ABSTRACTS: April 1993

Journal Archive

Platinum Metals Rev., 1993, 37, (2), 108

ABSTRACTS: April 1993

of current literature on the platinum metals and their alloys

PROPERTIES

The Transitions (5d ⁸+5d ⁷6s)−5d ⁷6p of Pt III

a. n. ryabtsev, j.-f. wyart, y. n. joshi, a. j. j. raassen
and p. h. m. uylings, Phys. Scr., 1993, 47, 45–58

The sliding spark and triggered spark spectra of Pt have been observed in the range 559–2020 Å. More than 800 lines have been classified as transitions between 40 levels of 5d ⁸ + 5d ⁷6s and 93 levels of 5d ⁷6p in doubly ionised Pt, with the support of accurate predictions using energy parameter regularities in the isoelectronic sequence Ir III-Bi VIII, and by transition probability calculations which include explicitly the configuration mixing in the (5d + 6s )⁸ and 5d ⁷6p + 5d ⁶6s 6p .

The Magneto-Optical Kerr Effect of Multilayers Fe/Pt and Co/Pt

s. zhou, h. zhai, j. song and h. zhang, J. Appl. Phys., 1993, 73, (2), 986–988

The magneto-optical polar Kerr rotation spectra of multilayers Fe/Pt and Co/Pt were calculated based on two assumptions; the spin polarisation of the Pt layer was assumed to be negligible, and the Pt layer was assumed to be polarised and to contribute directly to Kerr rotation in the multilayers. The calculated results for Fe/Pt and Co/Pt multilayers d _co(Fe)/d _Pt = 1 showed the magneto-optical Kerr rotation at 300–800 nm increased with increasing modulation wavelength.

Atomic In-Plane Disorder in Co/Pt Superlattices

x. yan, t. egami, e. e. marinero, r. f. c. farrow and c. h. lee, Appl. Phys. A, 1992, A55, (6), 545–548

Studies of <111> and <001> oriented Co(3Å)/Pt(18Å) superlattices grown by molecular beam epitaxy via X-ray diffraction were made using synchrotron radiation. For the <111> oriented sample, the broadening was characterised by a Lorentzian peak shape with a positional correlation length of the order of 50 Å.

Thermodynamic Investigation of the Pt-Pb Binary Alloys

a. amzil and r. castanet, Ber. Bunsenges. Phys. Chem., 1992, 96, (12), 1872–1876

The enthalpy of formation of the Pt-Pb alloys was measured at 923–1316 K with respect to composition by direct reaction calorimetry with the help of high temperature Calvet-type calorimeters. The thermodynamic behaviour of the melts was characterised by moderate negative deviations to ideality, suggesting some chemical short-range order at 923 K. The associates are very sensitive to temperature since the excess heat capacity is positive with a maximum of ~10.2 J/K.mol near mole fraction x_Pt = 0.71.

Effect of Temperature Gradient on Concentration Profile of Hydrogen in a Palladium Lattice

w. m. lee and h. s. uhm, J. Appl. Phys., 1993, 73, (3), 1011–1017

The imposition of a linear temperature increase upon a one-dimensional Pd hydride rod caused a significant redistribution in H concentration. The induced concentration gradient was opposite to that of the imposed temperature gradient due to the positive heat of transport. A Pd hydride rod, in which the α and β phase co-existed prior to imposition of the thermal gradient will have a discontinuous H distribution.

Changes in Film Structure and Increase in Coercivity for Co/Pd Multilayered Films with Atmospheric Annealing

h. yamane, y. maeno and m. kobayashi, J. Appl. Phys., 1993, 73, (1), 334–338

Studies of changes in the film structure of Co/Pd multilayered sputtered films before and after atmospheric annealing showed that coercivity greatly increased to 2 kOe with atmospheric annealing at 300°C. However, this increase was only observed in atmospheric annealing but not in vacuum-annealing.

The Pd Polarization at the Pd/Fe Interface

h. nait-laziz, s. bouarab, c. demangeat, a. mokrani and h. dreysse, J. Magn. & Magn. Mater., 1993, 118, (3), 365–372

Studies of the electronic and magnetic properties for a film of n adlayers of Pd grown on semi-infinite Fe(001), for Fe_m/Pd_n/Fe_m sandwiches and (Fe_m/Pd_n)_p superlattices were performed by a mean-field parameterised tight-binding method. Antiparallel coupl ing of the Pd layers was observed in Pd₄/Fe(001). Ferromagnetic polarisation of the Pd_n layers were obtained up to n = 3. For n = 4, ferromagnetic polarisation of the nearest neighbour Pd overlayer was obtained, but negative polarisation was observed for the three other planes.

Strain Gradient-Induced Diffusion of Hydrogen in Palladium and Nickel Membranes

y. sakamoto, h. tanaka, f. a. lewis and x. q. tong, Int. J. Hydrogen Energy, 1993, 17, (12), 965–970

Studies of the “uphill” diffusion of H during permeation through flat sheets of Pd and Ni were made by an electrochemical permeation method at 303 K. For both annealed and “as cold rolled” Pd samples, uphill diffusion effects on H absorption and desorption were observed over a range of initial H contents from ~H:Pd = 0.01, which is near or slightly less than the α_max composition, up to H:Pd = 0.25–0.3.

Magnetic Phase Diagram of NdRhj.Jtu.SL.in High Magnetic Field

v. ivanov, l. vinokurova, a. szytula and a. zygmunt,
J. Alloys Compd., 1993, 191, (1), 159–163

The high field magnetisation and AC susceptibility of NdRh_2-xRu_xSi₂ compounds were studied up to 140 kOe and the magnetic phase diagram was obtained as a function of concentration, x, and magnetic field. Increases in x and in magnetic field caused changes in the magnetic properties of the NdRh_2-xRu_xSi₂ compounds. A difference between values determined by neutron diffraction and magnetic measurements was observed.

Magnetism and Growth of Ultrathin Co Films Grown Epitaxially on Ru(0001)

c. liu and s. d. bader, J. Magn. & Magn. Mater., 1993, 119, (1&2), 81–86

Ultrathin Co films were found to grow pseudomorphically on Ru(0001) at room temperature in an island structure, by evaporation from a resistively heated Co wire in UHV. The expanded Co lattice relaxed to its bulk spacing after a 500°C anneal. No ferromagnetic hysteresis loops were detected in the first four Co monolayer equivalents (MLE), possibly due to superparamagnetic effects, but ferromagnetic hysteresis loops with in-plane easy axes of magnetisation occurred for film thicknesses > 4 MLE.

Symmetry of the Gap in Superconducting URu₂Si₂

k. hasselbach, j. r. kirtley and j. flouquet, Phys. Rev. B, 1993, 47, (1), 509-513

The specific heat in the superconducting state of the heavy-fermion compound URu₂Si₂ was modelled by considering all symmetry-allowed gap functions. The overall agreement between the modelling and experiment suggests a gap symmetry of either E_u (1,1) or B_1g, with one or two lines of zeros, respectively.

CHEMICAL COMPOUNDS

Preparative and Structural Chemistry of Chiral P,N-Bidentate Complexes of Palladium(II) and Platinum(II)

a. albinati, f. lianza, h. berger, p. s. pregosin, h. rüegger and r. w. kunz, Inorg. Chem., 1993, 32, (4), 478–486

The valine-derived chiral (L) P,N-bidentate ligand (p -CH₃C₆H₄)₂PCH₂CH(Pr¹)NHCH₂(p -OCH₃C₆H₄) (1), PdCl2(l) (2) and PtCl2(l) (3) complexes, and the deprotonated dimeric compound [Pt(1-H)Cl]₂ (4), as well as the iodo analog of 3, were prepared. The results are discussed with the help of molecular mechanics calculations and solid-state ³¹P-NMR methods which are shown to be useful for determining 3-D structures of metal complexes in solution. The complexes exhibited different solution vs solid-state structures. The chiral pocket offered by the chelating ligand is likely to be rather flexible.

