Bipyridine Ruthenium Complex Research Articles

Ruthenium(II)/(III) bipyridine heterochelates incorporating phenolato imine functionalities. Synthesis, crystal structure, spectroscopic and electron-transfer properties and solution reactivities †

A new class of ruthenium–bipyridine complexes of the type [Ru(bpy)2(L′)]ClO4 [bpy = 2,2′-bipyridine; L′ = −OC6H3(R)C(R′)NH; R = R′ = H 1a; R = H, R′ = CH31b; R = NO2, R′ = H 1c] have been synthesized via cleavage of N–N and N–C (aliphatic and aromatic) bonds of binucleating imine functionalities. The formation of 1 has been authenticated by the single crystal structure determination of 1a. The complexes exhibit strong MLCT transitions in the visible region and intraligand transitions in the UV region and display moderately strong emission near 700 nm. The quantum yield (φ) of the emission process at 77 K (EtOH–MeOH, 4∶1 glass) varies in the range 2.2 × 10−2–6.5 × 10−3 depending on L′ in 1. The complexes show ruthenium(III)–ruthenium(II) and ruthenium(IV)–ruthenium(III) oxidations in the ranges 0.52–0.77 and 1.71–1.97 V versus SCE respectively. For 1a and 1b, one ligand centred oxidation near 2 V and for all the complexes two bipyridine based reductions have been detected in the ranges −1.51 to −1.56 V and −1.72 to −1.79 V versus SCE. Coulometric oxidation of 1 initially generates the unstable trivalent one-electron paramagnetic [RuIII(bpy)2(L′)]2+ congener, 1+. The complexes 1+ display one broad and moderately strong LMCT band near 750 nm and intraligand transitions in the UV region. The oxidised complexes 1+ exhibit rhombic EPR spectra at 77 K which have been analysed to furnish values of distortion parameters (Δ = 4543–5923 cm−1, V = 3251–5127 cm−1) and energy of the expected ligand field transitions (ν1 3086–3508, ν2 6409–8669 cm−1) within the t2 shell. One of the ligand field transitions has been experimentally observed (ν2 7092–7812 cm−1). The oxidised species 1+ slowly changes to diamagnetic dimeric species of the type [(bpy)2RuIII{−OC6H3(R)C(R′)NNC(R′)(R)C6H3O−}RuIII(bpy)2]4+2 where the ruthenium(III) centres are antiferromagnetically coupled. In the presence of water 1+ as well as 2 return to the parent bivalent species 1. The second order rate constants (k) of the conversion process 1+ → 2 in dry acetonitrile and first order rate constants (k′) of 1+ → 1 in ordinary acetonitrile and the thermodynamic parameters (ΔH‡ and ΔS‡) of both have been determined spectrophotometrically in the temperature range 303–333 K.

Light-emitting multifunctional rhenium (I) and ruthenium (II) 2,2′-bipyridyl complexes with bipolar character

A series of multifunctional molecules consisting of hole transport, electron transport, and light-emitting moieties were synthesized and fabricated into single-layer organic light-emitting devices. The light-emitting units were based on 2,2′-bipyridine complexes of rhenium and ruthenium. It was found that, due to the bipolar character of the molecules, the charge carrier mobilities, charge injection barrier, and the device performance were improved. The electron carrier mobilities are on the order of 10−4 cm2 V−1 s−1 and a maximum luminescence of 730 cd/m2 was observed.

Ruthenium(II/III) bipyridine complexes incorporating thiol-based imine functions: Synthesis, spectroscopic and redox properties

