Formula Ru Research Articles

Fusion Position-Dependent Aromatic Transitions of Ligand Backbone Rings for Controlling the Redox Energetics of Photoredox Catalysts.

To reveal, quantify, and rationalize the effect of backbone π-extension on ligand redox activity, we studied the ground- and excited-state reduction potentials of eight ruthenium photoredox catalysts with the formula Ru(ppy)2L (L is the redox-active ligand of the bipyridine family) using density functional theory. Our research underlines the profound importance of the fusion position of backbone aromatic C6 rings on the redox activity of ligands in transition metal photoredox catalysts. Namely, certain fusion positions lead to the dearomatization of C6 rings in ligand-centered electron transfer events, resulting in a thermodynamic penalty equivalent to a half-volt negative shift in the reduction potential. Contrarily, the extent of backbone delocalization shows a minimal impact on redox energetics, which can be explained by the charge concentration at the nitrogen contact atoms in ligand-centered reductions. Grounded in Caulton's conceptual framework, we reaffirm the predictive potency of Lewis structures in ligand-centered redox energetics with qualitative and quantitative data. Our hypothesis regarding the effect of backbone ring dearomatization on redox energetics is further corroborated using magnetic and structure-based aromaticity indicators. Highlighting fusion-dependent dearomatization as a determining factor of ligand-centered electron transfer energetics, our findings hold implications for molecular-level design in advanced electroactive materials and catalysts.

Synthesis and Characterization of New Ruthenium-Tungsten Bimetallic Complex Equipped With Anchoring Ligand

A new ruthenium-tungsten bimetallic complex equipped carboxylic as anchoring ligand and thiocyanate as bridging ligand has successfully synthesized. Ruthenium complex and tungsten hexacarbonyl are used as starting materials. The synthesis process involves two-step reactions in one-pot with ultraviolet light and monitored by FTIR spectroscopy. The final product fully characterized by UV-Vis, FTIR, 1HNMR, 13CNMR, and LCMS spectroscopies analysis confirms that the product is a bimetallic complex with molecular formula Ru(C12H8N2O4)2-(NCS)2-W(CO)4. Cyclic voltammetry of the complex exhibit one reversible redox couple, two quasi-reversible redox couples and one irreversible redox peak. The complex absorbs light energy in a wider solar spectrum compared to related ruthenium complex. The complex is supposed to be a good dye-sensitizer to improve TiO2 photoelectrode performance in artificial photosynthesis applications.

Structure–Function Relationship in Ester Hydrogenation Catalyzed by Ruthenium CNN-Pincer Complexes

A series of six pincer–ruthenium complexes has been synthesized and applied in the catalytic hydrogenation of esters. The ruthenium complexes have the formula Ru(pincer)HCl(CO), where the CNN-pincer ligands feature N-heterocyclic carbene (NHC), pyridine, and dialkylamino donor groups. Through systematic variation of the steric bulk of the NHC substituent and the amine substituents, a clear structure–function relationship emerges. The most active catalysts in this series feature the bulkiest NHC substituent employed, 2,6-diisopropylphenyl. For the dialkylamino group, catalysts substituted with isopropyl or ethyl groups were the most active, while catalysts substituted with methyl groups were significantly less active. The most active catalyst discovered catalyzes the complete hydrogenation of a range of esters at loadings of 0.05–0.2 mol %.

Alkoxylation of the imine carbon atom of a Schiff-base ligand upon coordination to arene ruthenium

The Schiff-base 5-methyl-4-{(pyridin-2-ylmethylene)amino}-4H-1,2,4-triazole-3-thiol (L-H) reacts in alcoholic solution (methanol, ethanol, isopropanol) at room temperature with the dinuclear precursor [(η6-MeC6H4Pri)RuCl2]2 to give a series of neutral complexes of the general formula (η6-MeC6H4Pri)Ru(L-OR) (R = Me, 1; R = Et, 2; R = Pri, 3). In these complexes, the Schiff-base ligand coordinates to the arene ruthenium unit in a S,N,N-tridentate fashion and concomitantly to the coordination process a nucleophilic addition of the alcohol occurs on the imine carbon of L, thus forming the corresponding L-OR ligand. The molecular structure of 3, solved by single-crystal X-ray analysis, shows a piano-stool arrangement with the p-cymene, the Sthiolato, the Nimine and Npyridyl surrounding the chiral-at-metal ruthenium center and an OPri group attached to the imine carbon. The insertion of an alkoxy group on the carbon atom reduces the imine function and also introduces chirality on the ligand, thus generating a second chiral center and potentially diastereoisomeric complexes. However, steric hindrance on the ligand forces the formation of only one pair of enantiomers.

