Peripheral Ru Research Articles

Efficient Convergent Energy Transfer in a Stereoisomerically Pure Heptanuclear Luminescent Terpyridine-Based Ru(II)-Os(II) Dendrimer.

The stereoisomerically pure synthesis of a novel heptanuclear Ru(II)-Os(II) antenna bearing multitopic terpyridine ligands is reported. An unambiguous structural characterization was obtained by 1H NMR spectroscopy and ion mobility spectrometry (IMS-MS). The heptanuclear complex exhibits large molar absorption coefficients (77900 M-1 cm-1 at 497 nm) and undergoes unitary, downhill, convergent energy transfer from the peripheral Ru(II) subunits to the central Os(II) that displays photoluminescence with a lifetime (τ = 161 ns) competent for diffusional excited-state electron transfer reactivity in solution.

Photoinactivation of Salmonella enterica (serovar Typhimurium) by tetra-cationic porphyrins containing peripheral [Ru(bpy)2Cl]+ units

In the last years, antimicrobial photodynamic therapy (aPDT) has been considered as one important alternative to be used in antimicrobial treatments. In the present work we report the first photoinactivation of Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) by cationic free-base meso-tetra-(phenyl)porphyrin and its Zn(II) complex containing peripheral Ru(II)-bipyridyl complexes. Bacterial inoculum (107 CFU mL-1) was incubated with the porphyrins (25 μM) with an irradiation system containing a halogen lamp with fluence values of 0, 180, 360, 720 and 1080 J cm-2. Both porphyrins demonstrate phototoxicity against bacteria, but higher efficiency was observed by Zn(II) complex. It was demonstrated that RuTPyP and ZnRuTPyP phototoxicity is due to their photodynamic activity associated with the formation of singlet oxygen, anion superoxide and hydroxyl radical at their irradiation by visible light. The formation of these reactive species was confirmed using flash-photolysis technique and spin-trap electron paramagnetic resonance (EPR) spectroscopy. The singlet oxygen quantum yield was determined by indirect method using the uric acid as singlet oxygen scavenger. Besides the characterization of optical absorption and fluorescence RuTPyP and ZnRuTPyP properties were realized using optical absorption and fluorescence spectroscopies. It was observed that complexation with Zn(II) ion increases the quantum yields of porphyrin fluorescence and singlet oxygen formation.

Chiral Tectonics: VCD and ECD Application for Epimerization of a Star-Burst Tetranuclear Complex with a Labile Central Core

The present article reports the application of vibrational circular dichroism (VCD) and temperature-dependent electronic circular dichroism (ECD) methods to reveal the dynamical aspects of a star-burst tetranuclear metal complex with a labile central core in a solution. One-handed chiral inert tecton, ∆- or Λ-[Ru(III)(acac)2(taetH)] (acacH = acetylacetone, taetH2 = tetraacetylethane), was prepared by reacting [Ru(acac)3] with taetH2 in solid at 120 °C. The ∆Λ-pair of pure enantiomers was obtained chromatographically. On adding Al(ClO4)3 to its enantiopure solution, three units of one-handed tecton were assembled spontaneously around an aluminum(III) ion to form a star-burst tetranuclear complex, [{∆- or Λ-Ru(acac)2(taet)}3Al(III)]. The VCD spectrum recorded on the CDCl3 solution of the complex showed that the central chirality around an Al(III) ion took dominantly the absolute configuration antipodal to those of peripheral Ru(III) units at the temperature lower than −10 °C. The complex underwent interconversion between the ∆- and Λ-configurations around a central Al(III) core (or epimerization) in solution. The activation energy barrier was determined from the time courses of ECD spectra in CHCl3 and CH3OH.

Interligand Interactions Dictate the Regioselectivity of trans-Hydrometalations and Related Reactions Catalyzed by [Cp*RuCl]. Hydrogen Bonding to a Chloride Ligand as a Steering Principle in Catalysis.

