The effect of the nature of the support on catalytic properties of ruthenium supported catalysts in partial oxidation of methane to syn-gas

The effect of the carrier on catalytic properties of ruthenium supported catalysts in partial oxidation of methane (POM) was investigated. A variety of supports differed in texture and reducibility (Al₂O₃, SiO₂, TiO₂, Cr₂O₃, CeO₂ and Fe₂O₃) were used. The catalyst activity is governed by ruthenium phase formation (RuO₂ → Ru⁰), and it depends on redox properties of the support as well as support-ruthenium phase interaction. The activity of Ru supported catalysts decreases in the order Al₂O₃ ≈ SiO₂ > Cr₂O₃ > TiO₂ > CeO₂ > Fe₂O₃. No significant effects of the specific surface area and porosity of catalysts on the methane conversion and selectivity of CO formation were found. The selectivity of CO₂ formation (total oxidation of CH₄) under conditions of POM (a ratio of CH₄/O₂ = 2) is associated with the contribution of reducible support oxides into the catalytic performance.     

FT-IR photoacoustic spectra of the surface of Ru3(CO)12/Al2O3 system

The FT-IR photoacoustic spectra of Ru₃(CO)₁₂/Al₂O₃ (acidic and basic alumina) system have been measured for different ageing times. The behaviors of oxidation states of Ru on the surface of basic or acidic alumina and their difference are discussed on the ground of CO stretching bands of their spectra.     

Metal‐catalyzed reversible conversion between chemical and electrical energy designed towards a sustainable society

Proton dissociation of an aqua‐Ru‐quinone complex, [Ru(trpy)(q)(OH₂)]²⁺ (trpy = 2,2′ : 6′,2″‐terpyridine, q = 3,5‐di‐t‐butylquinone) proceeded in two steps (pK_a = 5.5 and ca. 10.5). The first step simply produced [Ru(trpy)(q)(OH)]⁺, while the second one gave an unusual oxyl radical complex, [Ru(trpy)(sq)(O^?.)]⁰ (sq = 3,5‐di‐t‐butylsemiquinone), owing to an intramolecular electron transfer from the resultant O^2? to q. A dinuclear Ru complex bridged by an anthracene framework, [Ru₂(btpyan)(q)₂(OH)₂]²⁺ (btpyan = 1,8‐bis(2,2′‐terpyridyl)anthracene), was prepared to place two Ru(trpy)(q)(OH) groups at a close distance. Deprotonation of the two hydroxy protons of [Ru₂(btpyan)(q)₂(OH)₂]²⁺ generated two oxyl radical Ru‐O^?. groups, which worked as a precursor for O₂ evolution in the oxidation of water. The [Ru₂(btpyan)(q)₂(OH)₂](SbF₆)₂ modified ITO electrode effectively catalyzed four‐electron oxidation of water to evolve O₂ (TON = 33500) under electrolysis at +1.70 V in H₂O (pH 4.0). Various physical measurements and DFT calculations indicated that a radical coupling between two Ru(sq)(O^?.) groups forms a (cat)Ru‐O‐O‐Ru(sq) (cat = 3,5‐di‐t‐butylcathechol) framework with a μ‐superoxo bond. Successive removal of four electrons from the cat, sq, and superoxo groups of [Ru₂(btpyan)(cat)(sq)(μ‐O₂^?)]⁰ assisted with an attack of two water (or OH^?) to Ru centers, which causes smooth O₂ evolution with regeneration of [Ru₂(btpyan)(q)₂(OH)₂]²⁺. Deprotonation of an Ru‐quinone‐ammonia complex also gave the corresponding Ru‐semiquinone‐aminyl radical. The oxidized form of the latter showed a high catalytic activity towards the oxidation of methanol in the presence of base. Three complexes, [Ru(bpy)₂(CO)₂]²⁺, [Ru(bpy)₂(CO)(C(O)OH)]⁺, and [Ru(bpy)₂(CO)(CO₂)]⁰ exist as an equilibrium mixture in water. Treatment of [Ru(bpy)₂(CO)₂]²⁺ with BH₄^? gave [Ru(bpy)₂(CO)(C(O)H)]⁺, [Ru(bpy)₂(CO)(CH₂OH)]⁺, and [Ru(bpy)₂(CO)(OH₂)]²⁺ with generation of CH₃OH in aqueous conditions. Based on these results, a reasonable catalytic pathway from CO₂ to CH₃OH in electro‐ and photochemical CO₂ reduction is proposed. A new pbn (pbn = 2‐pyridylbenzo[b]‐1,5‐naphthyridine) ligand was designed as a renewable hydride donor for the six‐electron reduction of CO₂. A series of [Ru(bpy)_3‐n(pbn)_n]²⁺ (n = 1, 2, 3) complexes undergoes photochemical two‐ (n = 1), four‐ (n = 2), and six‐electron reductions (n = 3) under irradiation of visible light in the presence of N(CH₂CH₂OH)₃. © 2009 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 169–186; 2009: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.200800039     