Synthesis and in vitro Toxicity of d‐Glucose and d‐Fructose Conjugated Curcumin–Ruthenium Complexes

A series of carbohydrate‐conjugated bis(demethoxy)curcumin (BDC) ligands were synthesized by using the Huisgen copper(I)‐catalyzed cycloaddition between azido‐functionalized d‐glucose and d‐fructose as well as propargyl‐modified BDC. The unprotected sugar ligands were treated with Ru(bpy)2Cl2 to form curcumin‐conjugated Ru complexes of general formula Ru(bpy)2(L)Cl. The ligands as well as Ru complexes were analyzed by NMR, IR, UV/Vis, and fluorescence spectroscopy, mass spectrometry as well as by elemental analysis (EA). Incubation of L929, HepG2 and the breast cancer cell line MDA‐MB‐231 revealed lower cytotoxicity of all carbohydrate‐conjugated ligands compared with BDC. The Ru complexes exhibited higher cytotoxicity than the parent ligands, in particular against HepG2 cells, whereas the noncancerous L929 cell line remained unaffected. Unexpectedly, the d‐fructose‐conjugated ligand and its corresponding Ru complex did not show any significant toxicity against MDA‐MB‐231 cells.

Cyclopentadithiophene-functionalized Ru(II)-bipyridine sensitizers for dye-sensitized solar cells

Two ruthenium sensitizers TT-230 and TT-232 based on cyclopenta[2,1-b:3,4-b′]dithiophene (CDT) were tested in dye-sensitized solar cells (DSSCs) using a tri-iodide/iodide redox couple, and their performances compared to the benchmark Z907. Both dyes of general formula Ru(LL′)(NCS)2 feature the same 4,4′-dicarboxylic acid 2,2′-bipyridine moiety acting as the anchoring group (L) to attach the dye on the TiO2 surface, and two CDT subunits as ancillary groups (L′) either directly-linked (TT-230) or vinylene-linked (TT-232) to the bipyridine moiety. In comparison with TT-230, the π-extended conjugation in TT-232 caused significant redshift and broadening of the absorption bands. However, despite better light-harvesting properties, the DSSC device sensitized with TT-232 strikingly underperformed compared to TT-230 under same conditions (PCE=3.2% and 6.1%, respectively). The use of co-adsorbent (CHENO) or surfactants did not help to improve the photovoltaic properties of TT-230, and resulted in a degradation of the overall efficiency of the cell.

Synthesis, structure, and electrochemical characterization of a mixed-ligand diruthenium(iii,ii) complex with an unusual arrangement of the bridging ligands

A mixed-ligand metal-metal bonded diruthenium complex having the formula Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))Cl where ap is the anilinopyridinate anion was synthesized from the reaction of Ru(2)(O(2)CCH(3))(4)Cl and H(2,4,6-(CH(3))(3)ap), after which the isolated product was structurally, spectroscopically and electrochemically characterized. The crystal structure reveals an unusual arrangement of the bridging ligands around the dimetal unit where one ruthenium atom is coordinated to one anilino and two pyridyl nitrogen atoms while the other ruthenium atom is coordinated to one pyridyl and two anilino nitrogen atoms. To our knowledge, Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))Cl is the only example of a mixed-ligand diruthenium complex of the type [Ru(2)L(3)(O(2)CCH(3))](+), where L is an unsymmetrical anionic bridging ligand that has been structurally characterized with a "(2,1)" geometric conformation of the bridging ligands, all others being "(3,0)". The initial Ru(2)(5+) compound in CH(2)Cl(2) or CH(3)CN containing 0.1 M tetra-n-butylammonium perchlorate (TBAP) undergoes up to four one-electron redox processes involving the dimetal unit. The Ru(2)(5+/4+) and Ru(2)(5+/6+) processes were characterized under N(2) using thin-layer UV-visible spectroelectrochemistry and this data is compared to UV-visible spectral changes obtained during similar electrode reactions for related diruthenium compounds having the formula Ru(2)L(4)Cl or Ru(2)L(3)(O(2)CCH(3))Cl where L is an anionic bridging ligand. Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))Cl was also examined by UV-visible and FTIR spectroelectrochemistry under a CO atmosphere and two singly reduced Ru(2)(4+) species, [Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))(CO)Cl](-) and Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))(CO) were in situ generated for further characterization. The CO-bound complexes could be further reduced and exhibited additional reductions to their Ru(2)(3+) and Ru(2)(2+) oxidation states.