Reactions of internal alkynes with R3M-H (M = Si, Ge, Sn) follow an unconventional trans-addition mode in the presence of [Cp*Ru(MeCN)3]PF6 (1) as the catalyst; however, the regioselectivity is often poor with unsymmetrical substrates. This problem can be solved upon switching to a catalyst comprising a [Ru-Cl] bond, provided that the acetylene derivative carries a protic functional group. The R3M unit is then delivered with high selectivity to the alkyne-C atom proximal to this steering substituent. This directing effect originates from the ability of the polarized [Ru-Cl] bond to engage in hydrogen bonding with the protic substituent, which helps upload, activate, and lock the alkyne within the coordination sphere. An additional interligand contact of the chloride with the -MR3 center positions the incoming reagent in a matching orientation that translates into high regioselectivity. The proposed secondary interactions within the loaded catalyst are in line with a host of preparative and spectral data and with the structures of the novel ruthenium π-complexes 10 and 11 in the solid state. Moreover, the first X-ray structure of a [Ru(σ-stannane)] complex (12a) is presented, which indeed features peripheral Ru-Cl···MR3 contacts; this adduct also corroborates that alkyne trans-addition chemistry likely involves σ-complexes as reactive intermediates. Finally, it is discussed that interligand cooperativity might constitute a more general principle that extends to mechanistically distinct transformations. The presented data therefore make an interesting case for organometallic chemistry that provides inherently better results when applied to substrates containing unprotected rather than protected -OH, -NHR, or -COOH groups.

Ruthenium−Porphyrin Conjugates with Cytotoxic and Phototoxic Antitumor Activity

We report here two novel "extended-arms" porphyrins, TetbpyPP and TedabpyPP, in which four peripheral bpy fragments are connected to the meso positions of the macrocycle through flexible linkers of different length and hydrophilicity. We describe also the new, water-soluble, tetracationic conjugate [TedabpyPP{Ru([9]aneS3)Cl}(4)][Cl](4) (6). Compound 6 belongs to the series of cationic Ru-porphyrin conjugates 1-5, each bearing four peripheral Ru(II) half-sandwich coordination compounds, that we recently prepared as potential photosensitizing chemotherapeutic agents. The in vitro cell growth inhibition of conjugates 1-6 toward MDA-MB-231 human breast cancer cells and HBL-100 human nontumorigenic epithelial cells are reported, together with the phototoxic effects of 1, 4, and 6 on MDA-MB-231 cells. All conjugates have IC(50) values in the low micromolar range that decrease by 1 order of magnitude upon irradiation of cell cultures with visible light. The most promising compounds 1 and 6 are phototoxic at low light and drug doses.

Synthesis, spectral and excited state energy transfer studies on new supramolecular ruthenium polypyridyl triads with octakis(methylthio)tetraazaporphyrinzinc(II)

