Synthesis and spectroscopic studies of some halogen-dimethylsulphoxide/tetramethylenesulphoxide-ruthenium(II) and ruthenium(III) complexes with 2-aminobenzimidazole

Synthesis and characterization of seven ruthenium(II) and ruthenium(III) complexes of sulphoxide with 2-aminobenzimidazole are reported. Three different formulations exist; [cis-RuCl₂(SO)₃(2-ABZ)]; [trans-RuCl₂(SO)₃)(2-ABZ)]; and [trans-RuCl₄(SO)(2-ABZ (where SO?=?dimethylsulphoxide(DMSO)/tetramethylenesulphoxide(TMSO); 2-ABZ?=?2-aminobenzimidazole). These complexes are characterized by elemental analysis, conductivity magnetic susceptibility, ¹H-NMR, ¹³C{¹H}-NMR and electronic spectroscopy.     

Synthesis and characterization of ruthenium(II) phenanthroline complexes containing quaternary amine substituents

A series of mixed-ligand complexes of ruthenium(II) containing 5-methylphenanthroline and trimethylamino-5-methylphenanthroline have been synthesized to investigate the impact of the quaternary amine on the photophysical properties. Thermal stability studies indicate that the quaternary amine is stable with respect to hydrolysis. Mass spectral analysis of the complexes revealed only fragments consistent with homolytic cleavage of the amines and no parent ions were observed. Both electrochemical and photophysical investigations indicate that the quaternary amine has little or no impact on the properties of the complex when compared to complexes lacking the amine.     

Pyridine-2-olato chelated ruthenium(II) organometallics incorporating imine-phenol function: spectroscopic,structural, electrochemical,and theoretical studies

The heterogeneous phase reaction of excess sodium salt of 2-hydroxypyridine (OHpy) with [Ru(κ²C,O-RL)(PPh₃)₂(CO)Cl] (1) afforded complexes of the type [Ru(κ¹C-RL)(PPh₃)₂(CO)(Opy)] (2) in excellent yield [κ²C,O-RL is 4-methyl-6-((N-R-arylimino)methyl)phenolato-C²,O), κ¹C-RL is 4-methyl-6-((N-R-arylimino)methyl)phenol-C²) and R is H, Me, OMe, Cl]. The chelation of Opy is attended with the cleavage of Ru-O and Ru-Cl bonds and iminium-phenolato → imine-phenol prototropic shift. The 1→2 conversion is irreversible and the type 2 species are thermodynamically more stable than the acetate, nitrite, and nitrate complexes of 1. The spectral (UV-vis, IR, NMR) and electrochemical data of the complexes are reported. In dichloromethane solution the complexes display one quasi-reversible Ru^III/Ru^II cyclic voltammetric response with E_1/2 in the range 0.65–0.69 V versus Ag/AgCl. The crystal and molecular structures of [Ru(κ¹C-HL)(PPh₃)₂(CO)(Opy)]·2C₆H₆·0.5H₂O, 2(H)·2C₆H₆·0.5H₂O and [Ru(κ¹C-ClL)(PPh₃)₂(CO)(Opy)]·2C₆H₆·0.25H₂O, 2(Cl)·2C₆H₆·0.25H₂O are reported, which revealed a distorted octahedral RuC₂P₂NO coordination sphere. The pairs (P,P), (C,O), and (C,N) define the three trans directions. The electronic structures of the complexes are also scrutinized by density functional theory.     

Some organometallic chemistry of ruthenium(II)

Stoichiometric and catalytic reaction of Ru(II) phosphine complexes with alkynes, olefins, and enynes are described. The hydride complex RuCl(CO)H(PPh₃)₃ (1) reacts with the double bond of a cis-enyne whereas it reacts with triple bonds of trans-enynes. Metathesis of vinyl silanes with olefins are catalyzed by 1 where β-Si elimination is the key step. Dimerizations of ^tBu- and Me₃Si-substituted acetylanes into the corresponding butatrienes are catalyzed by Ru(II) active species as studied by isolation of the intermediates. A model reaction for the crucial step of the catalytic cycle, formation of a Ru vinylidene complex from acetylene, has been fully simulated by ab initio-MO calculations.     