Synthesis, Characterization, and Reactivity of Ruthenium Bis-Allyl Complexes with Chiral Phosphine-Phosphite Ligands

A series of ruthenium bis-allyl complexes of formula Ru(η3-2-MeC3H4)2(P-OP) (1) which incorporate chiral phosphine-phosphite ligands (P-OP) have been prepared and characterized. Compounds 1 exist in solution as a mixture of two diastereomers (maj and min) differing in the configuration at the metal. Both isomers are in equilibrium in solution, and their ratio varies with the nature of the P-OP ligand. Along the series, higher values of the maj/min ratio were observed with complexes bearing less sterically encumbered phosphite groups. In reactions of compounds 1 with protic reagents removal of one or two allyl ligands has been observed. Thus, reaction of 1h with pentachlorophenol produces the mixed allyl-phenoxide 3h, whereas reaction of 1a or 1h with tiglic acid produces the corresponding tiglates 4a,h, respectively. In addition, compounds 1 generate active catalysts for the hydrogenation of tiglic and 2-methyl-2-pentenoic acids. By appropriate optimization of the structure of the P-OP ligand, enantiosele...

Theoretical studies of the structures and spectroscopic properties of the photoelectrochemical cell ruthenium sensitizers, C101 and J13

A variety of heteroleptic ruthenium sensitizers have been engineered and synthesized because of their higher light-harvesting efficiency and lower charge-recombination possibility than the well known homoleptic N3 dye. As such, a great deal of attention has been focused on sensitizers with the general formula Ru(ancillary-ligand)(anchoring-ligand)(NCS)2, among which important examples are Ru(4,4′-bis(5-hexylthiophen-2-yl)-2,2′-bipyridine)(4,4′-carboxylic acid-4′-2,2′-bipyridine)(NCS)2 (C101) and Ru(N-(4-butoxyphenyl)-N-2-pyridinyl-2-pyridinamine)(4,4′-carboxylic acid-4′-2,2′-bipyridine)(NCS)2 (J13). In order to simulate experimental conditions with different pH values, the photosensitizing processes of these sensitizers possessing different degrees of deprotonation (2H, 1H to 0H) have been explored theoretically in this work. Their ground/excited state geometries, electronic structures and spectroscopic properties are first calculated using density functional theory (DFT) and time-dependent DFT (TDDFT). The absorption and emission spectra of all the complexes in acetonitrile solution are also predicted at the TDDFT (B3LYP) level. The calculated results show that the ancillary ligand contributes to the molecular orbital (MO) energy levels and absorption transitions. It is intriguing to observe that the introduction of a thiophene group into the ancillary ligand leads directly to the increased energy of the absorption transitions in the 380–450 nm region. The calculations reveal that although deprotonation destabilizes the overall frontier MOs of the chromophores, it tends to exert a greater influence on the unoccupied orbitals than on the occupied orbitals. Consequently, an obvious blue shift was observed for the absorptions and emissions in going from 2H, 1H to 0H. Finally, the optimal degree of deprotonation for C101 and J13 has also been evaluated, which is expected to lead to further improvements in the performance of dye-sensitized solar cells (DSSCs) coated with such sensitizers.