Synthesis and Structural Characterization of a Layer-Segregated Platinum-Ruthenium Cluster Complex that Exhibits Selective Coordination and a High Activity for the Catalytic Hydrogenation of Diphenylacetylene

r. d. adams, z. li, p. swepston, w. wu and j. yamamoto, J. Am. Chem. Soc, 1992, 114, (26), 10657–10658

The complex Pt₃Ru₆(CO)₂₁(μ-H)₃(μ₃-H) was obtained in 83% yield from the reaction of Ru₄,Pt₂(CO)₁₈ with H (1 atm) in a refluxing heptane solution. The alkyne PhC₂Ph was found to exhibit a co-ordination preference for a tri-Ru site in the monoalkyne derivative and also was highly active in the catalytic hydrogenation of PhC₂Ph to (Z )-stilbene, Ph(H)C=C-(H)Ph. The structure of this Pt-Ru complex consists of three triangular layers of nine metal atoms arranged in the form of a face-shared bioctahedron. The central layer consists of three Pt atoms while the outer layers are pure Ru.

New Molecular Superconductor, [Me₂Et₂N][Pd(dmit)₂]₂

h. kobayashi, k. bun, t. naito, r. kato and a. kobayashi, Chem. Lett. Jpn., 1992, (10), 1909–1912

A new superconductor [Me₂Et₂N][Pd(dmit)₂]₂ (where dmit is 4,5-dimercapto-1,3-dithiole-2-thione) was isolated with T_c = 4 K at 2.4 kbar. X-ray studies showed that this superconductor is not isomorphous to neither α-[Me₂Et₂N][Ni(dmit)₂]₂ nor to β-[(CH₃)₄N] [Pd(dmit)₂]₂. Its insulating phase emerged when the superconducting state was suppressed at high pressure.

A Novel Chain Compound Composed of Rhodium(II) Pivalate Dimer and 1,4-Benzoquinone

m. hand a, a. takata, t. nakao, k. kasuga, m. mikuriya and t. kotera, Chem. Lett. Jpn., 1992, (10), 2085–2088

A chain complex [Rh₂(O₂CCMe₃)₄.BQ]_n (I) (BQ = 1, 4-benzoquinone) with the Rh(II) pivalate aimers connected by the Afunctional ligation of the p -quinone through its carbonyl O or C=C double bond, was prepared by the reaction of Rh(II) pivalate dimer Rh₂(O₂CCMe₃)₄ (II) with BQ in hexane. X-ray crystal structure studies of (I) showed that its chain structure is formed by an alternated arrangement of (II) and BQ.

Magnetic Ordering in the New Ternary Stannide U₃Rh₄Sn₁₃

f. mirambet, b. chevalier, l. fournes, m. j. besnus, p. gravereau and j. etourneau, J. Magn. & Magn. Mater., 1993, 118, (1 & 2), 187–192

Studies of structural and magnetic properties of U₃Rh₄Sn₁₃, which melts non-congruently, showed that it crystallises in the cubic Yb₃Rh₄Sn₁₃-type structure with a = 9.6416 Å and it undergoes a magnetic transition near 17.5 K. At low temperature, U₃Rh₄Sn₁₃, had an enhanced electronic specific heat coefficient.

Building Blocks for Polymetallic Rutheiiium(II) and Osmium(II) Polypyridine Luminophores

s. k. sahni, m. g. b. drew, t. w. bell and b. s. brunschwig,building blocks for polymetallic rutheiiium (ii) and osmium(ii) polypyridine luminophores J. Chem. Soc, Chem. Commun., 1993, (2), 123–125

X-ray crystallographic studies were performed on the three mixed ligand complexes of Ru and Os, prepared by refluxing aqueous ethanol solutions of cis -[Ru(bpy)₂Cl₂ or cis -[Os(bpy)₂Cl₂] and an excess of die tridentate ligand for 6–28 h under N₂, and then precipitated as hexafluorophosphate salts. The complexes, of typical formula [Ru(bpy)₂bpaH] [PF₆]₂ [bpy = 2,2´-bipyridine; bpaH = bis(picolyl)amine], have a “dangling” pyridine ligand and a luminescence lifetime comparable with that of [Ru(bpy)₃]²⁺.

Stabilizing of the Ru₂⁶⁺ Core. Use of Highly Charged Ligands such as Sulfate and Phosphate

f. a. cotton, t. datta, l. labella and m. shang, Inorg. Chim. Acta, 1993, 203, (1), 55–60

The new Ru₂(II,III) phosphate complex, K₄[Ru₂(HPO₄),(PO₄)(H₂O)₂] (1), has been prepared by a new synthetic route starting from an Ru₂(II,III) carbonate complex to Ru₂(II,III) sulphate and phosphate complexes, which were further transformed by electrochemical oxidation to the corresponding Ru₂(III,III) complexes. Magnetic susceptibility measurements on K₂[Ru₂(SO₄)₄(H₂O)₂]^2- at 10–300K confirmed the assignment of the ground state as one arising from an unusual configuration.

ELECTROCHEMISTRY

Oxidation of Glucose at Electrodeposited Platinum Electrodes

c. p. wilde and m. zhang, J. Ekctroanal. Chem., 1992, 340, (1 and 2), 241–255

Studies of the oxidation of glucose at low concentrations at electrodeposited Pt electrodes in 0.1 M HClO₄ were performed using an electrochemical quartz crystal microbalance (EQCM). Adsorbate, which derived from glucose through the removal of features associated with the presence of adsorbed anions in the background electrolyte, occurred in the region of potential which gave adsorbed H.

Reductions of Nitrite and NO on Pt Single Crystal Electrodes in Alkaline Solution

s. ye, h. hattori and h. kita, Ber. Bunsenges. Phys. Chem., 1992, 96, (12), 1884–1886

The reductions of nitrite and NO on Pt single crys-tal electrodes were studied by a voltammetric method in alkaline solution. The reductions of nitrite and NO were very structure sensitive in alkaline solution and proceeded exclusively in a potential region of 0.3–0.5 V (RHE) at pH > 8. Product analysis and the pH dependence showed direct reduction of nitrite and NO to NH₃ occurring on Pt(100) in alkaline solution with an efficiency of > 80%.

Impedance Measurements of Platinum Electrodes on a Solid Protonic Conductor

s. f. chehab, j. d. canaday, a. k. kuriakose, a. ahmad, t. a. wheat and p. g. komorowski, Solid State Ionics, 1993, 59, (1), 125–132

Impedance measurements were performed on an electrochemical system consisting of a Pt-paste electrode, a protonic conductor, hydronium-NASICON electrolyte, and a N₂/H₂/H₂O gas phase, at room temperature. Dramatic changes in the electrode impedance with H partial pressure were shown. A comparison of the Pt-paste electrode morphology and reactions, with those of ZrO₂-based cells is given. A rise in diffusion-controlled effects at low H partial pressure is seen.

Cyclic Voltammetric Investigation of the Cu-Histidine System at Platinum Conventional and Microelectrodes

s. daniele and m. j. pena, Electrochim. Acta, 1993, 38, (2/3), 165–174

Cyclic voltammetric studies of the reduction of Cu(II) in solutions containing histidine (L) at Pt electrodes of conventional and microscopic size showed that the behaviour of the Cu-histidine system at the Pt working electrodes depended on the nature of the supporting electrolytes. When there was insufficient amount of ligand, L:Cu(II) ≤ 2, the voltammetric studies recorded with the macroelectrode displayed splitting or drawn out curves.

Methanol Oxidation at Carbon Supported Pt and Pt-Ru Electrodes: An on Line MS Study Using Technical Electrodes

s. wasmus and w. vielstich, J. Appl. Electrochem., 1993, 23, (2), 120–124

The oxidation of MeOH at highly porous Pt and Pt-Ru C-base electrodes, prepared by reduction of chloroplatinic acid and Ru(III) chloride with K formate in the presence of the C slurry and bonded with PTFE was studied in 0.05 M H₂SO₄. under acid methanol fuel cell conditions, by a combination of cyclic voltammetry and on line MSM, which was found to be a very suitable method, especially for C¹³-labelled MeOH. Pt(5% on Norit BRX) and Pt-Ru (40/60; 30% on Norit BRX) were used as the C-supported catalysts. Pt-Ru showed the best performance.