New bipyridyl/phenanthroline ruthenium(II) and ruthenium(III) complexes possessing acetate appended thioether. Evidence for oxidative linkage isomerization

The acetate bearing dithioether, sodium di(2-carboxymethylsufanyl)maleonitrile, L¹ upon reaction with [Ru^II(bpy)₂Cl₂]·2H₂O, [Ru^II(phen)₂Cl₂]·2H₂O, [Ru^III(bpy)₂Cl₂]⁺ or [Ru^III(phen)₂Cl₂]⁺ in methanol formed complexes of the type [(bpy)₂Ru{S₂(CH₂COO)₂C₂(CN)₂}], (1), [(phen)₂Ru{S₂(CH₂COO)₂C₂(CN)₂}], (2), [(bpy)₂Ru{(OOCCH₂)₂S₂C₂(CN)₂}]⁺, (5) and [(phen)₂Ru{(OOCCH₂)₂S₂C₂(CN)₂}]⁺, (6) respectively. Four other Ru(III) complexes with di(benzylsulfanyl)maleonitrile, L², [(bpy)₂Ru{S₂(PhCH₂)C₂(CN)₂}]³⁺, (7) and [(phen)₂Ru{S₂(PhCH₂)₂C₂(CN)₂}]³⁺, (8), and with acetate, [(bpy)₂Ru(OOCCH₃)₂]⁺, (9) and [(phen)₂Ru(OOCCH₃)₂]⁺, (10) were also synthesized. In the cyclic voltammetry, complexes (1) and (2) exhibited quasireversible oxidation waves at 1.01 and 1.02 V vs. Ag/AgCl over GC electrode in DMF, while the corresponding Ru(III) L¹ complexes (5) and (6) exhibit reversible oxidation at E_1/2 0.59 and 0.58 V, respectively, under identical conditions. This is unlike the voltammetric behavior of the Ru(II) and Ru(III) L² complexes, wherein the complex pairs (3), (7) and (4), (8) exhibited identical voltammograms with single reversible one electron waves at E_1/2 0.98 and 0.92 V, respectively under identical conditions. The voltammograms of Ru(II)-L² complexes (3) and (4) also became irreversible in presence of nearly four molar equivalent of sodium acetate. Hence, the irreversible redox behavior of complexes (1) and (2) has been interpreted in terms of rapid linkage isomerization, i.e. shift in κ²-S,S′ to κ²-O,O′ coordination, following the Ru(II)/Ru(III) electrode process. The electronic spectra of Ru(III)-L¹ complexes (5) and (6) resemble closely with that of (9) and (10) instead of Ru(III)-L² complexes (7) and (8), further supports proposed linkage isomerization. The cationic complexes were obtained as [PF₆]⁻ salts and all compounds were characterized using analytical and spectral (IR, ¹H NMR, UV-vis and mass) data.     

Half-sandwich ruthenium(II)-arene complexes: synthesis,spectroscopic studies,biological properties,and molecular modeling