Electron Transfer Across Modular Oligo-p-phenylene Bridges in Ru(bpy)2(bpy–phn–DQ)4+(n= 1–5) Dyads. Unusual Effects of Bridge Elongation

A series of dyads of general formula Ru(bpy)(2)(bpy-ph(n)-DQ)(4+) (n = 1-5), based on a Ru(II) polypyridine unit as photoexcitable donor, a set of oligo-p-phenylene bridges with 1-5 modular units, and a cyclo-diquaternarized 2,2'-bipyridine (DQ(2+)) as electron acceptor unit, have been synthesized. Their spectroscopic and photophysical properties have been investigated in CH(3)CN and CH(2)Cl(2) by time-resolved emission and absorption spectroscopy in the nanosecond and picosecond time scale. The experimental study has also been complemented with a computational investigation carried out on the whole series of dyads. The absorption spectra of the dyads show new spectroscopic transitions, in addition to those characteristic of the donor, bridge, and acceptor fragments. DFT calculations suggest the assignment of such bands as bridge-to-acceptor (π ph(n)) → (π* DQ) charge-transfer transitions. This assignment is consistent with the solvatochromic and spectroelectrochemical behavior of the new bands. For all the dyads at room temperature in fluid solution, the typical (3)MLCT luminescence of the Ru(II) polypyridine unit is strongly (>90%) quenched, supporting the occurrence of an efficient intramolecular photoinduced electron transfer. The study has revealed, however, that the photophysical mechanism is actually more complex than presumed on the basis of a simple photoinduced electron-transfer scheme. For n = 1, very fast (few picoseconds) photoinduced electron transfer from the MLCT state localized on the substituted bpy ligand to the DQ unit has been observed, followed by slower interligand hopping and charge recombination. For n = 2-5, MLCT excited-state quenching takes place without transient detection of charge-separated product, indicating that charge recombination is faster than charge separation. This behavior can be rationalized in terms of the superexchange couplings expected through this type of bridges for the two processes. The kinetics of MLCT quenching in the dyads with n = 1-5 does not follow the usual exponential falloff with bridge length: after a regular decrease for n = 1-3, the rate constants become almost insensitive to bridge length for n = 3-5. The rationale of this uncommon behavior, as suggested by DFT calculations, lies in a switch in the MLCT quenching mechanism with increasing bridge length, from oxidative quenching by the DQ acceptor to reductive quenching by the bridge.

Silyl and σ-silane ruthenium complexes: Chloride substituent effects on the catalysed silylation of ethylene

Silylation of ethylene by the chlorosilanes HSiMe(2)Cl and HSiMeCl(2) was catalysed by the bis(dihydrogen) complex RuH(2)(eta(2)-H(2))(2)(PCy(3))(2) (1). Dehydrogenative silylation leading to the formation of the corresponding vinylsilanes was in competition with hydrosilylation. The rate and selectivity of the reactions were influenced by the number of chloro substituents and the ethylene pressure. A comparative mechanistic study was performed in toluene-d(8) with the two chlorosilanes. Reaction of 1 with an excess of HSiMe(2)Cl (10 equiv.) produced the sigma-silane complexes RuH(2)(eta(2)-H(2))(eta(2)-HSiMe(2)Cl)(PCy(3))(2) (2Me(2)Cl), RuH(2)(eta(2)-HSiMe(2)Cl)(2)(PCy(3))(2) (3Me(2)Cl) and the silyl complex RuCl(SiMe(2)Cl)(eta(2)-H(2))(PCy(3))(2) (4Me(2)Cl), all characterised by multinuclear NMR spectroscopy. Complexes 2Me(2)Cl and 3Me(2)Cl adopt a cis configuration for the two bulky phosphine ligands as a result of stabilising SISHA (Secondary Interactions between Silicon and Hydrogen Atoms) interactions. Complex 4Me(2)Cl resulted from the stoichiometric reaction of HSiMe(2)Cl with 1 producing RuHCl(eta(2)-H(2))(PCy(3))(2)in situ which further reacted with evolution of H(2) and formation of 4Me(2)Cl. When reacting 1 with 10 equiv. of HSiMeCl(2), the corresponding complexes 3MeCl(2) and 4MeCl(2) were detected as well as traces of 2MeCl(2). The reactivity toward ethylene was then examined. Under catalytic conditions (excess silane in toluene-d(8), ethylene atmosphere) only two compounds could be characterised: free PCy(3) and the new (eta(6)-aryl)(disilyl) complexes of the general formula Ru(eta(6)-C(6)D(5)CD(3))(SiMe(3-n)Cl(n))(2)(PCy(3)) (6Me(3-n)Cl(n)-d(8), n = 1,2). The X-ray structure of 6MeCl(2) was obtained on a single-crystal at 160 K. When only 2 equiv. of HSiMe(2)Cl were added, the ethylene(silyl) complex RuH(SiMe(2)Cl)(C(2)H(4))(PCy(3))(2) (7Me(2)Cl) was obtained in addition to the organic products resulting from catalytic hydrogenation, hydrosilylation and dehydrogenative silylation, i.e. C(2)H(6) (major one), C(2)H(3)SiMe(2)Cl and C(2)H(5)SiMe(2)Cl. In the case of 2 equiv. of HSiMeCl(2), upon ethylene addition, 7MeCl(2) was formed in minority compared to a new disilyl complex Ru(SiMeCl(2))(2)(PCy(3))(2) (8MeCl(2)) characterised by NMR spectroscopy and X-ray diffraction on a single crystal at 160 K. In 8MeCl(2), a formal 14-electron species, stabilisation through two agostic C-H bonds of the cyclohexyl groups was ascertained by DFT calculations.

