Mixed-valent Diruthenium Research Articles

Mixed-valence di-ruthenium(II,III) complexes of redox non-innocent N-aryl-o-phenylenediamine derivatives.

A mononuclear ruthenium(ii), [(L1IQ)Ru2+(PPh3)2Cl2]·CHCl3 (1·CHCl3), a di-ruthenium(ii,ii), [(L2IQ)2Ru24+Cl4(PPh3)2] (2) and a mixed-valence di-ruthenium(ii,iii), [(L3IQ)Ru25+Cl5(PPh3)2]·MeOH (3·MeOH) complex, where L1IQ, L2IQ and L3IQ are, respectively, o-diiminobenzoquinone forms of redox non-innocent N-(5-nitropyridyl)-o-phenylenediamine (L1H2), N-(2,4-dinitrophenyl)-o-phenylenediamine (L2H2) and N-(3-nitropyridyl)-o-phenylenediamine (L3H2) derivatives, were successfully isolated. The molecular and electronic structures of 1·CHCl3, 2 and 3·MeOH were confirmed by single-crystal X-ray crystallography, EPR, UV-Vis-NIR spectroscopies and density functional theory (DFT) calculations. Both 1·CHCl3 and 2 exhibited reversible anodic waves due to the Ru(iii)/Ru(ii) redox couple, while the cyclic voltammogram of 3·MeOH displayed two successive cathodic waves due to ruthenium(iii)/ruthenium(ii) and (L3IQ/L3ISQ) redox couples. EPR spectroscopy and DFT calculations inferred that 1+ is a ruthenium(iii) complex of L1IQ, [(L1IQ)Ru3+(PPh3)2Cl2]+, 2+ is a mixed-valence di-ruthenium(ii,iii) complex of L2IQ, [(L2IQ)2Ru25+Cl4(PPh3)2]+ and 3- is a di-ruthenium(ii,ii) complex, [(L3IQ)Ru24+Cl5(PPh3)2]-, while 32- is a di-ruthenium(ii,ii) complex of L3ISQ, [(L3ISQ)Ru24+Cl5(PPh3)2]2-, where L3ISQ is the o-diiminobenzosemiquinonate anion radical form of the L3H2 with a significant contribution of the mixed-valence di-ruthenium(iii,ii) form, [(L3AM)Ru25+Cl5(PPh3)2]2- (L3AM is the di-amido form of the L3H2 ligand). The spin density obtained from the Mulliken spin population analyses of the broken-symmetry (BS) DFT calculations was localized on Ru(2) in 3, while it was delocalized over both Ru(1) and the o-phenylenediamine fragment in 32-. The inter-valence charge-transfer (IVCT) transitions of 2+ and 3 were relatively weaker and occurred at 1680 and 1685 nm, respectively, while 32- exhibited a broader NIR absorption band at 1500-2000 nm. The calculated electronic-coupling parameters (Hab) using the Mulliken-Hush equation for 3 and 2+ ion, respectively, were 62 and 103 cm-1, defining these as Robin-Day class II mixed-valence systems.

Redox-Induced Hydrogen Bond Reorientation Mimicking Electronic Coupling in Mixed-Valent Diruthenium and Macrocyclic Tetraruthenium Complexes.

We present the coordination-driven self-assembly of three tetranuclear metallacycles containing intracyclic NH2, OH, or OMe functionalities through the combination of various isophthalic acid building blocks with a divinylphenylene diruthenium complex. All new complexes of this study were characterized by means of nuclear magnetic resonance spectroscopy, ultrahigh-resolution ESI mass spectrometry, cyclic and square wave voltammetry and, in two cases, X-ray diffraction. The hydroxy functionalized macrocycle 4-BOH and the corresponding half-cycle 2-OH stand out, as their intracyclic OH···O hydrogen bonds stabilize their mixed-valent one- (2-OH, 4-BOH) and three-electron-oxidized states (4-BOH). Despite sizable redox splittings between all one-electron waves, the mixed-valent monocations and trications do not exhibit any intervalence charge-transfer band, assignable to through-bond electronic coupling, but nevertheless display distinct IR band shifts of their charge-sensitive Ru(CO) tags. We ascribe these seemingly contradicting observations to a redox-induced shuffling of the OH···O hydrogen bond(s) to the remaining, more electron-rich, reduced redox site.

