The Photoelectron Spectra of Ni,Pd, Pt-Diallyl

The He (I) photoelectron (PE.) spectra of bis (π-allyl)palladium (2a) , bis (π-allyl)platinum (3a) , bis (π-methallyl)palladium (2b) and bis (π-methallyl)-platinum (3b) have been recorded and compared with the PE. spectra of bis (π-allyl)nickel (1a) and bis (π-methallyl)nickel (1b) . By use of the He (II) PE. spectra 2a, 2b and 3b and correlations between the PE. spectra of 1–3 it is possible to assign the first seven to eight transitions in the PE. spectra of 1–3 . In contrast to previous assignments it is shown that the first band in the PE. spectrum of 1a corresponds to the ejection of an electron from 7a_u, a pure ligand orbital. The assignment proposed is supported by semiempirical calculations of the INDO-type by considering the relaxation effects explicitly using the ΔSCF and transition operator method.     

Synthesis of palladium nanoparticles by sonochemical reduction of palladium(II) nitrate in aqueous solution

The sonochemical synthesis of stable palladium nanoparticles has been achieved by ultrasonic irradiation of palladium(II) nitrate solution. The starting solutions were prepared by the addition of different concentrations of palladium(II) nitrate in ethylene glycol and poly(vinylpyrrolidone) (PVP). The resulting mixtures were irradiated with ultrasonic 50 kHz waves in a glass vessel for 180 min. The UV-visible absorption spectroscopy and pH measurements revealed that the reduction of Pd(II) to metallic Pd has been successfully achieved and that the obtained suspensions have a long shelf life. The protective effect of PVP was studied using Fourier transform infrared (FT-IR) spectroscopy. It has been found that, in the presence of ethylene glycol, the stabilization of the nanoparticles results from the adsorption of the PVP chain on the palladium particle surface via the coordination of the PVP carbonyl group to the palladium atoms. The effect of the initial Pd(II) concentration on the Pd nanoparticle morphology has been investigated by transmission electron microscopy. It has been shown that the increase of the Pd(II)/PVP molar ratio from 0.13 x 10(-3) to 0.53 x 10(-3) decreases the number of palladium nanoparticles with a slight increase in particle size. For the highest Pd(II)/PVP value, 0.53 x 10(-3), the reduction reaction leads to the unexpected smallest nanoparticles in the form of aggregates.     

Insertion of molecular oxygen into a palladium(II) hydride bond

Insertion of molecular oxygen into a palladium(II) hydride bond to form an (eta1-hydroperoxo)palladium(II) complex is reported. The hydroperoxo palladium(II) product has been crystallographically characterized. A second-order rate law (first-order in palladium and first-order in oxygen) is observed for the reaction and a large kinetic isotope effect implicates Pd-H bond cleavage in the rate-determining step. The results of studies with radical inhibitors and light suggest that the reaction does not proceed by a radical chain mechanism.     

Precipitation of bis(1,2-cyclohexanedionedioximato)palladium(II) from homogeneous solution

The reaction between hydroxylamine and cyclohexanedione in the presence of palladium ions has been made the basis of the precipitation of bis(1,2-cyclohexanedionedioximato)palladium(II) from homogeneous solution. The procedure provides a means of separating palladium from Cu(II), Co(II), Ni(II) and Pt(IV), and is a simple, rapid and accurate method for determining palladium.     

Kinetic studies of complexation reactions of water-soluble hydrazones with nickel(II) and palladium(II) ions

The kinetics of complexation reactions of five water-soluble heterocyclic hydrazones with nickel(II) and palladium(II) ions have been investigated by stopped-flow spectrophotometry. Rates of complexations with nickel(II) and palladium(II) in the absence of chloride ion were found to be proportional to the first order of the ligand and metal ion concentrations and to the inverse first order of the hydrogen ion concentration except for the complexation of alpha-(2-benzimidazolyl)-alpha-(5-nitro-2-pyridyl)hydrazono-3-toluenesulfonic acid with palladium(II). Rates of complexation with palladium(II) in the presence of chloride ion were best described by a two-term expression, both terms being first order in the palladium ion and ligand concentrations and inverse first order in the hydrogen ion concentration. The first term has zero dependence of the chloride ion concentration, whereas the second is first order with respect to the chloride ion concentration. The rate constant for each complexation reaction was determined. The complexation of the hydrazones with nickel(II) was estimated to go according to an Eigen mechanism and that with palladium (II) according to the associative mechanism.     

