Mixed-ligand Ruthenium Research Articles

Cis–trans Isomerism in mixed-ligand ruthenium(II) complexes containing bis(phosphine) and azoimine ligands

This study presents the syntheses and characterization of mixed-ligand azoimine-diphosphine ruthenium complexes of the general formula [RuCl2(Azo)(P–P)] (C1–C5) {Azo=C6H5NNC(COCH3)NC6H5; P–P=1,2-bis(dimethylphosphino)ethane (dmpe) (C1), cis-1,2-bis(diphenylphosphino)ethylene (depe) (C2), 1.1′-bis(diphenylphosphino)methane (dppm) (C3), 1,2-bis(diphenylphosphino)benzene (dbpe) (C4), 1,2-bis(di(pentaflurophenyl)phosphino)ethane (F-dppe) (C5)}. These complexes were synthesized via the reaction of RuCl3, azoimine and the diphosphine ligands in ethanol solutions. The X-ray structure of C2 reveals a cis-dichloro geometry, in spite of the bulky P–P ligand, and this is attributed to the presence of an intramolecular π–π interaction between benzene rings (on the Azo and P–P ligands) [centroid–centroid distances=3.596 and 3.654Å; dihedral angle between ring planes=13.2(3) and 15.4(4)° for the two independent molecules]. In contrast, the X-ray structure of C1, with a less bulky dmpe ligand in which no Ph rings are available for π–π bonding, revealed a trans-dichloro geometry. In addition to the X-ray structures of C1 and C2, this work presents and discusses the spectroscopic (IR, UV–Vis, 1H NMR and 31P NMR) and electrochemical (cyclic voltammetry) behavior of C1–C5.

Structural, photophysical and electrochemical studies of [RuN 6] 2+ complexes having polypyridine and azole mixed-donor sites

The mixed-ligand ruthenium(II) complexes [(phen) 2Ru(pzbzimH 3)](ClO 4) 2·3H 2O ( 1), [(phen) 2Ru(bzimH) 2](ClO 4) 2·3H 2O ( 2) and [(bpy) 2Ru(bpybzimH 2)](ClO 4) 2 ( 3), where phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine, pzbzimH 3 = pyrazole-3,5-bis(benzimidazole), bzimH = benzimidazole and bpybzimH 2 = 6,6′-bis(benzimidazole-2-yl)-2,2′-bipyridine have been synthesized and spectroscopically characterized. The X-ray structures of the three compounds have been determined which show that relative to the polypyridine ligands (phen or bpy) two donor nitrogens of the second ligand occupy cis position. In case of 3, bpybzimH 2 ligand is coordinated in puckered form where its bpy unit acts in a monodentate fashion. The electrochemical properties, absorption and emission spectral characteristics and lifetimes of luminescence decay of the complexes have been compared. Deprotonation of the azole NH moieties of the complexes lead to substantial lowering of redox potentials of the Ru II/Ru III couple as well as the MLCT and emission band energies. Spectrophotometric and spectrofluorometric titrations of complexes 1 and 3 have been carried out in 3:2 acetonitrile–water as a function of pH over the range 3.5–12.0 and the p K values have been determined. The kinetic parameters for the decay of the 3MLCT excited states of 1 at different pH at 298 K have been evaluated.

Synthesis and characterization of β-diketonato ruthenium(II) complexes with two 4-bromo or protected 4-ethynyl-2,2′-bipyridine ligands

Two new mononuclear mixed-ligand ruthenium(II) complexes with acetylacetonate ion (2,4-pentanedionate, acac) and functionalized bipyridine (bpy) in position 4, [Ru(bpyBr)2(acac)](PF6) (2; bpyBr = 4-Bromo-2,2′-bipyridine, acac = 2,4-pentanedionate ion) and [Ru(bpyOH)2(acac)](PF6) (3; bpyOH = 4-[2-methyl-3-butyn-2-ol]-2,2′-bipyridine) were prepared as candidates for building blocks. The 1H NMR, 13C NMR, UV–Vis, electrochemistry and FAB mass spectral data of these complexes are presented.