A mixed-valence diruthenium(II,III) complex endowed with high stability: from experimental evidence to theoretical interpretation.

We herein report the synthesis and multi-technique characterization of [Ru2Cl((2-phenylindol-3-yl)glyoxyl-l-leucine-l-phenylalanine)4], a novel diruthenium(ii,iii) complex obtained by reacting [Ru2(μ-O2CCH3)4Cl] with a dual indolylglyoxylyl dipeptide anticancer agent. We soon realised that the compound is very stable under several different conditions including aqueous buffers or organic solvents. It is also completely unreactive toward proteins. The high stability is also suggested by cellular experiments in a glioblastoma cell line. Indeed, while the parent ligand exerts high cytotoxic effects in the low μM range, the complex is completely non-cytotoxic against the same line, most probably because of the lack of ligand release. To investigate the reasons for such high stability, we carried out DFT calculations that are fully consistent with the experimental findings. The results highlight that the stability of [Ru2Cl((2-phenylindol-3-yl)glyoxyl-l-leucine-l-phenylalanine)4] relies on the nature of the ligand, including its steric hindrance that prevents the reaction of any nucleophilic group with the Ru2 core. Ligand displacement is the key step to allow reactivity with the biological targets of metal-based prodrugs. Accordingly, we discuss the implications of some important aspects that should be considered when active molecules are chosen as ligands for the synthesis of paddle-wheel-like complexes with medicinal applications.

A Gold Quartet Framework with Reversible Anisotropic Structural Transformation Accompanied by Luminescence Response

Summary Hierarchy and chirality are the fundamental characteristics of biomolecules. Chemistry on hierarchical self-assembly and spontaneous symmetry breaking helps to uncover the mechanism of living activities and the origin of chirality in nature. Herein, we describe a chiral gold quartet framework (GQF) with C4-symmetric structure hierarchically aggregated from an achiral anionic [Au10(dpptrz)4S4]2− (dpptrz-Au10), which was acquired via click-reaction-induced and Au(I)⋅⋅⋅Au(I)-interaction-directed cluster-to-cluster transformation (CCT) from the rationally designed [(dppa)6Au18S8]2+ (dppa-Au18). Inter-cluster hydrogen bonding and alkali ion coordination were observed to assist the hierarchical self-assembly and chiral self-organization of the GQF. Upon exposing the crystal to vacuum, the bottom-up constructed GQF showed an anisotropic structural transformation accompanied by a visual luminescence change in a single-crystal-to-single-crystal (SCSC) manner that became reversible upon removal of vacuum. This research largely advances the potential of polynuclear gold(I)-sulfido clusters in hierarchical self-assembly and luminescent materials.

Polyelectrochromic Vinyl Ruthenium-Modified Tritylium Dyes

A series of four mononuclear and one dinuclear ruthenium styryl complexes with redox active triarylmethylium ligands were prepared. All new compounds were characterized by NMR spectroscopy, MS spectrometry, cyclic voltammetry, and in various oxidation states by IR and UV/vis/NIR and EPR spectroscopy. The increase in conjugation length by the introduction of the vinyl ruthenium entity pushes the electronic absorption to low energy, almost into the near-infrared region. Electrochemical and spectroscopic properties are strongly influenced by the para substituents at the triarylmethylium ligands. The complexes were characterized in up to four different oxidation states up to the trication level and show pronounced electrochromism. The oxidized mixed-valent diruthenium complex 52+ shows a moderate degree of charge and spin delocalization over the styryl ruthenium sites.

Transition from a Metal-Localized Mixed-Valence Compound to a Fully Delocalized and Bridge-Biased Electrophore in a Ruthenium-Amine-Ruthenium Tricenter System.

