Diruthenium Tetracarboxylates Research Articles

Diruthenium(II,III) tetracarboxylates catalyzed H2O2 oxygenation of organic sulfides

Diruthenium(II,III) tetracarboxylates, Ru2(OAc)4Cl (A), Ru2(esp)2Cl (B, esp=tetramethyl-1,3-benzenedipropionate) and Ru2(3-HB)4Cl (C, 3-HB=3-hydroxybenzoate) were investigated for activating hydrogen peroxide in organic sulfide oxygenation. The speciation of the substrate and potential products, sulfoxide and sulfone, were investigated for each catalyst. With methyl phenyl sulfide as the substrate, A simultaneously produces sulfoxide and sulfone, B yields the highest turnover with complete conversion to sulfoxide at 6min before sulfone appears, and C facilitates complete conversion to sulfoxide in 20min but little subsequent conversion to sulfone. The dependence of the initial reaction rate on catalyst and H2O2 concentrations were investigated. A small set of other sulfides were subjected to catalytic reactions with C, and all reactions resulted in near quantitative conversion. Finally, the sulfide oxygenation activity and stability towards hydrogen peroxide of the diphosphonate complex Na4[Ru2(hedp)2(H2O)Cl] (D, hedp=1-hydroxyethylidenediphosphonate) was investigated, and D was found to be an effective catalyst, which retains its activity over an extended period of time due to its robustness at the (III,III) oxidation state.

Tert-Butyl Hydroperoxide Oxygenation of Organic Sulfides Catalyzed by Diruthenium(II,III) Tetracarboxylates

Diruthenium(II,III) carboxylates Ru2(esp)2Cl (1a), [Ru2(esp)2(H2O)2]BF4 (1b), and Ru2(OAc)4Cl (2) efficiently catalyze the oxygenation of organic sulfides. As noted in a previous work, 1a is active in oxygenation of organic sulfides with tert-butyl hydroperoxide (TBHP) in CH3CN. Reported herein in detail is the oxygenation activity of 1a, 1b, and 2, with the latter being highly selective in oxo-transfer to organic sulfides using TBHP under ambient conditions. Solvent-free oxidation reactions were achieved through dissolving 1a or 1b directly into the substrate with 2 equiv of TBHP, yielding TOF up to 2056 h(-1) with 1b. Also examined are the rate dependence on both catalyst and oxidant concentration for reactions with catalysts 1a and 2. Ru2(OAc)4Cl may be kinetically saturated with TBHP; however, Ru2(esp)2Cl does not display saturation kinetics. By use of a series of para-substituted thioanisoles, linear free-energy relationships were established for both 1a and 2, where the reactivity constants (ρ) are negative and that of 1a is about half that of 2. Given these reactivity data, two plausible reaction pathways were suggested. Density functional theory (DFT) calculation for the model compound Ru2(OAc)4Cl·TBHP, with TBHP on the open axial site, revealed elongation of the O-O bond of TBHP upon coordination.

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.

Chiral Induction at Octahedral Ru(II) via the Disassembly of Diruthenium(II,III) Tetracarboxylates Using a Variety of Chiral Diphosphine Ligands

Achiral [Ru2(μ-O2CR)4(MeOH)2](PF6) (R = CH3 or C6H5) reacts with the chiral diphosphines R,R- and S,S-Chiraphos (two chiral centers on ligand between the coordinating P atoms) and R-Prophos (one chiral center on ligand between the coordinating P atoms) leading to a disassembly of the paddlewheel core and the highly diastereoselective production of Λ-[Ru(η(2)-O2CC6H5)(η(2)-R,R-Chiraphos)2](PF6) (Λ-R,R-III), Δ-[Ru(η(2)-O2CC6H5)(η(2)-S,S-Chiraphos)2](PF6) (Δ-S,S-III) (the R = CH3 complexes of Chiraphos were reported in a earlier communication in this journal), and Λ-[Ru(η(2)-O2CCH3)(η(2)-R-Prophos)2](PF6) (Λ-R,R-VI), respectively, in high yield and purity. Reactions of the same starting material with R,R- and S,S-o-tolyl-Dipamp (chiral centers are the coordinating P-atoms) lead to an inversion in the chirality-at-metal producing Λ-[Ru(η(2)-O2CC6H5)(η(2)-S,S-o-tolyl-Dipamp)2](PF6) (Λ-S,S-IV), Δ-[Ru(η(2)-O2CC6H5)(η(2)-R,R-o-tolyl-Dipamp)2](PF6) (Δ-R,R-IV), Λ-[Ru(η(2)-O2CCH3)(η(2)-S,S-o-tolyl-Dipamp)2](PF6) (Λ-S,S-V), and Δ-[Ru(η(2)-O2CCH3)(η(2)-R,R-o-tolyl-Dipamp)2](PF6) (Δ-R,R-V). X-ray crystallography of all but Λ-S,S-V and Δ-R,R-V and solid-state circular dichroism (CD) show that only the indicated diastereomers are present in the solid-state. Solution CD measurements and (31)P NMR also indicate their predominance in solution.