Microwave synthesis of mixed ligand diimine–thiosemicarbazone complexes of ruthenium(ii): biophysical reactivity and cytotoxicity

A novel microwave-assisted synthetic method has been used to synthesise a series of mixed ligand ruthenium(II) compounds containing diimine as well as bidentate thiosemicarbazone ligands. The compounds contain the diimine 1,10-phenanthroline (phen) or 2,2'-bipyridine (bpy) and the thiosemicarbazone is derived from 9-anthraldehyde. Based on elemental analyses and spectroscopic data, the compounds are best formulated as [(phen)(2)Ru(thiosemicarbazone)](PF(6))(2) and [(phen)(2)Ru(thiosemicarbazone)](PF(6))(2) where thiosemicarbazone = 9-anthraldehydethiosemicarbazone, 9-anthraldehyde-N(4)-methylthiosemicarbazone, and 9-anthraldehyde-N(4)-ethylthiosemicarbazone. Fluorescence competition studies with ethidium bromide, along with viscometric measurements suggests that the complexes bind calf thymus DNA (CTDNA) relatively strongly via an intercalative mode possibly involving the aromatic rings of the diimine ligands. The complexes show good cytotoxic profiles against MCF-7 and MDA-MB-231 (breast adenocarcinoma) as well as HCT 116 and HT-29 (colorectal carcinoma) cell lines.

Water-Soluble Mixed-Ligand Ruthenium(II) and Osmium(II) Arene Complexes with High Antiproliferative Activity

The synthesis of ruthenium(II) and osmium(II) arene complexes of the general formula [(η6-p-cymene)M(oxine)(Hazole)]X, where M = Ru, Os; oxine = deprotonated 8-hydroxyquinoline, and Hazole = azole heterocycle, i.e., pyrazole (Hpz), indazole (Hind), imidazole (Him), benzimidazole (Hbzim), or 5,6-dimethylbenzimidazole (Hdmbzim); X = CF3SO3−, PF6−, or Cl−, combining ligands involved in metal-based complexes that are currently in clinical development, is reported. The compounds have been comprehensively characterized by elemental analysis, ESI mass spectrometry, spectroscopy (IR, UV−vis, NMR), and X-ray crystallography. The synthesis of these complexes was performed in order to achieve a balance between aqueous solubility and lipophilicity. The ruthenium(II) and osmium(II) compounds exhibit excellent cytotoxic effects in the tumor cell lines CH1 and SW480, with IC50 values ranging from 3.3 to 9.4 μM. As expected, the compounds are water soluble and show no evidence of hydrolysis or ligand exchange in aqueous media, which makes them noteworthy candidates for further development. The complexes [(η6-p-cymene)M(oxine)(Hazole)]+ do not react with DNA purine bases, even if the latter are present in excess. However, the complex [(η6-p-cymene)Os(oxine)Cl] reacts with 9-methyladenine (meade) to form [(η6-p-cymene)Os(oxine)meade]+, which was isolated and characterized by X-ray diffraction as a hexafluorophosphate salt.

Synthesis and characterization of bis(bipyridine)ruthenium(II) complexes with bromo or protected ethynyl β-diketonato ligands