A series of cyclometalated diruthenium complexes with a redox-active amine bridge were synthesized. Depending on the terminal ligands of the ruthenium components and the substituent on the amine unit, the one-electron-oxidized state can be either in the form of a weakly or strongly coupled mixed-valence diruthenium complex, a fully charge-delocalized three-center system, or a bridge-biased electrophore. This transition among different electronic forms was supported by electrochemistry, near-infrared absorption, electron paramagnetic resonance, and density functional theory analysis.

Pressure-driven high-to-low spin transition in the bimetallic quantum magnet[Ru2(O2CMe)4]3[Cr(CN)6]

Synchrotron-based infrared and Raman spectroscopies were brought together with diamond anvil cell techniques and an analysis of the magnetic properties to investigate the pressure-induced high $\ensuremath{\rightarrow}$ low spin transition in $[{\mathrm{Ru}}_{2}{({\mathrm{O}}_{2}\mathrm{CMe})}_{4}{]}_{3}{[\mathrm{Cr}(\mathrm{CN})}_{6}]$. The extended nature of the diruthenium wave function combined with coupling to chromium-related local lattice distortions changes the relative energies of the ${\ensuremath{\pi}}^{*}$ and ${\ensuremath{\delta}}^{*}$ orbitals and drives the high $\ensuremath{\rightarrow}$ low spin transition on the mixed-valence diruthenium complex. This is a rare example of an externally controlled metamagnetic transition in which both spin-orbit and spin-lattice interactions contribute to the mechanism.

Mixed-valent diruthenium diphosphonate containing zigzag chain structure of {Ru2(hedp)2(SCN)}n4n−

This paper reports the crystal structure and magnetism properties of a novel mixed-valent diruthenium(II,III) complex, [C(NH2)3]4[Ru2(hedp)2(SCN)]·4H2O (1), where hedp represents 1-hydroxyethylidenediphosphonate. It shows a zigzag chain structure in which the paddlewheel diruthenium(II,III) dimers of Ru2(hedp)23− linked by SCN− bridges. The chains are stacked along the [011] direction with strong intra- and interchain hydrogen bonds. Magnetic studies show that significant antiferromagnetic exchanges are mediated between the [Ru2(hedp)2]3− (S=3/2) units through thiocyanate ion bridges. Structural analysis proves that the RuRu bond weakening ability is H2O<Br−<Cl−<μ-NCS−<μ-NC−<μ-SCN−.

Near-infrared electrochromism in mixed-valent diruthenium complexes

The potential applications and evaluation parameters of electrochromic devices are first introduced, together with the basic requirements and current research status of near-infrared electrochromic materials. On the basis of the recent research progress in this laboratory, the design, synthesis, electrochemical and spectroscopic properties, and the metal-metal electronic coupling of cyclometalated diruthenium complexes are then presented. The presence of M-C bonds significantly decreases the redox potential of the metal center and enhances the intermetallic electronic coupling. In the mixed-valent state, these diruthenium complexes display intense intervalence charge-transfer transitions in the near-infrared region and the energy and intensity of these transitions can be modulated by changing the bridging and/or terminal ligands. By using reductive or oxidative electropolymerization, these dimetallic complexes can be deposited onto electrode surfaces as metallopolymeric films. The resulting films exhibit multistage near-infrared electrochromism with low operation potential, short response time, good contrast ratio, and long optical memory time.

Thermotropic mesomorphism of mixed-valent diruthenium aliphatic carboxylates with axial anion bearing two aliphatic chains

A homologous series of binuclear mixed-valent diruthenium tetracarboxylates, Ru2(O2C(CH2)n−2CH3)4DHDP (DHDP = di(hexadecyl)phosphate axial anion, n = 10, 12, 14, 16, and 18), have been synthesized and characterized, and the liquid crystalline properties of these compounds were examined. All the compounds exhibit a room-temperature crystalline lamellar phase and a high temperature (above 140°) Colh mesophase. Another, probably semi-crystalline, lamellar intermediate phase has also been found for all the studied compounds but for the n = 18 derivative. Comparison with related mesogenic homologous series where the equatorial ligands are also linear carboxylates, but the axial anions bear just one aliphatic chain (carboxylates, octylsulfonate, and dodecylsulfate), shows that the presence of a second aliphatic chain in the axial anion both lowers the transition temperatures and modifies the nature of the intermediate lamellar phase. Structural models at the molecular level are suggested for the crystalline lamellar and the Colh phases.