A group of five new ruthenium(II) bipyridine heterochelates of the type [Ru II(bpy) 2L] + 1a– 1e have been synthesized (bpy=2,2′-bipyridine; L=anionic form of the thiol-based imine ligands, HS–C 6H 4NC(H)C 6H 4(R) (R=OMe, Me, H, Cl, NO 2). The complexes 1a− 1e are 1:1 conducting and diamagnetic. The complexes 1a− 1e exhibit strong MLCT transitions in the visible region and intra-ligand transitions in the UV region. In acetonitrile solvent complexes show a reversible ruthenium(III)–ruthenium(II) couple in the range 0.2–0.4 V and irreversible ruthenium(III)→ruthenium(IV) oxidation in the range 1.15–1.73 V vs. SCE. Two successive bipyridine reductions are observed in the ranges −1.43 to −1.57 and −1.67 to −1.78 V vs. SCE. The complexes are susceptible to undergo stereoretentive oxidations to the trivalent ruthenium(III) congeners. The isolated one-electron paramagnetic ruthenium(III) complex, 1c + exhibits weak rhombic EPR spectrum at 77 K ( g 1=2.106, g 2=2.093, g 3=1.966) in 1:1 chloroform–toluene. The EPR spectrum of 1c + has been analyzed to furnish values of distortion parameters ( Δ=8988 cm −1; V=0.8833 cm −1) and energy of the expected ligand field transitions ( ν 1=1028 nm and ν 2=1186 nm) within the t 2 shell. One of the ligand field transitions has been experimentally observed at 1265 nm.

Chiral Separation of Carboxymethyl Derivatives of Amines by Liquid Chromatography on Reversed-phase Silica Gel Coated with N-n-Dodecyl-L-hydroxyproline

Carboxymethyl derivatives of amines containing a chiral α-carbon were separated into enantiomers by high-performance liquid chromatography using octadecylsilanized silica gel coated with N-n-dodecyl-L-hydroxyproline as the stationary phase and an aqueous solution containing copper(II) as the mobile phase. Detection was by post-column reaction involving derivatization to tertiary amine and chemiluminescence reaction of ruthenium bipyridine complex.

Yellow Light–Emitting Poly(phenylenevinylene) Incorporated with Pendant Ruthenium Bipyridine and Terpyridine Complexes

Simultaneous emission from PPV and ruthenium (II) complexes is demonstrated in the title materials (see Fig). The PPV backbone emits green light and the ruthenium polypyridine complexes emit red light resulting in overall yellow emission. At low metal complex content the hexamethylene spacer of the pendant ruthenium complexes prevents quenching of the backbone emission but at higher loading quenching becomes dominant, allowing the emission color of the materials to be tuned by adjusting the metal complex content.

Dinuclear ruthenium(II) bipyridine complexes having non-symmetric α,α′-diimine based neutral bridging ligands.: Synthesis, spectroscopic and electrochemical properties

A group of three dinuclear ruthenium(II) complexes of the type [(bpy) 2Ru II(L)Ru II(bpy) 2](ClO 4) 4·2H 2O, 1a–1c [bpy=2,2′-bipyridine, L=bridging ligand, N pC 5H 4CH=N i–(R)–N i=CHC 5H 4N p; R=none, 1a; R=–C 6H 4–, 1b; R=–CH 2–C 6H 4–CH 2–, 1c] have been synthesized and characterized. The complexes are essentially diamagnetic and behave as 1:4 electrolytes in acetonitrile solution. The mass of the molecular ion for the complex 1a and the geometry of the complexes 1 in solution have been assessed by fast atom bombardment (FAB) mass spectrometry and 1H/ 13C NMR spectroscopy, respectively. Complexes 1 display three metal-to-ligand charge-transfer (MLCT) transitions in the visible region, where the lowest energy MLCT transition is considered to be a dπ(Ru II)→π *(L) transition. The other two higher energy MLCT transitions are believed to be dπ(Ru II)→π *(bpy) transitions. Highly intense ligand-based π→π * transitions are observed in the UV region. In acetonitrile solvent, complexes 1 show one quasi-reversible two-electron oxidation process near 1.5 V vs. Ag/AgCl, due to simultaneous one-electron oxidations [ruthenium (III)⇌ruthenium(II)] of both of the ruthenium centers in 1 and multiple reductions in the range −0.5–−2.7 V vs. Ag/AgCl, due to successive reductions of the coordinated bridging ligand, L, as well as bipyridine. The chemically and electrochemically generated oxidized trivalent congeners of 1 are unstable at room temperature.

Trifunctional Light-Emitting Molecules Based on Rhenium and Ruthenium Bipyridine Complexes

The synthesis and light-emitting properties of two novel, trifunctional, light-emitting molecules based on rhenium(I) and ruthenium(II) bipyridine complexes are described. The hole-transporting, electron-transporting, and light-emitting functional groups are incorporated into one molecule. The authors report that their approach provides flexibility since the optoelectronic properties can be modified by varying the ligand and/or the metal component. For example, a multicolor display is claimed to be possible by preparing mixed metal complexes.

