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Platinum Metals Rev., 1997, 41, (2), 89

ABSTRACTS: April 1997

of current literature on the platinum metals and their alloys

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PROPERTIES

Properties of PdCu(11O) Single Crystal Alloy Surfaces: Temperature-Induced Processes in the Surface Microstructure

j. loboda-cackovic, Vacuum, 1996, 47, (12), 1405–1411

PdCu(110) alloy single crystal surfaces, with atomic concentration ratio Cu:Pd of 1:1 in the bulk, were prepared with a Cu:Pd ratio of 0.3–2 in the ∼ 4 layers deep, surface region. The PdCu(110) surface consists of small crystalline domains containing ∼10–20 lattice cells depending on preparation. Two temperature-induced surface processes change the surface microstructure: surface roughening and partial surface disordering, starting at ∼ 550 and ∼ 700 K, respectively.

Study of the Reactions I + IrCl62− and Fe(CN)64− + S2O22− in Micellar Solutions

r. jimÉnez, m. m. graciani, a. rodrÍguez, m. l. moyÁ, f. sÁnchez and p. lÓpez-cornejo, Langmuir, 1997, 13, (2), 187–191

The kinetics of the reactions I + IrCl62− and Fe(CN)64− + S2O82− were studied in anionic micelles of Na dode-cylsulfate at 298.2 K. The present work and the results in Na bis-2-ethylhexyl sulfosuccinate/decane/H2O microemulsions and aqueous Na nitrate were explained by using as a starting point the Brönsted equation.

CHEMICAL COMPOUNDS

Chloride Anion Recognition by Neutral Platinum(II) and Palladium(II) 5,5′-bisamide Substituted Bipyridyl Receptor Molecules

p. d. beer, n. c. fletcher, m. g. b. drew and t. j. wear, Polyhedron, 1997, 16, (5), 815–823

A series of new acyclic neutral Pt(II) and Pd(II) 5,5′-bisamide substituted 2,2′-bipyridyl receptors have been synthesised and the X-ray structures of two receptors determined. Proton NMR anion binding studies in deuterated dimethylsulfoxide solution reveal that these neutral receptors complex the halide anion via favourable amide CO-NH- - -CI H bonding interactions.

Self-Assembly of Tetraalkylammonium Salt-Stabilized Giant Palladium Ousters on Surfaces

m. t. reetz, m. winter and b. tesche, Chem. Commun ., 1997, (2), 147–148

Nanostructural Pd clusters, stabilised by a monomolecular coat of surfactants N(C8H17)4Br or N(C18H37)4Br, self-assembled on C surfaces in an ordered manner to form h.c.p. structures. These structures self-organised into two-dimensional films and three-dimensional superlattices, controlled by varying the length of the alkyl chains on the ammonium ions.

Synthesis and Structural Characterisation of [Pd2(μ-Br)2(PBut3)2], an Example of a Palladium(I)-Palladium(I) Dimer

r. vilar, d.m. p. mingos and c.j. cardin, J. Chem. Soc., Dalton Trans ., 1996, (23), 4313–1314

The synthesis, spectroscopic characterisation and, when X = Br, the single-crystal structure, of the novel PdI-PdI dimers [Pd2(μ-X)2(PBut3)2] (X = Br or I) are described. Preliminary results on their reactions with CO3 H2, CNC6H3Me2 and C2H2 are also reported. When dissolved in toluene, [Pd2(μ-X)2(PBut3)2] were good initiators for the polymerisation of acetylene; with X = I the dimer was catalytic.

Formation of Zerovalent Palladium from the Cationic Complex Pd(PPh3)2(BF4)2 in the Presence of PPh3 and Water in DMF

c. amatore, a. jutand and m. j. medeiros, New J. Chem ., 1996, 20, (11), 1143–1148

Stable Pd(0) complexes were spontaneously and slowly generated in situ from the cationic Pd(II) complex Pd(PPh3)2(BF4)2 in the presence of triphenylphosphine (PPh3) and H2O. The generated (PPh3) oxide shows that (PPh3) can reduce the Pd(II) to Pd(0), probably via a Pd(II) hydroxy-containing intermediate.

Large Second-Order Nonlinear Optical Properties of Novel Organometallic (σ-Arylenynyl)Ruthenium Complexes

s. houbrechts, k. clays, a. persoons, v. cadierno, m. p. gamasa and j. gimeno, Organometallics, 1996, 15, (25), 5266–5268

A series of novel Ru σ-acceptor aryl-enynyl complexes, including homo- and heterobimetallic complexes, have been synthesised and their nonlinear properties evaluated. The effects upon the hyperpolarisability of chain length, configuration of the metal donor group, and nature of the metal acceptor group are reported. These complexes are found to possess the largest quadratic hyperpolansabilities, reported to date, for bimetallic compounds.