In search for antitumor metal-based drugs that would mitigate the severe side-effects of cisplatin, Ru(II) complexes are gaining increasing recent interest. In this work, we report on the synthesis, characterization (¹H- and ¹³C-NMR, FT-IR), and cytotoxicity studies of two new half-sandwich organometallic Ru(II) complexes of the general formula [Ru(η⁶-arene)(XY)Cl](PF₆) where arene?=?benzene or toluene and XY?=?bidentates: dipyrido[3,2-a:2′,3′-c]phenazine (dppz) or 2-(9-anthryl)-1H-imidazo[4,5-f][1,10]phenanthroline (aip), which are bound to Ru(II) via two phenanthroline-N atoms in a characteristic “piano-stool” configuration of Ru(II)-arene complexes—as confirmed by vibrational and NMR spectra. In addition, cytotoxic studies were performed for similar half-sandwich organometallic [Ru(η⁶-p-cymene)(Me₂dppz)Cl]PF₆ complex (Me₂dppz = 11,12-dimethyl-dipyrido[3,2-a:2′,3′-c]phenazine). This study is complemented with elaborate modeling with density functional theory (DFT) calculations, which provided insight into reactive sites of Ru(II) structures, further detailed by molecular docking on the B-DNA dodecamer, which identified binding sites and affinities: most pronounced for the [Ru(η⁶-benzene)(aip)Cl](PF₆) in both A-T and G-C regions of the DNA minor groove. Cytotoxic activity was probed versus tumor cell lines B16, C6, and U251 (B16 mouse melanoma, C6 rat glioma, U251 human glioblastoma) and non-tumor cell line HACAT (HACAT normal human keratinocytes).     

Synthesis,spectroscopic characterization and antibacterial sensitivity of some chloro dimethylsulfoxide/tetramethylenesulfoxide ruthenium(II) and ruthenium(III) complexes with 2-aminobenzothiazole

Synthesis and characterization of seven ruthenium(II) and ruthenium(III) complexes of sulfoxide with 2-aminobenzothiazole are reported. Three different formulations exist: [cis,cis,cis-RuCl₂(SO)₂(2-abtz)₂] and [trans,trans,trans-RuCl₂(SO)₂(2-abtz)₂] and [trans-RuCl₄(SO)(2-abtz)] ^? [X]⁺ (where SO?=?dimethyl sulfoxide (dmso) or tetramethylenesulfoxide (tmso); 2-abtz?=?2-aminobenzothiazole and [X]⁺?=?[H(abtz)]⁺, [Na⁺]. These complexes were characterized by elemental analyses, conductivity measurements, magnetic susceptibility, FTIR, ¹H NMR, ¹³C{¹H} NMR and electronic spectroscopy. Some of the complexes were screened for their antibacterial activity and are found to be potent against the gram negative bacteria Escherichia coli.     

Methyl-oxygen bond cleavage in hemilabile phosphine-ether ligand of ruthenium(II) complexes

The preparation and characterization are described for four ruthenium(II) complexes containing hemilabile phosphine-ether ligand o-(diphenylphosphino)anisole (Ph₂PC₆H₄OMe-o) and/or bidentate ligand diphenylphosphino-phenolate ([Ph₂PC₆H₄O-o]⁻) Ru(RCN)₂(κ²-Ph₂PC₆H₄O-o)₂ (1a: R = Me; 1b: R = Et) and [Ru(RCN)₂(κ²-Ph₂PC₆H₄O-o)(κ²-Ph₂PC₆H₄OMe-o)](PF₆) (2a: R = Me; 2b: R = Et). The ruthenium(II) phosphine-ether complexes undergo mild methyl-oxygen bond cleavage. Two different kinds reaction mechanism are proposed to describe the methyl-oxygen bond cleavage, one involving attack of anionic nucleophiles and another involving the phosphine. The new reactions define novel routes to phosphine-phenolate complexes. The structures of complexes 1a, 1b and 2a were confirmed by X-ray crystallography.     

Paramagnetic NMR shift,spectroscopic and molecular modeling studies of lanthanide(III)-morin complexes

Studies on nine-coordinate lanthanide complexes of morin are described. The complexes were characterized by elemental analysis, molar conductance, UV–Vis spectra, IR spectra, thermal analysis and NMR spectra. Molecular modeling studies were also carried out. The complexes are non-electrolytes in DMSO. TGA showed anhydrous nature of the complexes. The electronic spectra of the complexes were recorded in methanol. ¹H NMR spectra of lanthanum, praseodymium, neodymium, samarium and dysprosium complexes have been studied in DMSO-d₆. The complexes do not dissociate in DMSO and retain their coordination. ¹H NMR spectra of paramagnetic and diamagnetic complexes exhibit downfield as well as upfield shifts of morin resonances that shows change in geometry during coordination.     