Ligand-Protected Ultrasmall Pd Nanoclusters Supported on Metal Oxide Surfaces for CO Oxidation: Does the Ligand Activate or Passivate the Pd Nanocatalyst?

Herein, we report on the synthesis of ultrasmall Pd nanoclusters (∼2 nm) protected by L-cysteine [HOCOCH(NH₂)CH₂SH] ligands (Pd_n(L-Cys)_m) and supported on the surfaces of CeO₂, TiO₂, Fe₃O₄, and ZnO nanoparticles for CO catalytic oxidation. The Pd_n(L-Cys)_m nanoclusters supported on the reducible metal oxides CeO₂, TiO₂ and Fe₃O₄ exhibit a remarkable catalytic activity towards CO oxidation, significantly higher than the reported Pd nanoparticle catalysts. The high catalytic activity of the ligand-protected clusters Pd_n(L-Cys)_m is observed on the three reducible oxides where 100 % CO conversion occurs at 93–110 °C. The high activity is attributed to the ligand-protected Pd nanoclusters where the L-cysteine ligands aid in achieving monodispersity of the Pd clusters by limiting the cluster size to the active sub-2-nm region and decreasing the tendency of the clusters for agglomeration. In the case of the ceria support, a complete removal of the L-cysteine ligands results in connected agglomerated Pd clusters which are less reactive than the ligand-protected clusters. However, for the TiO₂ and Fe₃O₄ supports, complete removal of the ligands from the Pd_n(L-Cys)_m clusters leads to a slight decrease in activity where the T_100% CO conversion occurs at 99 °C and 107 °C, respectively. The high porosity of the TiO₂ and Fe₃O₄ supports appears to aid in efficient encapsulation of the bare Pd_n nanoclusters within the mesoporous pores of the support.     

Highly Dispersed Ruthenium Hydroxide Supported on Titanium Oxide Effective for Liquid‐Phase Hydrogen‐Transfer Reactions

Supported ruthenium hydroxide catalysts (Ru(OH)_x/support) were prepared with three different TiO₂ supports (anatase TiO₂ (TiO₂(A), BET surface area: 316 m² g^?1), anatase TiO₂ (TiO₂(B), 73 m² g^?1), and rutile TiO₂ (TiO₂(C), 3.2 m² g^?1)), as well as an Al₂O₃ support (160 m² g^?1). Characterizations with X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and X‐ray absorption fine structure (XAFS) showed the presence of monomeric ruthenium(III) hydroxide and polymeric ruthenium(III) hydroxide species. Judging from the coordination numbers of the nearest‐neighbor Ru atoms and the intensities of the ESR signals, the amount of monomeric hydroxide species increased in the order of Ru(OH)_x<Ru(OH)_x/TiO₂(C)<Ru(OH)_x/Al₂O₃<Ru(OH)_x/TiO₂(B)<Ru(OH)_x/TiO₂(A). These supported ruthenium hydroxide catalysts, especially Ru(OH)_x/TiO₂(A), showed high catalytic activities and selectivities for liquid‐phase hydrogen‐transfer reactions, such as racemization of chiral secondary alcohols and the reduction of carbonyl compounds and allylic alcohols. The catalytic activities of Ru(OH)_x/TiO₂(A) for these hydrogen‐transfer reactions were at least one order of magnitude higher than those of previously reported heterogeneous catalysts, such as Ru(OH)_x/Al₂O₃. These catalyses were truly heterogeneous, and the catalysts recovered after the reactions could be reused several times without loss of catalytic performance. The reaction rates monotonically increased with an increase in the amount of monomeric ruthenium hydroxide species, which suggests that the monomeric species are effective for these hydrogen‐transfer reactions.     