A protected ethynyl group was introduced into a γ-position of a (β-diketonato)bis(bipyridine)ruthenium(II) complex through the reaction of the bromo complex and (triisopropylsilyl)-acetylene with very good yield under microwave irradiation. Two new mononuclear mixed-ligand ruthenium(II) complexes with bipyridine (bpy) and functionalized acetylacetonate ion (2,4-pentanedionate, acac −), [Ru(bpd)(bpy) 2](PF 6) ( 2; bpy = 2,2′-bipyridine, bpd = 3-Bromo-2,4-pentanedionate ion) and [Ru(tipsepd)(bpy) 2](PF 6) ( 3; tipsepd = 3-((triisopropylsilyl)ethynil)-2,4-pentanedionate ion) were then prepared as candidates for building blocks. The 1H NMR, UV–Vis, electrochemistry and FAB mass spectral data of these complexes are presented. X-Ray single crystal diffraction analysis has been made on complex 2, it crystallized with empirical formula of C 25H 22BrF 6N 4O 2PRu, in a monoclinic crystal system and space group C2/ c with a = 29.340(5) Å, b = 13.282(2) Å, c = 15.7492 (14) Å, β = 109.452(8)°, V = 5786.9(13) Å 3 and Z = 8.

Non-covalent DNA binding and cytotoxicity of certain mixed-ligand ruthenium(ii) complexes of 2,2′-dipyridylamine and diimines

A series of mixed ligand ruthenium(II) complexes [Ru(Hdpa)2(diimine)](ClO4)2, 1-5 where Hdpa is 2,2'-dipyridylamine and diimine is 1,10-phenanthroline (phen) and a modified/extended 1,10-phenanthroline such as, 5,6-dimethyl-1,10-phenanthroline (5,6-dmp), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), 5-methyldipyrido[3,2-d:2',3'-f]quinoxaline (mdpq) and dipyrido[3,2-a:2',3'-c]phenazine (dppz) have been isolated and characterized by analytical and spectral methods. The complex [Ru(Hdpa)2(phen)](PF6)2 1 has been structurally characterized and the coordination geometry around Ru(II) in it is described as distorted octahedral. 1H NMR spectral data reveal that 1-5 should have a C2 symmetry lying on the diimine plane due to the rapid flapping of the coordinated Hdpa ligands. The interaction of the complexes with calf thymus (CT) DNA has been explored by using absorption and emission spectral and viscometry and electrochemical techniques and the mode of DNA binding of the complexes has been proposed. The DNA binding affinity of the complexes decreases with decrease in number of planar aromatic rings in the co-ligand supporting the intercalation of the diimine co-ligands in between the DNA base pairs. Circular dichroic spectral studies reveal that the complexes 3-5 exhibit induced circular dichroism upon binding to CT DNA. Interestingly, upon interaction with CT DNA all the complexes show an increase in anodic current in the cyclic voltammograms suggesting that they are involved in electrocatalytic guanine oxidation. Interestingly, of all the complexes, only 5 alters the DNA superhelicity upon binding with supercoiled pBR322 DNA, which is consistent with its higher DNA binding affinity. Further, the cytotoxicities of the complexes against human cervical epidermoid carcinoma cell line (ME180) have been examined. Interestingly, 5 exhibits a cytotoxicity against ME180 higher than other complexes with potency approximately 8 times more than cisplatin for 24 h incubation but 4 times lower than cisplatin for 48 h incubation.

Mixed ligand ruthenium(ii) complexes of bis(pyrid-2-yl)-/bis(benzimidazol-2-yl)-dithioether and diimines: Study of non-covalent DNA binding and cytotoxicity

