Ru Edge Research Articles

Ruthenium/TiO2‐Catalyzed Hydrogenolysis of Polyethylene Terephthalate: Reaction Pathways Dominated by Coordination Environment

AbstractPolyethylene terephthalate (PET) hydrogenolysis can produce benzene, toluene, and xylene (BTX), where the selectivity control is challenging. We report a reaction pathway dictated by the Ru coordination environment by examining the binding geometries of adsorbates on differently coordinated Ru centers and their evolution during PET hydrogenolysis. A BTX yield of 77 % was obtained using a Ru/TiO2 with a Ru coordination number of ca. 5.0 where edge/corner sites are dominant, while more gas and saturated products were formed for Ru/TiO2 containing primarily terrace sites. Density functional theory and isotopic labelling revealed that under‐coordinated Ru edge sites favor “upright” adsorption of aromatic adsorbates while well‐coordinated Ru sites favor “flat‐lying” adsorption, where the former mitigates ring hydrogenation and opening. This study demonstrates that reaction pathways can be directed through controlled reactant/intermediate binding via tuning of the Ru coordination environment for efficient conversion of PET to BTX.

Ruthenium/TiO2 -Catalyzed Hydrogenolysis of Polyethylene Terephthalate: Reaction Pathways Dominated by Coordination Environment.

Polyethylene terephthalate (PET) hydrogenolysis can produce benzene, toluene, and xylene (BTX), where the selectivity control is challenging. We report a reaction pathway dictated by the Ru coordination environment by examining the binding geometries of adsorbates on differently coordinated Ru centers and their evolution during PET hydrogenolysis. A BTX yield of 77 % was obtained using a Ru/TiO2 with a Ru coordination number of ca. 5.0 where edge/corner sites are dominant, while more gas and saturated products were formed for Ru/TiO2 containing primarily terrace sites. Density functional theory and isotopic labelling revealed that under-coordinated Ru edge sites favor "upright" adsorption of aromatic adsorbates while well-coordinated Ru sites favor "flat-lying" adsorption, where the former mitigates ring hydrogenation and opening. This study demonstrates that reaction pathways can be directed through controlled reactant/intermediate binding via tuning of the Ru coordination environment for efficient conversion of PET to BTX.

Identifying Key Descriptors for the Single-Atom Catalyzed CO Oxidation

Identifying Key Descriptors for the Single-Atom Catalyzed CO Oxidation

Reaction of a Triruthenium μ3-Borylene Complex with Benzonitrile: Formation of a μ3-η3-BCN Ring on a Cationic Ru3 Plane via Photo-Induced Intramolecular Borylene Transfer

A μ3-η2(||)-iminobenzoyl complex supported by a μ3-borylene ligand, [(Cp*Ru)3(μ3-BH)(μ3-η2-PhCNH)(μ-H)2] (5a; Cp* = η5-C5Me5), was synthesized as an equilibrated mixture with its isomer, 5b, by the reaction of a μ3-borylene complex, [{Cp*Ru(μ-H)}3(μ3-BH)] (1), with benzonitrile. Although the structure of 5a is very similar to that of the previously reported μ3-η2(||)-phenylacetylene complex, [(Cp*Ru)3(μ3-BH)(μ3-η2-PhCCH)(μ-H)3] (2), the reactivity of 5a is different from that of 2. While the thermolysis of 2 resulted in the reductive elimination of dihydrogen, a μ3-2-amino-2-boraruthenacyclopentenyl complex, [{Cp*Ru(μ-H)}2{Cp*Ru(−C6H4–CH-BNH2−)}] (6), was obtained by the thermolysis of 5a at 140 °C without hydrogen elimination. In contrast, a cationic μ3-η2(||)-iminobenzoyl complex, [(Cp*Ru)3(μ3-BH)(μ3-η2-PhCNH)(μ-H)3]+ (9), which was obtained by the protonation of 5a, showed reactivity similar to that of 2. Irradiation of 10 at a wavelength of 436 nm induced an intramolecular borylene transfer to the μ3-η2(||)-iminobenzoyl moiety and a cationic complex containing a μ3-η3-BCN ring, [{Cp*Ru(μ-H)}3{μ3-η3-B(H)N(H)C(Ph)−}]+ (10), was obtained. The crystal structure of 10 showed long B–N (1.634(6) Å) and B–C (1.719(6) Å) bonds in the μ3-η3-BCN skeleton, which are consistent with the small bond indices of 0.539 and 0.433, respectively, and suggest the unsupported nature of these bonds. Time-dependent density functional theory calculations of 2, 5a, and 9 suggested the importance of a μ-hydride at the Ru–Ru edge where the borylene ligand migrates upon irradiation.