The Mechanism of Electrocatalytic Hydrogenation of Organic Molecules at Palladium Black Cathodes

s. j. c. cleghorn and d. pletcher, Electrochim. Acta, 1993, 38, (2/3), 425–30

The range of hydrogenation reactions possible at a Pd black cathode, prepared by electrodeposition onto graphite in an acid chloride bath, was assessed by voltammetry at rotating and stationary disc electrodes. Studies of the mechanism for the electrocatalytic hydrogenation of organic molecules at this cathode in MeOH/ethanoic acid showed that a Pd(H) species is the key intermediate and its electrogenated form causes reduction of the organic molecules.

Mechanism of Deuterium Cracking in Palladium

d. sun, y. lei, y. chen, j. wu and q. wang, Acta Metall. Sin., 1992, 28, (10), 456–460

Optical and transmission electron microscopy studies of D₂ cracking in Pd after 290 h electrochemically D charging showed an increase in the density of dislocations in well-annealed Pd from 10⁸cm² to above 10¹²/cm², and a large amount of bubble-like structure or cracks. XRD data showed that the lattice constant of Pd increased from 0.3890 to 0.4034 nm. The mechanism of D cracking was considered to be the formation of D₂ which resulted from the segregation and recombination of D atoms around dislocations.

Electrochemistry of Colloidal Palladium. An Experimental Study of Sol Formation and Electrocatalysis

a. m. t. von der putten, j.-w. g. de bakker and l. g. j. fokkink, J. Electrochem. Soc, 1992, 139, (12), 3475–3480

Small colloidal Pd particles were formed in aqueous solution by electroless reduction of PdCl₄ species by hydrophosphorus acid, both in the presence and absence of polymer. The presence of H₂O-soluble polymers, such as polyvinylalcohol (PVA) and polyvinylpyrrolidone improved the colloid-chemical stability against flocculation and stabilised the particle size of the sols. PVA-stabilised Pd sols were highly catalytical for electroless Ni deposition, in contrast to conventional SnPd colloids.

Direct Electrosynthesis of Halo and Mixed-Halo Complexes of Palladium(H and IV) by the Dissolution of a Sacrificial Palladium Anode in Aqueous Medium

m. c. chakravorti and g. v. b. subrahmanyam, Polyhedron, 1992, 11, (24), 3191–3195

Chloro and bromo complexes of Pd(II and IV), such as M₂[PdX₄] and M₂[PdX₆] (M = Rb, Cs, NH₄ and (CH₃)₄N; X = Cl or Br), were electrosynthesised rapidly in a single-step method by the dissolution of a Pd foil anode in chloride or bromide containing media. Electrolysis of dilute HX solution in the presence of pyridine, 2,2´-bipyridyl or 1,10-phenanthroline yielded non-electrolytes, such as trans -[PdX₂(py)₂].

Electrode Kinetics of Oxygen Reduction at Carbon-Supported and Unsupported Platinum Microcrystallite/Nafion^RInterface

a. parthasarathy, s. srintvasan, a. j. appleby and c. r. martin, J. Electroanal. Chem., 1992, (1 and 2), 101–121

Electrode kinetics of O reduction at the Pt microcrystallite/Nafion^R interface was studied as a function of temperature and pressure, using porous gas-diffusion electrodes containing unsupported Pt or Pt/C, in proton exchange membrane fuel cells, and H₂ and O₂ as reactants. At current densities of 1–1000 mA/cm² the Tafel slope was ∼60 mV per decade and was independent of temperature and O₂ pressure.

Kinetics and Mechanism of the Substitution Reaction of Ethylene Diaminetetra-acetatoruthenate(III) with Cyanide in Aqueous Solutions

m. m. taqui khan, d. chatterjee, h. c. bajaj, k. n. bhatt and s. sanalkumar, Indian J. Chem., 1992, 31A, (9), 714–715

Studies of the kinetics of the ligand substitution of Ru_m (EDTA)/(H₂O)^- (EDTA = ethylenediaminetetraacetate anion) with CN were performed spectrophotometrically as a function of ligand concentration, pH (5.0–11.0) and temperature (20–50°C). The kinetic and activation parameters were consistent with an associative interchange mechanism. The substitution reaction was studied at four different temperatures.

Molecular Structure and Electrochemistry of Ru₂(dpf)₄(C≡CC₆H₅)₂ (dpf = N,N’- Diphenylformamidinate Ion): A Novel Ru(III)-Ru(III) Dimer

j. l. bear, b. han and s. huang, J. Am. Chem. Soc, 1993, 115, (3), 1175–1177

The synthesis, structural characterisation, and spectroscopic and electrochemical studies were performed on the novel Ru₂⁶⁺ title complex. The Ru complex (1) was obtained from the reaction of Ru₂(dpf)₄Cl with excess LiC≡CC₆H₅, in THF under Ar at room temperature. The red solution was opened to air, and the residue was dissolved in CH₂C1₂. The product was purified on a SiO₂ gel column, and after evaporation of CH₂C1₂ (1) was obtained in ∼ 30% yield.

Effect of Composition on the Point of Zero Charge of RuO₂+TiO₂ Mixed Oxides

l. a. de faria and s. trasatti, J. Electroanal. Chem., 1992, 340, (1 and 2), 145–152

Studies of RuO₂+TiO₂ mixed oxides prepared by thermal decomposition of RuCl₃+TiCl₄ at 450°C were carried out. The point of zero charge (pzc) was measured by Potentiometrie titration of oxide suspensions in KNO₃, solution. The charge-pH curves were transformed into capacitance values which were used at the pzc to estimate in-situ the real surface area and the inner layer capacitance. The rutile form of TiO₂ has a pzc close to that of RuO₂ which results in a pzc varying very little between 40 and 100% RuO₂.

PHOTOCONVERSION

A Study of Ultraweak Luminescence in Evolution of Oxygen at Pt Electrodes

z. wang, x. jin, s. cai, y. liu and a. fujishima, Electrochim. Acta, 1993, 38, (2/3), 267–269

Studies of ultraweak photoemission at a Pt electrode in aqueous solutions containing no luminescer were made using a photon counter. Weak photoemission accompanied O evolution at the Pt electrode in solutions H₂SO₄ or KOH, and borate or NaHCO₃ buffer systems. It is suggested that the ultraweak photo-emission comes from the recombination of singlet O.

Generation of Homogeneous Rhodium Particles by Photoreduction of Rh(III) on TiO₂ Colloids Grafted on SiO₂

a. fernÁndez, a. r. gonzÁlez-elipe, c. real, a. caballero and g. munuera, Langmuir, 1993, 9, (1), 121–125

Spectroscopic studies of photochemical deposition of metallic Rh on three TiO₂/SiO₂ samples, containing 3, 6 and 12 wt.% TiO₂, prepared by the reaction of OH groups and H₂O on the SiO₂ surface with Ti(OCH(CH₃)₂)₄ showed the formation of RhTiO₂/SiO₂ composite materials. Small metallic particles with very narrow size distributions were formed which depended on the amounts of TiO₂ grafted on the SiO₂ and on the initial concentration of Rh.

Visible Light Induced Hydrogen Production with Cu(II)/Bi₂O, and Pt/Bi₂O₃/RuO₂ from Aqueous Methyl Viologen Solution

p. maruthamuthu, k. gurunathan, e. subramanian and m. v. c. sastri, Int. J. Hydrogen Energy, 1993, 18, (1), 9–13

The oxide semiconductor γ-Bi₂O₃ was doped individually with Cu(II) ions, or loaded with Pt and/ or RuO₂ (0.5 at.%) and used as a fine powder for photocatalytic production of H₂ from H₂O in the presence of methyl viologen (MV²⁺) as an electron relay. The aqueous slurry of the catalyst was irradiated for 90 min in the presence of MV²⁺ resulting in generation of 0.79 and 0.66 ml of H₂ by 4 at.% Cu(II)/Bi₂O₃ and Pt/Bi₂O₃/RuO₂, respectively.