A Novel Route to Butatrienylidene Complexes: Stabilisation of:C=C=C=CH2 on Ru5 Clusters

c. j. adams, m. i. bruce, b. w. skelton and a. h. white, Chem. Commun ., 1996, (23), 2663–2664

The addition of C2(SiMe3)2 to [Ru55-C2)(μ-PPh2)2(μ-SMe)2(CO)11] gave [Ru54-CCCCH(SiMe3)}(μ-PPh2)2(μ-SMe)(μ3-SMe)(CO)10](1) as a mixture of geometrical isomers in 94% yield. Alkaline hydrolysis of (1) resulted in the first stable butatrienylidene complex [Ru54-CCCCH2)(μ-PPh2)2(μ-SMe)(μ3-SMe)(CO)10] (2) in 84% yield. The spiked-rhom-boidal pentanuclear complex [Ru5(μ5-CCCCH2)(μ-PPh2)2(μ-SMe)2(CO)11] was isolated in 62% yield from the carbonylation of (2).

Synthetic, Structural, Electrochemical and Electronic Characterisation of Heterobimetallic bis(acetylide) Ferrocene Complexes

m. c. b. colbert, j. lewis, n. j. long, p. r. raithby, a. j. p. white and d. j. williams, J. Chem. Soc., Dalton Trans ., 1997, (1), 99–104

A series of novel heterobimetallic bis(acetylide) ferrocene complexes of the form [(C5H5)Fe11(C5H4)C≡ CRu11(dppm)2(C≡CR)] (dppm = 1,2-bis(diphenyl-phosphino)methane) are reported. Incorporation of donor-substituted aromatic acetylide ligands causes a cathodic shift in the RuII/III redox potential, while electron-withdrawing substituents lead to an anodic shift. The structure of trans -[Ru(dppm)2 {C≡C(C5H4)-Fe(C5H5)}2] shows the Ru centre linearly bound to 2 ferrocene units by rigid rod-like acetylene linkages.

Thermal Decomposition of the bis(dihydrogen) Complex RuH2(H2)2(PCy3)2 in the Solid State

b. chaudret, p. dagnac, d. labroue and s. saboetienne, New J. Chem ., 1996, 20, (11), 1137–1141

Temperature programmed decomposition studies of RuH2(H2)2(PCy3)2 (1) were performed under a flow of He. Study of the H2 evolution revealed a two-step process. In the first step, (1) was reversibly transformed into a mixture of RuH3[(η3-C6H8)PCy2](PCy3) and RuH(η3-C6H8)PCy2][(η2-C6H9)PCy2]. In the second step, C6H6 was lost and the Ru complexes transformed into unidentified species. Under H2, C6H6 was converted into cyclohexane, thus demonstrating the catalytic properties of the Ru complexes.

Temperature Independent Ru → Os Electronic Energy Transfer in a Rodlike Dinuclear Complex with a 2.4 urn Intermetal Separation

l. hammarstrÖm, f. barigelletti, l. flamigni, n. armaroli, a. sour, j.-p. collin and j.-p. sauvage, J. Am. Chem. Soc ., 1996, 118, (47), 11972–11973

Energy transfer is studied in a rodlike dinuclear complex, (ttp)Ru(tpy-ph-bco-ph-tpy)Os(tpp)4+ (tpy = 2,2′:6′,2″-terpyridine, tpp = 4′-p -tolyl-tpy, ph = 1,4-phenylene and beo = bicyclo[2.2.2]octane), which has a rigid, linear geometry. The Ru → Os energy transfer rate was found to be 5.2 × 106 s1 (± 20%) at 90–200 K. Energy transfer is therefore unaffected by the temperature changes and state of the solvent.

ELECTROCHEMISTRY

Kinetic Study of the Hydrogen Oxidation Reaction on Platinum and Nailon® Covered Platinum Electrodes

r. m. q. mello and e. a. ticianeli, Electrochim. Acta, 1997, 42, (6), 1031–1039

Hydrogen oxidation at Pt and Pt/polymer electrolyte interfaces in contact with solutions of H2SO4 and K2SO4 at pH 0.2–7.5 was studied using cyclic voltammetry, rotating disk electrode and potential step chronoamperometry. The solubility and the diffusion coefficient of H2 gas in the solutions and the permeability in the polymer electrolyte were determined.

Electrocrystallization of a Halogen-Bridged Mixed-Valence Platinum Complex

h. awano, t. kumazawa and k. kasuya, Electrochim. Acta, 1997, 42, (3), 483–488

Electrocrystallisation of [Pt(en)2] [PtCl2(en)2](CIO4)4 (1), a halogen-bridged mixed-valence Pt complex with PtII…X-PtIV-X… chains, is reported. Electrochemical reduction of trans - [PtCl2(en)2]Cl2 in a solution of perchloric acid at –1.5 to –1.6 V vs. a Pt counter electrode gave red needle crystals of (1) several mm long, on a Sn-doped In oxide substrate. No crystals formed during electrochemical oxidation of a PtII complex.

On the Nature of the Interaction of H2PdCl4with the Surface of Graphite-Like Carbon Materials

p. a. simonov, a. v. romanenko, i. p. prosvirin, e. m. moroz, a. i. boronin, a. l. chuvilin and v. a. likholobov, Carbon, 1997, 35, (1), 73–82

The adsorption of H2PdCl4 from aqueous solutions onto the surface of graphite-like C materials proceeded through two competitive pathways: (1) reduction, giving rise to Pd0 particles of 6–100 nm in size localised near the exterior surface of the porous C particles and (2) formation of π-complexes of PdCl2 with >C=C< fragments of the C matrix, which takes place on the whole surface of the particles. The ratio, dispersion and morphology of the adsorbed Pd2− and Pd0 species are found to be dependent upon many factors.

