Cyclometalated Ruthenium Research Articles

Cytotoxicity of cyclometallated ruthenium complexes: the role of ligand exchange on the activity

The cyclometallated Ru(II) complexes cis-[Ru(phpy)(phen)(CH3CN)2](PF6) (1; phpy(-)=deprotonated 2-phenylpyridine, phen=1,10-phenanthroline) and cis-[Ru(phpy)(bpy)(CH3CN)2](PF6) (2; bpy=2,2'-bipyridine) were investigated as potential agents for photodynamic therapy. The presence of phpy(-) in the coordination sphere results in a red-shift of the Ru→phen and Ru→bpy metal-to-ligand charge transfer of 1 and 2, respectively, thus improving the tissue penetration of light while maintaining the efficient photo-induced ligand exchange required for DNA binding. The 14-fold enhancement of OVCAR-5 cell death that occurs upon irradiation with 690 nm light can be attributed to photo-aquation. The role of glutathione (GSH) on the toxicity of the complex was also explored. Complexes 1 and 2 undergo ligand substitution in the presence of GSH in the dark, such that the metal may covalently bind to biomolecules. The combination of photo-induced ligand exchange and GSH-facilitated ligand exchange may explain the observed cytotoxicity.

Design and development of cyclometalated ruthenium complexes containing thiophenyl-pyridine ligand for dye-sensitized solar cells

Two new cyclometalated ruthenium sensitizers NC102 (1) and NC103 (2), where the two NCS- ligands of the N3 analog were replaced with the 2-thiophen-2-yl-pyridine and 2-benzo[b]thiophen-2-yl-pyridine ligands, respectively, were designed and synthesized for dye-sensitized solar cell applications. The effects of these two ligands on the photophysical behavior of ruthenium complexes were investigated by their optical, electrochemical, and photovoltaic properties. The sensitizer NC103 (2) with the fluoride substitution in the ligand exhibited the best cell performance with a short-circuit current (Jsc) of 9.45 mA/cm2, an open-circuit voltage (Voc) of 630 mV, and a fill factor (FF) of 0.71, giving an overall power conversion efficiency of (η) 4.22% under simulated AM 1.5 irradiation.

New class of thiocyanate-free cyclometalated ruthenium(II) complexes having a pyridylquinoline derivative for near-infrared sensitization of dye-sensitized solar cells

A new class of thiocyanate-free cyclometalated ruthenium(II) complexes [Ru(dcpq) 2 (C^N)]Cl (where dcpq is 4-carboxy-2-(4′-carboxypyridin-2′-yl)quinoline and C^N is a bidentate cyclometalating ligand) ( FT22 and FT61 ) was synthesized as near-infrared (IR) sensitizers for dye-sensitized solar cells (DSSCs). Modification of the ligand improves photovoltaic performance, and DSSCs sensitized with FT61 show large photocurrents (> 21 mA cm − 2 ) as well as a 55% incident photon-to-current conversion efficiency (IPCE) at 800 nm and 25% IPCE at 900 nm. The complexes exhibit superior light-harvesting properties in the near-IR region. A new class of thiocyanate-free cyclometalated ruthenium(II) complexes was synthesized as near-IR sensitizers for DSSCs. FT61 -based cells show large photocurrents as well as a superior light-harvesting properties in the near-IR region. • We synthesize new thiocyanate-free Ru complexes as near-IR sensitizers for DSSCs. • Modification of the ligand improves the photovoltaic performance. • FT61-based cells exhibit J sc of 21.2 mA cm − 2 . • FT61 exhibits superior light-harvesting properties in the near-IR region. • DSSCs based on FT61 show 55% IPCE at 800 nm and 25% IPCE at 900 nm.