A series of mixed ligand ruthenium(II) complexes [Ru(pdto)(diimine)](ClO4)2/(PF6)2 1-3 and [Ru(bbdo)(diimine)](ClO4), 4-6, where pdto is 1,8-bis(pyrid-2-yl)-3,6-dithiooctane, bbdo is 1,8-bis(benzimidazol-2-yl)-3,6-dithiooctane and diimine is 1,10-phenanthroline (phen), dipyrido-[3,2-d:2',3'-f]-quinoxaline (dpq) and dipyrido[3,2-a:2',3'-c]phenazine (dppz), have been isolated and characterised by analytical and spectral methods. The complexes [Ru(pdto)(phen)](PF6)2 la, [Ru(pdto)(dpq)(Cl](PF6) 2a, [Ru(bbdo)(phen)](PF6)2 4a and [Ru(bbdo)(dpq)](ClO4)2 5 have been structurally characterized and their coordination geometries around ruthenium(II) are described as distorted octahedral. In la, 4a and 5 the two thioether sulfur and two py/bzim nitrogen atoms of the tetradentate pdto/bbdo ligand are folded around Ru(II) to give predominantly a "cis-alpha" configuration. (I)H NMR spectral data of the complexes support this configuration in solution. In [Ru(pdto)(dpq)Cl](PF6) 2a with a distorted octahedral coordination geometry, one of the two py nitrogens of pdto is not coordinated. The DNA binding constants (Kb: 2, 2.00 +/- 0.02 x 10(4) M(-1), s = 1.0; 3, 3.00 +/- 0.01 x 10(6) M(-1), s = 1.3) determined by absorption spectral titrations of the complexes with CT DNA reveal that 3 interacts with DNA more tightly than 2 through partial intercalation of the extended planar ring of coordinated dppz with the DNA base stack. The DNA binding affinities of the complexes increase with increase in the number of planar aromatic rings in the co-ligand, and on replacing both the py moieties in pdto complexes (1-3) by bzim moieties to give bbdo complexes (4-6). Upon interaction with CT DNA the complexes 1, 2, 5 and 6 show a decrease in anodic current in the cyclic voltammograms. On the other hand, interestingly, 3 and 4 show an increase in anodic current suggesting their involvement in electrocatalytic guanine oxidation. Interestingly, of all the complexes, only 6 alters the superhelicity of DNA upon binding with supercoiled pBR322 DNA. The cytotoxicities of the dppz complexes 3 and 6, which avidly bind to DNA, have been examined by screening them against cell lines of different cancer origins. It is noteworthy that 6 exhibits selectivity with higher cytotoxicity against the melanoma cancer cell line (A375) than other cell lines, potency approximately twice that of cisplatin and toxicity to normal cells 3 and 90 times less than cisplatin and adriamycin respectively.

Synthesis, spectral and electrochemical properties of mixed-ligand ruthenium(II) complexes of bis(pyrid-2-yl)- and bis(benzimidazol-2-yl)-dithioether ligands: Effect of an asymmetric diimine co-ligand

Two new mixed-ligand Ru(II) complexes [Ru(pdto)(dppt)](ClO 4) 2 ( 1) and [Ru(bbdo)(dppt)](ClO 4) 2 ( 2), where pdto = 1,8-bis(pyrid-2-yl)-3,6-dithiaoctane, bbdo = 1,8-bis(benzimidazol-2-yl)-3,6-dithiaoctane and dppt = 3-(pyridin-2-yl)-5,6-diphenyl-1,2,4-triazine, have been isolated and characterised by elemental analysis. NMR and electronic absorption and emission spectral and electrochemical techniques have been used to investigate the solution structures and electronic properties of the complexes. The 1H and 13C spectra of the complexes in solution reveal that the N 2S 2 donor set of the pdto and bbdo ligands is “ cis-α” coordinated and the dppt ligand is chelated to Ru(II) through both triazine N2 and pyridine nitrogen atoms. The proton chemical shifts of the phenyl rings of dppt are not affected much upon coordination, supporting the triazine N2 rather than N4 coordination. The anomalous upfield shifts of the H 61 and H 62 ( 1) and H 72 and H 81 ( 2) protons are caused by the shielding magnetic anisotropy due to the ring currents of the py and tra rings of dppt, which are forced to be coplanar by coordination. The py and bzim rings of pdto and bbdo are obliged to rotate away from dppt and the Ru–N py and Ru–N bzim bonds lengthen in order to minimise the steric clashes with dppt. The c.i.s values for 1 are less positive than those for 2 suggesting that the ligand bzim nitrogens of bbdo rather than the py nitrogens of pdto are involved in stronger σ-bonding with Ru(II). Both the complexes display a strong MLCT transition ( 1, 470; 2, 515 nm) along with intense intraligand transitions in the UV region, and when excited in the MLCT band an emission band (650 nm) is observed for both 1 and 2. In acetonitrile solution they show a quasi-reversible Ru(II)/Ru(III) redox couple ( E 1/2, 1, 1.18; 2, 0.90 V). Two more redox processes ( E 1/2, 1, −0.97, −1.09; 2, −1.06, −1.42 V) involving the coordinated dppt ligand are also observed. A plot of the difference between the metal oxidation and ligand reduction potentials of the complexes versus the absorption or emission maxima is linear, illustrating that the lowest π ∗ orbitals of dppt are involved in the redox, absorption and emission processes in the complexes. Electrochemical parameterisation of the Ru(II)/Ru(III) redox potentials of the present complexes has been carried out using Lever’s method and the calculated ligand reduction potential E L(L) correlates well with the observed Ru(II)/Ru(III) redox potentials.