Oligothiophene-2-yl-vinyl bridged mono- and binuclear ruthenium(II) tris-bipyridine complexes: Synthesis, photophysics, electrochemistry and electrogenerated chemiluminescence

A series of mono- and binuclear ruthenium(II) tris-bipyridine complexes tethered to oligothienylenevinylenes have been synthesized and characterized by ¹H NMR, ¹³C NMR and TOF-MS spectrometry. Photophysics, electrochemistry and electrogenerated chemiluminescence (ECL) properties of these complexes are investigated. The electronic absorption spectra of the mononuclear ruthenium complexes show a significant red shift both at MLCT (metal-to-ligand charge transfer) and π-π^∗ transitions of oligothienylenevinylenes with increase in the number of thiophenyl-2-yl-vinyl unit. For the binuclear complexes these two absorption bands are overlapped. All the metal complexes have very weak emission compared to that of the reference complex Ru(bpy)²⁺₃. The first reduction potentials of all mononuclear ruthenium complexes are less negative than that of Ru(bpy)²⁺₃, due to the moderate electron-withdrawing effect of oligothienylenevinylenes. For binuclear ruthenium complexes, only one Ru(II/III) oxidation peak (E_1/2 = 0.96 V vs. Ag/Ag⁺) was observed, suggesting a weak interaction between two metal centers. Three successive reduction processes of bipyridine ligands are similar among all ruthenium complexes except for RuTRu, which has a very sharp peak owing to the accumulation of neutral product on the electrode surface. All these ruthenium complexes exhibited different ECL property in CH₃CN solution without any additional reductant or oxidant. For three mononuclear ruthenium complexes, the ECL intensity strengthens with increase in the number of thiophene-2-yl-vinyl unit. However, the ECL efficiency dramatically decreased in the binuclear ruthenium complexes. The ECL efficiencies of all the reported complexes do not exceed that of Ru(bpy)²⁺₃, where the ECL efficiency decreases in the order of RuTRu > Ru3T > Ru2T > RuT > Ru2TRu (RuT,bis-2,2′-bipyridyl-(4-methyl-4′-(2-thienylethenyl)-2,2′-bipyridine) ruthenium dihexafluorophosphate; Ru2T, bis-2,2′-bipyridyl-(4-methyl-4′-{(E)-2-[5-((E)-2-thienylethenyl)-thienylethenyl]}-2,2′-bipyridine) ruthenium dihexafluorophosphate; Ru3T, bis-2,2′-bipyridyl-(4-methyl-4′-{(E)-2-{(E)-2-[5-((E)-2-thienylethenyl)-thienylethenyl]}}-2,2′-bipyridine) ruthenium dihexafluorophosphate; RuTRu, bis-2,2′-bipyridyl-ruthenium-bis-[2-((E)-4′-methyl-2, 2′-bipyridinyl-4)-ethenyl]-thienyl-bis-2,2′-bipyridyl-ruthenium tetrahexafluorophosphate; Ru2TRu, bis-2,2′-bipyridyl-ruthenium-(E)-1,2-bis-{2-[2-((E)-4′-methyl-2,2′-bipyridinyl-4)-ethenyl]-thienyl}-ethenyl-bis-2,2′-bipyridyl-ruthenium tetrahexafluorophosphate).     