N‐Heterocyclic Gallylene Supported Organoruthenium Derivatives – Synthesis, Structure, and C–H Bond Cleavage

AbstractThe reaction of the low‐valent and sterically bulky gallium(I) compound Ga(DDP) (1, DDP = 2‐diisopropylphenylamino‐4‐diisopropylimino‐2‐pentene) with an equimolar amount of the tetrahydrido‐bridged complex [Cp*Ru(μ‐H)2]2 (2, Cp* = pentamethylcyclopentadiene) in toluene at 70 °C results in the Ga(DDP)‐bridged diruthenium complex [(Cp*Ru)2(μ‐H)2{μ‐Ga(DDP)}] (3). Furthermore, a cyclometallated ruthenium complex, [(η6‐p‐cymene)Ru(DDP)Ga(µ‐Cl){Ga(Cl)(N{C6H3iPr2})2(µ2‐CH2C4H5)}] (6), is isolated from the reaction of five equivalents of 1 with [(η6‐p‐cymene)RuCl2]2 (4) in n‐hexane at reflux. The red crystalline compound 3 contains a [Cp*Ru] dimer bridged by Ga(DDP) and two hydrido ligands with a Ga–Ru–Ru triangle. Compound 6 is obtained by a C–H bond cleavage process of a CH3 group in 1 followed by intramolecular rearrangement. The new compounds are fully characterized by NMR (1H, 13C) spectroscopy, liquid injection field desorption MS (LIFDI‐MS), and single‐crystal X‐ray diffraction analysis.

Cyclometalated Ruthenium Complexes of 1,2,3‐Triazole‐containing Ligands: Synthesis, Structural Studies, and Electronic Properties

AbstractSix bis‐tridentate and two tris‐bidentate cyclometalated ruthenium complexes with a 1,2,3‐triazole‐containing ligand have been prepared and characterized. Single‐crystal X‐ray analyses of complexes [(MeOptpy)Ru(Budtab)](PF6) and [(Mebip)Ru(Budtab)](PF6) are presented, where MeOptpy is 4′‐p‐methoxyphenyl‐2,2′:6′,2′′‐terpyridine, Budtab is the 2‐deprotonated form of 1,3‐di(N‐n‐butyl‐1,2,3‐triazol‐4‐yl)benzene, and Mebip is bis(N‐methyl‐benzimidazolyl)pyridine. The electronic properties of these complexes are probed by spectroscopic and electrochemical analyses. Time‐dependent density functional theory calculations have been performed to assist the assignment of the absorption spectra.

Reactions of CO2 and CS2 with [RuH(η2-CH2PMe2)(PMe3)3

Carbon disulfide reacted with the cyclometalated ruthenium complex [RuH(η2-CH2PMe2)(PMe3)3] (1) at low temperature to yield the dithioformate complex [Ru(η1-SC(═S)H)(η2-CH2PMe2)(PMe3)3] (4), where the CS2 inserts into the metal hydride bond. On warming, complex 4 rearranges to give the known complex [Ru(S2CHPMe2CH2-κ3S,S,C)(PMe3)3] (3), where the CS2 is inserted in a metal phosphorus bond. Further reaction of this complex with excess CS2 over a period of days resulted in insertion of a second CS2 unit into one Ru–S bond to yield [Ru(SC(═S)SCH(-S)PMe2CH2-κ3S,S,C)(PMe3)3] (5). Complex 5 was characterized crystallographically and by multinuclear NMR spectroscopy. In contrast, reaction of [RuH(η2-CH2PMe2)(PMe3)3] (1) with CO2 resulted in insertion of CO2 into the Ru–C bond to give [RuH(OC(═O)CH2PMe2-κ2O,P)(PMe3)3] (2). Low-temperature NMR spectroscopic studies did not show any evidence for prior formation of a formate complex.

Cyclometalated Ruthenium Oligomers with 2,3-Di(2-pyridyl)-5,6-diphenylpyrazine: A Combined Experimental, Computational, and Comparison Study with Noncyclometalated Analogous

Recent investigations on polypyridine transition-metal complexes as potential molecular wires have provided new impetus for these long-studied and well-established systems. Using bridging ligands 2,3-di(2-pyridyl)-5,6-diphenylpyrazine (dpdpz) and 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz), a tetrametallic cyclometalated ruthenium complex has been prepared and characterized, with each metal having one Ru-C bond. The electronic properties of this complex and two known monoruthenium and diruthenium complexes with dpdpz (DPDPZ series) were probed by electrochemical and spectroscopic techniques and compared to the previously reported tppz-based noncyclometalated ruthenium complexes (TPPZ series). The frontier orbital energy levels and electronic structures of the two series have been characterized by density functional theory (DFT) calculations. In accordance with the experimental results, these studies suggest that the DPDPZ series oligomers generally have a narrower energy gap relative to the TPPZ series. In addition, the large energy density of states in longer oligomers suggests the possibility of band-type conduction. The DPDPZ series exhibits red-shifted light absorption with enhanced intensity relative to the TPPZ series congeners. Time-dependent DFT computations have been performed to rationalize the electronic absorption of the DPDPZ series. Oxidative spectroelectrochemical measurements of the DPDPZ tetrametallic complex indicate the presence of intervalence charge-transfer transitions among ruthenium sites.