Mixed ligand ruthenium(II) complexes of 5,6-dimethyl-1,10-phenanthroline: The role of ligand hydrophobicity on DNA binding of the complexes

A series of mixed ligand Ru(II) complexes of 5,6-dimethyl-1,10-phenanthroline (5,6-dmp) as primary ligand and 1,10-phenanthroline (phen), 2,2′-bipyridine (bpy), pyridine (py) and NH 3 as co-ligands have been prepared and characterized by X-ray crystallography, elemental analysis and 1H NMR and electronic absorption spectroscopy. The X-ray crystal structure of the complex [Ru(phen) 2(bpy)]Cl 2 reveals a distorted octahedral coordination geometry for the RuN 6 coordination sphere. The DNA binding constants obtained from the absorption spectral titrations decrease in the order, tris(5,6-dmp)Ru(II) > bis(5,6-dmp)Ru(II) > mono(5,6-dmp)Ru(II), which is consistent with the trend in apparent emission enhancement of the complexes on binding to DNA. These observations reveal that the DNA binding affinity of the complexes depend upon the number of 5,6-dmp ligands and hence the hydrophobic interaction of 5,6-dimethyl groups on the DNA surface, which is critical in determining the DNA binding affinity and the solvent accessibility of the exciplex. Among the bis(5,6-dmp)Ru(II) complexes, those with monodentate py ( 4) or NH 3 ( 5) co-ligands show DNA binding affinities slightly higher than the bpy and phen analogues. This reveals that they interact with DNA through the co-ligands while both the 5,6-dmp ligands interact with the exterior of the DNA surface. All these observations are supported by thermal denaturation and viscosity measurements. Two DNA binding modes – surface/electrostatic and strong hydrophobic/partial intercalative DNA interaction – are suggested for the mixed ligand complexes on the basis of time-resolved emission measurements. Interestingly, the 5,6-dmp ligands promote aggregation of the complexes on the DNA helix as a helical nanotemplate, as evidenced by induced CD signals in the UV region. The ionic strength variation experiments and competitive DNA binding studies on bis(5,6-dmp)Ru(II) complexes reveal that EthBr and the partially intercalated and kinetically inert [Ru(phen) 2(dppz)] 2+ (dppz = dipyrido[3,2- a:2′,3′- c]phenazine) complexes revert the CD signals induced by exciton coupling of the DNA-bound complexes with the free complexes in solution.

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)(H 2O)]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.

“Dimers of Dimers” of Ruthenium(I): Ru···BRu vs. Ru···BO Axial Interactions

Two new mixed ligand ruthenium(I) complexes of the composition [Ru2(O2CR)2(CO)5] (where R = (2,4-CF3)2C6H3 (1) and (3,5-CF3)2C6H3 (2)) have been prepared by melt reactions, and both have been fully characterized. Crystals of 1 and 2 have been obtained by gas phase sublimation of crude products at 124 and 150°C, respectively. The X-ray diffraction studies have revealed a tetranuclear ‘dimer of dimers’ core structure in both cases. In 1 two diruthenium(I) units cis-bridged by two carboxylates each are coordinated through the Ru···FO axial interactions at 2.301(2) A. In contrast, complex 2 shows the direct Ru···FRu bonding of two diruthenium units at 2.9065(9) A. The Ru–Ru distances within the dinuclear units are 2.6654(7) and 2.6859(8) A in 1 and 2, respectively.