Study of Photoelectrochemical Cells: Micellar Effect on the [Ru(bpy)₃]²⁺-Sensitized Photoreduction of Dyes by Na₂EDTA

s. lingamurthy, b. sethuram and t. n. rao, Transition Met. Chem., 1992, 17, (6), 506–508

Studies on photoelectrochemical cells using [Ru(bpy)₃]²⁺ as sensitiser in the presence of Na₂EDTA reducing agent along with various dyes in various types of anionic, neutral or cationic micellar media were performed in order to find out the ability of the Ru sensitiser to generate photocurrents and photo-voltages. The yield of photocurrent was found to be dependent upon the dye and micellar medium.

Photoresponsive Electrode Based on the Reaction between Oxygen and the Excited Ru(bpy)₃²⁺ Complex Incorporated in a Coated Nafion Film

y. ueno, k. yamada, t. yokota, k. ikeda, n. takamiya and m. kaneko, Electrochim. Acta, 1993, 38, (1), 129–133

A photoresponsive electrode was prepared by coating a Nafion film on an InSn oxide (ITO) electrode having the Ru(bpy)₃²⁺ complex in the film. A photocurrent was induced at the coated electrode dipped in an aqueous electrolyte in the presence of O. Viologen molecules present as a solute or as the second film on the top of the Nafion [Ru(bpy)₃²⁺] film increased the induced photocurrent by ∼ a factor of 2.

Formation of a Stabilized Coordinatively Unsaturated Metal Carbonyl Cluster, H₂Ru₄(CO)₁₂, by Photochemical Reaction of H₂Ru₄(CO)₁₃ Adsorbed on the Surface of Silica

s. yamamoto, k. asakura, k. mochida, a. nitta and h. kuroda, J. Phys. Chem., 1993, 97, (3), 656–660

Studies of the photochemistry of H₂Ru₄(CO)₁₃ (1) adsorbed on the surface of SiO₂ showed that during irradiation by UV-visible light, (1) lost one CO lig and, giving selectively co-ordinatively unsaturated H₂Ru₄(CO)₁₂ on the SiO₂ surface. The initial photo-product, H₂Ru₄(CO)₁₂ interacts weakly with surface hydroxyl groups, which are the only functionality available to act as a stabilising ligand.

ELECTRODEPOSITION AND SURFACE COATINGS

Thermal Stability of a Platinum Aluminide Coating on Nickel-Based Superalloys

h. m. tawancy, n. sridhar, b. s. tawabini, n. m. abbas and t. n. rhys-jones, J. Mater. Sei., 1992, 27, (23), 6463–6474

The thermal stability of a Pt aluminide coating on the directionally solidified alloy MAR M 002 and its single crystal version alloy, SRR 99, was studied at 800, 1000 and 1100°C. The morphology of the coating was characterised. In the as-deposited state the coating was two layers, most Pt was in the outer coating layer, which consisted of a fine dispersion of PtAl₂ in a matrix of β-(Ni, Pt)Al containing Co and Cr.

Interdiffusion of the Aluminized and Pt-Aluminized Coatings on MAR-M247 Superalloy

k.-l. lin and c.-m. hwang, Surf. Coat. Technol, 1992, 56, (1), 81–87

The interdiffusion behaviour of Pt-aluminised (1) and aluminised (2) coatings were investigated on MAR-M247 superalloy. A NiAl phase formed for the (2) coating, while the PtAl₂ phase was identified as well as the NiAl phase for coating (1). It was concluded that Ni diffuses outwards for coating (2) but for coating (1) Pt acts as the diffusion media, which enhances the outwards diffusion of Ni and the inward diffusion of Al to form the two phases.

The Roles of the Ruthenium Concentration Profile, the Stabilizing Component and the Substrate on the Stability of Oxide Coatings

v. m. jovanovic, a. dekanski, p. despotov, b. z. nikolic and r. t. atanasoski, J. Electroanal. Chem., 1992, 339, (1 and 2), 147–165

Electrochemical studies of oxide coatings with variable concentration profiles of RuO₂ as the active component, were performed on components obtained through a combination of separately applied layers of RuO₂, TiO₂ IrO₂, RuO₂⁺TiO₂, and RuO₂⁺IrO₂ on Ti and glassy C substrates. Both the stability of the coatings and their related charge depended strongly on the sequence of layers in the RuO₂-TiO₂ coating.

APPARATUS AND TECHNIQUE

Mediated Micro-Glucose Sensors Using 2 μm Platinum Electrodes

k. yokoyama, k. nakajima, s. uchiyama, s. suzuki, m. suzuki, t. takbuchi, e. tamiya and i. karube, Ekctroanalysis, 1992, 4, (9), 859–864

Glucose-oxidase (GOD) and glucose-dehydrogenase (GDH) sensors, immobilised in a photocrosslinkable polymer, were fabricated on a cylindrical Pt micro-electrode of 2 µm diameter, and characterised by using 1,4-benzoquinone and ferricyanide as electron mediators, respectively. For the GOD micro-glucose sensor, a calibration plot was obtained that was linear up to ∼ 40 mM glucose, which is superior to values obtained with a disk electrode of 1 mm diameter.

Trimemylamine-Sensing Mechanism of TiO₂-Based Sensors. 1. Effects of Metal Additives on Trimethylamine-Sensing Properties of TiO₂ Sensors

y. takao, y. iwanaga, y. shimizu and m. egashira, Sens. Actuators B, 1993, 10, (3), 229–234

Studies were performed of the eflect of Pt, Pd, Rh, Ru, In or Au additives on the trimethylamine (TMA)-sensing properties of TiO₂. The sensitivity to TMA was enhanced by the addition of 0.5 wt.% Ru, 2.0% In or 0.5 wt.% Au, while the addition of 0.5 wt.% Pt, 1.5 wt.% Pd or 1.5 wt.% Rh lead to a decrease in the sensitivity. Ru acted as a stronger electron donor from TiO₂ than expected from its work function.

HETEROGENEOUS CATALYSIS

The Catalytic Effect of Platinum on the Oxidation of Carbon Fibres

r. g. iacocca and d. j. duquette, J. Mater. Set., 1993, 28, (4), 1113–1119

The effects of Pt on the oxidation behaviour of PAN-based 5C carbon fibres has been investigated at 500, 550 and 600°C in air. Fibres oxidised in Pt holders had a higher activation energy than those oxidised in SiO₂. The pre-exponential term for fibres oxidised in Pt was six orders of magnitude larger than the fibres oxidised in the SiO₂ holders. Spheres formed along the longitudinal axis of many fibres and one fibre bifurcated with a sphere forming on each remaining fibril.

Isomerization of Xylene Isomers on a PtRe-H-Mordenite Catalyst

a. k. aboul-ghett, s. m. abdel-hamid and f. m. abdel- hay, Appl. Catal. A: Gen., 1993, 93, (2), 131–140

Studies of the isomerisation of xylene isomers performed on a 0.35 wt.%Pt-0.35 wt.% Re/H-mordenite catalyst in a pulse catalytic microreactor showed the presence of para -xylene as the highest C8 aromatic component of the hydroconversion of any xylene isomer, whereas ortho -xylene was the lowest. Trimethylbenzenes and ethylbenzenes were not detect-ed in the reaction products. The results indicate an excellent shape-selectivity for para -xylene production on the PtRe/H-mordenite catalyst.