Cadmium diruthenium(ii,iii) carbonates showing diverse magnetism behavior arising from variety configuration of [Ru2(CO3)4]n3n− layer

Two hetero-metallic carbonates, namely KCd(H2O)3Ru2(CO3)4·4H2O (1) and KCd(H2O)3Ru2(CO3)4·3.5H2O (2), have been synthesized in a neutral aqueous solution. Both of the 3D dimensional structured complexes contain mixed-valent diruthenium(II,III) carbonate paddlewheel cores of Ru2(II,III)(CO3)4(3-) that are connected to each other in trans- or cis-modes by carbonate oxygen atoms, forming rectangular square-grid and isomeric parallelogram layers [Ru2(CO3)4]n(3n-) in 1 and 2, respectively. The reaction temperature is found to play an important role in directing the final products with particular topologies and their layered structural diversity is due to the various linking modes between the Ru2(CO3)4(3-) units. The magnetic studies show that ferromagnetic interactions are propagated between the diruthenium units in both complexes 1 and 2 but their magnetic properties differ at low temperatures, in which the trans linking mode parallelogram layer [Ru2(CO3)4]n(3n-) in complex 2 leads to long-range magnetic ordering below 4.0 K. However, no Curie ordering down to 1.8 K is detected for complex 1 containing the isomeric rectangle square-grid layer linking in the cis mode.

Electrochemically Controlled 2D Assembly of Paddle-Wheel Diruthenium Complexes on the Au(111) Surface and Identification of Their Redox States

The 2D molecular assemblies of chloride-coordinated mixed-valence diruthenium complexes, each possessing phenyl, naphtyl, or anthracenyl moieties, were examined on an Au(111) at electrochemical interface. In situ scanning tunneling microscopy images revealed a clear dependence of the molecular assembly on both the nature of the aryl functional groups and on the redox state of the dinuclear ruthenium complex, either chloride-coordinated RuII/RuIII or noncoordinated RuII/RuII. At potentials where the RuII/RuIII and RuII/RuII redox states were in equilibrium, two distinct redox states were clearly identified at the single-molecular level. We found that manipulating both the electrochemical potential and the aryl functional group substitution was important for controlling the 2D molecular assembly of a chloride-coordinated diruthenium complex on an Au(111) surface.

Metal-catalyzed nitrogen-atom transfer methods for the oxidation of aliphatic C-H bonds.

For more than a century, chemists have endeavored to discover and develop reaction processes that enable the selective oxidation of hydrocarbons. In the 1970s, Abramovitch and Yamada described the synthesis and electrophilic reactivity of sulfonyliminoiodinanes (RSO(2)N═IPh), demonstrating the utility of this new class of reagents to function as nitrene equivalents. Subsequent investigations by Breslow, Mansuy, and Müller would show such oxidants to be competent for alkene and saturated hydrocarbon functionalization when combined with transition metal salts or metal complexes, namely those of Mn, Fe, and Rh. Here, we trace our own studies to develop N-atom transfer technologies for C-H and π-bond oxidation. This Account discusses advances in both intra- and intermolecular amination processes mediated by dirhodium and diruthenium complexes, as well as the mechanistic foundations of catalyst reactivity and arrest. Explicit reference is given to questions that remain unanswered and to problem areas that are rich for discovery. A fundamental advance in amination technology has been the recognition that iminoiodinane oxidants can be generated in situ in the presence of a metal catalyst that elicits subsequent N-atom transfer. Under these conditions, both dirhodium and diruthenium lantern complexes function as competent catalysts for C-H bond oxidation with a range of nitrogen sources (e.g., carbamates, sulfamates, sulfamides, etc.), many of which will not form isolable iminoiodinane equivalents. Practical synthetic methods and applications thereof have evolved in parallel with inquiries into the operative reaction mechanism(s). For the intramolecular dirhodium-catalyzed process, the body of experimental and computational data is consistent with a concerted asynchronous C-H insertion pathway, analogous to the consensus mechanism for Rh-carbene transfer. Other studies reveal that the bridging tetracarboxylate ligand groups, which shroud the dirhodium core, are labile to exchange under standard reaction conditions. This information has led to the generation of chelating dicarboxylate dinuclear rhodium complexes, exemplified by Rh(2)(esp)(2). The performance of this catalyst system is unmatched by other dirhodium complexes in both intra- and intermolecular C-H amination reactions. Tetra-bridged, mixed-valent diruthenium complexes function as effective promoters of sulfamate ester oxidative cyclization. These catalysts can be crafted with ligand sets other than carboxylates and are more resistant to oxidation than their dirhodium counterparts. A range of experimental and computational mechanistic data amassed with the tetra-2-oxypyridinate diruthenium chloride complex, [Ru(2)(hp)(4)Cl], has established the insertion event as a stepwise pathway involving a discrete radical intermediate. These data contrast dirhodium-catalyzed C-H amination and offer a cogent model for understanding the divergent chemoselectivity trends observed between the two catalyst types. This work constitutes an important step toward the ultimate goal of achieving predictable, reagent-level control over product selectivity.