Synthesis,structural, electrochemical,and spectroscopic studies of some (diimine)ruthenium nitrile complexes

The syntheses of cationic ruthenium(II) complexes [Ru(Me₂-bpy)(PPh₃)₂RR?][PF₆]_x {Me₂-bpy = 4,4?-dimethyl-2,2?-bipyridine, (3) R = Cl, R? = N≡CMe, x = 1, (4) R = Cl, R? = N≡CPh, x = 1, (5) R = R? = N≡CMe, x = 2} and [Ru(Me₂-bpy)(κ²-dppf)RR?][PF₆]_x {dppf = 1,1?-bis(diphenylphosphino)ferrocene, (6) R = Cl, R? = N≡CMe, x = 1, (7) R = Cl, R? = N≡CPh, x = 1, (8) R = R? = N≡CMe, x = 2} are reported, together with their structural confirmation by NMR (³¹P, ¹H) and IR spectroscopy and elemental analysis, and, in the case of trans-[Ru(Me₂-bpy)(PPh₃)₂(N≡CCH₃)Cl][PF₆] (3), by X-ray crystallography. Electronic absorption and emission spectra of the complexes reveal that all complexes except 4 and 6 are emissive in the range 370–400 nm with 8 exhibiting an emission in the blue. Cyclic voltammetry studies of 3–8 show reversible or quasi-reversible redox processes at ca. 1 V, assigned to the Ru(II/III) couple.     

Mono and dinuclear arene ruthenium complexes containing 6,7-dimethyl-2,3-di(pyridine-2-yl)quinoxaline as chelating ligand: Synthesis and molecular structure

The mononuclear cations of the general formula [(η⁶-arene)RuCl(dpqMe₂)]⁺ (dpqMe₂ = 6,7-dimethyl-2,3-di(pyridine-2-yl)quinoxaline; arene = C₆H₆, 1; C₆H₅Me, 2; p-PrⁱC₆H₄Me, 3; C₆Me₆, 4) as well as the dinuclear dications [(η⁶-arene)₂Ru₂Cl₂(μ-dpqMe₂)]²⁺ (arene = C₆H₆, 5; C₆H₅Me, 6; p-PrⁱC₆H₄Me, 7; C₆Me₆, 8) have been synthesised from 6,7-dimethyl-2,3-di(pyridine-2-yl)quinoxaline (dpqMe₂) and the corresponding chloro complexes [(η⁶-C₆H₆)Ru(μ-Cl)Cl]₂, [(η⁶-C₆H₅Me)Ru(μ-Cl)Cl]₂, [(η⁶-p-PrⁱC₆H₄Me)Ru(μ-Cl)Cl]₂ and [(η⁶-C₆Me₆)Ru(μ-Cl)Cl]₂, respectively. The X-ray crystal structure analyses of [1][PF₆], [3][PF₆] and [6][PF₆]₂ reveal a typical piano-stool geometry around the metal centre; in the dinuclear complexes the two chloro ligands, with respect to each other, are found to be trans oriented.     

Mono- and dinuclear ruthenium complexes of bridging ligands incorporating two di-2-pyridylamine motifs: Synthesis, spectroscopy and electrochemistry

Mono- and dinuclear ruthenium(II) complexes of six bridging ligands that contain a central arene (phenyl, naphthalenyl or biphenyl) core to which are attached two di-2-pyridylamine groups have been prepared. These complexes possess six-membered chelate rings. Full assignments of their ¹H NMR spectra are described which provides insight into the comformations of the ligands in these complexes. The extent of metal–metal communication in the dinuclear complexes was probed by electrochemical measurements and related to metal–metal distances.     

The valence structure analysis for dirhodium(II) tetracarboxylato complexes with nitric oxide as axial ligand

Density functional theory has been used to study the trans-influence of Rh–Rh and Rh–L bonds in dirhodium(II) tetracarboxylates with axial ligands L=H₂O, pyridine, CO, triphenylphosphine, NO and NO₂. The absence of the chemical bond between metal atoms in Rh₂(μ-O₂CR)₄(NO)₂ complexes and the formation of two covalent Rh–NO bonds explain the very long Rh–Rh and very short Rh–N distances in these compounds.     