Ruthenium Carbonyl Cluster Complexes with Phenylgermyl Ligands from the Reactions of Ph<Subscript>3</Subscript>GeH with Ru(CO)<Subscript>5</Subscript> and Ru<Subscript>3</Subscript>(CO)<Subscript>12</Subscript>

Four new triphenylgermylruthenium carbonyl compounds HRu(CO)₄GePh₃, 14; Ru(CO)₄(GePh₃)₂, 15; Ru₂(CO)₈(GePh₃)₂, 16; and Ru₃(CO)₉(GePh₃)₃(μ-H)₃, 17 were obtained from the reaction of Ru(CO)₅ with Ph₃GeH in hexane solvent at reflux, 68 °C. The major product 14 was formed by loss of CO from the Ru(CO)₅ and an oxidative addition of the GeH bond of the Ph₃GeH to the metal atom. This six coordinate complex contains one terminal hydrido ligand. Compound 15 is formed from 14 and contains two trans-positioned GePh₃ ligands in the six coordinate complex. Compound 16 contains two Ru(CO)₄(GePh₃) fragments joined by an Ru–Ru single bond. Compound 17 contains a triangular cluster of three ruthenium atoms with three bridging hydrido ligands and one terminal GePh₃ ligand on each metal atom. When heated to 125 °C, 14 was converted to the new triruthenium compound Ru₃(CO)₁₀(μ-GePh₂)₂, 18. Compound 18 consists of a triangular tri-ruthenium cluster with two GePh₂ ligands bridging two different edges of the cluster and one bridging CO ligand. Ru₃(CO)₁₂ was found to react with Ph₃GeH at 97 °C to yield three products: 15, and two new compounds Ru₃(CO)₉(μ-GePh₂)₃, 19 and Ru₂(CO)₆(μ-GePh₂)₂(GePh₃)₂, 20 were obtained. Compound 19 is similar to 18 having a triangular tri-ruthenium cluster but has three bridging GePh₂ ligands, one on each Ru–Ru bond. Compound 20 contains only two ruthenium atoms joined by a single Ru–Ru bond that has two bridging GePh₂ ligands and a terminal GePh₃ ligand on each metal atom. All compounds were characterized by a combination of IR, ¹H NMR, single-crystal X-ray diffraction analyses. This report is dedicated to Professor Dieter Fenske on the occasion of his 65th birthday for his many pioneering contributions to the chemistry of metal chalcogenide cluster complexes.     

Mercury-bridged,nitrosyl substituted,triruthenium carbonyl clusters: Synthesis and x-ray crystal structure of [Ru3(NO)(CO)10]2Hg

The neutral mixed-metal cluster [Ru₃(NO)(CO)₁₀]₂Hg has been prepared by the reaction of the [Ru₃(NO)(CO)₁₀], with HgCl₂. An X-ray crystal structure shows that the mercury atom links two Ru₃ triangular units by bridging an RuRu edge of each unit. The dihedral angle between the two Ru₂Hg triangles is 27.6°. In each Ru₃ triangle a nitrosyl ligand bridges the same RuRu edge as the bridging Hg atom while the ten carbonyl groups are all terminal.     

Water Adsorption and Dissociation on Ceria‐Supported Single‐Atom Catalysts: A First‐Principles DFT+U Investigation

Single‐atom catalysts have attracted wide attention owing to their extremely high atom efficiency and activities. In this paper, we applied density functional theory with the inclusion of the on‐site Coulomb interaction (DFT+U) to investigate water adsorption and dissociation on clean CeO₂(111) surfaces and single transition metal atoms (STMAs) adsorbed on the CeO₂(111) surface. It is found that the most stable water configuration is molecular adsorption on the clean CeO₂(111) surface and dissociative adsorption on STMA/CeO₂(111) surfaces, respectively. In addition, our results indicate that the more the electrons that transfer from STMA to the ceria substrate, the stronger the binding energies between the STMA and ceria surfaces. A linear relationship is identified between the water dissociation barriers and the d band centers of STMA, known as the generalized Brønsted–Evans–Polanyi principle. By combining the oxygen spillovers, single‐atom dispersion stabilities, and water dissociation barriers, Zn, Cr, and V are identified as potential candidates for the future design of ceria‐supported single‐atom catalysts for reactions in which the dissociation of water plays an important role, such as the water–gas shift reaction.     