Electronic Delocalization in Coordination Polymers Based on Bimetallic Carboxylates.

Computational methods (DFT at the B3LYP, PBE0 and m06 levels, MO fragments decomposition, and the broken symmetry approach) have been used to evaluate the influence of the bridging ligand (BL) on the extent of electron delocalization in coordination polymers based on diruthenium tetracarboxylates. The efficiency of three different nitrogenated axial ligands, namely pyrazine (pz), phenazine (phz), and tetrazine (tz), to mediate electron coupling between Ru2(II,II) or Ru2(II,III) centers has been estimated through four different parameters: calculated Ru-N distances, HOMO-LUMO gaps, HOMO and LUMO compositions, and magnetic coupling constants J. All these parameters pointed toward a coordination polymer based on Ru2(II,II) centers axially linked by tetrazine being the best candidate for exhibiting electron delocalization through the Ru2-BL framework. Such a compound has been synthesized and characterized; its vis-NIR spectrum exhibited the predicted features, mainly an intense low-energy MLCT band, assigned to the expected Ru2(II,II) → tz process associated with electron delocalization.

Sterically-directed disassembly of diruthenium(II,III) tetraacetate using substituted and unsubstituted 2,2′-bipyridines and 1,10-phenanthrolines

A novel synthetic methodology that involves the “disassembly” of diruthenium(II,III) tetracarboxylates using the modestly π-acidic bidentate 2,2′-bipyridine and 1,10-phenanthroline ligands and their substituted derivatives as disassembling agents was exploited to generate, in high yield, heteroleptic bis-diamine-mono-carboxylate-Ru(II) complexes. The reactions proceed so that these heteroleptic complexes are only formed when steric hindrance is introduced directly adjacent to the binding nitrogen atoms otherwise the homoleptic tris-diamine Ru(II) complexes are formed exclusively. Two novel heteroleptic complexes have been synthesized in high yield, namely [Ru(η2-O2CCH3)(6,6′-Me2-2,2′-bipy)2](PF6) 4 and [Ru(η2-O2CCH3)(2,9-Me2-1,10-phen)2](PF6) 6. Both complexes have been characterized using X-ray crystallography, elemental analysis, IR, NMR and UV–visible spectroscopy and cyclic voltammetry.

Diruthenium(II,III) tetramidates as a new class of oxygenation catalysts

Two new diruthenium(II,III) tetramidate compounds, Ru(2)(NHOCC(CH(3))(2))(4)Cl (1) and Ru(2)(NHOCCH(2)CH(3))(4)Cl (2) have been prepared and structurally characterized by X-ray crystallography. The activity of promoting sulfide oxygenation using simple oxidants such as hydrogen peroxide (H(2)O(2)) and tert-butyl hydroperoxide (TBHP) was studied. A UV-kinetics study indicated that the initial rates of 1 and 2 are comparable to the previously studied diruthenium tetracarboxylates in promoting TBHP oxygenation of methyl phenyl sulfide (MPS). Using excess oxidant and CH(3)CN as the solvent, organic sulfides MPS and diphenyl sulfide (PPS) were oxidized using 1 mol% of the catalytic species. Compound 1 is more effective than 2 in converting sulfides to sulfoxide under the same conditions. Fast conversion was achieved when the reactions were carried out in the solvent-free conditions, and the major oxidation product was the sulfoxide. The electronic structure of the title compounds was studied with DFT calculations to gain an understanding of the activation of peroxy reagents.

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.