Asymmetric Mixed‐Valence Complexes that Consist of Cyclometalated Ruthenium and Ferrocene: Synthesis, Characterization, and Electronic‐Coupling Studies

Three bis-tridentate ferrocene-containing cyclometalated ruthenium complexes, [(Fcdpb)Ru(tpy)](+) (1(+)), [(Fctpy)Ru(dpb)](+) (2(+)), and [(Fcdpb)Ru(Fctpy)](+) (3(+)), have been prepared and characterized, where Fcdpb is the 2-deprotonated form of 1,3-di(2-pyridyl)-5-ferrocenylbenzene, tpy is 2,2':6',2"-terpyridine, dpb is the 2-deprotonated form of 1,3-di(2-pyridyl)benzene, and Fctpy is 4'-ferrocenyl-2,2':6',2"-terpyridine. Single crystals of compounds 2(+) and 3(+) have been studied by X-ray analysis. Complexes 1(+) and 2(+) displayed two anodic redox waves, whilst three well-separated redox couples were observed for compound 3(+). A combined experimental and computational study suggested that the ferrocene unit on the Fcdpb moiety in compounds 1(+) and 3(+) was oxidized first. In contrast, the order of the oxidation of ruthenium and ferrocene in complex 2(+) was reversed. Metal-to-metal-charge-transfer transitions (MM'CT) have been observed for the singly oxidized states 1(2+), 2(2+), and 3(2+) in the near-infrared region. Hush analysis showed that the metal-metal electronic couplings in compounds 1(2+) and 3(2+) were much stronger than those in compound 2(2+).

Light-Driven Living/Controlled Radical Polymerization of Hydrophobic Monomers Catalyzed by Ruthenium(II) Metalacycles

A versatile photoactivated catalytic system based on a cyclometalated ruthenium(II) complex, composed of strongly coordinating bidentate and relatively labile ligands, in conjunction with a traditional alkyl bromide initiator, has been developed for living/controlled radical polymerization. Polymerizations of three typical hydrophobic monomers—methyl methacrylate (MMA), styrene (St), and n-butyl acrylate (BA)—proceeded to high conversions under visible light irradiation. The polymerization process was photoresponsive, i.e., took place only under irradiation and immediately stopped when the light was turned off. Block copolymers of MMA with St and BA with St, as well as statistical copolymer of BA and St, could also be conveniently prepared. 1H NMR and electrochemical studies suggest a mechanism of the catalytic activation, which involves a photoinduced formation of the solvento 18-electron species cis-[Ru(o-C6H4-2-py)(phen)(MeCN)(acetone)]+ through the intermediacy of the 16-electron five-coordinated complex cis-[Ru(o-C6H4-2-py)(phen)(MeCN)]+ which is believed to be a crucial intermediate of the overall ATRP process.

Synthesis, Photophysics, and Photovoltaic Studies of Ruthenium Cyclometalated Complexes as Sensitizers for p-Type NiO Dye-Sensitized Solar Cells

We report the first application of cyclometalated ruthenium complexes of the type Ru[(N∧N)2(C∧N)]+ as sensitizers for p-type NiO dye-sensitized solar cells (NiO p-DSCs). These dyes exhibit broad absorption in the visible region. The carboxylic anchoring group is attached to the phenylpyridine ligand, which results in efficient hole injection. Moreover, the distance between the Ru[(N∧N)2(C∧N)]+ core and the carboxylic anchoring group is systematically varied by inserting rigid phenylene linkers. Femtosecond transient absorption (TA) studies reveal that the interfacial charge recombination rate between reduced sensitizers and holes in the valence band of NiO decreases as the number of phenylene linkers increases across the series. As a result, the solar cell made of the dye with the longest spacer (O12) exhibits the highest efficiency with both increased short-circuit current (Jsc) and open-circuit voltage (Voc). The incident photon-to-current conversion efficiency (IPCE) spectra match well with the absorpt...