Catalytic Activity and Characterization of Pt/SiO₂ Catalysts Prepared by the Sol-Gel Method

m. asomoza, t. lopez, a. zamalloa, r. gomez and e. garciafigueroa, New J. Chem., 16, 1992, (10), 959–963

Pt/SiO₂ catalysts were prepared by the sol-gel method by adding [PtCl₆]^-2 to tetraethoxysilane, followed by hydrolysis and condensation. The addition of H₂PtCl₆.6H₂O during the formation of the gel resulted in solids with surface area of up to 1,100 m²/g. The catalysts with a low metal concentration were active for the hydrognation of alkenes but not for the hydrognation of aromatics. Deactivation studies showed that sol-gel Pt catalysts were more resistant to poisoning by thiophene than impregnated ones.

High Catalytic Activity of Platinum-ZSM-5 Zeolite below 500 K in Water Vapor for Reduction of Nitrogen Monoxide

h. hirabayashi, h. yahiro, n. mizuno and m. iwamoto, Chem. Lett. Jpn., 1992, (11), 2235–2236

A pronounced catalytic activity of Pt ion-exchanged ZSM-5 (SiO₂/Al₂O₃ = 23.3) zeolite is reported below 500 K for the selective reduction of NO by ethene even in the presence of 8.6 vol.% of H₂O vapour. The most active temperature of Pt-MFI-97 (cation-zeolite structure-degree of exchange) in the absence of H₂O vapour was 485 Κ and the conversion into N₂ and N₂O were 18% and 36%, respectively. The conversion of C₂H₄ at 485 on Pt-MFI-97, Fe-MOR-71 and Cu-MFI-105 were 100, 4 and 1%, respectively.

Non-Faradaic Electrochemical Modification of Catalytic Activity. VII. The Case of Methane Oxidation on Platinum

p. tsiakaras and c. g. vayenas, J. Catal., 1993, 140, (1), 53–70

The catalytic activity of Pt for CH₄ oxidation increased reversibly by up to 7000 % by depositing polycrys-talline Pt films on Y₂O₃-doped ZrO₂, and by polarising the Pt-solid electrolyte interface. The catalytic rate is increased by supplying and by removing O^2- to or from the Pt catalyst through the gas-impervious solid electrolyte. The rate of CH₄ oxidation depended exponentially on catalyst potential and work function, eϕ, over wide (up to 0.8 eV) eϕ ranges.

Reactions of Labelled Hexanes on Pt-WO₃/Al₂O₃ Catalysts

j. m. farbotko, f. garin, p. girard and g. maire, J. Catal., 1993, 139, (1), 256–267

Hexane hydrocracking and isomerisation on Pt-WO₃/Al₂O₃, catalysts (Pt:W = 1:1), prepared by different methods, and studied by isotopic tracer measurements, showed that the systems catalysed the isomerisation with low selectivity. The reaction proceeded via classical cyclic and bond-shift mechanisms. No correlation between the relative contribution of the cyclic mechanism and the non-selective hydrogenolysis of the methylcyclopentane was found.

Highly Selective Pt-Cr/C Alloy Catalysts for Single-Step Vapour Phase Hydrogenation of Phenol to Give Cyclohexanone

s. t. srinivas and p. kanta rao, J. Chem. Soc, Chem. Commun., 1993, (1), 33–34

Studies of the catalytic activity of Pt-Cr/C catalysts during the single-step vapour phase hydrogenation of phenol showed them to be active for the hydrogenation of phenol with total selectivity to give cyclohexanone. Alloying of the 5 wt.%Pt/C with Cr improved the cyclohexanone selectivity from 84 to 100% in the hydrogenation without giving any side products. The H uptake on the alloy catalyst correlated direcdy with the phenol conversion.

Effects of Alcoholic Solvents on the Formation of Cyclohexanones in the Hydrogenation of Phenols over Pd-C Catalysts

m. higashijima and s. nishimura, Bull. Chem. Soc. Jpn., 1992, 65, (11), 2955–2959

Studies were performed of the hydrogenation of phenol and isomeric cresols in cyclohexane and t -pentyl alcohol (t -PeOH) as solvents with a commercial Pd/C and acid-treated Pd/C (P/C/A) catalysts under H pressure at 120°C. In both catalysts, the maximum yields of the cyclohexanone intermediates as well as the hydrogenation rates of the phenols decreased markedly in t -PeOH compared with hydrogenation in cyclohexane.

The Reactivity of High Oxygen Coverages on Pd(110) in Catalytic CO Oxidation

s. ladas, r. imbihl and g. ertl, Surf. Sei., 1993, 280, (1/2), 14–22

The catalytic oxidation of CO on a Pd(110) surface was studied during CO titration and under steady-state conditions at 10^-4 Torr. The titration studies with the O-saturated Pd(110) surface showed a change in the reaction mechanism from a uniform reduction of the O coverage at high temperatures,≈ 400 K, to a hole-eating mechanism at low temperature. High O coverages inhibited the rate of CO₂ production which was attributed to a lowering of the CO residence time and to a reduction of the CO sticking coefficient.

Effect of Sulfur on the Performance and on the Particle Size and Location of Platinum in Pt/KL Hexane Aromatization Catalysts

g. b. mcvicker, j. l. kao, j. j. ziemiak, w. e. gates, j. l. robbins, m. m. j. treacy, s. b. rice, t. h. vanderspurt, v. r. cross and a. k. ghosh, J. Catal., 1993, 139, (1), 48–61

When S was introduced to a working Pt/KL hexane aromatisation catalyst in the form of thiophene, it functioned as a very potent poison which reduced the number of Pt sites accessible within the channels of the KL zeolite. However, the intrinsic catalytic activity and selectivity of in-channel Pt sites were not significantly modified by the presence of S on the catalyst. Extremely low thiophene feed S concentrations at 50–200 wppb accelerated Pt agglomeration.

Phenylacetaldehyde and Carbon Monoxide as Effective Additives for the Selective Hydrogenation of Cyclooctadienes to Cyclooctene over Palladium Catalysts

m. higashijima, h. s. man and s. nishimura, Bull. Chem. Soc Jpn., 1992, 65, (11), 2960–2965

Isomeric 1,5-, 1,4- and 1,3-cyclooctadienes (COD) were hydrogenated with phenylacetaldehyde (PA)- or CO-treated Pd black in tetrahydrofuran at 25°C and atmospheric pressure of H. Catalysts poisoned by PAA greatly promoted isomerisation of 1,5-COD to 1,4-COD, while the rate of hydrogenation of 1,4- and 1,3-COD decreased.

n -Butane Hydrogenolysis as a Probe of Surface Sites in Rhodium Metal Particles: Correlation with Single Crystals

d. kalakkad, s. l. anderson, a. d. logan, j. penΝa, e. j. braunschweig, c h. f. peden and a. k. datye, J. Phys. Chem., 1993, 97, (7), 1437–1444

The effect of particle size and pre-oxidation on the hydrogenolysis activity and product selectivity was studied during n -butane hydrogenolysis, on Rh metal catalysts supported on Al₂O₃ and Si₂O with the metal particle size varied (from < 1 to 5 > nm) by changing the metal loading from 0.03-7.2 μmol of Rh/m² of support. The ethane selectivity of the highly dispersed Rh was very different from that of the low index single crystal surfaces of Rh. As particle size was increased, the selectivity of the catalysts approached that of Rh(111).

Zirconium-Based Intermetallics as Heterogeneous Catalysts for the Fischer-Tropsch Reaction: III. Zr-Co-Ni-Cu and Ru Catalysts

a. f. y. al-shammary, i. t. caga, a. y. tata, j. m. winterbottom and i. r. harris, J. Chem. Technol. Biotechnol, 1992, 55, (4), 375–378

Intermetallic alloys of type Zr₅₀M_xN_50-x, where 0 ≤ x ≤50, were prepared by Ar arc melting. M and Ν are combinations of Co, Ni, Cu and Ru. The alloys were powdered by H decrepitation, after which they were used in this form as catalysts. The H₂/CO reaction was performed in a semi-micro-tubular flow reactor.