DNA interaction and cytotoxicity studies of ruthenium(III) complexes containing 3-(benzothiazol-2-yliminomethyl)-naphthalen-2-ol ligand

A new Schiff base, 3-(benzothiazol-2-yliminomethyl)-naphthalen-2-ol, has been synthesized and characterized by elemental analysis, Fourier transform infrared spectroscopy (FT-IR), UV–vis, nuclear magnetic resonance, and single-crystal X-ray diffraction. Ruthenium(III) complexes of the Schiff base were synthesized and characterized by analytical and spectroscopic (FT-IR, UV–vis, and electron paramagnetic resonance) data as well as magnetic susceptibility measurements. DNA-binding properties of the ligand and its ruthenium(III) complexes have been investigated by electronic absorption spectroscopy. The three ruthenium(III) complexes were tested for DNA cleavage. Further in vitro study of the cytotoxity of the ligand and the complexes on human cervical cancer cell line and human laryngeal epithelial carcinoma cell line were carried out.     

Ground-state properties of ruthenium(II) and osmium(II) tin trihydride complexes: A DFT study

DFT methods have been applied for the calculation of several ground-state properties of neutral and charged ruthenium(II) and osmium(II) tin trihydride complexes bearing N-donor, P-donor and C-donor ancillary ligands in their coordination sphere. Complexes of the type M(SnH₃)(Tp)(PPh₃)P(OMe)₃, M(SnH₃)(Cp)(PPh₃)P(OMe)₃ and [M(SnH₃)(Bpy)₂P(OMe)₃]⁺ (M = Ru, Os; Tp = tris(pyrazol-1-yl)borate; Cp = cyclopentadienyl ion; Bpy = 2,2′-bipyridine) have been studied using the EDF2 and B3PW91 functionals. The same calculations have been carried out also on the corresponding [M]-CH₃ and [M]-H compounds, to compare the electronic features of the different reactive ligands coordinated to the same metal fragments. Charge distribution analyses were used to give insight into the roles of the transition metal centres and the ancillary ligands on the properties of the coordinated SnH₃ group. The molecular orbitals of the methyl- and trihydrostannyl-complexes were compared to understand the nature of the [M]-SnH₃ bond and the electronic transitions of these species.     

Synthesis,spectroscopic characterization and antibacterial studies of some derivatives of chlorodimethylsulphoxide/tetramethylenesulphoxide ruthenium(II) and ruthenium(III) with 4-aminoantipyrine

We report the synthesis of five complexes of three different formulations viz. [cis-RuCl₂(4-antp)₂], [trans-RuCl₂(4-antp)₂] and [X]⁺[trans-RuCl₄(4-antp)₂]^? (X⁺ = [(DMSO)₂H]⁺, Na⁺, or [(TMSO)H]⁺ and 4-antp = 4-aminoantipyrine) from different routes. These complexes were characterized on the basis of elemental analyses, molar conductance measurements, magnetic susceptibility, electronic spectra, FTIR, ¹H-NMR and ¹³C{¹H}-NMR spectroscopy. Complexes were screened for antibacterial activity and found to be potent against gram negative bacteria Escherichia coli.     

Synthesis, characterization and some properties of amide-linked porphyrin-ruthenium(II) tris(bipyridine) complexes

A new molecular dyad, comprised of a zinc-porphyrin and a ruthenium(II) tris(bipyridine) complex linked through an amide bond has been synthesized and characterized by ¹H, ¹³C NMR, UV-vis, mass-spectrometry and elemental analysis. The electrochemistry as well as the steady-state emission properties were investigated. The redox behavior of the dyad exhibits a favorable reversible characteristic. Substantial quenching of porphyrin emission was found when the Q band of 5 and 5-Zn was selectively photoexcited. This observation suggests a quenching mechanism with possible intramolecular electron transfer or energy transfer between the Ru(bpy)₃ moiety and the porphyrin free-base or Zn porphyrin moieties.