Spectroelectrochemical and photophysical properties of a (3,4-pyridyl) porphyrazine supermolecule containing four [Ru(bipy) 2Cl] + groups

Tetra(3-pyridyl)porphyrazine has been modified with four peripheral [Ru(bipy) 2CI] + groups, yielding a novel, dark green supramolecular species. The spectroscopic and electrochemical properties of the tetraruthenated porphyrazine have indicated a significant electronic interaction between the central and peripheral groups. In addition, fluorescence emission from the porphyrazine center has been observed at room temperature either by direct excitation at the Soret and Q bands, or by excitation at the peripheral ruthenium–bipyridine complexes, evidencing an efficient antenna effect. The generation of 1 O 2 species from the porphyrazine excited triplet states has also been demonstrated.

Unprecedented luminescence behaviour and structural characterization of a novel class of ruthenium(II) 2,2′-bipyridine complexes with orthometallated aminocarbene ligands

Novel luminescent ruthenium(II) bipyridine complexes with orthometallated aminocarbene ligands have been prepared and their photophysical properties studied.

Ruthenium(II) bipyridine complexes with modified phenolic Schiff base ligands. Synthesis, spectroscopic characterization and Redox properties

A group of stable new ruthenium(II) mixed-ligand tris-chelated complexes of the type [Ru(bpy) 2L]ClO 4 ( 1–6), (bpy = 2,2′-bipyridine; L = deprotonated form of the HL ligands, o-(HO)C 6H 3(R)C(R′)NCH 2C 6H 5 or o-(HO)C 6H 3(R)C(R′)NNHC 6H 5; where R = H, p-NO 2 and R′ = H, CH 3) have been synthesized and characterized. The complexes are essentially diamagnetic and behave as 1 : 1 electrolytes in acetonitrile solution. They display two metal-to-ligand-charge-transfer (MLCT) transitions near 500 and 400 nm respectively and intra ligand π-π ∗ transitions in the UV-region. In acetonitrile solution the complexes exhibit weak emission from the lowest energy MLCT band at room-temperature. The quantum yields of the complexes are found to be in the range 0.0004–0.01. In acetonitrile solution the complexes show quasi-reversible ruthenium(II)-ruthenium(III) oxidation couples in the range 0.33 a ̊ 0.70 V and irreversible ruthenium(III)-ruthenium(IV) oxidations in the range 1.53 a ̊ 1.95 V vs SCE . Two successive reversible bipyridine reductions are observed for each complex in the ranges −1.4 a ̊ −1.62 V and −1.59 a ̊ −1.85 V vs SCE respectively. The presence of trivalent ruthenium in the oxidized solution for one complex 5 is evidenced by the rhombic EPR spectrum with g values, g 1 = 2.389, g 2 = 2.081 and g 3 = 1.810. The EPR spectrum of the coulometrically oxidized species, 5 + has been analyzed to furnish values of axial ( Δ = 4745 cm −1) and rhombic (V = 3692 cm −1) distortion parameters as well as the energies of the two expected ligand field transitions ( ν 1 = 3071 cm −1 and ν 2 = 6819 cm −1) within the t 2 shell. One of the ligand field transitions has been observed experimentally at 6578 cm −1 by near-IR spectrum which is close to the computed ν 2 value.

