Showing papers on "Palladium published in 1990"

Palladium- and molybdenum-catalyzed hydrostannation of alkynes: a novel access to regio- and stereodefined vinylstannanes

Abstract: In the presence of catalytic amounts of dichlorobis (triphenylphosphine) palladium or of the π-allylmolybdenum complex 3, tributyltin hybride adds instantaneously at room temperature to various alkynes to give the corresponding vinylstannanes in good to excellent yields. The reaction is totally stereoselective (cis addition). With monoalkylacetylenes RC≡CH, good regioselectivity for the formation of 1-(tributylstannyl) alkenes (vs 2-tributylstannyl) alkenes) is attained only if the R substituent is sufficiently bulky

Palladium-catalyzed arylation of furan, thiophene, benzo[b]furan and benzo[b]thiophene

Abstract: Treatment of π-electron sufficient aromatic heterocycles such as title compounds with aryl bromides in the presence of tetrakis(triphenylphosphine)palladium gave the corresponding 2-aryl aromatic heterocycles.

The role of noble metals in the chemistry of solid-state gas sensors

Abstract: Surface reactions occurring on semiconductor- and pellistor-type sensors are related to the generation of a sensor signal. The role of chemisorbed and lattice oxygen on oxides and noble metals is demonstrated by examples. Reactions including spillover of hydrogen from the metal to the oxide are discussed. Finally the chemical aspects in the detection of hydrogen by three types of palladium-based sensors are compared.

Multistep electron transfer in palladium-catalyzed aerobic oxidations via a metal macrocycle-quinone system

Abstract: Selective palladium-catalyzed aerobic conditions of olefins and conjugated dienes with the aid of a metal macrocycle-quinone system have been developed. This involves a multistep electron transfer with three catalysts (Pd(OAc){sub 2}, hydroquinone, metal macrocycle). The triple catalytic system was applied to (i) 1,4-oxidation of conjugated dienes (1,4-diacetoxylation and 1,4-dialkoxylation), (ii) oxidation of terminal olefins to ketones, and (iii) allylic oxidation of cyclic olefins to 2-alken-1-yl acetates. The reactions occur under very mild conditions, (i) and (ii) at room temperature and (iii) at 60{degree}C, and are reminiscent of aerobic processes occurring in living organisms. Thus, there is an electron transfer from the substrate to Pd(II) giving Pd(0), followed by another electron transfer from Pd(0) to benzoquinone. The hydroquinone thus formed transfers electrons to the oxidized form of the metal macrocycle, which is reduced.

Palladium clusters: H2, D2, N2, CH4, CD4, C2H4, and C2H6 reactivity and D2 saturation studies

Abstract: In this paper both deuterium saturation measurements and gas‐phase kinetic measurements of chemisorption of H2, D2, N2, CD4, CH4, C2H4, and C2H6 on neutral palladium clusters are reported Saturation studies with D2 show that small palladium clusters can bind up to three deuterium atoms per palladium atom in the cluster, in contast to H/M ratios near unity typically reported for metal surfaces In addition, the small palladium clusters exhibit pronounced discontinuities in deuterium uptake which may be indicative of structural transformations or selective desorption of deuterium From the kinetic studies we find that, in general, the rate constants for a given size cluster towards different reagents tend to order as D2, H2>N2>C2H4>CD4, CH4, C2H6 The shape of the reactivity pattern with the different reagents varies strongly with cluster size for clusters containing less than 25 atoms Finally, an inverse hydrogen isotope effect is observed for both hydrogen and methane, ie, the D2 and CD4 rate constants are significantly larger than those of H2 and CH4, respectively

Catalyst for the production of alcohols by hydrogenation of carboxylic acids and process for the preparation of the catalyst

Abstract: An improved catalyst comprising a Group VIII noble metal, such as palladium, and rhenium is supported on a high surface area graphitized carbon. In an embodiment the Group VIII metal, e.g., palladium, has an average crystallite size in the range from 30 to 150 Angstroms. A process for making a catalyst is provided in which a support is impregnated with a solution of a Group VIII metal compound, the solvent is removed and the Group VIII metal impregnated support is impregnated with a solution of a rhenium compound using a solvent in which the Group VIII metal compound is insoluble, and thereafter the solvent is removed.