Kinetics-assisted discrimination of active sites in Ru catalyzed hydrolytic dehydrogenation of ammonia borane

The kinetics-assisted method is simple yet effective in discriminating Ru edge atoms as the dominant active sites for the reaction.

Formation of N, N-Dimethylacrylamide by a Multicenter Hydrocarbamoylation of C2H2 with N, N-Dimethylformamide Activated by Ru5(μ5-C)(CO)15.

Hydrocarbamoylation of C2H2 by N, N-dimethylformamide (DMF) to N, N-dimethylacrylamide was effected by a series of cluster-opening reactions with Ru5(μ5-C)(CO)15 (1). The reaction of 1 with DMF yielded the new complexes Ru5(μ5-C)(CO)14(μ-η2-O═CNMe2)(μ-H) (2) and a minor coproduct Ru5(μ5-C)(CO)13(HNMe2)(μ-η2-O═CNMe2)(μ-H) (3) by a cluster-opening activation of the formyl C-H bond of DMF. Compound 3 was obtained from 2 by a further reaction with DMF. Compound 3 reacted with C2H2 (1 atm, 70 °C) to yield Ru5(μ5-C)(CO)13(μ-η3-O═CNMe2CHCH)(μ-H) (4) by the addition and coupling of C2H2 to the bridging dimethylformamido ligand. Compound 4 contains a σ-π-coordinated, dimethylformamido-substituted vinyl ligand that bridges a Ru-Ru edge of an open Ru5C cluster. The formamido group is also coordinated to one of the metal atoms. The addition of CO (1 atm, 25 °C) to 4 yielded the CO adduct Ru5(μ5-C)(CO)14(η2-O═CNMe2CH═CH)(μ-H) (5) containing a chelating dimethylacrylamido ligand, which released dimethylacrylamide by the reductive elimination of a C-H bond upon a further addition of CO (400 psi, 125 °C) with the re-formation of 1. All of the products were characterized by single-crystal X-ray diffraction analyses.

Experimental and computational studies on the reaction of silanes with the diphosphine-bridged triruthenium clusters Ru3(CO)10(μ-dppf), Ru3(CO)10(μ-dppm) and Ru3(CO)9{μ3-PPhCH2PPh(C6H4)}