Theoretical and Experimental Studies of Diruthenium Tetracarboxylates Structure, Spectroscopy, and Electrochemistry

Quantum mechanical calculations at the density functional theory (DFT) level have been performed on diruthenium tetracarboxylates of different levels of molecular complexity: from unsolvated monomers to oligomers. The agreement between the calculated and experimental molecular structures and vibrational modes of the simple [Ru2(micro-O2CCH3)4]0/+ and [Ru2(micro-O2CCH3)4(H2O)2]0/+ systems made us confident in our calculation methodology. Therefore, it has been applied to the analysis of two different kinds of properties of these compounds: the trends in the UV/vis spectroscopy and electrochemistry along the [Ru2(micro-O2CCH3)4X2]- (X=Cl-, Br-, I-) series, and the crystalline polymorphism related to the polymeric strand conformation in extended Ru2(micro-O2CR)4Cl compounds. For the [Ru2(micro-O2CCH3)4X2]- series, we report new spectroscopic and electrochemical results and interpret the trends on the basis of time dependent DFT-polarized continuum model calculations, local charge and spin analysis, and X donor properties. As far as the polymeric conformation is concerned, it has been previously suggested that the Ru-Cl-Ru angle results from a compromise between packing, orbital overlap, and microsegregation. Our calculations on [Ru2(micro-O2CCH3)4Cl]2Cl- and [Ru2(micro-O2CCH3)4Cl]3Cl- oligomers provide insights on the influence of the first two factors on the strand conformation and allows a suggestion on what is the equatorial aliphatic chain's influence on this issue.

Diruthenium tetraacetate monocation, [RuII/III2(O2CMe)4]+, building blocks for 3-D molecule-based magnets.

Diruthenium tetracarboxylates monocations are utilized as building blocks for cubic 3-D network structured molecule-based magnets. [Ru(II/III)(2)(O(2)CMe)(4)](3)[M(III)(CN)(6)] [M = Cr (1a), Fe (2), Co (3)] were prepared in aqueous solution. Powder X-ray diffraction indicates that they have body-centered cubic structures (space group = Imm, a = 13.34, 13.30, and 13.10 A for 1a, 2, and 3, respectively), which was confirmed for 1a by Reitveld analysis of the synchrotron powder data [a = 13.3756(5) A]. [Ru(2)(O(2)CMe)(4)](3)[M(III)(CN)(6)].xMeCN [M = Cr, x = 1.8 (1b); M = Mn, x = 3.3 (4)] were prepared from acetonitrile. The magnetic ordering of 1a (33 K), 1b (34.5 K), 2 (2.1 K), and 4 (9.6 K) was determined from the temperature dependencies of the in-phase (chi') alternating current (AC) susceptibility. The field dependence of the magnetization, M(H), at 2 K for 1a showed an unusual constricted hysteresis loop with a coercive field, H(cr), of 470 Oe while the M(H) data for 1b, 2, and 4 showed a normal hysteresis loop with a coercive field of 1670, 10, and 990 Oe, respectively. The (57)Fe Mössbauer spectrum of 2 is consistent with the presence of low spin Fe(III) (delta = -0.05 mm/s; DeltaE = 0.33 mm/s) at room temperature, and the onset of 3-D magnetic ordering at lower temperature (<2 K). The effects of M(III) in [M(III)(CN)(6)](3-), and the large zero-field splitting (D) of diruthenium tetracarboxylates are discussed. The increasing critical temperatures T(c), with increasing S could not be accounted for by mean field models without significantly different J values for 1a, 4, and 2. By fitting the T(c) data with mean field models [H = -2JS(Ru).(S(M) - micro(B)(g(Ru)S(Ru) + g(M)S(M))H], J/k(B) are 4.46, 1.90, and 0.70 K for 1a, 4, and 2, respectively.

Electronic, Magnetic, and Spectroscopic Properties of Binuclear Diruthenium Tetracarboxylates: A Theoretical and Experimental Study

The electronic structure of binuclear diruthenium tetracarboxylates, in both the divalent Ru2II,II(O2CR)4 and the mixed-valent Ru2II,III(O2CR)4X (X = anion) states is studied by means of ZINDO/S-MRCI and DFT calculations. Both methods predict a (π*)2(δ*)2 ground-state configuration for the divalent species, contrary to the (π*)3(δ*)1 previously predicted by SCF-Xα calculations, but in agreement with magnetic measurements that show a strong Zero Field Splitting. Our ZINDO/S-MRCI calculations on compounds containing axial ligands with different degree of π bonding to the bimetallic center (water, chloride, carboxylate, pyridine, pyrazine), for both (II,II) and (II,III) ruthenium cores, show the important role played by the ligands. These theoretical calculations allow us to explain the differences observed in the UV/vis and resonance Raman spectra, both in solution and in the solid state, when varying the axial ligands. The ZINDO/S-MRCI calculations are also capable of solving some controversies found in th...