Preparation and properties of a new chelating resin containing 1-nitroso-2-naphthol as the functional group

A macroreticular polystyrene-based chelating ion-exchanger containing 1-nitroso-2-naphthol as the functional group has been synthesized. The exchange-capacity of the resin for a number of metal ions such as copper(II), iron(III), cobalt(II), nickel(II), palladium(II) and uranium(VI) as a function of pH has been determined. The sorption and elution characteristics for palladium(II) and uranium(VI) have been thoroughly examined with a view to utilizing the resin for separation and concentration of uranium and palladium. Uranium(VI) has been separated from a mixture of ten other metal ions by sorption on the chelating resin and selective elution with 0.5M sodium carbonate. Palladium(II) has been separated from various metal ions by selective sorption on the resin in 1M hydrochloric acid medium.     

Liquid-liquid extraction of palladium(II) from hydrobromic acid media by hexadecylpyridinium bromide.

A simple and rapid liquid-liquid extraction of palladium has been studied involving ion-pairing of bromocomplexes of palladium(II) with hexadecylpyridinium bromide (HDPB) dissolved in chloroform. The stoichiometry and distribution of (HDP)2PdBr4 between the aqueous and organic phase was investigated by spectrophotometric mole ratio method. The extraction efficiency of palladium(II) by HDPB was studied as a function of several variables: acid, salt, surfactant concentration and equilibrium time. The results showed that PdBr4(2-) extraction could be explained by assuming the formation of (HDP)2PdBr4 complexes in the aqueous solution and transfer to organic phase. The extraction was fast and the shaking time was only a few min. The average recovery of palladium(II) from an aqueous solution containing 10 microg/ml of analyte was 99% with an RSD% of 0.95. The percentage recovery of 0.2 microg/ml palladium(II) was 96%.     

Co-precipitation of metal dimethylglyoximates generated from biacetyl monoxime or biacetyl and hydroxylamine

A study has been made of some aspects of the co-precipitation of gold and platinum(II) and (IV) with palladium(II) precipitated from homogeneous solution initially containing biacetyl and hydroxylamine in 0.3M hydrochloric acid. The co-precipitation of nickel(II) with palladium(II) and vice versa from near neutral solutions initially containing biacetyl and hydroxylamine was also explored; the solid is enriched in the minor constituent in both cases. As with biacetyl monoxime-hydroxylamine systems, both nickel(II) and palladium(II) promote formation of dimethylglyoxime from such solutions between pH 7 and 8. Factors leading to this unusual behaviour in co-precipitation are discussed and a qualitative explanation tentatively advanced. The co-precipitation of nickel and palladium(II) is different when biacetyl monoxime solutions are used; the former comes out of solution faster than the latter irrespective of their concentration ratio. This disparity in the reaction rates can be used to separate nickel directly from palladium(II) by precipitation or extraction of the dimethylglyoximate into chloroform.     

Synthesis of N-o-methylphenyl-N'-(sodium p-aminobenzene-sulfonate) thiourea and its chromogenic reaction with palladium(II).

A new chromogenic reagent, N-o-methylphenyl-N'-(sodium p-aminobenzenesulfonate)thiourea (MSAT), has been synthesized and characterized by elemental analysis, (1)H-NMR, FT-IR and UV-Vis spectra. Based on the absorption spectrum of the colored complex of MSAT with palladium(II), a novel spectrophotometric method for the determination of palladium has been developed. In a pH 4.0 - 5.5 HAc-NaAc buffer solution, palladium(II) reacted with MSAT to form a stable yellow water-soluble complex with an apparent molar absorptivity of epsilon = 2.04 x 10(5) L mol(-1) cm(-1) at the maximum absorption of 318.0 nm. Beer's law was obeyed in the concentration range of 1.2 - 11.8 microg per 25 mL for palladium(II) with a correlation coefficient of 0.9997. The probable interfering ions and their tolerable limits have also been investigated in detail. The proposed method is simple, rapid, and sensitive, and has been applied to the determination of palladium in anode mud and ore samples with satisfactory results.     