New Tetranuclear Ruthenium(I) Carbonyl Trifluoroacetate Complex: Gas-Phase Transformations and Coordination Reactions

A new mixed ligand ruthenium(I) complex of the composition [Ru2(O2CCF3)2(CO)5] (1) has been prepared by refluxing Ru3(CO)12 with trifluoroacetic acid in a dichloromethane/benzene mixture. Crystals of 1 were obtained by gas phase sublimation of the crude product at 110°C. The X-ray diffraction study has revealed a tetranuclear `8dimer of dimers' 9 structure [Ru2(O2CCF3)2(CO)5]2 in 1. Complex 1 can be re-sublimed without decomposition at temperatures up to 130°C, while at higher temperatures fragmentation accompanied by a ligand re-distribution reaction has been observed. As a result, two new ruthenium(I) complexes have been isolated from the gas phase transformation of 1 at 160°C: [Ru2(O2CCF3)2(CO)6] (2) and [Ru2(O2CCF3)2(CO)4] (3). Complex 2 has a dinuclear cis-trifluoroacetato-bridged core, while 3 exhibits a polymeric structure built on axial Ru···O interactions of the dimetal units, [Ru2(O2CCF3)2(CO)4]∞. The above reaction suggests the possible gas phase dissociation of the tetranuclear molecule 1 to the dimetal fragments, [Ru2(O2CCF3)2(CO)5] that have one open axial coordination site. The latter was proved by codeposition of 1 with an aromatic hydrocarbon, [2. 2]paracyclophane, that afforded a new sandwich compound, [Ru2(O2CCF3)2(CO)5·(μ2-C16H16)·Ru2(O2CCF3)2(CO)5] (4), in which the ligand is entrapped between two dimetal complexes. In contrast, when 3 is codeposited with [2. 2]paracyclophane, a new 1D polymeric product, [Ru2(O2CCF3)2(CO)4·(μ2-C16H16)]∞ (5) has been isolated. Complexes 1–5 have been fully characterized by IR and NMR spectroscopy, as well as by X-ray diffraction.

Photoinduced electron transfer reactions of ruthenium(II) complexes containing 2,2′-bipyridine-4,4′-dicarboxylic acid with phenols: Steric and charge effects

Luminescent mixed-ligand ruthenium(II) complexes of type RuL n X 3− n (L = 2,2′-bipyridine, X = 2,2′-bipyridine-4,4′-dicarboxylic acid, n = 0,1,2,3) have been synthesized and their photophysical and electrochemical properties are investigated. The emission lifetime measured for RuL n X 3− n reveals that the lifetime increases as the ligand L is replaced by X. The luminescence quenching of *RuL n X 3− n with several substituted phenolate ions in aqueous medium is efficient and the change of quenching rate data with the change of structure of ligand of RuL n X 3− n and phenolate ion is explained in terms of exergonicity of the reaction, electron transfer distance and charge effect. The semiclassical theory of electron transfer has been successfully applied to this photoredox system.