Morphology‐Engineered Highly Active and Stable Ru/TiO2 Catalysts for Selective CO Methanation

Ru/TiO₂ catalysts exhibit an exceptionally high activity in the selective methanation of CO in CO₂‐ and H₂‐rich reformates, but suffer from continuous deactivation during reaction. This limitation can be overcome through the fabrication of highly active and non‐deactivating Ru/TiO₂ catalysts by engineering the morphology of the TiO₂ support. Using anatase TiO₂ nanocrystals with mainly {001}, {100}, or {101} facets exposed, we show that after an initial activation period Ru/TiO₂‐{100} and Ru/TiO₂‐{101} are very stable, while Ru/TiO₂‐{001} deactivates continuously. Employing different operando/in situ spectroscopies and ex situ characterizations, we show that differences in the catalytic stability are related to differences in the metal–support interactions (MSIs). The stronger MSIs on the defect‐rich TiO₂‐{100} and TiO₂‐{101} supports stabilize flat Ru nanoparticles, while on TiO₂‐{001} hemispherical particles develop. The former MSIs also lead to electronic modifications of Ru surface atoms, reflected by the stronger bonding of adsorbed CO on those catalysts than on Ru/TiO₂‐{001}.     

Structure and catalytic activity of the ruthenium(I) sawhorse‐type complex [Ru2{μ,η2‐CF3(CF2)5COO}2(DMSO)2(CO)4]

The title compound, cis‐di‐μ‐perfluoroheptanoato‐κ⁴O:O′‐bis[dicarbonyl(dimethyl sulfoxide‐κS)ruthenium(I)](Ru—Ru), [Ru₂(C₇F₁₃O₂)₂(C₂H₆OS)₂(CO)₄], is a sawhorse‐type dinuclear ruthenium complex with two bridging perfluoroheptanoate ligands, and with two dimethyl sulfoxide (DMSO) ligands in the axial positions coordinating via the S atoms. It is a new example of a compound with an aliphatic fluorinated carboxylate ligand. The Ru—Ru bond distance of 2.6908 (3) Å indicates a direct Ru—Ru interaction. The compound is an active catalyst in transvinylation of propionic acid with vinyl acetate.     

Water‐Splitting Electrocatalysis in Acid Conditions Using Ruthenate‐Iridate Pyrochlores

The pyrochlore solid solution (Na_0.33Ce_0.67)₂(Ir_1?xRu_x)₂O₇ (0≤x≤1), containing B‐site Ru^IV and Ir^IV is prepared by hydrothermal synthesis and used as a catalyst layer for electrochemical oxygen evolution from water at pH<7. The materials have atomically mixed Ru and Ir and their nanocrystalline form allows effective fabrication of electrode coatings with improved charge densities over a typical (Ru,Ir)O₂ catalyst. An in situ study of the catalyst layers using XANES spectroscopy at the Ir L_III and Ru K edges shows that both Ru and Ir participate in redox chemistry at oxygen evolution conditions and that Ru is more active than Ir, being oxidized by almost one oxidation state at maximum applied potential, with no evidence for ruthenate or iridate in +6 or higher oxidation states.     

Carbon monoxide and oxygen interaction with Ru/MgF<Subscript>2</Subscript> catalyst: IR and EPR studies

Electron paramagnetic resonance (EPR) and infrared (IR) spectroscopy were used to study the formation of ruthenium and adsorbed species appearing on the catalyst upon the adsorption of CO and O₂ on 1.37 wt% Ru/MgF₂ catalysts derived from Ru₃(CO)₁₂. The presence of Ru ^x+ sites in spite of a reductive H₂ treatment at 673 K was observed by EPR and IR spectroscopy beside metallic Ru⁰ species. Both IR and EPR results provided clear evidence for the interaction between surface ruthenium and probe molecules. The IR spectra recorded after admission of CO showed a band at approx. 2000 cm⁻¹, due to linearly adsorbed CO on Ru⁰/MgF₂ and two bands at higher frequencies (approx. 2140 and approx. 2070 cm⁻¹), related to CO on oxidized Ru ⁿ⁺ species, e.g., to Ru(CO)₃ complex with Ru in the 1+ and/or 2+ state of oxidation and Ru(CO)₂ with Ru in the 3+ and/or 4+ state of oxidation. A weak anisotropic EPR signal with g _‖ = 2.017 and g _⊥ = 2.003 is due to O ₂ ⁻ radicals and a formation of Ru⁴⁺-O ₂ ⁻ complex is postulated. The Ru³⁺ appears to oxidize to Ru⁴⁺ and the resulting dioxygen anion is coordinated to the ruthenium. The strong, isotropic EPR signal at g ₀ = 2.003 detected upon admission of CO is attributed to CO radical anion rather than to any ruthenium carbonyl complexes.     

