectroscopic and magnetic studies

The μ-oxo dinuclear complex {Fe₂O(tptz)₂[N(CN)₂]₂(NO₃)₂} (1) (where tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine) has been synthesised and characterised by elemental analysis, FT-IR, UV-vis, cyclic voltammetry, Mössbauer spectroscopy, and variable-temperature magnetic susceptibility measurements and single crystal X-ray diffraction. The iron centres have a pentagonal-bipyramidal geometry. The dimeric neutral complex exhibits typical Fe-μ-O bond lengths of 1.763(1) Å and a bridge angle of 180.00°. The Fe?Fe separation is 3.526(3) Å. The Mössbauer spectrum at room temperature consists of one quadrupole doublet with an isomer shift of 0.41 mm/s and a quadrupole splitting of 1.12 mm/s. Variable-temperature magnetic susceptibility measurements have been measured in the temperature range 300-2 K, revealing an intramolecular antiferromagnetic coupling (J = −211.6 cm⁻¹).     

Synthesis, characterization and emission properties of yttrium(III) and europium(III) complexes of a tripodal heptadentate Schiff-base ligand N[CH2CH2NCH(2-OH-3-MeC6H3)]3

The preparation and characterization of yttrium(III) and europium(III) complexes of tripodal heptadentate Schiff-base ligand N[CH₂CH₂NCH(2-OH-3-MeC₆H₃)]₃ (H₃L¹) have been studied. These complexes were prepared by the reaction of tris(2-aminoethyl)amine with 3-methylsalicylaldehyde in presence of M(CF₃SO₃)₃ (M = Y, Eu) in methanol. The molecular structures of [YL¹] (1) and [EuL¹] (2) were determined by X-ray crystallography. The crystal structure analysis revealed that the Schiff-base behaves as a tri-deprotonated heptadentate ligand encapsulating the metal ion within the N₄O₃ cavity. Under the excitation of UV light, the solid state of these complexes exhibited blue and red emission, respectively. The optical properties of 1 and 2 in solution and in the solid state were examined.