Palladium-catalyzed glycal imidate rearrangement: formation of alpha- and beta-N-glycosyl trichloroacetamides

A novel palladium(II)-catalyzed stereoselective synthesis of alpha- and beta-N-glycosyl trichloroacetamides has been developed. The alpha- and beta-selectivity at the anomeric carbon depends on the nature of the palladium-ligand catalyst. While the cationic palladium(II) promotes the alpha-selectivity, the neutral palladium(II) favors the beta-selectivity.     

The application of infrared spectroscopy to probe the surface morphology of alumina-supported palladium catalysts

Five alumina-supported palladium catalysts have been prepared from a range of precursor compounds [palladium(II) nitrate, palladium(II) chloride, palladium(II) acetylacetonate, and tetraamminepalladium(II) tetraazidopalladate(II)] and at different metal loadings (1-7.3 wt %). Collectively, this series of catalysts provides a range of metal particle sizes (1.2-8.5 nm) that emphasize different morphological aspects of the palladium crystallites. The infrared spectra of chemisorbed CO applied under pulse-flow conditions reveal distinct groupings between metal crystallites dominated by low index planes and those that feature predominantly corner/edge atoms. Temperature-programmed infrared spectroscopy establishes that the linear CO band can be resolved into contributions from corner atoms and a combination of (111)(111) and (111)(100) particle edges. Propene hydrogenation has been used as a preliminary assessment of catalytic performance for the 1 wt % loaded catalysts, with the relative inactivity of the catalyst prepared from palladium(II) chloride attributed to a diminished hydrogen supply due to decoration of edge sites by chlorine originating from the preparative process. It is anticipated that refinements linking the vibrational spectrum of a probe molecule with surface structure and accessible adsorption sites for such a versatile catalytic substrate provide a platform against which structure/reactivity relationships can be usefully developed.     

Spectrophotometric determination of palladium using 4-methyl-l ,2-cyclohexanedionedioxime

A procedure for the determination of palladium with 4-methyl-1,2-cyclohexanedionedioxime by an extraction -spectrophotometric method has been developed. Interference by coppcr(II), cobalt(Il), iron(II), or iron(III) can be eliminated by suitable masking agents. Ruthenium(III) must be absent or separated prior to the determination of palladium. The molar absorptivity of the bis(4-methyl-1,2-cyclohexanedionedioximato-N,N') palladium(II) complex has been calculated and found to be 1.51?10⁴ 1/moles-cm in chloroform at 280 mμ.     

Theoretical Study on the Mechanism of Sonogashira Coupling Reaction

The mechanism of palladium-catalyzed Sonogashira cross-coupling reaction has been studied theoretically by DFT （density functional theory） calculations. The model system studied consists of Pd（PH3）2 as the starting catalyst complex, phenyl bromide as the substrate and acetylene as the terminal alkyne, without regarding to the co-catalyst and base. Mechanistically and energetically plausible catalytic cycles for the cross-coupling have been identified. The DFT analysis shows that the catalytic cycle occurs in three stages： oxidative addition of phenyl bromide to the palladium center, alkynylation of palladium（Ⅱ） intermediate, and reductive elimination to phenylacetylene. In the oxidative addition, the neutral and anionic pathways have been investigated, which could both give rise to cis-configured palladium（Ⅱ） diphosphine intermediate. Starting from the palladium（Ⅱ） diphosphine intermediate, the only identifiable pathway in alkynylation involves the dissociation of Br group and the formation of square-planar palladium（Ⅱ） intermediate, in which the phenyl and alkynyl groups are oriented cis to each other. Due to the close proximity of phenyl and alkynyl groups, the reductive elimination of phenylacetylene proceeds smoothly.     

Electrochemical behaviour ofcis-dichloro(arylisocyanide)(tertiaryphosphine) platinum (II) and palladium(II) complexes in an aprotic solvent

Summary The electrochemical behaviour of neutral platinum(II) and palladium(II) isocyanide complexes has been investigated in an aprotic medium at platinum and mercury electrodes. Platinum(II) derivatives are reduced to platinum(0) species, Palladium(II) compounds give rise to palladium(0) species at room temperature, while at 0° it is possible to obtain palladium(I) compounds.     