Electrochemical and Spectroscopic Characterization of a Series of Mixed-Ligand Diruthenium Compounds

The electrochemistry and spectroelectrochemistry of a novel series of mixed-ligand diruthenium compounds were examined. The investigated compounds having the formula Ru(2)(CH(3)CO(2))(x)(Fap)(4-x)Cl where x = 1-3 and Fap is 2-(2-fluoroanilino)pyridinate anion were made from the reaction of Ru(2)(CH(3)CO(2))(4)Cl with 2-(2-fluoroanilino)pyridine (HFap) in refluxing methanol. The previously characterized Ru(2)(Fap)(4)Cl as well as the three newly isolated compounds represented as Ru(2)(CH(3)CO(2))(Fap)(3)Cl (1), Ru(2)(CH(3)CO(2))(2)(Fap)(2)Cl (2), and Ru(2)(CH(3)CO(2))(3)(Fap)Cl (3) possess three unpaired electrons with a Ru(2)(5+) dimetal core. Complexes 1 and 2 have well-defined Ru(2)(5+/4+) and Ru(2)(5+/6+) redox couples in CH(2)Cl(2), but 3 exhibits a more complicated electrochemical behavior due to equilibria involving association or dissociation of the anionic chloride axial ligand on the initial and oxidized or reduced forms of the compound. The E(1/2) values for the Ru(2)(5+/4+) and Ru(2)(5+/6+) processes vary linearly with the number of CH(3)CO(2)(-) bridging ligands on Ru(2)(CH(3)CO(2))(x)(Fap)(4-x)Cl and plots of reversible half-wave potentials vs the number of acetate groups follow linear free energy relationships with the largest substituent effect being observed for the oxidation. The major UV-visible band of the examined compounds in their neutral Ru(2)(5+) form is located between 550 and 800 nm in CH(2)Cl(2) and also varies linearly with the number of CH(3)CO(2)(-) ligands on Ru(2)(CH(3)CO(2))(x)(Fap)(4-x)Cl. The electronic spectra of the singly oxidized and singly reduced forms of each diruthenium species were characterized by UV-visible spectroelectrochemistry in CH(2)Cl(2).

Parallel oxygen and chlorine evolution on Ru 1− xNi xO 2− y nanostructured electrodes

Nanocrystalline materials with chemical composition corresponding to formula Ru 1− x Ni x O 2− y (0.02 < x < 0.30) were prepared by sol–gel approach. Substitution of Ru by Ni has a minor effect on the structural characteristics extractable from X-ray diffraction patterns. The electrocatalytic behavior of Ru 1− x Ni x O 2− y with respect to parallel oxygen (oxygen evolution reaction, OER) and chlorine (chlorine evolution reaction, CER) evolution in acidic media was studied by voltammetry combined with differential electrochemical mass spectrometry (DEMS). The DEMS data indicate a significant decrease of the over-voltage for chlorine evolution with respect to that of pure RuO 2. The oxygen evolution is slightly hindered. The increasing Ni content affects the electrode material activity and selectivity. The overall material's activity increases with increasing Ni content. The activity of the Ru–Ni–O oxides towards Cl 2 evolution shows a distinguished maximum for material containing 10% of Ni. Further increase of Ni content results in suppression of Cl 2 evolution in favor of O 2 evolution. A model reflecting the cation–cation interactions resulting from Ni-doping is proposed to explain the observed trends in electrocatalytic behavior.