HOMOGENEOUS CATALYSIS

Palladium-Catalyzed Aldol-Type Condensation by Enol Esters with SnCl₂

y. masuyama, t. sakai and y. kurusu, Tetrahedron Lett., 1993, 34, (4), 653–656

Enol esters caused aldol-type condensation with aldehydes in the presence of PdCl₂(PhCN)₂.SnCl₂ catalyst at 50°C in acetonitrile to give (E )-a,β-unsaturated carbonyl compounds. Cyclic enol ester, such as a-angelicalactone, also reacted with aldehydes under the same conditions to produce γ-substituted β-acetyl-γ-butyrolactones and/or 5-substituted 4-acetyl-2(5H )-furanones. γ-Butyrolactones were only obtained with arenecarbaldehydes.

Palladium-Catalyzed Carbonylative Vinylation of Arylmercuric Chlorides with Carbon Monoxide and Olefins

d.-s. ryu, k.-h. song, j.-t. lee and j.-i. kÍm, Bull. Korean Chem. Soc., 1992, 13, (4), 345–355

Arylmercuric chlorides reacted with CO and olefins in the presence of PdCl₂(PPh₃)₂ catalyst, a base and CuCl₂, under mild conditions, to give the corresponding aryl vinyl ketones in moderate to good yields. An increase in CO pressure enhanced the yields of the desired aryl vinyl ketones. The mechanism of this carbonylative vinylation involves transmetallation of the Pd(II) catalyst, CO insertion to give the aroyl Pd(II) complex, reaction with olefins, and reoxidation of Pd(0) to Pd(II) with CaCl₂.

Catalytic Asymmetric Synthesis of Optically Active Alcohols via Hydrosilylation of Olefins with a Chiral Monophosphine-Palladium Catalyst

t. hayashi and y. uozumi, Pure Appl Chem., 1992, 64, (12), 1911–1916

The reaction of terminal alkenes with trichlorosilane at 40°C in the presence of 0.1 and 0.01 mol% of Pd catalyst prepared in situ from [PdCl(π-C₃H₅)]₂ and (S)-2-(diphenylphosphino)-2’-methoxy-1,1’-binaph-thyl proceeded with unusual regioselectivity at up to 94% and with high enantioselectivity to give high yields of 2-(trichlorosilyl)alkanes and a minor amount of l-(trichlorosilyl)alkanes. Oxidation of C-Si bond gave optically active alcohols with enantiomeric purity ranging between 94% and 97% ee.

The Palladium-Catalyzed Cross-Coupling Reaction of Enol Acetates of α-Bromo Ketones with 1-Alkenyl-, Aryl-, or Alkylboron Compounds; A Facile Synthesis of Ketones and Their Enol Acetates

s. abe, n. miyaura and a. suzuki, Bull. Chem. Soc. Jpn., 1992, 65, (10), 2863–2865

Pd-catalysed cross-coupling reaction between alkyl-, aryl- or 1-alkenylboron reagents with enol acetates of α-bromo ketones using Pd(PPh₃)₄ catalyst readily produced stereodefined enol acetates of ketones. Hydroboration of alkene with 9-borabicyclo-[3.3.1 jnonane followed by coupling with (Z )-2-ethoxy-1-bromoethene gave the enol ether of aldehyde.

Synthesis of Phthalides through Palladium-Catalysed Heteroannulation of Acetylenic Compounds

n. g. kundu and m. pal, J. Chem. Soc, Chem. Commun., 1993, (1), 86–88

The heteroannulation of acetylenic compounds in the presence of (PPh₃)₂PdCl₂ and Pd(OAc)₂ catalysts, yielded phthalides [l-(3H )isobenzofuran-3-ones] as major products and isocoumarins as minor products. The reactions were carried out by heating a mixture of o-iodobenzoic acid and acetylenic compound in the presence of the Pd catalyst, Cu(I) iodide and a base in dimethylformamide.

Formation of 2-Imino-1,3-Oxathioles and 2(3H )-Oxazolethione by the Rhodium(II) Acetate-Catalyzed Reaction of α-Diazo-carbonyl Compounds with Isothiocyanates

t. ibata and h. nakano, Bull. Chem. Soc. Jpn., 1992, 65, (11), 3088–3093

Studies of Rh₂(OAc)₄ catalysed reaction of various a-diazocarbonyl compounds with alkyl, phenyl and benzoyl isothiocyanates showed good yields of 2-imino-1,3-oxathioles and a by-product 2(3H )-ox-azolethione, which was only produced in the reaction of dia-zodimedone with methyl isothiocyanate. The preferable formation of thiocarbonyl ylide was explained by heat of formation and frontier molecular orbital calculations.

Rhodium(II)-Catalyzed Cyclization of 2-Alkynyl 2-Diazo-3-oxobutanoates as a Method for Synthesizing Substituted Furans

a. padwa and f. r. kinder, J. Org. Chem., 1993, 58, (1), 21–28

Studies of a series of 2-alkynyl 2-diazo-3-oxobutanoates treated with a catalytic quantity of Rh(II) acetate showed the synthesis of furo[3,4-c ]furans in good yield. The reaction occurred by addition of a Rh-stabilised carbenoid onto the acetylenic π-bond to produce a vinyl carbenoid which cyclises onto the adjacent carbonyl group to produce the furan ring.

Electronic and Steric Control in Carbon-Hydrogen Insertion Reactions of Diazoacetoacetates Catalyzed by Dirhodium(II) Carboxylates and Carboxamides

m. p. doyle, l. j. westrum, w. n. e. wolthuis, m. m. see, w. p. boone, v. bagheri and m. m. pearson, J. Am. Chem. Soc., 1993, 115, (3), 958–964

Studies of the unique capabilities of Rh(II) carboxylates and carboxamides in modifying regiocontrol in C-H insertion reactions were performed in order to identify the electronic and steric factors which control regioselectivity. 2,3,4-Trimethyl-3-pentyl diazoace-toacetate formed γ-lactone products from insertion into primary and tertiary C-H bonds in a statistical distribution (61:39) with diRh(II) tetrakis(perfluorobutyrate), but only tertiary C-H insertion was observed with diRh(II) tetraacetamide.

Highly Efficient Regioselective Silylcarbonylation of Alkynes Catalyzed by Dirhodium(II) Perfluorobutyrate

m. p. doyle and m. s. shanklin, Organometallics, 1993, 12, (1), 11–12

Studies of the activity of Rh(II) perfluorobutyrate catalyst during silylcarbonylation of terminal acetylenes showed it to be highly effective, giving high catalyst turnovers, exceptional E:Z isomer ratios and high yield of β-silylacrylaldehydes with substantial stereo-control at atmospheric pressure, and at or below room temperature. The stereochemistry of the major isomer formed is that of cis addition.

Room-Temperature Catalytic Hydrogenation of Aromatic Hydrocarbons Using [(1,5-COD)RhH]₄ as a Catalyst Precursor

z. duan and m. j. hampden-smith, Chem. Mater., 1992, 4, (6), 1146–1148

[(1,5-COD)RhH]4 (1) (COD = cyclooctadiene) was synthesised by the reaction of [(1,5-COD)RhCl]₂ with LiBEt₃H at room temperature in THF under N₂ conditions, and used as a source of 2-nm-sized Rh crystallites under mild conditions. Solutions of (1) were very stable in aromatic and aliphatic hydrocarbon solvents under inert atmosphere in the absence of H, but aromatic HC solvents were unstable in H.

Acetic Anhydride Synthesis from Methyl Formate Catalysed by Rhodium-Iodide Complexes

b. seuillet, y. castanet, a. mortreux and f. petit, Appl. Catal. A: Gen., 1993, 93, (2), 219–229

Studies of a “one pot” synthesis of acetic anhydride from methyl formate in the presence of a RhI₂(CO)₂ showed that it requires a two stage procedure, due to the incompatibility of the activations used to sustain the two consecutive reactions of homologation and carbonylation. In the first stage, an alkaline iodide, Lil, was used with an accurate LiI:Rh ratio, to avoid acetic acid production, while in the second stage, an alkyl iodide was required to provide the synthesis of acetic anhydride.