Ionic crystals based on Keggin anion and mixed-valent diruthenium tetracetate: [Ru2(CH3COO)4(H2O)2]2[HnXW12O40]·[Ru2(CH3COO)4(H2O)Cl]·12H2O (X = B, Si, Ge)

Three new ionic crystals based on Keggin anion and mixed-valent diruthenium tetracetate, [Ru2(CH3CO2)4(H2O)2]2[HnXW12O40]·[Ru2(CH3CO2)4(H2O)Cl]·12H2O {X = B, n = 3 (1); X = Si, n = 2 (2); X = Ge, n = 2 (3)}, have been prepared in acidic aqueous solution at about pH 3.0 by reaction of K4BW12O40·mH2O, K8SiW11O39·mH2O and K8GeW11O39·mH2O with diruthenium tetracetate Ru2(CH3COO)4Cl, respectively, and their structures were determined by X-Ray diffraction analysis. They are isostructural structure with the ratio of heteropolytungstate anion, Ru2(CH3CO2)4+ cation and neutral molecular Ru2(CH3CO2)4Cl of 1:2:1. The cyclic voltammetry in 0.5 M KNO3 aqueous solution at pH 3.0 show the respective electrochemical behaviors of the W-centers and Ru2-centers for these three complexes. Magnetic data analysis shows that diruthenium units display the ground state electronic configuration π*2δ* with large positive D value.

Remarkable Effect of Valence Electrons in Thiolato-Bridged Diruthenium Complexes toward Catalytic Dimerization of α-Methylstyrenes

The dicationic diruthenium complex 1c (RuIII–RuIII) catalytically promotes the dimerization of α-methylstyrenes into the corresponding acyclic dimers, while the use of the mixed-valence diruthenium...

Air Oxidation of HS– Catalyzed by An Mixed-Valence Diruthenium Complex, an Near-IR Probe for HS– Detection

The strongly near-IR-active mixed-valence diruthenium complex [Ru(2)TIEDCl(4)]Cl, where TIED = tetraiminoethylenedimacrocycle, was found to be a highly active catalyst for air oxidation of HS(-) forming polysulfide species and H(2)O(2). The reaction provides a convenient method for the detection of the HS(-) generation rate of a H(2)S donor of medical importance.

Metamagnetic phase transition in a diruthenium compound with interpenetrating sublattices

The diruthenium compound [Ru 2(O 2CMe) 4] 3[Cr(CN) 6] may be the only known material that contains two weakly-coupled, magnetically-ordered sublattices occupying the same three-dimensional volume. Due to the strong easy-plane anisotropy on each Ru 2 complex, the moment of each sublattice is constrained to one of the eight cubic diagonals. At low fields, the two sublattices are antiferromagnetically aligned by weak dipolar and deformation energies. But above a metamagnetic critical field of about 1000 Oe, the sublattice moments become ferromagnetically aligned and the net magnetization increases dramatically. We have successfully modeled this metamagnetic transition by assuming that the individual sublattice spin configurations are only weakly distorted by the magnetic field. This model suggests that the ground state of each sublattice undergoes a phase transition at a pressure of about 7 kbar. The drop in the sublattice moment and the rise in the sublattice susceptibility above 7 kbar can be explained by a high- to low-spin transition ( S = 3/2 to 1/2) on the mixed-valent diruthenium complexes.