Mononuclear ruthenium complexes containing two different phosphines in trans position: II. Catalytic hydrogenation of C [dbnd]C and C [dbnd]O bonds

Bis(acetate) ruthenium(II) complexes of the general formula Ru(CO) 2(OAc) 2(P n Bu 3)[P( p-XC 6H 4) 3] (OAc = acetate, X = CH 3O, CH 3, H, F or Cl), containing different phosphine ligands trans to P n Bu 3, have been employed as catalyst precursors for the hydrogenation of 1-hexene, acetophenone, 2-butanone and benzylideneacetone. For comparative purposes, analogous reactions have been performed using the homodiphosphine precursors Ru(CO) 2(OAc) 2(P n Bu 3) 2 and Ru(CO) 2(OAc) 2(PPh 3) 2. The catalytic activity of the heterodiphosphine complexes depends on the basicity of the triarylphosphine trans to P n Bu 3 as this factor controls, inter alia, the rate of formation of hydride(acetate), Ru(CO) 2(H)(OAc)(P n Bu 3)[P( p-XC 6H 4) 3], or dihydride, Ru(CO) 2(H) 2(P n Bu 3)[( p-XC 6H 4) 3], complexes, by hydrogenation of the bis(OAc) precursors. The catalytic hydrogenation of the C C double bond is best accomplished by homodiphosphine dihydride catalysts, while heterodiphosphine monohydrides are more efficient catalysts than the homo- and heterodiphosphine dihydrides for the reduction of the keto C O bond.

Synthesis, characterization, spectroscopic and electrochemical properties of trans, trans, trans-bis(triphenyl phosphine) bis(aroyl hydrazonato)ruthenium(II) complexes

Four ruthenium (II) complexes of general formula Ru(PPh 3) 2(L) 2 have been synthesized and characterized. The spectroscopic and cyclic voltammetric studies of these complexes are also reported. X-ray crystal structure determination of two of the complexes reveal that Ru(II) occupies trans, trans, trans-( t, t, t) N 2O 2P 2 centrosymmetric octahedral environments, with the ligand pair occupying the equatorial plane. 31P NMR confirms the presence of two trans-PPh 3 groups in all the complexes. The transformation of the complexes in dichloromethane solution is studied by spectrophotometry and 31P NMR spectroscopy.

Evaluation of redox mediators for amperometric biosensors: Ru-complex modified carbon-paste/enzyme electrodes

The properties of reagentless amperometric biosensors are mainly governed by the interaction of the used redox enzyme and the redox mediators used to facilitate the electron-transfer reaction. Both the used redox mediators and the redox enzymes differ concerning their hydrophilicity and their properties within the matrix of a carbon-paste electrode. Since there is no general procedure which is applicable for any enzyme in combination with any redox mediator, optimisation is necessary for each possible combination. Three approaches for the development of biosensors were investigated using carbon-paste electrodes enriched with redox mediator as a base in all sensor architectures. A class of redox mediators with the common formula Ru(LL) 2(X) 2 (where LL are 1,10-phenantroline or 2,2′-bipyridine type ligands, and X is an acido ligand) was investigated. In the first approach, enzymes were integrated into the carbon paste; in the second, the enzymes were adsorbed on the surface of the mediator-containing carbon-paste electrode and held in place by a Nafion film; and in the third approach, enzymes were entrapped in polymer films, which were electrochemically deposited onto the electrode's surface. The properties of the obtained biosensors strongly depend on the sensor architecture and the specific features of the used enzyme. Thus, our investigation using three different sensor architectures can provide valuable information about the possible interaction between a specific enzyme and a redox mediators with specific properties.

Kinetics of Substitution of Weakly Coordinating Nitrate by Chloride in (η5-Cp)Ru(CO)(ER3)ONO2 (ER3 = AsPh3, PPh3, P(p-anisyl)3, PPh2(o-anisyl), P(OPh)3) in Dichloromethane