Palladium-catalyzed heteroannulation of 1,3-dienes by functionally substituted aryl halides

Abstract: Wittig-Horner reactions in the solid state of the inclusion compound of 4-methyl- or 3,5-dimethylcyclohexanone and an optically active host compound with (carbethoxymethylene) triphenylphosphorane gave optically active 4-methyl- and 3,5-dimethyl-1-carbethoxymethylene) cyclohexane, respectively

Influence of adsorbed carbon monoxide on the electrocatalytic oxidation of simple organic molecules at platinum and palladium electrodes in acidic solution : a survey using real-time FTIR spectroscopy

Abstract: The influence of adsorbed CO formed by dissociative chemisorption on the electrooxidation pathways and kinetics of 22 alcohols and aldehydes on polycrystalline platinum and palladium electrodes in relation to the adsorbed CO formed by dissociative chemisorption has been examined systematically by means of real-time sequences of FTIR spectra obtained during slow (2 mV s{sup {minus}1}) voltammetric sweeps in 0.1 M HClO{sub 4}. The overall objective is to explore the reactant structure-dependent role that adsorbed CO (and other CO{sub 2}-producing species) plays in the organic electrooxidation. The reactants examined include short-chain primary and secondary alcohols, aldehydes, and small bifunctional molecules (e.g., ethylene glycol) containing alcohol, aldehyde, and/or carboxylic acid units.

Method for the preparation of metal colloids in inverse micelles and product preferred by the method

Abstract: A method is provided for preparing catalytic elemental metal colloidal particles (e.g. gold, palladium, silver, rhodium, iridium, nickel, iron, platinum, molybdenum) or colloidal alloy particles (silver/iridium or platinum/gold). A homogeneous inverse micelle solution of a metal salt is first formed in a metal-salt solvent comprised of a surfactant (e.g. a nonionic or cationic surfactant) and an organic solvent. The size and number of inverse micelles is controlled by the proportions of the surfactant and the solvent. Then, the metal salt is reduced (by chemical reduction or by a pulsed or continuous wave UV laser) to colloidal particles of elemental metal. After their formation, the colloidal metal particles can be stabilized by reaction with materials that permanently add surface stabilizing groups to the surface of the colloidal metal particles. The sizes of the colloidal elemental metal particles and their size distribution is determined by the size and number of the inverse micelles. A second salt can be added with further reduction to form the colloidal alloy particles. After the colloidal elemental metal particles are formed, the homogeneous solution distributes to two phases, one phase rich in colloidal elemental metal particles and the other phase rich in surfactant. The colloidal elemental metal particles from one phase can be dried to form a powder useful as a catalyst. Surfactant can be recovered and recycled from the phase rich in surfactant.

Cyclometallation reactions of 6-phenyl-2,2′-bipyridine; a potential C,N,N-donor analogue of 2,2′: 6′,2″-terpyridine. Crystal and molecular structure of dichlorobis(6-phenyl-2,2′-bipyridine)ruthenium(II)

Abstract: Metallated and non-metallated complexes of the ligand 6-phenyl-2,2′-bipyridine (HL) with ruthenium(II), rhodium(II), platinum(II), palladium(II), and gold(III) have been prepared. The crystal and molecular structure of the complex [Ru(HL)2Cl2][triclinic, a= 8.671(1), b= 10.360(2), c= 16.139(3)A, α= 89.18(2), β= 81.26(1), γ= 67.11 (1)°, direct methods, least-squares refinement and Fourier difference synthesis, R= 0.0310, R′= 0.0359] indicates that it contains two N-bonded ligands and a cis arrangement of the chlorides.

The dinuclear palladium(II) complex of pyridine-2-thiol. Synthesis, structure, and electrochemistry

Abstract: Reaction of pyridine-2-thiol (pytH) with Pd 3 (CH 3 COO) 6 gives [Pd 2 (pyt) 4 ] (1), but that with PdCl 2 (CH 3 CN) 2 gives [Pd(pytH) 4 ]Cl 2 (2), the alkalization of which yields 1. Reaction of 1 with iodine yields neither a dinuclear Pd II Pd III nor Pd III Pd III complex but tetranuclear [Pd 4 I 2 (pyt) 6 ]. The structures have been investigated by X-ray crystallography

Catalytic destruction of organohalogen compounds

Abstract: This application relates to a catalyst and a process using this catalyst to convert or destroy organic compounds including organohalogen compounds. A preferred catalyst contains as catalytic components titania, vanadium oxide, tungsten oxide, tin oxide and at least one noble metal selected from the group consisting of platinum, palladium and rhodium, characterized in that the vanadium oxide, tungsten oxide and noble metals are uniformly dispersed on the titania. The process of this invention comprises contacting the gas stream, which contains organohalogen compounds and other organic compounds, at a temperature of about 200° to about 500° C. with the catalyst described above in the presence of an oxidizing agent and water. The oxidizing agent can be oxygen or air.