Effect of a Graphite Pad on the Adsorption and the Electrocatalytic Activity of Microdeposits of Rhodium

e. horozova, z. jordanova and m. velkov, Electrochim. Acta, 1997, 42, (3), 369–376

The effect of a graphite pad on the adsorption and electrocatalytic activity of Rh microdeposits electro-chemically dispersed on graphite was studied with regard to H2 and electrocatalysis towards camodic H2evolution. The type of graphite affects adsorptivity and the energy spectrum of H2 adsorption, and has some effect on the specific currents and kinetic parameters of the cathodic liberation of H2. Electron microscopic studies of rhodanised graphite electrodes showed that the role of the graphite pad is in the formation of Rh deposits of different structure.

Supramolecular Electrode Materials Derived from Pyrrole-Substituted Ruthenium(II) Bipyridyl Calix [4] arenes

h. c.-y. bettega, m. hissler, j.-c. moutet and r. ziessel, Chem. Mater ., 1997, 9, (1), 3–5

Electropolymerisation of calixarenes bearing pendant Ru complexes, to produce poly(calixarene-[Ru(bpy)3]2+) (bpy = 2,2′-bipyridine)(1) modified electrodes is reported. Pyrrole-substituted (1) were prepared by heating the bipyridyl mono- and disubstituted calixarenes with Ru(L)2Cl2 (L = 4-(pyrrol-l-yl)-4′-methyl-2,2′-bipyridine) at 60°C in EtOH, followed by precipitation as hexafluorophosphate salts. Electrodes were coated by oxidative homo- and copolymerisation, with N -methylpyrrole, of the monomer complexes.

PHOTOCONVERSION

Photocatalytic Transfer Hydrogenation of Schiff Bases with Propan-2-ol by Suspended Semiconductor Particles Loaded with Platinum Deposits

b. ohtani, y. goto, s.-i. nishimoto and t. inui, J. Chem. Soc., Faraday Trans ., 1996, 92, (21), 4291–4295

Photoirradiation at >300 nm of a propan-2-ol solution of Schiff bases (N -benzylidenebenzylamine and N -benzylideneaniline) containing platinised TiO2(TiO2-Pt), or CdS loaded with PtO2, gave the corresponding secondary amines (dibenzylamine and N- benzylaniline, respectively) via catalytic transfer hydrogenation. The most efficient catalyst has small Pt deposits dispersed uniformly on each TiO2 particle.

Photocatalytic Hydrogen Production by Dye-Sensitized Pt/SnO2 and Pt/SnO2/RuO2 in Aqueous Methyl Viologen Solution

k. gurunathan, p. maruthamuthu and m. v. c. sastri, Int. J. Hydrogen Energy, 1997, 22, (1), 57–62

H2 photoproduction by a wide band gap SnO2 semiconductor in powder form loaded with Pt and RuO2, and sensitised by Ru(bpy)32+ and organic dyes or with low band gap CdS semiconductor, was studied. Acriflavin, Eosin Blue, Rhodamine B, Rose Bengal and Fluorescein were used as photosensitisers in the presence of methyl viologen (MV2+), with or without EDTA as a sacrificial agent. The maximum rate of H2 production was observed at [Ru(bpy)32+] = 3.75 × 10 −5 mol dm−3 and [MV2+] = 2.5 × 10−5 mol dm−3.

Femtosecond Dynamics of Excited-State Evolution in [Ru(bpy)3]2+

n. h. damrauer, g. ceruixo, a. yeh, t. r. boussie, c. v. shank and j. k. mccusker, Science, 1997, 275, (5296), 54–57

The earliest events associated with excited-state relaxation in tris(2,2′-bipyridine)Ru(II) were monitored by time-resolved absorption spectroscopy on the femtosecond time scale. The data revealed dynamics associated with the temporal evolution of the Franck-Condon state to the lowest energy excited state of this molecule, which was completed in ∼ 300 femtoseconds after the initial excitation.

Hydrogen Generation Using Water-Insoluble Polymer-Bound Ruthenium(II) Complexes

m. suzuki, s. kobayashi, m. kimura, k hanabusa and h. shirai, Chem. Commun ., 1997, (2), 227–228

Water-insoluble free-standing films of partially quaternised poly(l-vinylimidazole)-bound Ru(II) complexes were prepared and used as polymer-solid photosensitisers for H2 generation. When an aqueous solution containing the polymer-bound Ru(II) complex film, methyl viologen (MV2+), triethanolamine and bis (2,2′-bipyridine)Pt(II) was irradiated with light (λ > 440 nm) H2 was generated. Electron transfer from the photoexcited Ru(II) complex to the MV2+ species on the polymer surface forms MV·+ species which diffuse into the bulk solution and react with Pt giving H2.

Excited State Properties of bis-Tetraaza-phenanthrene-Ru(II) Diad Complexes with a Ferrocenyl Unit

s. choua, a. kirsch-de mesmaeker, l. jacquet, c. marzin and n. chabert, J. Photochem. Photobiol., A: Chem ., 1996, 99, (2–3), 127–136

The excited state properties of the diad complexes Ru(tap)2(ppFc)2+ and Ru(bpy)2(ppFc)2+ (tap = 1,4,5,8-tetraazaphenanthrene and bpy = 2,2′-bipyridine), bearing a reducing ferrocenyl (Fc) centre on a derivatised (pyridine)pyrazole (pp) ligand, were compared with those of the corresponding complexes lacking a Fc unit. Intermolecular photoelectron transfer with ferrocene was favoured when bpy was replaced by tap. The different excited state behaviour in the absence of reducing agent was explained on the basis of photophysical data available for other tap complexes.