Mononuclear Cyclometalated Ruthenium(II) Complexes of 1,2,4,5-Tetrakis(N-methylbenzimidazolyl)benzene: Synthesis and Electrochemical and Spectroscopic Studies

A series of mononuclear cyclometalated ruthenium complexes with 1,2,4,5-tetrakis(N-methylbenzimidazolyl)benzene have been prepared, where two N-methylbenzimidazoles bind to the metal center and others remain intact. Electronic properties of these complexes were investigated by electrochemical and spectroscopic studies and DFT/TDDFT computations. The RuII/III redox potentials of theses complexes can be modulated by attaching substituents of various electronic natures on the non-cyclometalating ligand. These complexes display enhanced visible light absorption compared to those without two free-standing N-methylbenzimidazolyl units as a result of the three-chromophore effect.

Aerobic oxidative dehydrogenation of benzyl alcohols to benzaldehydes by using a cyclometalated ruthenium catalyst

The ruthenium(III) complex bearing phenylpyridine as a cyclometalated ligand serves as an efficient catalyst for the aerobic oxidative dehydrogenation of benzyl alcohols to the corresponding benzaldehydes under mild conditions and for the one-pot synthesis of benzonitriles from benzyl alcohols with ammonia.

A new thiocyanate-free cyclometallated ruthenium complex for dye-sensitized solar cells: Beneficial effects of substitution on the cyclometallated ligand

A new thiocyanate-free cyclometallated 2-phenylpyridine Ru(II) complex, [Ru(dFppyCF3)(dcbpy)2]+PF6− (dFppyCF3 = 2-(2,4-difluorophenyl)-5-trifluoromethyilpyridine; dcbpy = 2,2′-bipyridine-4,4′-dicarboxylic acid), containing an electronwithdrawing trifluoromethyl group on the pyridine ring of the cyclometallated ligand, was synthesized and used as photosensitizer in DSSC devices. Its optical and electrochemical properties and stability behaviour towards ligand exchange with the common solar cell additive 4-tert-butylpyridine was compared to that of benchmark DSSC dye N719 and of the reference complex [Ru(dFppy)(dcbpy)2]+PF6−. Substitution of the pyridine ring by the CF3 group afforded enhanced optical properties and a larger overall power conversion efficiency of the corresponding DSSC (3.7%), with a significant improvement compared to the reference cyclometallated complex under the same fabrication conditions.

Ruthenium(II) Photosensitizers of Tridentate Click‐Derived Cyclometalating Ligands: A Joint Experimental and Computational Study

A systematic series of heteroleptic bis(tridentate)ruthenium(II) complexes of click-derived 1,3-bis(1,2,3-triazol-4-yl)benzene N^C^N-coordinating ligands was synthesized, analyzed by single crystal X-ray diffraction, investigated photophysically and electrochemically, and studied by computational methods. The presented comprehensive characterization allows a more detailed understanding of the radiationless deactivation mechanisms. Furthermore, we provide a fully optimized synthesis and systematic variations towards redox-matched, broadly and intensely absorbing, cyclometalated ruthenium(II) complexes. Most of them show a weak room-temperature emission and a prolonged excited-state lifetime. They display a broad absorption up to 700 nm and high molar extinction coefficients up to 20 000 M(-1)cm(-1) of the metal-to-ligand charge transfer bands, resulting in a black color. Thus, the complexes reveal great potential for dye-sensitized solar-cell applications.

Cyclometalated Ruthenium Dyes for DSSC

A novel thiocyanate-free cyclometalated ruthenium sensitizer for solar cells is designed and developed. Upon anchoring to nanocrystalline TiO2 films, it exhibits a remarkable incident monochromatic photon-to-current conversion efficiency of 83%. The solar cell employing a liquid-based electrolyte exhibits a short circuit photocurrent density of 17 mA/cm2, an open circuit voltage of 800 mV, and a fill factor of 0.74, corresponding to an overall conversion efficiency of 10.1% at standard AM 1.5 sunlight. To understand the structural, electronic, and optical properties of the cyclometalleted ruthenium sensitizer, we have investigated using density functional theory (DFT) and time-dependent DFT (TDDFT). Our results show the HOMO is located mostly on ruthenium and cyclometalated ligand, while the LUMO is on 4-carboxylic acid-4’-carboxylate-2,2’-bipyridine. Molecular orbitals analysis confirmed the experimental assignment of redox potentials, and TDDFT calculations allowed assignment of the visible absorption bands. The present findings provide new design criteria for the next generation of ruthenium sensitizers and help foster widespread interest in the engineering of new sensitizers that interact effectively with the I-/I3 -redox couple.