New bichromophoric di- and trinuclear complexes were synthesized through coordinate strapping of one or two (bpy) 2Ru II/(phen) 2Ru II/Cp(PPh 3)Ru II moieties to [Zn{(MeS) 8TAP}] 1, core. Thus five new complexes of the type [Zn{(MeS) 8TAP}{Ru(bpy) 2}][PF 6] 2 2, bent and linear [Zn{(MeS) 8TAP}{Ru(bpy) 2}{Ru(phen) 2}][PF 6] 4 3 and 4, bent and linear [Zn{(MeS) 8TAP}{Ru(bpy) 2}{RuCp(PPh 3)}][PF 6] 3 5 and 6, were synthesized and characterized using IR, 1H NMR, UV–visible, and mass spectral data. The trinuclear complexes 3– 6 possessed bent (κ 4-S 2,S 3,S 7,S 8)[Ru II] 2 and linear (κ 4-S 2,S 3,S 12,S 13)[Ru II] 2 arrangements of the peripheral metallo-chromophore units. Unlike the two reversible reduction waves in complex 1 observed at E 1/2 −0.34 and −0.60 V, only one reversible reduction wave was observed, between E 1/2 −0.56 to −0.58 V vs. Ag/AgCl, in the di- and trinuclear complexes 2– 6. Also in the anodic scans, the dinuclear complexes 2, as well as linear trinuclear complexes 4 and 6, exhibited two successive one electron oxidations, the first at E 1/2 ∼ 0.62 V due to Ru(II)/Ru(III) process and second at E 1/2 ∼ 1.16 V vs. Ag/AgCl due to {(MeS) 8TAP}/{(MeS) 8TAP} + processes, while the bent trinuclear complexes 3 and 5 exhibited three successive one electron oxidations, i.e. one additional oxidation wave at E 1/2 0.88 and 0.90 V vs. Ag/AgCl, respectively. In the fluorescence measurements, Soret excitation led to strong [Zn{(MeS) 8TAP}] centered S 2 emission together with a rapid intercomponent excitation energy transfer ( k 10 7–10 8 s −1) to peripheral Ru(II) unit that showed emission maxima between 535 and 545 nm. Lifetime analysis showed that Ru(II) ∗ emission predominated in the dinuclear complex 2, but its contribution dropped significantly upon formation of the trinuclear complexes, which has been explained in terms of relative variation of the LUMO energies of the linked chromophores in the excited states.

Switchable Antenna: A Star‐Shaped Ruthenium/Osmium Tetranuclear Complex with Azobis(bipyridine) Bridging Ligands

A star-shaped Ru/Os tetranuclear complex, in which a central Os unit is linked to three peripheral Ru units by 4,4''-azobis(2,2'-bipyridine) (azobpy) bridging ligands, was prepared to examine the unique photodynamics regulated by its redox state. The Ru/Os tetranuclear complex exhibits Ru-based luminescence at 77 K, whereas the three-electron reduction (one for each azobpy) of the Ru/Os complex results in luminescence from the Os unit. The photoexcited state of the Ru/Os complex rapidly decays into low energy metal-to-ligand charge-transfer states, in which the excited electron is localized in the azobpy ligand in the form of azobpy(.-). Upon the one-electron reduction of the azobpy ligands, the above-mentioned low-energy states become unavailable to the photoexcited complex. As a result, an energy transfer from the Ru-based excited state to the Os-based excited state becomes possible. Ultrafast transient absorption measurements revealed that the energy transfer process consists of two steps; intramolecular electron transfer from the terminal bipyridine ligand (bpy(.-)) to form azobpy(2-) followed by a metal-to-metal electron transfer. Thus, the Ru/Os tetranuclear complex collects light energy into the central Os unit depending on the redox state of the bridging ligands, qualifying as a switchable antenna.

Towards New Organometallic Wires: Tetraruthenium Complexes Bridged by Phenylenevinylene and Vinylpyridine Ligands