Reactions of Ru3(CO)10(μ-dppf) (1) (dppf = 1,1′-bis(diphenylphosphino)ferrocene), Ru3(CO)10(μ-dppm) (2) (dppm = bis(diphenylphosphino)methane), and the orthometalated derivative Ru3(CO)9{μ3-PPhCH2PPh(C6H4)} (3) with silanes (Ph3SiH, Et3SiH, Ph2SiH2) are reported. Treatment of 1 with Ph3SiH and Ph2SiH2 at room temperature leads to facile Si–H bond activation to afford Ru3(CO)9(μ-dppf)(SiPh3)(μ-H) (4) (60% yield) and Ru3(CO)9(μ-dppf)(SiPh2H)(μ-H) (6) (53% yield), respectively. The reaction of 1 with Ph3SiH has been investigated by electronic structure calculations, and these data have facilitated the analysis of the potential energy surface leading to 4. Compound 1 does not react with Et3SiH at room temperature but reacts at 68 °C to give Ru3(CO)9(μ-dppf)(SiEt3)(μ-H) (5) in 45% yield. Reaction of 2 with Ph3SiH at room temperature yields two new products: Ru3(CO)9(μ-dppm)(SiPh3)(μ-H) (7) in 40% yield and Ru3(CO)6(μ3-O)(μ-dppm)(SiPh3)(μ-H)3 (8) in 15% yield. Interestingly, at room temperature compound 7 slowly reverts back to 2 in solution with decomposition and liberation of Ph3SiH. Complex 8 can also be prepared from the direct reaction between 7 and H2O. Similar reactions of 2 with Et3SiH and Ph2SiH2 give only intractable materials. The orthometalated compound 3 does not react with Ph3SiH, Et3SiH and Ph2SiH2 at room temperature but does react at 66 °C to give Ru3(μ-CO)(CO)7{μ3-PPhCH2PPh(C6H4)}(SiR2R1)(μ-H)](9, R = R′ = Ph, 71% yield; 10, R = R′ = Et, 60% yield; 11, R = Ph, R′ = H, 66% yield) by activation of the Si–H bond. Compounds 4 and 8–11 have been structurally characterized. In 4, both the dppf and the hydride bridge a common Ru–Ru vector, whereas NMR studies on 7 indicate that two ligands span different Ru–Ru edges. Compound 8 contains a face-capping oxo moiety, a terminally coordinated SiPh3 ligand, and three bridging hydride ligands, whereas 9–11 represent simple oxidative addition products. In all of the compounds examined, the triruthenium framework retains its integrity and the silyl groups occupy equatorial sites.

Magnetic structure and orbital state ofCa3Ru2O7investigated by resonant x-ray diffraction

Resonant x-ray diffraction at the ${\text{L}}_{2}$- and ${\text{L}}_{3}$-absorption edges of Ru has been used to investigate the magnetic structure of ${\text{Ca}}_{3}{\text{Ru}}_{2}{\text{O}}_{7}$, a material with a bilayer perovskite structure that undergoes a transition from a high-temperature metallic to a low-temperature insulating phase at 48 K. In the insulating phase, magnetic Bragg reflections characteristic of $A$-type antiferromagnetic order (that is, ferromagnetic ${\text{RuO}}_{2}$ bilayers coupled antiferromagnetically along the $c$-axis) were identified. The azimuthal-angle dependence of the diffracted intensity implies that the magnetic moments are aligned along the $b$-axis in the ${\text{RuO}}_{2}$ planes. In the metallic phase, the $A$-type magnetic order persists up to the N\'eel temperature of 56 K, but the sublattice magnetization decreases by a factor of $\ensuremath{\sim}1.7$ and rotates by $90\ifmmode^\circ\else\textdegree\fi{}$ within the planes. Resonant signals characteristic of uniform or staggered orbital order were not found within the experimental sensitivity, probably reflecting a weak orbital polarization in the insulating state.

Reactivity of [Ru2(CO)6(μ-PFu2)(μ -η1,η2-Fu)] (Fu = furyl) Towards Tri(2- furyl)phosphine