Cyclometalated ruthenium(ii) complexes with a bis-carbene CCC-pincer ligand

The first series of cyclometalated ruthenium complexes with a CCC-pincer bis-carbene ligand have been obtained as bench-stable compounds. Single-crystal X-ray analysis of one of these complexes with 4'-di-p-anisylamino-2,2':6',2''-terpyridine is presented. The Ru(II/III) redox potentials and MLCT absorptions of these complexes can be varied by attaching an electron-donating or -withdrawing group on the noncyclometalating ligand.

Photophysical properties of new cyclometalated ruthenium complexes and their use in dye sensitized solar cells

A new class of cyclometalated ruthenium complexes, Ru(C^N^N')(N^N'^N'')·Cl where N^N'^N'' = 4,4',4''-tricarboxy-2,2':6',2''-terpyridine and C^N^N' = substituted 6-phenyl-2,2'-bipyridine, for Dye Sensitized Solar Cells (DSSCs) is proposed. We have investigated the effect of different substituents (R = COOH, thiophen-2-yl, F and OCH(3)) on the ancillary C^N^N' ligand on the photophysical properties and performance of the six different cyclometalated ruthenium complexes in DSSCs. Using an ionic liquid based electrolyte, efficiencies up to η = 3.06% have been attained under 1 sun irradiation. Moreover, the T66 based DSSC exhibited a good stability under 1000 W m(2) light soaking at 60 °C for 24 days, retaining 92.8% of its initial efficiency.

Thiocyanate-free cyclometalated ruthenium sensitizers for solar cells based on heteroaromatic-substituted 2-arylpyridines

The first examples of thiocyanate-free thiophene-substituted Ru(II) cyclometalated complexes, based on thiophene-derived 2-(2,4-difluorophenyl)pyridine ligands, are presented and investigated as photosensitizers in DSCs. Upon thiophene substitution the complexes presented enhanced optical properties compared to the reference dye with no thiophene substitution. DSCs based on the dithienyl-derived dye showed power conversion efficiencies up to 5.7%, more than twice that containing the complex without the thiophene substitution.

Synthesis, characterization, and catalytic behavior of a PSiP pincer-type ruthenium(II) complex

Abstract The synthesis and characterization of a cyclometalated ruthenium(II) complex [RuCl(PSiPCy)] containing monoanionic, tridentate coordinating PSiP-pincer ligand [κ3-(2-Cy2PC6H4)2SiMe]− ([PSiPCy]) are reported. Complex 3 is one of the few examples of halogenated ruthenium(II) complexes supported by the pincer-like bis(phosphino)silyl ligand. The structure of complex 3 was unambiguously determined by multinuclear NMR and single crystal X-ray analysis. This compound has also been shown to catalyze the transfer hydrogenation of ketones to the corresponding secondary alcohols efficiently with 2-propanol as the hydrogen source instead of using molecular dihydrogen gas or hazardous reducing agents (e.g., NaBH4 and LiAlH4), and tBuOK as the base.

A New Class of Cyclometalated Ruthenium Sensitizers of the Type ĈN̂N for Efficient Dye-Sensitized Solar Cells

A new class of cyclometalated ruthenium sensitizers incorporating a ĈNN ligand and conjugated 2,2'-bipyridine in the ancillary ligand have been designed and synthesized. The photovoltaic performance of JK-206 using an electrolyte containing 0.6 M 1,2-dimethyl-3-propylimidazolium iodide, 0.05 M I(2), 0.1 M LiI, and 0.5 M tert-butylpyridine in CH(3)CN gave a short-circuit photocurrent density of 19.63 mA cm(-2), an open-circuit voltage of 0.74 V, and a fill factor of 0.72, affording an overall conversion efficiency of 10.39%. The efficiency is the highest one reported for dye-sensitized solar cells based on the cyclometalated ruthenium sensitizer of the type ĈNN. Moreover, the same device using a polymer gel electrolyte exhibited a remarkable stability under 1000 h of light soaking at 60 °C, retaining 91% of the initial efficiency of 7.14%.