ルテニウム（ＩＩ）多核金属錯体のＥＳＩ‐ＭＳ

A number of polynuclear ruthenium(II), rhodium(III), and cobalt(III) bipyridine complexes have been examined by electrospray ionization mass spectrometry (ESI-MS). ESI-MS is shown to be a powerful tool for the identification of polymetallic complexes and for detecting the contamination, because ESI mass spectra for the complexes showed a simple enough mass pattern for easy structural assignment. Multiply charged ions with the charge state from 8+ to 3+ were observed in the full scan ESI mass spectra of star-burst type tetranuclear complexes denoted by [Met(II)(bpy)2B]3RuX8 (Met=Ru, Os, and bpy=2,2′-bipyridine, B=bridging ligands, X=ClO4-). Different charged ions were found to be generated by the combination of counterion loss and protonation/deprotonation at the proton site of the bridging ligand B. These ion intensities are qualitatively explained in terms of acidity of metal complexes depending upon bridging ligand structures and the charge of metal ions. Ions produced by a removal of ligands were not observed in the ESI spectra unlike the FAB spectra. For tetranuclear complexes, collision-induced dissociation (CID) of the multiply charged ions has made it clear that loss of one or more HX neutral is a major process for lower charge states, while complete fragmentation takes place for higher charge states and the fragments are based on a subunit group of [Met(II)(bpy)2B]2+. Insertion of formal O2- produced from ClO4- counterion was observed for the complexes without active protons even if low energy CID experiments, but not for the complexes with active protons. Advantages of ESI mass spectrometry are demonstrated for these polynuclear compounds and CID chemistry of the investigated ions will be discussed.

Bipyridine functionalized molecular clips. Self-assembly of their ruthenium complexes in water

Ruthenium-bipyridine complexes of molecular clips self-assemble in water to form scroll- and cigar-like nanostructures.

Quinoxaline‐based conjugated polymers containing ruthenium(II) bipyridine metal complex

AbstractA series of novel quinoxaline‐based conjugated polymers which contain a ruthenium(II) bipyridine complex were synthesized by the Suzuki coupling reactions. UV/VIS spectroscopy showed that the spectral features of the polymers are dependent on the amount of metal complex present. Results from excitation and emission spectroscopy suggest an energy transfer between the backbone and the metal complex. The polymers exhibit hole carrier mobilities of ≈ 10−5 cm2 · V−1 · s−1, which is comparable to organic photoconductors.

Excited-State Processes in Ruthenium(II) Bipyridine Complexes Containing Covalently Bound Arenes

The photophysical properties of a series of ruthenium trisbipyridine complexes covalently linked to aromatic chromophores of the type [Ru(bpy)2(4-methyl-4‘-(2-arylethyl)-2,2‘-bipyridine)]2+(ClO4)2,...

Temperature and viscosity dependence of the electron-transfer reaction between plastocyanin and cytochrome c labeled with a ruthenium(II) bipyridine complex

The temperature and viscosity dependence of the photo-induced electron-transfer reaction between plastocyanin and cytochrome c labeled at Lys13 with Ru(4,4′-dicarboxybipyridine)(bipyridine) 2 +2 have been investigated. In these studies, a short pulse of 450 nm light was used to excite the ruthenium complex which was oxidatively quenched by the iron center of cytochrome c. The resulting Fe(II) cytochrome c was then rapidly reoxidized by plastocyanin. The reactions were investigated over a temperature range of 3.5 to 37°C under low ionic strength conditions such that protein/protein complex formation was favored. The enthalpy of activation was 7 kcal mol −1 and the entropy of activation was −20 cal mol −1 K −1. Increasing the viscosity by the addition of sucrose up to 70% resulted in a 4-fold decrease in the rate constant for electron transfer. The overall results suggest a rate-limiting step that involves either dissociation of the dominant protein/protein complex or surface diffusion of the associated proteins.

Singlet and triplet energy transfer processes in ruthenium(II) bipyridine complexes containing covalently bound arenes

Singlet and triplet energy transfer processes in [Ru(bipy) 2(4-methyl-4′-(2-arylethyl)-2,2′-bipyridine)] 2+ have been investigated, where aryl = 2-naphthyl (Ru-Naph), 9-anthryl (Ru-Anth) and 1-pyrenyl (Ru-Pyrene). In each case fluorescence from the aromatic chromophore is quenched by intramolecular energy transfer to Ru(bipy) 3 2+ whereas emission from the Ru(bipy) 3 2+ moiety is controlled by the relative energy of its 3MLCT state and the pendant arene triplet states. Consequently 3MLCT emission is observed for Ru-Naph whereas it is fully quenched for Ru-Anth. When the two states are isoenergetic (e.g. Ru-Pyrene) a long-lived 3MLCT emission is observed which delays with the same lifetime as the pyrene triplet state (5.23 μs).