Supramolecular architecture elucidation of the room temperature columnar mesophases exhibited by mixed-valent diruthenium alkoxybenzoates

Three series of mesogenic coordination polymers based on mixed-valent diruthenium tetracarboxylates, namely Ru2(3,4-B2OCn)4Cl, Ru2(3,5-B2OCn)4Cl and Ru2(3,4,5-B3OCn)4Cl [3,4-B2OCn = 3,4-(CnH2n+1O)2C6H3CO2−, 3,5-B2OCn = 3,5-(CnH2n+1O)2C6H3CO2− and 3,4,5-B3OCn = 3,4,5-(CnH2n+1O)3C6H2CO2−] have been synthesized and characterized, with the aim of obtaining columnar liquid crystalline phases. These equatorial BmOCn ligands have been selected under the assumption that they will efficiently fill the intermolecular space around the axial Cl atoms, thus warranting a parallel arrangement of the polymeric ⋯Ru2–Cl–Ru2–Cl⋯ strands in the crystalline phase, which should facilitate the occurrence of Col mesophases. The liquid crystalline character of the synthesized compounds has been studied by means of polarized optical microscopy, differential scanning calorimetry, and variable temperature X-ray diffraction. They all exhibit thermotropic ColH mesophases, the 3,4-B2OCn derivatives also exhibit a lamellar mesophase. Many of the studied compounds exhibit room temperature mesomorphism. The thermal stability domain of the ColH mesophases of the 3,5-B2OCn and 3,4,5-B3OCn derivatives is remarkably wide, from below 0 °C to ca. 300 °C in some cases. Based on pieces of structural information coming from XRD experiments, dilatometry, and local probes (magnetic susceptibility measurements, resonance Raman and IR spectroscopies, and Exafs) we suggest a model for the structural arrangement of the polymeric strands in the mesophase, in which the central polar backbone of the polymeric strands is in a zig-zag conformation, surrounded by a continuum of molten aliphatic chains. A crystallographic study of the non-mesogenic light homologue Ru2(3,4,5-B3OC2)4Cl confirms these aspects of the model, and shows the predicted preorganization of the polymeric strands in the crystalline phase.

A mixed-valence diruthenium complex, triply bridged by mixed-moieties of chloro and methoxo ligands

A mixed-valence diruthenium complex, whose metal centres were triply bridged by one chloro and two methoxo ligands, was synthesized and characterized by X-ray structural analysis, electrochemistry and spectroscopy, and its mixed-valence state was classified into Class III.

Na 3Ru 2(hedp) 2⋅4H 2O: A mixed valent diruthenium diphosphonate with three-dimensional structure

Hydrothermal treatment of RuCl 3, hedpH 4 [hedp = 1-hydroxyethylidenediphosphonate, CH 3C(OH)(PO 3) 2] and NaOH at 180 °C gives a mixed valence diruthenium(II,III) compound Na 3Ru 2(hedp) 2⋅4H 2O ( 1). In this compound, the paddlewheel diruthenium units of Ru 2 ( hedp ) 2 3 − are cross-linked into a square-grid layer. The layers are further connected through {NaO 6} octahedra, forming a three-dimensional framework structure. Crystal data: monoclinic, space group C2/c, a = 19.285 ( 5 ) , b = 9.528 ( 3 ) , c = 10.050 ( 3 ) Å , β = 96.499 ( 5 ) , V = 1834.8 ( 9 ) Å 3 , Z = 4 . Ferromagnetic interactions are mediated between the Ru 2 ( hedp ) 2 3 − dimers within the layer.