ELECTRODEPOSITION AND SURFACE COATINGS

Epitaxial Growth of Thin Films of SrTil-xRuxO3-δ by Pulsed Laser Deposition

a. gupta, b. w. hussey and t. m. shaw, Mater. Res. Bull ., 1996, 31, (12), 1463–1470

Pulsed laser deposition is used to epitaxially grow SrTi1-xRuxO3-δ (0 ≤ × ≤ 1) thin films on (100)-orientated SrTiO3 substrates. The films are grown in a low pressure O2 ambient with in situ characterisation of the surface using RHEED. The solid solution films are potentially useful as latticed-matched buffer layers for heteroepitaxial growth, or as barrier layers in tunnel junctions with controlled resistive properties.

APPARATUS AND TECHNIQUE

Amperometric Determination of Nitrite via Reaction with Iodide Using Microelectrodes

m. bertotti and d. pletcher, Anal. Chim. Acta, 1997, 337, (1), 49–55

The measurement of steady state currents at Pt microdisk electrodes (radii 2.5–10 μm), generated from the quantitative conversion of iodide to triiodide by nitrite in 0.1 M H2SO4, is the basis of a method for the determination of nitrite in H2O. This rapid and simple procedure can be used to reliably determine levels ≥ 0.1 μM in natural H2O and human saliva.

Glucose Detection at Bare and Sputtered Platinum Electrodes Coated with Polypyrrole and Glucose Oxidase

p. j. h. j. van os, a. bult, c. g. j. koopal and w. p. vanbennekom, Anal. Chim. Acta, 1996, 335, (3), 209–216

Glucose sensors have been fabricated by the galvanostatic polymerisation of 0.3 M pyrrole in 4-(2-hydroxyethyl)-l-piperazine-ethane sulfonic acid buffer (pH 7.0) with 200 U ml−1 glucose oxidase using a current of 1 μA at bare and sputtered Pt electrodes. Addition of flavine adenine dinucleotide did not increase the glucose response. The selectivity for other sugars (lactose, galactose and fructose) was good.

Development of a Novel Manganese OxideClay Humidity Sensor

k. miyazaki, m. hieda and t. kato, Ind. Eng. Chem. Res ., 1997, 36, (1), 88–91

Clay materials, such as kaolinite (1), muscovite (2), etc., were used as components in a potential-type humidity sensor, Pt/EMD/M, where EMD is electrolytic MnO2, and M is Cu or Al. With (1) and (2), the humidity-sensing characteristics of EMD were enhanced, giving good linearity and fast response. A mechanism for this enhancement was proposed, based on the role of inter-layer H2O molecules in the EMD-additive system.

Fluorescence-Based Thin Plastic Film Ion-Pair Sensors for Oxygen

a. mills and m. thomas, Analyst, 1997, 122, (1), 63–68

Thin-film sensors for O2, which incorporate the dye ion-pair, tris(4,7-diphenyl-1,10-phenanthroline) Ru(II) ditetraphenylborate in a variety of thin film polymer/plasticiser matrices, have been prepared. When poly(methyl methacrylate) was used as the polymer and tri-n -butyl phosphate as the plasticiser, the sensitivity of the film towards O2 increased markedly with increasing level of the plasticiser, but was largely independent of temperature and age. An O2 sensor exposed to alternating O2 and N2 showed a 0–90% response and recovery times of 0.4 and 4.4 s, respectively.

HETEROGENEOUS CATALYSIS

Transient and Resonant Behavior for NO Reduction by CO over a Pt/Al2O3 Catalyst during Forced Composition Cycling

r. r. sadhankar and d. t. lynch, Can. J. Chem. Eng ., 1996, 74, (5), 674–682

The reduction of NO by CO over a Pt/Al2O3 catalyst was studied in an isothermal recycle reactor at 485 K. Maximum time-average CO and NO conversions of 66 and 78%, respectively, were achieved from out-of-phase feed concentration cycling at a frequency of 5.5 mHz, compared with the steady-state conversions of 2 and 3.8%, respectively. The difference in the CO and NO conversions was due to the formation of N2O. Higher NO conversions were obtained by decreasing the NO phase lead to below 180°.

Catalytic Testing of TiO2/Platinum/Silicalite-l Composites

n. van der puil, e. j. creyghton, e. c. rodenburg, t. s. sie, h. van bekkum and j. c. jansen, J. Chem. Soc., Faraday Trans ., 1996, 92, (22), 4609–4615

The synthesis, characterisation and testing of composite TiO2-supported Pt catalyst particles, covered with a 0.8–1.3 μm thick silicalite-1 layer, are described. The composite shows mass transport selectivity giving high ratios of the initial conversion rates (35 at 100°C) in the competitive hydrogenation of a linear and a dibranched alkene. Steric constraints observed at the catalytic sites lead to regioselectivity in the hydrogenation of long-chain alkenes. A linear alkene with a terminal double bond is converted preferentially over an isomer with an internal double bond.