Control of the co-ordination mode of 1,8-naphthyridine ligated to ruthenium(II) bipyridine complexes

The complexes [Ru(bipy)2(napy-N)(MeCN)][PF6]21 and [Ru(bipy)2(napy-N,N′)][PF6]22(bipy = 2,2′-bipyridine, napy = 1,8-naphthyridine) were prepared, and their crystal structures determined by X-ray analysis. The crystal structure of 1 displays an octahedral co-ordination with monodentate napy, acetonitrile and two chelating bipy. Despite the inequivalency of two nitrogens of napy in 1 in the solid state, the 1H NMR spectra in the aromatic region resemble those of 2 over the range –90 to 60 °C, which implies dynamic behaviour of napy in 1 in solution. Both 1 and 2 were reduced irreversibly at –0.98 V (vs. Ag–AgCl) in dimethylformamide at –20 °C, and the process gradually becomes a reversible redox reaction on increasing the temperature to 30 °C. An EPR study revealed that one-electron reduction of 1 takes place in the napy-localized orbital without appreciable increase in electron density on one of the nitrogens of napy. The distinct inequivalence in the charge density between the two nitrogen atoms of singly reduced napy results in stabilization of the N rather than N,N′ co-ordination mode.

The ground and excited state electronic structures of ruthenium quinones and related species

Electronic and resonance Raman spectroscopy are used to probe the electronic structures of bipyridine ruthenium complexes of quinone and a series of derivatives in which the oxygen atoms of quinone are successively replaced by NH. The electronic structures of some benzoquinonediimine species are probed by variation of substituent in the benzene ring, and the properties of a diaminophenyl substituted benzoquinonediimine are explored as a function of the twist at the 1.1'-link.

Towards mediator design: Characterization of tris-(4,4′-substituted-2,2′-bipyridine) complexes of iron(II), ruthenium(II) and osmium(II) as mediators for glucose oxidase of Aspergillus niger and other redox proteins

A range of novel tris-(4,4′-substituted-2,2′-bipyridine) complexes of the group VIII metals iron(II), ruthenium(II) and osmium(II) have been synthesized and characterized electrochemically with respect to their ability to act as electron-transfer mediators for redox enzymes, notably glucose oxidase (GOD, EC 1.1.3.4) of Aspergillus niger. The complexes present a wide range of redox potentials (−325 to +610 mV in phosphate-buffered saline solution relative to the standard calomel electrode) and high second-order rate constants k med for electron transfer from reduced glucose oxidase (to approx. 10 7 M −1 s −1) as determined by an electrochemical method. These rate constants were treated following Marcus theory to yield a value for the reorganization energy λ for the mediation reaction of 0.70 eV. Complexes bearing amino substituents gave particularly high rate constants with GOD, suggesting a specific interaction with the enzyme's active site. The tris-(4,4′-dimethoxy-2,2′-bipyridine) complex of osmium is a versatile mediator, presenting high rate constants k med for a variety of unrelated redox proteins. Enzyme electrodes, formed by coadsorption of a mediator with a redox enzyme on the surface of graphite rods, responded chronoamperometrically to the addition of substrate to the surrounding phosphate- buffered saline. The family of mediators may be useful for redox protein electron-transfer studies and for application in amperometric biosensors. By appropriate choice of the 4,4′ substituent, the physicochemical and electrochemical properties of a complex could be tuned to suit the intended redox protein.

Novel synthesis of [Ru(phen) 2Br 2]X (X=Br, ClO 4 or BPh 4) and convenient synthesis of bis(2,2′-bipyridine) complexes of ruthenium(III) and tris(2,2′-bipyridine) or (1,10-phenanthroline) complexes of ruthenium(II)

Synthesis of the new ruthenium complexes [Ru(phen) 2Br 2]X (X=Br, ClO 4 or BPh 4) and convenient synthesis of [Ru(bipy) 2Cl 2]X, (X=Cl or ClO 4) are reported using [RuBr 3(Me 2SO) 3] and fac- and mer-[RuCl 3(Me 2SO) 3]. Syntheses of ruthenium(II) complexes [Ru(bipy) 3]X 2 (X=Cl, Br, ClO 4 or BPh 4) and [Ru(phen) 3]X 2, (X=ClO 4 or BPh 4) are reported using [RuBr 3(Me 2SO) 3], fac- and mer-[RuCl 3(Me 2SO) 3], [RuBr 2(Me 2SO) 3] and (RuCl 2(Me 2SO) 4]. The compounds are characterised using various physical methods.