Formation and Reaction of Acyl Substituted Nitrile Ylide through the Rh₂(OAc)₄-Catalyzed Reaction of α-Diazocarbonyl Compounds with Benzonitrile

t. ibata and k. fukushima, Chem. Lett. Jpn., 1992, (11), 2197–2200

The Rh₂(OAc)₄ catalysed decomposition of p-chloro-α-diazoacetophenone in benzonitrile in the presence of dimethyl acetylene-dicarboxylate produced 5-(p-chlorophenyl)-2-phenyloxazole and dimethyl 2-(p-chlorobenzoyl)-5-phenylpyrrole-3,4-dicarboxylate in 63 and 11% yields, respectively. The reaction gave oxazoles and pyrrole-3,4-dicarboxylates through the 1,5-cyclisation and 1,3-dipolar cycloaddition of the acyl substituted nitrile ylide intermediates generated by the reaction of ketocarbenoids with benzonitrile.

Rhodium(II) Trifluoroacetamide; an Excellent Catalyst for Carbenoid O-H Insertion Reactions

g. g. cox, j. j. kulagowski, c. j. moody and e.-r. h. b. sie, Synlett, 1992, (12), 975–976

Studies of Rh (II) acetate and trifluoroacetamide catalysts during cyclopropanation of ethyl diazoacetate with alkenes showed very rapid conversion of the diazo compound in the presence of Rh(II) trifluoroacetamide (1) catalyst when using an intermolecular insertion reaction into the O-Η bond of 2-propanol. Catalyst (1) was found to be extremely effective for inter- and intra-molecular carbenoid O-Η insertion reactions.

Diastereo selectivity in the Osmium Tetraoxide Promoted Dihydroxylation of Chiral (E )-Crotylsilanes: Asymmetric Synthesis of Silyl-Functionalized γ-Lactones

j. s. panekand j. zhang, J. Org. Chem., 1993, 58, (2), 294–296

Studies of the catalytic osmylation of enantiomeri-cally enriched (E )-crotylsilanes (2S,3R )-l and (2R,3.R )-2 containing a homoallylic, N-bearing stere-ocentre, using OsO₄ catalyst, showed good to high levels of diastereoselection generating silyl-function-alised trans-4,5 substituted γ-lactones as the major diastereomers. The selectivity exhibited by the silane reagents together with the high degree of functional-isation contained in the derived γ-lactones showed them to be intermediates in asymmetric synthesis.

Catalytic Oxidation of Partially and Fully Fluorinated Olefins with Osmium Tetroxide

w. a. herrmann, s. j. eder and w. scherer, Angew. Chem. Int. Ed. Engl., 1992, 31, (10), 1345–1347

The formation of cycloadducts of partially and fully fluorina ted olefins and their conversion into fluorinated diols and products of subsequent reactions in the presence of OsO₄ is reported, which is contrary to a previous assumption that very electron-poor olefins do not react with the OsO₄. Fluoroalkenes reacted with OsO₄ in hexane in the presence of pyridine and N-containing bases at room temperature giving cyclic osmate(VT) esters quickly and quantitatively.

Asymmetric Hydrogenation of 2-Fluoro-2-alkenoic Acids Catalyzed by Ru-binap Complexes: A Convenient Access to Optically Active 2-Fluoroalkanoic Acids

m. saburi, l. shao, t. sakurai and y. uchida, Tetrahedron Lett., 1992, 33, (51), 7877–7880

Studies of asymmetric hydrogenation of (Z )-2-fluoro-2-alkenoic acid (1) in the presence of Ru₂Cl₄(binap)₂(NEt₃) catalyst (binap = (R )- or (S )-2,2′-bis(diphenylphosphino)-1,1 -binaphthyl) showed a yield of 2-fluoroalkanoic acids with high enantiomeric purities of up to 90% ee. When the (R )-binap catalyst was used, both (Z )- and (E )-(1) were smoothly hydrogenated to give (R )-2-fluorohexanoic acid with comparable asymmetric induction.

Reactivity of Cp^*Ru⁺ with Acyclic Unsaturated Hydrocarbons: A Novel Catalytic Carbon-Carbon Bond Activation Reaction

r. carreno, b. chaud ret, d. labroue and s. sabo-etienne, Organometaüics, 1993, 12, (1), 13–14

The versatile reactivity of the electrophilic fragment Cp^*Ru⁺, which was generated in situ through protonation of [Cp^*Ru(OMe)]₂by CF₃SO₃H with 1,3,5-hexatriene, toward unsaturated acyclic hydrocarbons is described. A catalytic reaction performed with neohexene produced three different types of products: (a) neohexene oligomers, (b) 2,3-dimethyl-2-butene and 2,3-dimethyl-l-butene in 92% yield, and (c) CH₄ together with C₁₁ and C₁₇ hydrocarbons.

Ruthenium Catalyzed Reconstitutive Condensation. Application to Functionalized Steroid Side Chains

b. m. trost, r. j. kulawiec and a. hammes, Tetrahedron Lett., 1993, 34, (4), 587–590

bis(Triphenylphosphine)cyclopentadienylruthenium chloride catalysed the addition of steroidal acetylenes with ally] alcohols to introduce functionalised side chains illustrated by the construction of the side chain of ganoderic acid which is a novel angiotensin-con-verting enzyme inhibitor. The excellent chemoselec-tivity and atom economy of the Ru catalysed reconstitutive condensation make it a useful method for elaborating steroid side chains with minimal need for protecting groups.

Studies on Transition-Metal Oxo and Nitride Complexes. 13. Perruthenate and Ruthenate Anions as Catalytic Organic Oxidants

a. j. bailey, w. p. griffith, s. i. mostafa and p. a. sherwood, Inorg. Chem., 1993, 32, (3), 268–271

The [RuO₄]^- ion, which was generated in aqueous base at pH 11 from aquated RUCl₃.n H₂O with BrO₃^- as co-oxidant, catalytically oxidised primary alcohols, activated alkyl halides, aldehydes, 1,2-diols and nitroalkanes to carboxylic acids. However, the secondary alcohols and halides were oxidised to ketones, brómate being the co-oxidant.

FUEL CELLS

A Unitized Approach to Regenerative Solid Polymer Electrolyte Fuel Cells

h. p. dhar, J. Appl. Electrochem., 1992, 23, (1), 32–37

Unitised regenerative fuel cell data were obtained with a cell design which allows the same unit to function both as a power producer and as an electrolyser. The cell contained Pt/C and Pt/Ir/C gas diffusion electrodes on the O side and Pt/C electrodes on the H side, membranes and a solid polymer electrolyte, usually used in fuel cells. The current-potential data in the regenerative electrolysis decreased with time but the fuel cell current was very stable. The membrane-electrode assemblies functioned well, and no visible corrosion was observed.

Surface and Catalytic Properties of Iron-Platinum/Carbon Electrocatalysts for Cathodic Oxygen Reduction in PAFC

_{k. t. kim, j. t. hwang, y. g. kim} and j. s. chung, j. Electrochem. Soc, 1993, 140, (1), 31–36

Studies of surface and catalytic properties of Pt-Fe catalysts were made in phosphoric acid fuel cells, on catalysts prepared by impregnation of Fe(NO₃)₂ solution into Pt/C. The catalyst was heat-treated in a flow of Ar at 450, 750 and 900°C, or this process was followed by an acid-treatment in 1 M H₂SO₄. With increased heat-treatment temperature, the Pt surface area measured by H chemisorption decreased rapidly due to particle sintering, an alloying effect and enrichment of Fe on the surface.