Hydrodesulfurization over PdMo/HY Zeolite Catalysts

b. pawelec, r. navarro, j. l. g. fierro, j. f. cambra, f. zugazaga, m. b. gÜemez and p. l. arias, Fuel, 1997, 76, (1), 61–71

A series of binary PdMo/HY zeolite catalysts has been prepared by a two-step impregnation procedure and tested in the hydrodesulfurisation (HDS) of dibenzothiophene and diesel oil (1.1 wt.% S). Pd/HY was more active than PdMo/HY, suggesting an inhibitory effect of Mo on activity, due to the formation of HxMoS2 and S[PdH+] hydride-type sulfides in the PdMo zeolites. The initial S conversion in HDS of gas oil over Pd/HY was similar to that on a CoMo/Al2O3 catalyst, but both Pd/HY catalyst and the blank HY zeolite deactivated rapidly at short times on-stream.

The Semihydrogenation of Acetylenes over Pd Catalyst on BER in the Presence of CsI

n. m. yoon, k. b. park, h. j. lee and j. choi, Tetrahedron Lett ., 1996, 37, (47), 8527–8528

Pd(OAc)2 on borohydride exchange resin (BER) in 95% ethanol, in the presence of CsI, was found to be a highly selective catalyst for the semihydrogenation of acetylenes. Terminal acetylenes were converted to the corresponding terminal olefins and internal acetylenes to the corresponding cis -olefins in virtually quantitative yield at room temperature.

Polymer-Supported Palladium and Rhodium Species as Hydrogenation Catalysts

p. c. selvaraj and v. mahadevan, J. Polymer Sci., A: Polymer Chem ., 1997, 35, (1), 105–122

New copolymers containing amino and heterocyclic ligands were prepared and used to anchor Pd(OAc)2 and RhCl3.xH2O to give highly active catalysts for the hydrogenation of alkenes, dienes, alkynes and nitrobenzene under very mild conditions. Relative reactivities and the effects of substrate structure, solvents, catalyst loading, anchoring ligands, metal species and particle size on the hydrogenation rates were determined. Recycling efficiencies of the catalysts were very good.

Fullerene-Based Ruthenium Catalysts: A Novel Approach for Anchoring Metal to Carbonaceous Supports. I. Structure. II. Hydrogénation Activity

t. braun, m. wohlers, t. belz, g. nowitzke, g. wortmann, y. uchida, n. pfÄnder and r. schlÖgl, Catal. Lett ., 1997, 43, (3, 4), 167–173; 175–180

The effect of fullerenes and related carbonaceous support materials on the structural and catalytic properties of Ru was studied. Catalysts based on C60, raw fullerene black, extracted fullerene black, cathode deposit and graphite were prepared by a combined impregnation/activation reaction based on the thermally induced decomposition of Ru3(CO)12. The catalysts were studied using low-temperature CO hydrogenation and liquid-phase hydrogenation of 2-cyclohexenone. The role of non-six-membered C rings in the support materials on the stability and catalytic performance of the Ru particles is discussed.

Ruthenium Porphyrin Encapsulated in Modified Mesoporous Molecular Sieve MCM-41 for Alkene Oxidation

c.-j. liu, s.-g. li, w.-q. pang and c.-m. che, Chem. Commun ., 1997, (1), 65–66

[RuL(CO)(EtOH)] (where H2L is meso -tetrakis(4-chlorophenyl)porphyrin) encapsulated in MCM-41, modified with 3-aminopropyltriethoxysilane, is reported as a stable catalyst for the oxidation of alkenes by tert -butyl hydroperoxide. When 0.1 wt.% Ru/MCM-41 catalyst was used, significantly higher turnovers and longer catalyst lifetimes were achieved for a range of alkenes, than with free [RuL(CO)(EtOH)].

The Nature of Ruthenium Sulfide Clusters Encaged in a Y Zeolite

b. moraweck, g. bergeret, m. cattenot, v. kougionas, c. geantet, j.-l. portefaix, j. l. zotin and m. breysse, J. Catal ., 1997, 165, (1), 45–56

Catalysts of RuS2 supported in a dealuminated KY zeolite were prepared by ion exchange and subsequent sulfidation by H2S/H2. They were characterised by HREM, EDX, TPR and EXAFS. The activity for the hydrogenation of tetralin, carried out in the presence of excess H2S (1.85%), was very high and roughly 300 times that (expressed per metal atom) of an industrial NiMo/Al2O3 hydrotreating catalyst. The active phase was found to consist of clusters of < 50 Ru atoms of a RuS2-like phase with very small domains of Ru metal.

HOMOGENEOUS CATALYSIS

Hydration of Alkynes by a PtCl4-CO Catalyst

w. baldossi, m. lahav and j. blum, J. Org. Chem ., 1997, 62, (3), 669–672

The treatment of PtCl4 with CO at 40–110°C forms a HPtCl(CO)2 complex, which acts as a highly efficient and selective catalyst for the hydration of aliphatic and aromatic acetylenes. The catalyst operates both under homogeneous conditions in wet THF and under phase-transfer conditions in (CHCl2)2/H2O in the presence of tricaprylmethylammonium chloride (Aliquat 336). This system is more environmentally friendly than the conventionally used Hg-based process and more efficient than other transition metal-catalysed processes.