Activation of a carbon—nitrogen triple bond in the presence of Ru3(CO)12 and H4Ru4(CO)12

The reaction of PhCN with Ru₃ (CO)₁₂ in the presence of acetic acid gives H₄Ru₄(CO)₁₂, (I), (μ-H)Ru₃(CO)₁₀(μ-NCHPh) (II) and (μ-H)Ru₃(CO)₁₀(μ-NH-CH₂Ph) (III) as the main products. Reaction under 110 atm of H₂ gives more III and also gives benzylamine. Replacement of acetic acid by H₂ at atmospheric pressure gives only II. When H₄Ru₄CO)₁₂ reacts with PhCN alone or in the presence of NaOH, II is formed as the only product.The structures of II and III have been fully elucidated by X-ray methods. The nitrogen atom of the NCHPh ligand in II and that of the NHCH₂Ph ligand in III, interact with the isosceles-triangular metal cluster, symmetrically bridging the shortest Ru(1)-Ru(2) edge. A hydride ligand in both II and III bridges the same Ru(1)-Ru(2) edge of the cluster. Under mild conditions acetic acid is an essential requirement for the activation of Ru₃(CO)₁₂ for reaction with PhCN to give III, which cannot be obtained under these conditions from II.     

One‐Pot Cooperation of Single‐Atom Rh and Ru Solid Catalysts for a Selective Tandem Olefin Isomerization‐Hydrosilylation Process

Realizing the full potential of oxide‐supported single‐atom metal catalysts (SACs) is key to successfully bridge the gap between the fields of homogeneous and heterogeneous catalysis. Here we show that the one‐pot combination of Ru₁/CeO₂ and Rh₁/CeO₂ SACs enables a highly selective olefin isomerization‐hydrosilylation tandem process, hitherto restricted to molecular catalysts in solution. Individually, monoatomic Ru and Rh sites show a remarkable reaction specificity for olefin double‐bond migration and anti‐Markovnikov α‐olefin hydrosilylation, respectively. First‐principles DFT calculations ascribe such selectivity to differences in the binding strength of the olefin substrate to the monoatomic metal centers. The single‐pot cooperation of the two SACs allows the production of terminal organosilane compounds with high regio‐selectivity (>95 %) even from industrially‐relevant complex mixtures of terminal and internal olefins, alongside a straightforward catalyst recycling and reuse. These results demonstrate the significance of oxide‐supported single‐atom metal catalysts in tandem catalytic reactions, which are central for the intensification of chemical processes.     

Active Sites for Adsorption and Reaction of Molecules on Rutile TiO2(110) and Anatase TiO2(001) Surfaces (cited: 1)

The reactivity of specific sites on rutile TiO₂(110)-(1×1) surface and anatase TiO₂(001)-(1×4) surface has been comparably studied by means of high resolution scanning tunneling microscopy. At the rutile TiO₂(110)-(1×1) surface, we find the defects of oxygen vacancy provide distinct reactivity for O₂ and CO₂ adsorption, while the terminal fivefold-coordinated Ti sites dominate the photocatalytic reactivity for H₂O and CH₃OH dissociation. At the anatase TiO₂(001)-(1×4) surface, the sixfold-coordinated terminal Ti sites at the oxidized surface seem to be inert in both O₂ and H₂O reactions, but the Ti-rich defects which introduce the Ti³⁺ state into the reduced surface are found to provide high reactivity for the reactions of O₂ and H₂O. By comparing the reactions on both rutile and anatase surfaces under similar experimental conditions, we find the reactivity of anatase TiO₂(001) is actually lower than rutile TiO₂(110), which challenges the conventional knowledge that the anatase (001) is the most reactive TiO₂ surface. Our findings could provide atomic level insights into the mechanisms of TiO₂ based catalytic and photocatalytic chemical reactions.     