Reaction of (Ru2(CO)6(μ-PFu2)(μ- 1 , 2 -Fu)) (Fu = furyl) 1 with tri(2-furyl)phosphine under thermal conditions produces simple mono- and disubstitution products (Ru2(CO)5(PFu3)(μ-PFu2)(μ- 1 , 2 -Fu)) 2a and (Ru2(CO)4(PFu3)2(μ- PFu2)(μ- 1 , 2 -Fu)) 2b. Both complexes were fully characterized by spectroscopic and analytical methods and the molecu- lar structures of 2a and 2b were established by X-ray crystallography. The Ru Ru edge bridged by the μ- 1 , 2 -bound PFu2 fragment remains intact after the substitution reaction. The product yields of both complexes depend on the stoichiometry of the reactants. All of these new diruthenium complexes are electron precise with 34 cluster valence elec- trons. tion metals in low oxidation states (4). The pioneering work by Farina and co-workers showed the use of PFu3- derived palladium catalysts to be highly advantageous in the Stille cross-coupling reaction with significant rate ac- celerations being observed over traditional PPh3-based catalysts, presumably by virtue of its low electron-donating ability toward Pd(II) center (5). Since then, numerous re- searchers have sought to evaluate the performance of PFu3 in a wide variety of metal-catalyzed processes for the preparation of small molecules, complex natural products as well as polymers (3). In many cases, Stille coupling with the PFu3 ligand allows for milder reaction conditions and hence the attenuation of unwanted side reactions. How- ever, accurate prediction of whether this poor  -donating PFu3 ligand will lead to beneficial effects for a given proc- ess still remains elusive.

Facile E−E and E−C Bond Activation of PhEEPh (E = Te, Se, S) by Ruthenium Carbonyl Clusters: Formation of Di- and Triruthenium Complexes Bearing Bridging dppm and Phenylchalcogenide and Capping Chalcogenido Ligands

Reactions of [Ru3(CO)10(μ-dppm)] (1) and its ortho-metalated derivative [Ru3(CO)9{μ3-η3-P(C6H5)CH2P(C6H5)(C6H4)}] (11) with PhEEPh (E = Te, Se, S) have been investigated. Treatment of 1 with PhTeTePh at room temperature afforded the dinuclear compound [Ru2(CO)4(μ-TePh)2(μ-dppm)] (2) and the 54-electron triruthenium compounds [Ru3(CO)6(μ3-Te)2(μ-TePh)2(μ-dppm)] (3) and [Ru3(CO)6(μ3-Te)(μ-TePh)3(η1-COPh)(μ-dppm)] (4). Analogous reactions of 1 with PhEEPh (E = Se, S) led to [Ru2(CO)4(μ-EP[Ru3(CO)6(μ3-E)2(μ-EPh)2(μ-dppm)])2(μ-dppm)] (E = Se, 5; E = S, 8) and the 54-electron triruthenium compounds (E = Se, 6; E = S, 9), and [Ru3(CO)6(μ3-E)(μ-EPh)3(Ph)(μ-dppm)] (E = Se, 7; E = S, 10). Reactions of the ortho-metalated complex 11 with PhEEPh (E = Te, Se, S) in refluxing THF gave exclusively [Ru3(CO)6(μ-EPh)2{μ3-η3-P(C6H5)CH2P(C6H5)(C6H4)}] (E = Te, 12; E = Se, 13; E = S, 14). The new compounds have been characterized by a combination of analytical and spectroscopic methods, and molecular structures of 2−4, 7, 10, and 13 have been determined by single-crystal X-ray diffraction studies. Compounds 2, 5, and 8 have the classical “sawhorse” structure with two bridging EPh (E = Te, Se, S) moieties and one bridging dppm ligand. Compounds 3, 6, and 9 contain a Ru3 framework with two bridging EPh (E = Te, Se, S) groups, one bridging dppm ligand, and two capping chalcogenido ligands. Compound 4 contains an Ru3 core with a capping tellurido ligand, three bridging TePh moieties, one bridging dppm ligand, and a terminally coordinated benzoyl group, formed from multiple fragmentation of the PhTeTePh ligand and migratory insertion of a Ph group into a CO ligand. Compounds 7 and 10 comprise a capping chalcogenido ligand, three bridging EPh (E = Se, 7; E = S, 10) moieties, a bridging dppm ligand, and a terminally coordinated σ-bonded phenyl group. In compounds 12–14, the coordination of ortho-metalated diphosphine ligand is the same as in 11 and both the EPh moieties bridge the same unbridged Ru−Ru edge. Compounds 3, 6, 7, and 10 exhibit restricted fluxional behavior involving the μ-EPh moieties.