Chirality Transfer via the Palladium-Catalyzed Cross-Coupling Reaction of Optically Active 2-Cyclohexenylsilane: Stereochemical and Mechanistic Aspects

t. hiyama, h. matsuhashi, a. fujita, m. tanaka, k. hirabayashi, m. shimizu and a. mori, Organometallics, 1996, 15, (26), 5762–5765

The cross-coupling of the optically active silane (S)-(2-cyclohexenyl)difluorophenylsilane (1) with aryl halide or triflate, catalysed by Pd(PPh3)4, in the presence of fluoride ion proceeds stereospecifjcally, strongly depending upon the nature of the reactants. The reaction of (1) with 4-iodoacetophenone and tetrabuty-lammonium fluoride gave the product with retention of configuration, but the reaction with the corresponding triflate using CsF gave the inversion product.

Palladium-Catalyzed Additions of Terminal Alkynes to Acceptor Alkynes

b. m. trost, m. t. sorum, c. chan, a. e. harms and g. rÜhter, J. Am. Chem. Soc ., 1997, 119, (4), 698–708

The addition of the C-H bond of terminal alkynes to either terminal alkynes (self-coupling) or activated internal alkynes (cross-coupling) to produce conjugated enynes, in the presence of a catalytic amount of Pd acetate and the electron-rich sterically encumbered lig-and, tris(2,6-dimethoxyphenyl)phosphine, is reported. This system gives excellent yields of both 1:1 homo-and cross-coupled products. The extraordinary chemo-selectivity suggests that any functionality will be compatible with this reaction. The chemoselectivity and excellent regio- and diastereoselectivity make this a very valuable reaction in organic synthesis.

A New Approach to the Solid-Phase Suzuki Coupling Reaction

s. r. piettre and s. baltzer, Tetrahedron Lett ., 1997, 38, (7), 1197–1200

The reaction of polymer-bound aryl halides with a pinacol ester of diboron under a catalytic Pd(0) system gave the corresponding polymer-bound boronates. The Suzuki coupling reaction was then carried out with a variety of aryl halides under the most efficient system, Pd(PPh3)4/K3PO4/DMF, at 80°C Cleavage from the support with trifluoroacetic acid gave the expected products in unusually good yields and with high purity (> 98%).

RhCl(PPh3)3 and RhH(PPh3)4 Catalyzed Hydrogenation of Acrylonitrile-Butadiene Copolymers

j. s. parent, n. t. mcmanus and g. l. rempel, Ind. Eng. Chem. Res ., 1996, 35, (12), 4417–4423

Both RhCl(PPh3)3 (1) and RhH(PPh3)4 (2) are efficient catalytic systems for the selective hydrogenation of acrylonitrile-butadiene copolymers under severe reaction conditions. Detailed kinetic and selectivity data and the effect of varying process conditions upon the rate of hydrogenation are reported. Dilute solution viscosity data are used to show the uniform selectivity of (1) and (2) catalysed hydrogenations. A probable reaction mechanism for the RhCl(PPh3)3 system was derived using analysis of variance model discrimination procedures.

Isomerization of Hexene Using Dihydridorhodium Complex in Dimethyl Sulfoxide

n. kameda and r. sango, Nippon Kagaku Kaishi, 1996, (12), 1014–1018

The isomerisation of 1-hexene with a dihydrido(1,3-diphenyltriazenido)bis(triphenylphosphine)Rh(III) (dihydridoRh complex)-dimethyl sulfoxide system was studied under 1 atm pressure of H2 or N2 at 30°C. Under H2, the isomerisation and hydrogenation of 1-hexene decreased in the order: trans -2-hexene > cis-2- hexene > hexane, whereas under N2, isomerisation was slower and the reaction products were initially found to be in the order: cis -2-hexene > trans -2-hexene.

Phosphoramidites: Novel Modifying Ligands in Rhodium Catalysed Hydroformylation

a. van rooy, d. burgers, p. c. j. kamer and p. w. n. m. vanleeuwen, Recl. Trav. Chim. Pays-Bas, 1996, 115, (11/12), 492–498

Several monodentate and bidentate phosphoramidites were prepared and tested as ligands in the hydroformylation of oct-l-ene and styrene using Rh(CO)2Acac as catalyst precursor. The monodentate ligands are probably too bulky to give satisfactory results. The diphosphoramidite ligands, especially those that co-ordinate bis-equatorially in the trigonal bipyramidal Rh complexes, give hydroformylation catalysts with good rates and selectivities. With modification, chiral phosphoramidites can be readily obtained, which may be suitable for enantioselective catalysis.

Hydroformylation of 2,4,4-Trimethyl-l-pentene Catalyzed by the High Nuclearity Carbonyl Cluster [Rh12(CO)30]2−

r. della pergola, l. garlaschelli, s. martinengo and a. repossi, J. Mol. Catal. A: Chem ., 1997, 115, (2), 265–271

The hydroformylation of 2,4,4-trimethyl-l-pentene in tetrahydrofuran was catalysed by the precursor Na2[Rh12(CO)30], which readily fragmented to give derivatives of lower nuclearity, under high pressures of CO/H2 (20–120 atm) at 300–400 K. The reaction is highly chemioselective, approaching 100% selectivity to 3,5,5-trimethylhexanal. Typical turnover numbers are 100–1000 mol olefin/mol cluster. The order of the reaction with CO was positive.