Koordinativ ungesättigte Dirutheniumkomplexe: Synthese und Kristallstrukturen von [Ru2(CO)n(μ‐H)(μ‐PtBu2)(μ‐Ph2PCH2PPh2)] (n = 4; 5) und [Ru2(CO)4(μ‐CH2)(μ‐H)(μ‐PtBu2)(μ‐Ph2PCH2PPh2)]

Coordinatively Unsaturated Diruthenium Complexes: Synthesis and X‐ray Crystal Structures of [Ru₂(CO)_n(μ‐H)(μ‐P^tBu₂)(μ‐Ph₂PCH₂PPh₂)] (n = 4; 5) and [Ru₂(CO)₄(μ‐CH₂)(μ‐H)(μ‐P^tBu₂)(μ‐Ph₂PCH₂PPh₂)] The reaction of [Ru₂(μ‐CO)(CO)₅(μ‐H)(μ‐P^tBu₂)(^tBu₂PH)] ( 2 ) with dppm yields the dinuclear species [Ru₂(μ‐CO)(CO)₄(μ‐H)(μ‐P^tBu₂)(μ‐dppm)] ( 3 ) (dppm = Ph₂PCH₂PPh₂). Under thermal or photolytic conditions 3 loses very easily one carbonyl ligand and affords the corresponding electronically and coordinatively unsaturated complex [Ru₂(CO)₄(μ‐H)(μ‐P^tBu₂)(μ‐dppm)] ( 4 ). 4 is also obtainable by an one‐pot synthesis from [Ru₃(CO)₁₂], an excess of ^tBu₂PH and stoichiometric amounts of dppm via the formation of [Ru₂(CO)₄(μ‐H)(μ‐P^tBu₂)(^tBu₂PH)₂] ( 1 ). 4 exhibits a Ru–Ru double bond which could be confirmed by addition of methylene to the dimetallacyclopropane [Ru₂(CO)₄(μ‐CH₂)(μ‐H)(μ‐P^tBu₂)(μ‐dppm)] ( 5 ). The molecular structures of 3 , 4 and 5 were determined by X‐ray crystal structure analyses.     

Cationic Heterocycles as Ligands: Synthesis and Reactivity with Anionic Nucleophiles of Cationic Triruthenium Clusters Containing C‐Metalated N‐Methylquinoxalinium or N‐Methylpyrazinium Ligands

The cationic cluster complexes [Ru₃(CO)₁₀(μ‐H)(μ‐κ²N,C‐L¹Me)]⁺ ( 3 ⁺; HL¹=quinoxaline) and [Ru₃(CO)₁₀(μ‐H)(μ‐κ²N,C‐L²Me)]⁺ ( 5 ⁺; HL²=pyrazine) have been prepared as triflate salts by treatment of their neutral precursors [Ru₃(CO)₁₀(μ‐H)(μ‐κ²N,C‐Lⁿ)] with methyl triflate. The cationic character of their heterocyclic ligands is responsible for their enhanced tendency to react with anionic nucleophiles relative to that of hydrido triruthenium carbonyl clusters that have neutral N‐heterocyclic ligands. These clusters react instantaneously with methyl lithium and potassium tris‐sec‐butylborohydride (K‐selectride) to give neutral products that contain novel nonaromatic N‐heterocyclic ligands. The following are the products that have been isolated: [Ru₃(CO)₉(μ‐H)(μ₃‐κ²N,C‐L¹Me₂)] ( 6 ; from 3 ⁺ and methyl lithium), [Ru₃(CO)₉(μ‐H)(μ₃‐κ²N,C‐L¹HMe)] ( 7 ; from 3 ⁺ and K‐selectride), [Ru₃(CO)₉(μ‐H)(μ₃‐κ²N,C‐L²Me₂)] ( 8 ; from 5 ⁺ and methyl lithium), and [Ru₃(CO)₉(μ‐H)(μ₃‐κ²N,C‐L²HMe)] ( 11 ; from 5 ⁺ and K‐selectride). Whereas the reactions of 3 ⁺ lead to products that arise from the attack of the corresponding nucleophile at the C atom of the only CH group adjacent to the N‐methyl group, the reactions of 5 ⁺ give mixtures of two products that arise from the attack of the nucleophile at one of the C atoms located on either side of the N‐methyl group. The LUMOs and the atomic charges of 3 ⁺ and 5 ⁺ confirm that the reactions of these clusters with anionic nucleophiles are orbital‐controlled rather than charge‐controlled processes. The N‐heterocyclic ligands of all of these neutral products are attached to the metal atoms in nonconventional face‐capping modes. Those of compounds 6 – 8 have the atoms of a ligand C?N fragment σ‐bonded to two Ru atoms and π‐bonded to the other Ru atom, whereas the ligand of compound 11 has a C? N fragment attached to a Ru atom through the N atom and to the remaining two Ru atoms through the C atom. A variable‐temperature ¹H NMR spectroscopic study showed that the ligand of compound 7 is involved in a fluxional process at temperatures above ?93 °C, the mechanism of which has been satisfactorily modeled with the help of DFT calculations and involves the interconversion of the two enantiomers of this cluster through a conformational change of the ligand CH₂ group, which moves from one side of the plane of the heterocyclic ligand to the other, and a 180° rotation of the entire organic ligand over a face of the metal triangle.     