Chemistry of Unsaturated Group 6 Metal Complexes with Bridging Hydroxy and Methoxycarbyne Ligands. 3. Formation and Cleavage of C−C and C−O Bonds in the Reactions of the Complexes [Mo2Cp2(µ-COMe)(µ-COR)(µ-PCy2)]BF4(R = Me, Et)

The reactions of the 30-electron complexes [Mo2Cp2(µ-COMe)(µ-COR)(µ-PCy2)]BF4 (Cp = η5-C5H5; R = Me, Et) with CO, CNtBu, or tetraethylpyrophosphite (tedip) lead to the new 32-electron complexes [Mo2Cp2{µ-η2:η2-C(OMe)C(OR)}(µ-PCy2)(CO)2]BF4, [Mo2Cp2{µ-η2:η2-C(OMe)C(OMe)}(µ-PCy2)(CNtBu)2]BF4, and [Mo2Cp2{µ-η2:η2-C(OMe)C(OMe)}(µ-PCy2)(µ-tedip)]BF4, respectively. These products contain a bonded dialkoxyacetylene molecule resulting from the coupling of two alkoxycarbyne ligands, induced by the addition of the donor molecules to the unsaturated dimetal center of the starting material, and this coupling can be fully reversed in the dicarbonyl product upon photochemical treatment. The structure of the diisocyanide and tedip complexes, both displaying quite short intermetallic lengths (ca. 2.66 Å), was confirmed crystallographically. The structure of the dicarbonyl derivative, which in solution exhibits cis and trans isomers, was optimized using DFT methods, which also led to the prediction of short intermetallic distances (2.75 Å). Demethylation of the dicarbonyl complexes leads to the new carboxycarbyne derivatives [Mo2Cp2{µ-C(CO2R)}(µ-PCy2)(CO)2] (R = Me, Et) as a result of the unexpected 1,2-shift of the methoxyl group occurring in the ketenyl intermediate (not detected) presumably formed first. This proposal is supported by DFT calculations, these predicting a moderate activation barrier (ΔG⧧298 = 78 kJmol−1) for the spontaneous transformation (ΔG298 = −51 kJ mol−1) of the ketenyl intermediate into the carbyne complex finally isolated. The bis(methoxycarbyne) complex is also reactive toward the 16-electron fragment Ru(CO)4, to give the 46-electron cluster [Mo2RuCp2(µ-COMe)2(µ-PCy2)(CO)4]BF4, which concentrates most of its electronic unsaturation at the dimolybdenum center (Mo−Mo = 2.686(1) Å), in spite of the rearrangement of the carbyne ligands, both of them now bridging one of the Mo−Ru edges, according to an X-ray diffraction study.

Absence of local magnetic moments in Ru and Rh impurities and clusters on Ag(100) and Pt(997)

The magnetism of quench-condensed Ru and Rh impurities and metal films on Ag(100) and Pt(997) has been studied using x-ray magnetic circular dichroism. In the coverage range between 0.22 and 2.0 ML, no dichroic signal was detected at the ${M}_{3,2}$ absorption edges of Ru on Ag(100) at a temperature of $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in the presence of an applied magnetic field. The same was found for coverages between 0.12 and 0.5 ML of Rh on Ag(100) and Pt(997). It is concluded that the magnetic moments of single impurities, small clusters of various shape, and monolayers of the $4d$ metals are below the detection limit of $0.04\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{B}$ per atom. These results provide an unambiguous determination of the local magnetic moment of Ru and Rh deposited on nonmagnetic transition-metal surfaces, which are in contrast with theoretical predictions.

Nonacarbonyl(μ2-methanethiolato)(μ3-trimethylsilylacetylene)triruthenium

The structure of the title compound, [Ru3(μ2CH3S){μ3-C2Si(CH3)3}(CO)9], contains an open triangle of Ru atoms. The open edge is bridged on one side by a μ2-S(CH3) unit, and the other side of the triangle is capped by a [C≡CSi(CH3)3] group, with the acetyl­enic bond perpendicular to the open Ru⋯Ru edge.