Direct Electrooxidation of Methanol on Highly Dispersed Platinum-Based Catalyst Electrodes: Temperature Effect

g. mÉli, j.-m. lÉger, c. lamy and r. durand, J. Appl. Electrochem., 1993, 23, (3), 197–202

The direct electrooxidation of MeOH in acid medium was studied on a perfluorinated Nafion mem-brane containing small amounts of Pt, about 1 mg/cm², and other metal catalysts, incorporated by chemical reduction. Pt modified by other metals was the best catalyst to obtain oxidation potentials much more compatible with a working anode in a direct MeOH fuel cell. Ru and Sn lead to a negative shift of > 250 mV as compared to the potential obtained with pure Pt.

Platinum-Iridium Bimetal Catalyst-Based Porous Carbon Electrodes for H₂-Cl₂ Fuel Cells

s. m. a. shibli and m. noel, Int. J. Hydrogen Energy, 1192, 18, (2), 141–147

Teflon bonded Pt-Ir bimetal catalyst-based porous electrodes were prepared for use in H₂-Cl₂ fuel cells. These gas diffusion electrodes, fabricated by a hot pressing technique, had optimised performance at 2.5 wt.% Pt and 5 wt.% Ir, for both H₂ oxidation and Cl₂ reduction reactions. The fuel cells has optimised operation at 333 K, gas pressure of 60 mm Hg on both electrodes, 5 M HCl electrolyte and interelec-trode distance of 6 mm. Under these conditions voltages of 1.0 V at current densities of 100 mA/cm² for 300 h were obtained.

CORROSION PROTECTION

The Nature of the Passive Film on Cathodically Modified Stainless Steels

j. h. potgieter, w. skinner and a. m. heyns, J. Appl. Electrochem., 1993, 23, (1), 11–18

The effect of additions of platinum group metals on the composition of the passive surface layer formed on stainless steels in reducing acid media was studied. An accumulation of the platinum group metals occurred on the surface of the alloy during the period of active dissolution.

CHEMICAL TECHNOLOGY

Alloys of Palladium with Metals of the Platinum Group as Hydrogen-Permeable Membrane Components at High Temperatures of Gas Separation

f. n. berseneva, n. i. timofeev and a. b. zakharov, Int. J. Hydrogen Energy, 1993, 18, (1), 15–18

Studies of the effect of phase composition of the binary Pd-Pt and Pd-Rh matrices in which the concentration of Pt and Rh in the uniform f.c.c. solid solution was 0-25%, were performed. The effects of dissolved H on the phase composition and mechanical properties of Pd-Pt and Pd-Rh alloys were examined. Multicomponent alloys of Pd with platinum group metals are suitable membrane materials.

ELECTRICAL AND ELECTRONIC ENGINEERING

Optimization of the Tradeoff between Switching Speed of the Internal Diode and On-Resistance in Gold- and Platinum-Implanted Power Metal-Oxide-Semiconductor Devices

m. f. catania, f. frisina, n. tavolo, g. ferla, s. coffa and s. u. campisano, IEEE Trans. Electron Devices, 1992, 39, (12), 2745–2749

The effect of Pt and Au doping on the switching characteristics of the internal diode of power MOS devices was studied. The tradeoff curve between the on-resis-tance of the device and the reverse recovery charge of its internal diode was measured after diffusion of the metallic impurities. It is concluded that Pt implantation applied to power MOS device fabrication gives an improved tradeoff between dynamic and static device characteristics with respect to Au doping. High-voltage n -channel power MOS devices with a fast internal diode and a limited increase in the on-resis-tance were produced by this fabrication process.

Ti/Pt/Au Ohmic Contacts to n -Type ZnSe

t. miyajima, h. okuyama and k. akimoto, Jpn. J. Appl. Phys., Part 2 Lett., 1992, 31, (12B), L1743–L1745

A Ti/Pt/Au multilayered metal structure was found to form a nonalloy ohmic contact to n -ZnSe with an electron concentration of > 10¹⁹/cm³. A specific contact resistance as low as 3.4 × 10^-4 Ω cm² was obtained for an n -type Cl-doped ZnSe layer with a high electron concentration of 2 × 10¹⁹/cm³. The lower contact resistance can be ascribed to the higher reactivity and adhesion of Ti metal with the surface of ZnSe at low temperature, and to the lower work function of Ti metal. A small improvement in the specific contact resistance was made by thermal annealing at 250°C for 5 min, which yielded the lowest value of 1.1 × 10^-4 Ω cm². The electrical properties of the contact are stable up to 300°C.

Magnetooptical Spectra in Pt/Co and Pt/Fe Multilayers

k. sato, h. hongu, h. ikekame, j. w atan abe, k. tsuzukiyama, y. togami, m. fujisawa and t. fukazawa, Jpn. J. Appl. Phys., 1992, 31, (11), 3603–3607

Magnetooptical (MO) spectra were measured at 1.2–5.9 eV in Pt/Co and Pt/Fe multilayers and corresponding Pt-Co and Pt-Fe alloys which were produced by DC magnetron sputtering. Simulation of MO spectra performed by the virtual optical constant method showed that spectral behaviour of multilayers can be explained by formation of an alloy layer of thickness ∼ 6.5 Å at the interface between the Pt layer and the transition metal layer comprising the multilayers. The off-diagonal conductivities obtained suggest that magnetooptical spectra of multilayers are caused by those of corresponding alloys formed at the interface.

Microstructures of Pt/Co Films Deposited on Sputter-Etched Underlayers

s. sumi, k. tanase, y. teragaki, k. torazawa, s. tsunashima and s. uchiyama, Jpn. J. Appl. Phys., 1992, 31, (10), 3328–3331

Pt/Co multilayered films deposited on a sputter etched SiN underlayer show larger magnetic anisotropy, 1 × 10⁶ erg/cm³, and better squareness = 1, than those on non-etched underlayers. The etching is shown to improve the multilayer structural order. The etching of underlayers transforms the Pt/Co films from island structure to continuous structure in an early stage of film growth. SEM and STM suggest that the sputter etching flattens the surface of the underlayer.

Subpicosecond Photoinduced Switching of Second-Harmonic Generation from a Ruthenium Complex in Supported Langmuir-Blodgett Films

h. sakaguchi, l. a. gomez-jahn, m. prichard, t. l. penner, d. g. whitten and t. nagamura, J. Phys. Chem., 1993, 97, (8), 1474–1476

Ultrafast modulation of the second harmonic (SH) intensity from a Langmuir-Blodgett film consisting of a Ru complex, Ru bipyridyl, with one of the ligands being substituted by amide groups, is shown by laser irradiation of the film at 1064 nm. The switching of the SH intensity is shown to occur in less than 2 ps by a picosecond pump-probe experiment.

Size Effect on the Electrical Conduction and Noise of RuO₂-Based Thick Film Resistors

b.-s. chiou, j.-y. sheu and w.-f. wu, J. Electron. Mater., 1992, 21, (12), 1105–1110

The temperature dependence of sheet resistance for a generic RuO₂-based resistor of composition 20 wt.%RuO₂-80 wt.% glass (63 wt.%PbO-25 wt.%oB₂O₅-12 wt.%SiO₂) was evaluated. A combined tunnel/parallel conduction model was used to describe the resistance behaviour with respect to temperature variation. The geometry of the film, such as aspect ratio and thickness, has a significant effect on the electrical characteristic of the thick film assembly.

MEDICAL USES

Crosslinking of Adjacent Guanine Residues in an Oligonucleotide by cis -[Pt(NH₃)₂(H₂O)₂]²⁺: Kinetic Analysis of the Two-Step Mechanism

f. gonnet, j. kozelka and j.-c. chottard, Angew. Chem. Int. Ed. Engl, 1992, 31, (10), 1483–1485

A new method for determination of the four rate constants of the two-step reaction between an oligonucleotide containing a GpG unit and cis -[Pt(NH₃)₂(H₂O₂)]²⁺ has been developed. The method consists of treating known amounts of oligonucleotide with nearly stoichiometric Pt complex in aqueous solution, and periodically taking aliquots which are quenched by addition of a saturated KCl solution followed by cooling to liquid N₂ temperature.