Comparative Study of Ruthenium(II) and Ruthenium(III) Complexes with the Ligand dmbpy (dmbpy = 4, 4′‐Dimethyl‐2, 2′‐bipyridine)

The complex cis‐[Ru^III(dmbpy)₂Cl₂](PF₆) ( 2 ) (dmbpy = 4, 4′‐dimethyl‐2, 2′‐bipyridine) was obtained from the reaction of cis‐[Ru^II(dmbpy)₂Cl₂] ( 1 ) with ammonium cerium(IV) nitrate followed by precipitation with saturated ammonium hexafluoridophosphate. The ¹H NMR spectrum of the Ru^III complex confirms the presence of paramagnetic metal atoms, whereas that of the Ru^II complex displays diamagnetism. The ³¹P NMR spectrum of the Ru^III complex shows one signal for the phosphorus atom of the PF₆^– ion. The perspective view of each [Ru^II/III(dmbpy)₂Cl₂]^0/+ unit manifests that the ruthenium atom is in hexacoordinate arrangement with two dmbpy ligands and two chlorido ligands in cis position. As the oxidation state of the central ruthenium metal atom becomes higher, the average Ru–Cl bond length decreases whereas the Ru–N (dmbpy) bond length increases. The cis‐positioned dichloro angle in Ru^III is 1.3° wider than that in the Ru^II. The dihedral angles between pair of planar six‐membered pyridyl ring in the dmbpy ligand for the Ru^II are 4.7(5)° and 5.7(4)°. The observed inter‐planar angle between two dmbpy ligands in the Ru^II is 89.08(15)°, whereas the value for the Ru^III is 85.46(20)°.     

Di‐μ‐benzoato‐bis­[di­carbonyl­(pyri­dine)­ruthenium(I)] (new polymorph) and di‐μ‐tri­fluoro­acetato‐bis­[di­carbonyl­(pyridine)­ruthenium(I)]

The syntheses and crystal structure determinations of a pair of `sawhorse' dimers are reported, viz. [Ru₂(C₆H₅CO₂)₂(C₅H₅N)₂(CO)₄] [a new polymorph, cf. Kepert, Deacon, Spiccia, Fallon, Skelton & White (2000). J. Chem. Soc. Dalton Trans. pp. 2867–2874] and [Ru₂(CF₃CO₂)₂(C₅H₅N)₂(CO)₄]. The Ru⋯Ru distances are 2.6724 (2) and 2.7122 (5) Å, respectively.     

A trichloro‐bridged binuclear ruthenium complex with 1,1,1‐tris(diphenylphosphinomethyl)ethane

The tri­chloro‐bridged dinuclear Ru^II complex tri‐μ‐chloro‐bis{[1,1,1‐tris­(di­phenyl­phosphino­methyl)­ethane‐κ³P,P′,P′′]ruthenium(II)} hexa­fluoro­phosphate ethanol solvate, [Ru₂Cl₃(tripod)₂]PF₆·C₂H₆O, containing the tripod [1,1,1‐tris­(di­phenyl­phosphino­methyl)­ethane, C₄₁H₃₉P₃] ligand, was unexpectedly obtained from the reaction of [Ru^IIICl₃(tripod)] with 1,4‐bis­(di­phenyl­phosphino)­butane (dppb), followed by pre­cipitation with NH₄PF₆. The magnetic moment of the compound at room temperature indicates that the dinuclear [Ru₂(μ‐Cl)₃(tripod)₂]⁺ cation is diamagnetic. A single‐crystal X‐ray structure determination revealed that the two Ru atoms are bridged by the three Cl atoms. The coordination sphere of each Ru atom is completed by the three P atoms of a tripod ligand. The two P₃Ru units are exactly eclipsed, while the bridging Cl atoms are staggered with respect to the six P atoms. The Ru⋯Ru distance is 3.3997 (7) Å and the mean Cl—Ru—Cl bond angle is 77.7°.