Interactions of mixed ligand ruthenium(II) complexes containing an amino acid and 1,10-phenanthroline with DNA

Mixed ligand ruthenium(II) complexes containing an amino acid (AA) and 1,10-phenanthroline (phen), i.e. [Ru(AA)(phen) 2] n+ ( n=1,2, AA=glycine (gly), l-alanine ( l-ala), l-arginine ( l-arg)) have been synthesized. The interactions of these complexes and [Ru(phen) 3] 2+ with DNA have been examined by absorption, luminescence, and circular dichroism spectroscopic methods. Absorption spectral properties revealed that [Ru(AA)(phen) 2] + (AA=gly, l-ala) interacted with CT-DNA by the electrostatic binding mode. [Ru( l-arg)(phen) 2] 2+ exhibited the greatest hypochromicity, red shift, and binding constant, indicating that this complex may partially intercalate into the base-pairs of DNA. These results were also suggested by luminescence spectroscopy. CD spectral properties have been examined to understand the detailed interactions of the ruthenium(II) complexes with artificial DNA. In the case of Δ-[Ru( l-arg)(phen) 2] 2+, the solution on adding [poly(dG-dC)] 2 exhibited two well-defined positive peaks, which the shorter and longer wavelength peaks were assigned as originating from the major and the minor groove binding modes, respectively. Then, the solution on adding [poly(dA-dT)] 2 exhibited only one positive peak, which was assigned as a peak corresponding to the minor groove binding mode.

Preparation and reactivity of mixed-ligand ruthenium(II) hydride complexes with phosphites and polypyridyls.

Chloro complexes [RuCl(N-N)P3]BPh4 (1-3) [N-N = 2,2'-bipyridine, bpy; 1,10-phenanthroline, phen; 5,5'-dimethyl-2,2'-bipyridine, 5,5'-Me2bpy; P = P(OEt)3, PPh(OEt)2 and PPh2OEt] were prepared by allowing the [RuCl4(N-N)].H2O compounds to react with an excess of phosphite in ethanol. The bis(bipyridine) [RuCl(bpy)2[P(OEt)3]]BPh4 (7) complex was also prepared by reacting RuCl2(bpy)2.2H2O with phosphite and ethanol. Treatment of the chloro complexes 1-3 and 7 with NaBH4 yielded the hydride [RuH(N-N)P3]BPh4 (4-6) and [RuH(bpy)2P]BPh4 (8) derivatives, which were characterized spectroscopically and by the X-ray crystal structure determination of [RuH(bpy)[P(OEt)3]3]BPh4 (4a). Protonation reaction of the new hydrides with Brønsted acid was studied and led to dicationic [Ru(eta2-H2)(N-N)P3]2+ (9, 10) and [Ru(eta(2-H2)(bpy)2P]2+ (11) dihydrogen derivatives. The presence of the eta2-H2 ligand was indicated by a short T(1 min) value and by the measurements of the J(HD) in the [Ru](eta2-HD) isotopomers. From T(1 min) and J(HD) values the H-H distances of the dihydrogen complexes were also calculated. A series of ruthenium complexes, [RuL(N-N)P3](BPh4)2 and [RuL(bpy)2P](BPh4)2 (P = P(OEt)3; L = H2O, CO, 4-CH3C6H4NC, CH3CN, 4-CH3C6H4CN, PPh(OEt)2], was prepared by substituting the labile eta2-H2 ligand in the 9, 10, 11 derivatives. The reactions of the new hydrides 4-6 and 8 with both mono- and bis(aryldiazonium) cations were studied and led to aryldiazene [Ru(C6H5N=NH)(N-N)P3](BPh4)2 (19, 21), [[Ru(N-N)P3]2(mu-4,4'-NH=NC6H4-C6H4N=NH)](BPh4)4 (20), and [Ru(C6H5N=NH)(bpy)2P](BPh4)2 (22) derivatives. Also the heteroallenes CO2 and CS2 reacted with [RuH(bpy)2P]BPh4, yielding the formato [Ru[eta1-OC(H)=O](bpy)2P]BPh4 and dithioformato [Ru[eta1-SC(H)=S](bpy)2P]BPh4 derivatives.