A Novel Water-Soluble Rhodium-Poly(enolate-co -vinyl alcohol-co -vinyl acetate) Catalyst for the Hydroformylation of Olefins

j. chen and h. alper, J. Am. Chem. Soc ., 1997, 119, (5), 893–895

The water-soluble polymer, poly(enolate-co -vinyl alcohol-co -vinyl acetate) (PEVV) is reported as a valuable ligand for the Rh biphasic catalytic hydroformylation of olefins, especially aliphatic olefins. The average turnover frequency for the catalytic hydroformylation of 1-octene was 5.46 × 10−5 kmol (kg(Rh)s)−1 at 90°C and of 1-dodecene was 2.36 × 10−4 kmol (kg(Rh)s)−1 at 60°C. Selective hydroformylation of styrene and its derivatives gave up to 97% of branched-chain aldehyde using Rh-PEW under biphasic reaction conditions but at low conversions.

Catalytic Dehydrogenation of Cycloalkanes to Arenes by a Dihydrido Iridium P-C-P Pincer Complex

m. gupta, c. hagen, w. c. kaska, r. e. cramer and c. m. jensen, J. Am. Chem. Soc ., 1997, 119, (4), 840–841

The Ir P-C-P pincer complex IrH2{C6H3-2,6-(CH2-PBut2)2} is reported as a highly active, completely catalytic homogeneous system for the transfer dehydrogenation of cycloalkanes to arenes. The unique reactivity is due to the P-C-P ligand, which renders the metal centre reactive with saturated hydrocarbons, but restricts its access to the ligand P-C bonds.

Ruthenium-Catalyzed Dimerization of Terminal Alkynes Initiated by a Neutral Vinylidene Complex

c. slugovc, k. mereiter, e. zobetz, r. schmid and k. kirchner, Organometallics, 1996, 15, (25), 5275–5277

The complexes RuTp(PPh3)2Cl, RuTp(PPh3)(py)Cl and RuTp(PPh3)2H (Tp = trispyrazolylborate, py = pyridine) catalyse the dimerisation of HC=CR (R = Ph, SiMe3, n -Bu and t -Bu) to give 1,4− and 2,4-di-substituted butenynes. The conversion depends upon the choice of solvent, and both the conversion and selectivity depend strongly upon the nature of the alkyne substituent.

FUEL CELLS

CO-Stabilized Supported Pt Catalysts for Fuel Cells: Radiolytic Synthesis

b. le gratiet, h. remita, g. picq and m. o. delcourt, J. Catal ., 1996, 164, (1), 36–43

K2PtCl4 was radiolytically reduced in a CO-saturated H2O/2-propanol mixed solvent, either into molecular carbonyl clusters of the [Pt3(CO)6]n 2− series or into colloidal metal particles by changing the CO:Pt ratio. The colloidal Pt and also the molecular clusters can be easily impregnated on C black, giving catalysts which are efficient for MeOH or H2 electrooxidation and O2 electroreduction. These particles, 2–3 nm in size, are independent of the catalyst loading and support surface area, even for high loadings.

Analysis of the Electrochemical Characteristics of a Direct Methanol Fuel Cell Based on a Pt-Ru/C Anode Catalyst

a. s. aricÒ, p. cretÌ, h. kim, r. mantegna, n. giordano and v. antonucci, J. Electrochem. Soc ., 1996, 143, (12), 3950–3959

A vapour-feed DMFC based on a Nafion 117® solid polymer electrolyte was studied using Pt-Ru/C (1) and Pt/C (2) catalysts for MeOH oxidation and O2 reduction, respectively. Crystalline f.c.c. phases were found in the Pt and Pt-Ru catalysts, but the alloy composition in the latter differed from the nominal composition. An increase in the average particle size and particle agglomeration was observed in (1) compared to (2). The electrochemical performance of a DMFC was thus enhanced and output power density of ∼ 150 mWcm−2 was achieved with low Pt loadings.

Electrooxidation of CO and CO/H2 Mixtures on a Pt-Sn Catalyst Prepared by an Implantation Method

n. m. markoviĆ, a. widelÔv, p. n. ross, o. r. monteiro and i. g. brown, Catal. Lett ., 1997, 43, (3,4), 161–166

A novel ion implantation technique is used to create a non-equilibrium Pt-Sn(IMP) (IMP is implanted) near surface alloy with ∼ 8.6 at.% Sn. The kinetics of the electrooxidation of CO and 2% CO/H2 mixtures on Pt-Sn(IMP) are nearly identical to those of Pt3Sn(110). This method may lead to a new Pt-Sn alloy fuel cell catalyst with a unique surface composition of Sn.

Five Percent Platinum-Tungsten Oxide-Based Electrocatalysts for Phosphoric Acid Fuel Cell Cathodes

o. savadogo and p. beck, J. Electrochem. Soc ., 1996, 143, (12), 3842–3846

A Pt-W oxide-based electrocatalyst was produced by an inexpensive chemical route for use as an O2 cathode in 99% H3PO4 at 180°C. The electrocatalytic properties for the O2 reduction reaction (ORR), such as exchange current density and mass activity, of a 5% Pt-40% WO3-based electrode (1) were twice as high as those of 10% Pt, due to an increase in its electrochemically active surface. The performance of (1) for ORR was compared to that for a 2% Pt-1% H2WO4-based electrode, and found to be lower.