Reactions of μ3‐Alkenyl Triruthenium Carbonyl Clusters with Alkynes: Synthesis of Trinuclear μ‐//‐Alkyne, μ‐Vinylidene, and μ‐Dienoyl Derivatives

The reactions of doubly face-capped triruthenium cluster complexes of the type [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-R(2)CCHR(1))(mu-CO)(2)(CO)(6)] (HNNMe(2) = 1,1-dimethylhydrazide; R(2)CCHR(1) = alkenyl ligand) with terminal and internal alkynes have been studied in refluxing toluene. The following derivatives have been isolated from these reactions: [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-R(2)CCHR(1))(mu-kappa(2)-//-HCCH)(CO)(7)] (R(1) = R(2) = H, 5; R(1) = Ph, R(2) = H, 6; R(1) = CH(2)OMe, R(2) = H, 7 a; R(1) = H, R(2) = CH(2)OMe, 7 b) from acetylene, [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-HCCH(2))(mu-kappa(2)-//-PhCCPh)(CO)(7)] (11) from diphenylacetylene, and three isomers of [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-HCCH(2))(mu-kappa(2)-//-PhCCH)(CO)(7)] (14, 15 a, and 15 b) from phenylacetylene. These products result from substitution of a CO ligand by the alkyne and contain an Ru--Ru edge bridged by the alkyne ligand in a parallel manner. DFT calculations on selected isomeric products have helped to establish that the type of Ru--Ru edge bridged by the alkyne depends more on kinetic factors related to the size of the alkyne substituents than on the thermodynamic stability of the final products. The preparation of triruthenium cluster complexes with mu-//-alkyne ligands is unprecedented and seems to relate to the fact that the starting trinuclear complexes have their two triangular faces protected by capping ligands. The clusters bearing mu-//-acetylene (5-7) are thermodynamically unstable with respect to their transformation into edge-bridging vinylidene derivatives, [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-HCCHR)(mu-kappa(1)-CCH(2))(CO)(7)] (R = H, 8; Ph, 9; CH(2)OMe, 10). DFT calculations have shown that complex 8 is 11.2 kcal mol(-1) more stable than its precursor 5. The thermolysis of compound 11 leads to [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu-kappa(4)-H(2)CCHCPhCPhCO)(mu-CO)(2)(CO)(5)] (12), which contains a novel edge-bridging dienoyl ligand that arises from an unusual coupling of diphenylacetylene, carbon monoxide, and the ethenyl ligand of complex 11. A chloro-bridged dimer of trinuclear clusters, [Ru(6)(mu-Cl)(2)(mu(3)-kappa(2)-HNNMe(2))(2)(mu(3)-kappa(2)-HCCH(2))(2)(mu-kappa(2)-PhCCHPh)(2)(mu-CO)(2)(CO)(10)] (13), has been prepared by treating compound 11 with hydrogen chloride. Therefore, edge-bridging parallel alkynes are susceptible to protonation to give edge-bridging alkenyl ligands. Compound 13 is the first complex to contain two alkenyl ligands on a trinuclear cluster, one face-capping and the other edge-bridging.

Synthesis, structure, and property of a triruthenium cluster having a μ-alkyl ligand: Transformation of a μ 3(⊥)-alkyne ligand into a μ-alkyl ligand via a μ 3-vinylidene complex