The d6 complexes of formula (η5-Cp)Ru(CO)(ER3)ONO2, where ER3 = AsPh3, PPh3, P(p-anisyl)3, PPh2(o-anisyl), and P(OPh)3, were prepared by reaction of their chloro analogues with AgNO3 in CH2Cl2. They underwent moderately slow substitution of the relatively weakly coordinating nitrate by chloride in dry CH2Cl2 in the presence of excess [N(PPh3)2+]Cl-. A kinetics study showed the reaction to be first order in nitrato complex and independent of chloride salt concentration under pseudo-first-order conditions. First-order rate constants for nitrate metathesis follow the trend P(OPh)3 < PPh3 < P(p-anisyl)3 < AsPh3 ≪ PPh2(o-anisyl), with k1 at 25 °C for the first four in the series from 1.4 to 4.4 × 10-5 s-1. Activation parameters for conversion of (η5-Cp)Ru(CO)(AsPh3)ONO2 to its chloride are ΔH‡ = 17(2) kcal/mol and ΔS‡ = −21(5) eu. Even use of a slightly moist solvent increased the rate of nitrate metathesis by 20−30% without changing the form of the rate law. The complex containing PPh2(o-anisyl) was approximately 2 orders of magnitude more reactive (k1 = 4.9 × 10-3 s-1). A likely explanation is stabilization of a coordinatively unsaturated intermediate by weak coordination of the potentially chelating o-OMe group. A mechanism entailing rate-limiting conversion of the neutral nitrato complex into a coordinatively unsaturated ion-paired species is consistent with this set of data. Semiempirical calculations (PM3(tm)), which model the structures of complexes in these systems quite well, supported such behavior. X-ray crystal structures were determined for the AsPh3 nitrato and chloro complexes and for the PPh3 chloro complex.

A new route for the synthesis of bis(pyridine dicarboxylato)bis(triphenylphosphine) complexes of ruthenium(II) and X-ray structural characterisation of the biologically active trans-[Ru(PPh 3) 2(L 1H) 2] (L 1H 2=pyridine 2,3-dicarboxylic acid)

Ruthenium(II) complexes of the general formula Ru(LH) 2(PPh 3) 2, (LH 2=pyridine 2,3-; 2,4-; 2,5- and 2,6-dicarboxylic acid) are synthesised by a new method. All the pyridine dicarboxylic acids are found to behave as bidentate, monobasic chelating donors, with one carboxyl group remaining idle. The electrochemical behaviour of the compounds is explored with the help of cyclic voltammetry. The antibacterial activities of these compounds were examined against Escherichia coli in nutrient broth in order to check their potential for antitumour activity. Single-crystal X-ray analysis of the complex involving pyridine 2,3-dicarboxylic acid (L 1H 2) revealed that the coordination environment consists of a centrosymmetric, axially elongated N 2P 2O 2 octahedron with a pair of coordinated L 1H ligands occupying the equatorial plane.

Ru-σ-alkynyl compounds of tetraanilinopyridinato-diruthenium(II,III) core: synthesis and structural characterization

Synthesis and characterizations are reported for three diruthenium(II,III) compounds of general formula Ru 2(ap) 4(CCR), where ap=2-anilinopyridinate and R=Si(CH 3) 3 ( 3), H ( 4), and CH 2OCH 3 ( 5). Molecular structure determination reveals that the Ru–Ru bond lengths are 2.3162(5) and 2.3234(7) Å for 3 and 5, respectively, while the CC bond is not significantly elongated compared with the free alkyne. Compounds 3– 5 undergo reversible one-electron oxidation and reduction at potentials around 200 and −1030 mV, respectively. At more positive potential, compounds 3 and 4 undergo the second one-electron oxidation quasireversibly or irreversibly without decomposition, while compound 5 is oxidatively degraded.

Thermal decomposition of mixed-valent diruthenium pentakis(alkanoates) enhanced by their liquid crystalline state

The thermal decomposition of mixed-valent diruthenium pentakis(alkanoates) of general formula Ru 2 (II,III)(O 2C(CH 2) n−2 CH 3) 5 (for n=3, 4, 5, 6, 8, 10, 12, 16), studied by a combination of several complementary physicochemical techniques, has been found to take place in two differentiated steps. The first one gives the divalent analogues Ru 2 (II,II)(O 2C(CH 2) n−2 CH 3) 4 as the main product, in a one-electron reduction of the bimetallic core likely provided by oxidative decarboxylation of the axial anion. The second one involves the reduction of the binuclear core to metallic ruthenium, and the oxidation of the equatorial carboxylates. The first step is very much influenced by the aggregation state of the system, the occurrence of a liquid–crystalline phase in compounds with n>6 facilitates the thermolysis: decomposition temperatures fall from ≈300°C for compounds with n=3 to ≈175°C for compounds with n=10–16.