The tetranuclear complexes [{(PiPr(3))(2)(CO)ClRu(mu-CH=CHpy)Ru Cl(CO)(PPh(3))(2)}(2)(mu-CH=CH-C(6)H(4)- CH=CH-1,4)] (3 a) and [{(PiPr(3))(2)(CO)ClRu(mu-CH=CHpy)RuCl(CO)(PPh(3))(2)}(2)(mu-CH=CH-C(6)H(4)-CH=CH-1,3)] (3b), which contain vinylpyridine ligands that connect peripheral Ru(PiPr(3))(2)(CO)Cl units to a central divinylphenylene-bridged diruthenium core, have been prepared and investigated. These complexes, in various oxidation states up to the tetracation level, have been characterized by standard electrochemical and spectroelectrochemical techniques, including IR, UV/Vis/NIR and ESR spectroscopy. A comparison with the results for the vinylpyridine-bridged dinuclear complex [PiPr(3))(2)(CO)ClRu(mu-CH=CHpy)RuCl(CO)(PPh(3))(2)(CH=CHPh)] (6) and the divinylphenylene-bridged complexes [{(EtOOCpy)(CO)Cl(PPh(3))(2)Ru}(2)(mu-CH=CH-C(6)H(4)-CH=CH-1,4)] (8a) and [{(EtOOCpy)(CO)Cl(PPh(3))(2)Ru}(2)(mu-CH=CH-C(6)H(4)-CH=CH-1,3)] (8b), which represent the outer sections (6) or the inner core (8a,b) of complexes 3a,b, and with the mononuclear complex [(EtOOCpy)(CO)(PPh(3))(2)RuCl(CH=CHPh)] (7) indicate that every accessible oxidation process is primarily centred on one of the vinyl ligands, with smaller contributions from the metal centres. The experimental results and quantum chemical calculations indicate charge- and spin-delocalization across the central divinylphenylenediruthenium part of 3a,b or the styrylruthenium unit of 6, but not beyond. The energy gap between the higher lying styryl- or divinylphenylenediruthenium-based and the lower occupied vinylpyridineruthenium-based orbitals increases in the order 6<3 b<3 a and thus follows the conjugation within the non-heteroatom-substituted aromatic vinyl ligand.

A Multifunctional Tetrametallic Ru−Pt Supramolecular Complex Exhibiting Both DNA Binding and Photocleavage

A new tetrametallic supramolecular complex, [{(bpy)2Ru(dpp)}2Ru(dpp)PtCl2](PF6)6 (bpy = 2,2'-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine), has been prepared and characterized. This supramolecular assembly is multifunctional, forming coordinate covalent bonds to DNA through its cis-PtCl2 moiety and photocleaving DNA through its Ru polypyridine chromophores. Electronic absorption spectroscopy shows ligand-based pi-->pi* transitions in the UV with Ru-based metal-to-ligand charge transfer transitions throughout much of the visible. The Ru-->dpp CT transitions center at 542 nm (eta = 35 000 M-1 cm-1). This complex has a HOMO localized on peripheral Ru with E(1/2)oxd = 1.58 V vs Ag/AgCl, and a LUMO based on the mu-dpp connecting Ru and Pt, E(1/2)red = -0.40 V. Gel electrophoresis analysis shows the tetrametallic coordinates to pUC18 DNA and, when excited with visible light, cleaves DNA through an oxygen-mediated pathway.

Intervalence charge transfer in a “chain-like” ruthenium trinuclear assembly based on the bridging ligand 4,7-phenanthrolino-5,6:5′,6′-pyrazine (ppz)

The IVCT characteristics of the mixed valence forms of the trinuclear complex [{Delta-Ru(bpy)2}2{Delta(t)-Ru(bpy)(mu-ppz)2}]n+ (n = 7, 8; t = trans), and the diastereoisomers (meso and rac) of the dinuclear complex [{Ru(bpy)2}2(mu-ppz)]5+, display a marked dependence on the nuclearity and extent of oxidation of the assemblies. The dinuclear species are classified as borderline localised-delocalised mixed valence species while the two mixed valence states of the trinuclear complex exhibit localised behaviour. One-electron oxidation of a terminal Ru centre in the trinuclear case gives rise to a broad, low intensity IVCT band for the +7 mixed valence species which is composed of two underlying Gaussian-shaped bands. The transitions are identified as adjacent and remote IVCT transitions, with the former dominating the intensity of the IVCT manifold. The +8 mixed valence species exhibits a single dominant IVCT band arising from the equivalent IVCT transitions from the central Ru(II) to peripheral Ru(III) centres.