Catalytic kinetic spectrophotometric determination of trace amounts of palladium with dahlia violet after separation and preconcentration on sulphydryl dextran gel

A sensitive and selective kinetic catalytic spectrophotometric method has been described for the determination of trace amounts of palladium(II). The method is based on the catalytic effects of palladium(II) on the reduction reactions of Dahlia Violet with sodium dihydrogen hypophosphite (NaH₂PO₂) in a sulfuric acid medium. Under optimal conditions, trace amounts of palladium(II) can be determined. A good linear range has been obtained in the concentration range of Pd(II) over 0.001–0.028 μg/mL with a detection limit of 5.9 × 10⁻¹⁰ g/mL. The method has been successfully applied to the determination of palladium(II) in ore and soil samples. The relative standard deviation was less than 5.0% (n = 11). The coexisting ions were eliminated by preconcentration and separation on sulphydryl dextran gel with satisfactory results. The text was submitted by the authors in English.     

Catalytic Oxidation of Iron(II) Aqua Complex by Oxygen in the Presence of Palladium(II) Tetraaqua Complex

The catalytic oxidation of iron(II) with oxygen occurs along with an autocatalytic reaction between palladium(II) tetraaqua complex and iron(II) aqua complex in an oxygen atmosphere. The reaction is catalyzed by a compound of palladium in an intermediate oxidation state, presumably by a small palladium cluster formed in the course of the reduction of palladium(II) tetraaqua complex with iron(II) aqua complex.     

Self-Consistent-Field potential-energy surfaces for hydrogen atom pairs within small palladium clusters

An ab initio electronic structure study is presented of hydrogen–hydrogen interactions in an electronic environment perturbed by the presence of palladium atom clusters. In particular, we investigated changes in the interatomic potential when the atomic centers are trapped inside an fcc palladium octahedral hole and when they are separated from each other by a (111) plane of palladium atoms. The (111) plane was modeled with a cluster of three palladium atoms. Self-consistent field (SCF ) level calculations were performed, and palladium atom pseudopotentials were employed to make the systems studied computationally tractable. For pairs of atoms placed within the octahedral hole, various lines of approach were considered [along the (100), (110), and (111) directions]. Lattice deformations and electronic excitations were examined for their effect on the interatomic potential.     

A facile highly regio- and stereoselective preparation of N-tosyl allylic amines from allylic alcohols and tosyl isocyanate via Palladium(II)-catalyzed aminopalladation-beta-heteroatom elimination

The high regio- and stereoselectivity have been obtained from the allylic substitution reaction catalyzed by palladium(II) species. From allylic alcohols, one-pot reaction with tosyl isocyanate followed by palladium(II)-catalyzed allylic substitution gives N-tosyl (E)-allylic amines in high yield. The substitution occurs only at the gamma-position of the 1- or 3-substituted allylic alcohols.     

Reaction of palladium (I) carbonyl acetate with phosphorus-containing ligands and the molecular structure of tris(triphenylphosphine)palladium

Conclusions Neutral and cationic carbonyl-containing palladium (II) complexes with phosphine ligands have been synthesized; they are not very stable in solution and undergo disproportionation to give palladium (0) and (II) compounds. The structure of one of these disproportionation products, namely, tris(triphenylphosphine)palladium, was solved by x-ray structural analysis.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 894–897, April, 1987.     

Solvent extraction and spectrophotometric determination of palladium(II) with some nitrogen-containing heterocyclic hydrazones in the presence of chloride ions

Three terdentate hydrazones, all containing the 1-phthalazino grouping in the hydrazine moiety but differing in the heterocyclic substituent in the aldehyde moiety, have been used as analytical reagents for palladium(II), the optimal conditions for the extractive spectrophotometric determination of palladium(II) in the presence of chloride ions being deduced. These compounds are highly selective and sensitive reagents for palladium(II), since they are not extracted into chloroform from sulfuric acid solutions and do not react with other platinum group metals. The desirable spectral properties of the palladium(II) complex of benzothiazole-2-aldehyde-1-phthalazinohydrazone (BAPhH) have also been discussed with respect to preference of the C  N structural form in the heterocyclic ring on the aldehyde moiety of the ligand.