A triruthenium μ-alkyl complex, (Cp ∗Ru) 3(μ-η 2-HCHCH 2R)(μ-CO) 2(μ 3- CO) ( 2a, R = Ph; 2b, R = t Bu, Cp ∗ = η 5-C 5Me 5), which contains a two-electron and three-center interaction among Ru, C, and H atoms, has been synthesized by the reaction of a perpendicularly coordinated 1-alkyne complex, {Cp ∗Ru(μ-H)} 3(μ 3-η 2:η 2(⊥)-RCCH) ( 1a; R = Ph, 1b; R = t Bu), with carbon monoxide. A diffraction study for 2b clearly represented the bridging neohexyl group on one Ru–Ru edge. This μ-alkyl group exhibited dynamic behavior resulting in site-exchange of the α-hydrogen atoms between the terminal and bridging positions, which was synchronized with the migration of the μ-alkyl groups between the two ruthenium atoms. The agostic C–H bond was readily cleaved upon pyrolysis. Whereas the μ-phenethylidene intermediate resulting from the σ-C–H bond cleavage has never been observed, a μ 3-phenethylidyne complex, {Cp ∗Ru(μ-CO)} 3(μ 3-CCH 2Ph) ( 7a), and a μ 3-methylidyne complex, {Cp ∗Ru(μ-CO)} 3(μ 3-CH) ( 8), were obtained by the successive C–H/C–H and C–H/C–C bond cleavages at the μ-alkyl moiety, respectively.

Mechanisms of Concurrent Hydride Migration Processes in a Triruthenium Cluster Capped by a Phenylphosphinidene (PPh) Ligand

AbstractTwo methods were used to synthesise [Ru3(μ‐H)2(μ3‐PPh)(CO)7(μ‐dppm)] (3) (dppm = Ph2PCH2PPh2), the subject of this paper. Treatment of [Ru3(CO)10(μ‐dppm)] (1) with phenylphosphane in refluxing THF gave both [Ru3(μ‐H)(μ‐PHPh)(CO)8(μ‐dppm)] (2) and [Ru3(μ‐H)2(μ3‐PPh)(CO)7(μ‐dppm)] (3). Cluster 2 converts to 3 in refluxing THF. Alternatively the phenylphosphinidene cluster [Ru3(μ‐H)2(μ3‐PPh)(CO)9] (4), prepared by the reported method of treating [Ru3(CO)12] with phenylphosphane, reacts with dppm to produce cluster 3. The single‐crystal X‐ray structures of 2 and 3 are reported. Hydride mobility in [Ru3(μ‐H)2(μ3‐PPh)(CO)7(μ‐dppm)] (3) was analysed by variable‐temperature 1H and 31P{1H} NMR methods. The variations in the spectra with temperature could not be interpreted by a single process, several of which were explored and which gave inadequately matching computed and experimental spectra. However, the spectra were successfully analysed by two concurrent processes, both involving the migration of hydride ligands between Ru–Ru edges. The faster process leads to the exchange of the non‐equivalent phosphorus nuclei but not hydride exchange, whereas the hydrides are also exchanged in the slower process. Both processes require hydride ligand migration from one Ru–Ru edge to a vacant one. The hydride ligand bridging the same pair of ruthenium atoms as the dppm ligand is the slower to migrate. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Orbital Ordering Transition inCa2RuO4Observed with Resonant X-Ray Diffraction

Resonant x-ray diffraction performed at the L(II) and L(III) absorption edges of Ru has been used to investigate the magnetic and orbital ordering in Ca2RuO4 single crystals. A large resonant enhancement due to electric dipole 2p-->4d transitions is observed at the wave-vector characteristic of antiferromagnetic ordering. Besides the previously known antiferromagnetic phase transition at T(N)=110 K, an additional phase transition, between two paramagnetic phases, is observed around 260 K. Based on the polarization and azimuthal angle dependence of the diffraction signal, this transition can be attributed to orbital ordering of the Ru t(2g) electrons. The propagation vector of the orbital order is inconsistent with some theoretical predictions for the orbital state of Ca2RuO4.