CORROSION PROTECTION

Hot Corrosion Behavior of Pt-Al Coating in Molten Sulphate or Mixed Salts

y. pang, h. guan, x. sun and x. jiang, Corros. Sci. Prot. Technol ., 1997, 9, (1), 34–37

The hot corrosion behaviour of a Pt-modified aluminide coating on superalloys in the presence of molten Na2SO4, or Na2SO4 + NaCl, salts was studied in air at 900°C. The coating displayed good hot corrosion resistance in molten sulfate, forming only a protective Al2O3 layer on the surface. The addition of NaCl into the Na2SO4 strongly decreased this resistance and the Pt-Al coating suffered from internal oxidation and sulfidation, while its inner NiAl phase showed even greater corrosion.

Corrosion Resistance of Titanium-Platinum Alloy Prepared by Spark Plasma Sintering

j. onagawa, t. goto, o. ise, n. ishii, t. horikawa and k. sawada, Mater. Trans. JIM, 1996, 37, (11), 1699–1703

The corrosion resistance and microstructure of Ti-Pt alloys, prepared from Ti and Pt powders using spark plasma sintering, were studied by SEM and XRD. The Pt phases were dispersed throughout the Ti matrix, and some Ti-Pt intermetallic compounds were formed around the Pt phases. The corrosion resistance of Ti was improved by the addition of traces of Pt and by annealing, which created a eutectic state between the Pt and TiPt phases.

CHEMICAL TECHNOLOGY

Purification of Rhodium-Filled Carbon Nanotubes Using Reversed Micelles

j. cook, j. sloan, r. j. r. heesom, j. hammer and m. l. h. green, Chem. Commun ., 1996, (23), 2673–2674

A non-invasive, external washing method for RhCl3 filled nanotubes used a reversed micelle medium formed from dodecylammonium propionate (dap)-solubilised water in benzene. Treatment with H2 at 500°C for 5h gave nanotubes filled with discrete crystals of Rh metal, but with no crystals on the exterior of the structures. These materials may find uses as nanowires, composites and catalysts.

ELECTRICAL AND ELECTRONIC ENGINEERING

Thermal Reliability and Characterization of InGaP Schottky Contact with Ti/Pt/Au Metals

c.-t. lee, h.-p. shiao, n.-t. yeh, c.-d. tsai, y.-t. lyu and y.-k. tu, Solid-State Electron ., 1997, 41, (1), 1–5

The characteristics of Ti/Pt/Au Schottky contacts on wide bandgap InGaP semiconductors, with surface pretreatment before Schottky contact deposition, and the effect of post heat treatment on Schottky diodes (1) are presented. Predeposition surface etching by dilute HCl, dilute NH4OH, or buffer oxide etchant greatly improved the performance of (1). After annealing (1) at 500°C, a drastic degradation of the barrier height and the ideality factor occurred. This may be due to the interdiffusion and penetration of metals into the semiconductor.

Au/Ge/Pd Ohmic Contacts to n-GaAs with the Mo/Ti Diffusion Barrier

c.-y. chai, j.-a. huang, y.-l. lai, j.-w. wu, c.-y. chang, y.-j. chan and h.-c. cheng, J. Electron. Mater ., 1996, 25, (12), 1818–1822

Three different barrier structures, Au/Ge/Pd/GaAs, Au/Ti/Ge/Pd/GaAs and Au/Mo/Ti/Ge/Pd/GaAs were studied to determine the effects of the As-outdiffusion and Au-indiffusion on their performance. The smoothest surface and the lowest specific contact resistivity were found on Au/Mo/Ti/Ge/Pd/n -GaAs samples, at the widest annealing temperature range. Mo/Ti was an efficient diffusion barrier, retarding Au-indiffusion and As-outdiffusion against thermal annealing.

The Effects of Processing Conditions on the Resistivity and Microstructure of Ruthenate-Based Thick Film Resistors

f. johnson, g. m. crosbie and w. t. donlon, J. Mater. Sci., Mater. Electron ., 1997, 8, (1), 29–37

Resistances were measured in situ during firing of blended resistors having a nominal sheet resistivity of 56 kΩ/⌍and TCR < ± 100 ppm K−1. XRD showed Pb ruthenate, A12O3 and Zr silicate in the resistors with the ruthenate lattice parameters increasing with increasing firing temperature and time. Resistance changes are attributed to increased separation of ruthenate particles by coarsening.

MEDICAL USES

Kinetics of Nitric Oxide Scavenging by Ruthenium(III) Polyaminocarboxylates: Novel Therapeutic Agents for Septic Shock

n. a. davies, m. t. wilson, e. slade, s. p. fricker, b. a. murrer, n. a. powell and g. r. henderson, Chem. Commun ., 1997, (1), 47–48

Two Ru(III) polyaminocarboxylates, K[Ru(Hedta)Cl], JM1226, and [Ru(Hedta) (H2O)], JM6245, have been shown to rapidly bind NO (rate constant > 107 M−1s−1) tightly (binding constant = 108 M−1) at physiological pH to form a stable 1:1 Ru(II) mononitrosyl. They have potential as NO scavengers in NO mediated diseases.

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