(Ln)Ru{η3-(tpdt)}] Complexes as Dithiolate Donors to Group 10 Metal Centers: Synthetic, Single-Crystal X-ray Diffraction and Electrochemical Studies {Ln = η6-C6Me6 (HMB) and η5-C5Me5 (Cp*); tpdt = S(CH2CH2S)2}

Trinuclear mixed metal cationic complexes of Ru−Pd, [{(Ln)Ru(μ-η2:η3-tpdt)}2Pd]2+ (4A, Ln = HMB; 8, Ln = Cp*), and of Ru−Pt, [{(Ln)Ru(μ-η2:η3-tpdt)}2Pt]2+ (5B, Ln = HMB; 9, Ln = Cp*), containing bare bridging M(II) (M = Pd, Pt) centers, are formed from the reaction of [(HMB)RuII(η3-tpdt)] (1) and [Cp*RuIII(η3-tpdt)] (2) (tpdt ≡ S(CH2CH2S)2) with Pd(MeCN)2Cl2 (or PdCl2) and PtCl2, respectively. With Pt(PPh3)2Cl2, both 1 and 2 displace the chloro ligands, thus forming dinuclear complexes [{(HMB)Ru(μ-η2:η3-tpdt)}{Pt(PPh3)2}]2+ (6) and [{(Cp*)Ru(μ-η2:η3-tpdt)}{Pt(PPh3)2}]2+ (10), in which Pt is coordinated to two thiolate atoms and two PPh3 ligands in a four-coordinate planar geometrical environment. X-ray diffraction analyses show that the arene complexes 4A and 5B also possess four-coordinate planar geometry at the central metal atom. In the Cp* complexes, the central MS4 moiety is tetrahedral for M = Pd, but planar for M = Pt, both metal centers being metal−metal bonded to the peripheral Ru atoms, presumab...

Tetranuclear Ru Complex Linked via Redox-Active Azobis(bipyridine) Ligands as a Redox-Responsive Photoswitch

Abstract A tetranuclear Ru complex linked by 4,4″-azobis(2,2′-bipyridine) (azobpy), [Ru{(azobpy)Ru(bpy)2}3][PF6]8 (bpy = 2,2′-bipyridine) has been prepared and fully characterized. Cyclic and differential pulse voltammetries show that two kinds of oxidation occur, the one at the less positive potential being assigned to the oxidation of the three peripheral Ru ions, while the other to that of the central Ru ion. On a cathodic scan, a pair of three-electron (one electron on each azobpy) reductions of azobpy ligands appear at less negative potentials than terminal bpy ligands. A low-energy metal-to-ligand charge transfer (MLCT) absorption band involving the π*-orbitals of azobpy ligands is observed in addition to the usual MLCT band involving terminal bpy ligands. These results indicate the presence of a low-lying π* level of azobpy. A selective reduction of azobpy ligands renders the non-luminescent complex into a moderately luminescent species. This light switch is reversible, implying the utility of this branched structure in energy delivering molecular systems.

Porphyrins bound to Ru(bpy) 2 clusters: electrocatalysis of sulfite

Mono-, di-, tri- and tetra-ruthenated porphyrins derived from phenyl/4-pyridyl mesosubstituted porphyrin and a trans di-ruthenated dipyridyl octaethylporphyrin have been synthesised. Coated on carbon electrodes, they have been tested as a sensor for sulfite using the oxidation wave of the Ru(II)/Ru(III) couples in hydroalcoholic solutions. At least two peripheral Ru are necessary to trigger the catalysis off. No major influence of the central metallic ions has been detected, but the Co (II) is coordinated by the sulfite.

New metallodendrimers containing an octakis(diphenylphosphino)-functionalized silsesquioxane core and ruthenium(II)-based chromophores.