Anode catalysts for enhanced methanol oxidation: An in situ XANES study of PtRu/C and PtMo/C catalysts

Pt/C, PtRu/C and PtMo/C electro catalysts were prepared in different compositions by incipient wetness impregnation method. These catalysts were characterized by X-ray diffraction (XRD) and X-ray absorption near-edge structure (XANES) to understand the miscibility into solid solution and to calculate the d-orbital vacancy, respectively. Pt with Ru and Mo forms a single alloy which was confirmed by XRD date. XANES was measured at Pt L II and L III edges and K edges of Ru and Mo to determine the oxidation states of these metals in different compositions. Further calculations of d-orbital vacancy of Pt revealed more information that increasing the Ru or Mo content increases d-orbital vacancy. As Mo oxidizes faster than Ru, magnitude of d-orbital vacancy is high in the case of Ru compared to Mo. In situ XENES study was also conducted in methanol fuel cell to understand the oxidation states and methanol oxidation mechanism.

A PEM fuel cell for in situ XAS studies

A miniature proton exchange membrane (PEM) fuel cell has been designed to enable in situ XAS investigations of the anode catalyst using fluorescence detection. The development of the cell is described, in particular the modifications required for elevated temperature operation and humidification of the feed gasses. The impact of the operating conditions is observed as an increase in the catalyst utilisation, which is evident in the EXAFS collected at the Pt L III and Ru K edges for a PtRu/C catalyst. The Pt component of the catalyst was found to be readily reduced by hydrogen in the fuel, while the Ru was only fully reduced under conditions of good gas flow and electrochemical contact. Under such conditions no evidence of O neighbours were found at the Ru edge. The results are interpreted in relation to the lack of surface sensitivity of the EXAFS method and indicate that the equilibrium coverage of O species on the Ru surface sites is too low to be observed using EXAFS.

Edge‐Bridging and Face‐Capping Coordination of Alkenyl Ligands in Triruthenium Carbonyl Cluster Complexes Derived from Hydrazines: Synthetic, Structural, Theoretical, and Kinetic Studies

The reactions of the triruthenium cluster complex [Ru3(mu-H)(mu3-eta2-HNNMe2)(CO)9] (1; H2NNMe2=1,1-dimethylhydrazine) with alkynes (PhC triple bond CPh, HC triple bond CH, MeO2CC triple bond CCO2Me, PhC triple bond CH, MeO2CC triple bond CH, HOMe2CC triple bond CH, 2-pyC triple bond CH) give trinuclear complexes containing edge-bridging and/or face-capping alkenyl ligands. Whereas the edge-bridged products are closed triangular species (three Ru-Ru bonds), the face-capped products are open derivatives (two Ru-Ru bonds). For terminal alkynes, products containing gem (RCCH2) and/or trans (RHCCH) alkenyl ligands have been identified in both edge-bridging and face-capping positions, except for the complex [Ru3(mu3-eta2-HNNMe2)(mu3-eta3-HCCH-2-py)(mu-CO)(CO)7], which has the two alkenyl H atoms in a cis arrangement. Under comparable reaction conditions (1:1 molar ratio, THF at reflux, time required for the consumption of complex 1), some reactions give a single product, but most give mixtures of isomers (not all the possible ones), which were separated. To determine the effect of the hydrazido ligand, the reactions of [Ru3(mu-H)(mu3-eta2-MeNNHMe)(CO)9] (2; HMeNNHMe=1,2-dimethylhydrazine) with PhC triple bond CPh, PhC triple bond CH, and HC triple bond CH were also studied. For edge-bridged alkenyl complexes, the Ru--Ru edge that is spanned by the alkenyl ligand depends on the position of the methyl groups on the hydrazido ligand. For face-capped alkenyl complexes, the relative orientation of the hydrazido and alkenyl ligands also depends on the position of the methyl groups on the hydrazido ligand. A kinetic analysis of the reaction of 1 with PhC[triple chemical bond]CPh revealed that the reaction follows an associative mechanism, which implies that incorporation of the alkyne in the cluster is rate-limiting and precedes the release of a CO ligand. X-ray diffraction, IR and NMR spectroscopy, and calculations of minimum-energy structures by DFT methods were used to characterize the products. A comparison of the absolute energies of isomeric compounds (obtained by DFT calculations) helped rationalize the experimental results.