Synthesis and characterization of mixed-ligand ruthenium(III) complexes with oxalate and acetylacetonate ions

Two mononuclear mixed-ligand ruthenium(III) complexes with oxalate dianion (ox 2−) and acetylacetonate ion (2,4-pentanedionate, acac −), K 2[Ru(ox) 2(acac)] ( 1) and K[Ru(ox)(acac) 2] ( 2), were prepared as a candidate for a building block. In fact, reaction of complex 2 with manganese(II) sulfate gave a heterometallic tetranuclear complex, TBA[Mn II{(μ-ox)Ru III(acac) 2} 3] ( 5) in the presence of tetrabutylammonium (TBA) bromide. The 1H NMR, UV–Vis, selected IR and FAB mass spectral data of these complexes are presented. Both mixed-ligand ruthenium(III) complexes gave a Nernstian one-electron reduction step in 0.1 mol dm −3 Na 2SO 4 aqueous solution on a mercury electrode at 25 °C. Comparison of observed reversible half-wave potentials with calculated values for a series of [Ru(ox) n (acac) 3 − n ] n− ( n=0–3) complexes by using Lever’s ligand electrochemical parameters is presented.

Synthesis of New Ruthenium (II) Bipyridyl Complexes and Studies on Their Photophysical and Photoelectrochemical Properties

AbstractTwo new mixed‐ligand ruthenium(II) complexes, Ru(dcbpy)‐(LL) (NCS)2[where dcbpy = 4, 4′‐dicarboxyl‐2,2′‐bipyridine, LL = 4,4′‐bis (N‐methyl‐anilinomethyl)‐2,2′‐bipyridine (1) or 4‐methyl‐4′‐N‐methyl‐anilinomethyl‐2,2′‐bipyridine (2)], were synthesized, and the photophysical properties of these complexes were studied. The metal‐to‐ligand charge transfer (MLCT) transitions of these complexes exhibited solvatochromic effect due to the existence of NCS ligands. The MLCT energies also strongly depend on the pH values of the solutions because of protonation and deprotonation of the carboxyl groups. The pKa, values of the ground state, 4.0 for 1 and 3.8 for 2, were obtained from the titration curves. The photoelectrochemical properties of 1 and 2 as sensitizers in sandwich‐type solar cells have been studied. Complex 1 exhibited better photoelectrochemical behavior than complex 2 as expected. It was proved that the design of mixed‐ligand complex by introducing electron donating group in one of the ligands should be a promising approach.

Easily accessible and robust olefin-metathesis catalysts based on ruthenium vinylidene complexes

Abstract Nine mixed ligand ruthenium(II) vinylidene complexes with the general formula: [RuCl 2 {CCHR′}(PCy 3 )(L)] and [RuCl{CCHR′}(PCy 3 )(sal-R)] (L= N -heterocyclic carbene, sal-R=salicylaldiminate anion, R′=Ph, SiMe 3 , t But ) has been synthesized and characterized. These complexes are easily accessible from [RuCl 2 ( p -cymene)] 2 , terminal alkynes, imidazolium salts or salicylaldimine salts and they have been found to serve as good catalyst precursors for ring-opening metathesis polymerization (ROMP) of norbornene, substituted norbornenes, polycyclic alkenes and cyclooctene and ring-closing metathesis (RCM) of α,ω-dienes. Furthermore, these precursors possess extremely high stability toward air, heat and moisture in comparison with other metathesis-active alkylidene ruthenium systems. No significant catalyst decomposition was found for several days at elevated temperatures.

Easily Accessible Ring Opening Metathesis and Atom Transfer Radical Polymerization Catalysts based on Arene, Norbornadiene and Cyclooctadiene Ruthenium Complexes Bearing Schiff Base Ligands

AbstractA group of four mixed ligand ruthenium(II)‐Schiff base complexes has been synthesized and characterized. These complexes are easily accessible from [RuCl2(p‐cymene)]2, [RuCl2(NBD)]n, [RuCl2(COD)]x and salicylaldimine salts. They have been found to serve as good catalyst precursors for ring‐opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP) of different vinyl monomers. The catalytic activity and the control over the produced polymer can be dramatically improved after the addition of additives such as Et2AlCl and (n‐Bu)2NH.