A new class of surface-modified dendrimers has been prepared by reactions of 8 equiv of the terpyridine-functionalized polyether monodendrons with a polyhedral oligomeric silsesquioxane (POSS) core. Subsequent reactions of these spherically shaped organic dendrimers with Ru(II)-based precursors afford photo- and redox-active metallodendrimers. These new dendrimers have been characterized using a combination of mass spectral analysis (MALDI-TOF/MS, ESI/MS, and FAB/MS), nuclear magnetic resonance (1H, 13C, 29Si, and 31P(1H) NMR), photophysical analyses (electronic absorption, emission, excited-state lifetime, and quantum yield) and electrochemical measurement (cyclic voltammetry). Specifically, 31P(1H) NMR is used to monitor the completion of reactions and the purity of dendrimers and metallodendrimers. These new metallodendrimers exhibit large extinction coefficients that coincide with the number of peripheral Ru(II)-based chromophores. With the use of (-CH2-Ph-tpy)RuII(bpy)2 type of chromophores, all metallodendrimers are found emissive at room temperature, with lifetimes in the range of 605-890 ns. Photophysical data also indicate similar steady-state emission maxima and single-exponential decay kinetics for all metallodendrimers, and the observed overall quantum yields of the G1, G2, and G3 metallodendrimers are found to be 14, 20, and 7 times higher than that of the monomeric model complex (CH3-Ph-tpy)Ru(bpy)2(PF6)2. Electrochemical studies reveal the presence of surface-confined species, in addition to the ligand-centered and metal-centered redox processes.

Tetranuclear Tetrapyrido[3,2-a:2',3'-c:3",2"-h:2"',3"'-j]phenazineruthenium Complex: Synthesis, Wide-Angle X-ray Scattering, and Photophysical Studies.

The tetranuclear ruthenium complex {Ru[(tpphz)Ru(bpy)(2)](3)}(8+), where tpphz is tetrapyrido[3,2-a:2',3'-c:3",2"-h:2"',3"'-j]phenazine, has been synthesized by reaction of [Ru(tpphz)(3)](2+) with [Ru(bpy)(2)Cl(2)] and by reaction of [Ru(bpy)(2)(tpphz)](2+) with [Ru(DMSO)(4)Cl(2)]. The large distance between the chiral centers allows full (1)H NMR interpretation despite the mixture of eight stereoisomers. The tetranuclear complex was further characterized by electrospray mass spectrometry and by the wide-angle X-ray scattering technique, which confirmed the starburst geometry. The photophysical properties of the tetranuclear complex in acetonitrile were studied and compared with those of [Ru(tpphz)(3)](2+) (1 x 10(-)(4) M acidic solution) and [(bpy)(2)Ru(tpphz)Ru(bpy)(2)](4+) model molecules. The tetranuclear complex gives rise to a single emission, attributed to metal-to-ligand charge-transfer states involving peripheral Ru centers and tpphz bridging ligands.

Equilibria and spectroelectrochemical studies on the formation of multibridged tris(bipyrazine) ruthenium(II) complexes with ruthenium—edta groups

The tris(bipyrazine) ruthenium(II) complex forms a series of complexes containing [Ru II/IIIEDTA] 2−/− groups coordinated to the peripheral nitrogen atoms of the bipyrazine bridging ligand. These groups exhibit similar redox potentials ( E 0 = 0.38 V vs. SHE) and a very weak electronic coupling through the central complex. When the peripheral Ru(III) groups are reduced to the Ru(II) state, strong charge-transfer bands appear at 490 and 670 nm and the stability constants increase by 7 orders of magnitude due to d π -p * π back-bonding interactions involving the peripheral ions and the bipyrazine ligand.

Synthesis and electrochemical behavior of a tetrametallated cobalt porphyrin

Reported is the chemistry of a new polynuclear cobalt porphyrin complex obtained by complexing the pyridine residues of meso-tetra(4-pyridyl)porphinate cobalt(III) chloride with ruthenium(III)-EDTA ions. The complex exhibited reversible spectroelectrochemical behavior, with two successive redox processes at E°=0.080 and 0.295 V versus SHE associated with the peripheral Ru(III)EDTA and central Co(III) ions, respectively. An enhanced electrocatalytic activity in the reduction of molecular oxygen was observed for the tetrametallated cobalt porphyrin, involving a cooperative effect between the cobalt(III) center and the peripheral Ru(II)-EDTA groups.