Mixed-Valent Diruthenium (II,III) Long-Chain Carboxylates. 1. Molecular Design of Columnar Liquid-Crystalline Order

Six series of binuclear mixed-valent diruthenium tetracarboxylates of formula Ru2(O2CR)4X, containing different combinations of equatorial carboxylates (RCO2-) and anions (X-) have been synthesized and characterized, and their liquid-crystalline properties have been examined by optical microscopy under polarized light, differential scanning calorimetry, and powder X-ray diffraction studies. Three series derived from linear aliphatic carboxylates, Ru2(O2C−(CH2)n-2−CH3)4X with X = Cl (n = 5−9, 12, 16), X = O2C−R (R = (CH2)n-2−CH3, n = 6−12, 14, 15, 16), and X = DOS (DOS = dodecyl sulfate, n = 6, 8, 9, 12, 16, 18), were studied. The nature of the counterion X strongly affects the appearance of the liquid-crystalline order: the chloro complexes are not mesomorphic, whereas the complexes with RCO2 or DOS anions exhibit a columnar hexagonal mesophase above ca. 150 °C. A structural model for the mesophase of the Ru2(O2C−(CH2)n-2−CH3)5 series is proposed. Three other types of Ru2(O2CR)4X complexes were obtained ...

Pyrazine-mediated antiferromagnetic intermolecular exchange in mixed-valent diruthenium tetracarboxylates

Two mixed-valent diruthenium tetracarboxylates [Rue 2-(AcO) 4(H 2O) 2]BPh 4 ( 1) [Ru 2(AcO) 4(pz)]BPh 4 ( 2) AcO = acetate, BPh 4 = tetraphenylborate pz = pyrazine), were synthesized and characterized by elemental analysis, IR and UVVis spectroscopies, magnetic susceptibility measurements between 6 320 K. The magnetic behaviour of 1 can be understood in terms of non-interacting spin 3/2 dimers undergoing a large ( c. 72 cm −1) zero-field splitting, whereas an intermolecular antiferromagnetic interaction ( c. −2 cm −1) in addition to a large zero-field splitting ( c. 63 cm −1), is required to account for the data for 2.

ChemInform Abstract: Chemistry, Structure, and Bonding in Diruthenium(II) Tetracarboxylates.

AbstractThe Ru2(II,III) complex (I) reacts with L‐mandelic acid (II) to convert 50% of the Ru to the Ru(II,II) mandelate (III) (space group P21, Z=4) and 50% to the accompanying disproportionation product (IV).

Chemistry, structure and bonding in diruthenium(II) tetracarboxylates

Ru{sub 2}(O{sub 2}CCH{sub 3}){sub 4}Cl reacts with L-mandelic acid (Hmand) to convert 50% of the ruthenium to Ru{sub 2}(mand){sub 4}(H{sub 2}O){sub 2} (2) and 50% to the accompanying disproportionation product, (Ru{sub 3}O(mand){sub 6}(H{sub 2}O){sub 3}){sup +}. The Ru{sub 2}(II,II) mandelate has been isolated and structurally characterized as Ru{sub 2}(mand){sub 4} {times} 2H{sub 2}O, which crystallizes in space group P2{sub 1} with the following unit cell parameters: a = 7.610 (2) {angstrom}, b = 32.181 (7) {angstrom}, {beta} = 90.28 (2) {degree}, V = 3,328 (3) {angstrom}{sup 3}, Z = 4. Two independent but essentially identical molecules having mandelate ions of the correct absolute chirality were found. The Ru-Ru distances are 2.266 (1) and 2.256 (1) {angstrom}; the water molecules are axially coordinated with a mean Ru-O distance of 2.35 {angstrom}. This is the first time a Ru{sub 2}(II,II) compound has been obtained directly, on a preparative scale from a Ru{sub 2}(II,III) compound.