Synthesis, structure and photoluminescence of a novel palladium(I) compound: [Pd3(μ3-Cl)2(dppp)3][Pd2(μ2-Cl)3(PPh3)2](PPh3)2

Pd(PPh₃)₂Cl₂ reacts with PdCl₂ and 1,3-bis(diphenylphosphine)propane (dppp) in ethanol–DMF–pyridine mixed solvent to yield a novel palladium(I) compound [Pd₃(μ₃-Cl)₂(dppp)₃][Pd₂(μ₂-Cl)₃(PPh₃)₂](PPh₃)₂. It features an isolated structure based on [Pd₃(μ₃-Cl)₂(dppp)₃]⁺ cations having triangulo-palladium clusters and [Pd₂(μ₂-Cl)₃(PPh₃)₂]⁻ anions in which the coordination environment of palladium is an unusual tetrahedral geometry. Its photoluminescence is measured.     

Molecular structures and vibrational frequencies for cis-[PdCl2(tmen)] and cis-[Pd(N3)2(tmen)]: A DFT study

Theoretical molecular structures of the complexes cis-[PdCl₂(tmen)] and cis-[Pd(N₃)₂(tmen)] (tmen = N,N,N′,N′-tetramethylethylenediamine) were investigated using B3LYP/DFT method. The calculated molecular parameters, bond distances and angles, revealed a square-planar geometry around the metallic center for both compounds with the azide being linear. The theoretical infrared spectra of C₁ symmetry (electronic state ¹A) of the compounds are in agreement with the experimental data.     

Electrochemical synthesis of Pd particles on poly(vinylferrocenium)

Electrochemical synthesis of Pd particles on poly(vinylferrocenium) (PVF⁺) support was described. K₂PdCl₄ was used as the metal particle precursor. Pd particles were incorporated into the polymer matrix electrochemically either by cyclic voltammetric scans (between +1.0 V and −0.8 V vs. SCE) or by reduction at constant potential (at −0.8 V vs. SCE) from aqueous solution of K₂PdCl₄. Scanning electron microscopy (SEM) studies showed that the Pd particles were well dispersed in the polymer matrix. Experimental parameters such as polymer film thickness, number of cycles during cyclic voltammetric scans in K₂PdCl₄ and electrolysis time in K₂PdCl₄ were studied. The Pd/PVF⁺ system showed catalytic activity towards hydrazine oxidation and appreciable results were obtained when compared with the related studies.     

The electrochemical reduction of PdCl4 and PdCl6 in polyaniline: Influence of Pd deposit morphology on methanol oxidation in alkaline solution

The controlled uptake and electrochemical reduction of metal precursors PdCl₄²⁻ and PdCl₆²⁻ in polyaniline (PANI) is demonstrated. The formation of PANI/Pd composites is achieved with a reduction in proton doping and an increase in the oxidation of the polymer with Pd deposits physically blocking the nitrogen groups. High surface area filaments (PdCl₄²⁻) or a rough encapsulation (PdCl₆²⁻) of Pd metal on PANI are obtained. The structural differences highlight the influence of the metal precursor oxidation state on the morphology of the Pd deposits in PANI. Thermal gravimetric analysis provides an estimate of the Pd content for each composite of ∼40%. X-ray Photoelectron Spectroscopy and X-ray-excited Auger Electron Spectroscopy analyses confirm the deposition of Pd metal. The catalytic oxidation of methanol was demonstrated for both PANI/Pd composites in alkaline solutions that prohibit proton doping of the polymer. The data indicates that Pd metal acts as a solid-state dopant that may delocalize the charge on the polymer backbone to maintain conductivity. Methanol oxidation at PANI/Pd composites produced using PdCl₄²⁻ was enhanced relative to the composite produced using PdCl₆²⁻ and a planar Pd electrode. Comparison of PANI/Pd composite produced using PdCl₄²⁻ with other Pd catalysts from the literature indicates surface poisoning is reduced when Pd is coupled with the polymer. The composite is robust and stable in alkaline solution with the charge density decreasing by 5% on the positive scan and 13% on the negative scan after 200 voltammetric cycles. The data also indicates that the reductive desorption of surface contaminants is possible, minimizing the catalytic loss due to surface poisoning.     

Selective Separation of Palladium from Organic Solutions Containing Nickel or Platinum using Polythioamide as a Sorbent

The feasibility of the selective recovery of Pd from organic liquid waste using polythioamide (PTA) as a sorbent has been investigated. PTA effectively sorbed Pd(II) in some organic solutions under not only acidic conditions but also basic conditions. PTA was also able to sorb Pd from organic solutions containing PdCl₂(PhCN)₂ and Pd₂(dba)₃. The results for the molecular structure of a model compound ([Pd(C₁₁H₁₅NS)₄]Cl₂) suggest that the presence of a S donor plays an important role in the sorption of Pd(II) by PTA. The sorbed Pd was quantitatively eluted using 1,3-bis(diphenylphosphino)propane in MeOH, and the recovered PTA can be reused at least five times. The selective separation of Pd(II) was achieved even from organic solutions containing a 100 times larger amount of Ni(II) or Pt(IV) under acidic conditions or basic conditions, respectively.     

Polymerization of N-substituted 2-propynamides with transition metal catalysts

Summary Polymerization of N-substituted 2-propynamides proceeded in the presence of Pd(II) catalysts such as [Pd(CH₃CN)₄](BF₄)₂, PdCl₂(PhCN)₂-n-BuLi, and PdCl₂(nbd)-n-BuLi. The molecular weights of the obtained polymers ranged 8,500 to 14,000, depending on the catalysts. From the ¹H NMR spectra, these polymers were found to have alternating double bonds in the main chain. Received: 25 December 2000/Revised version: 17 January 2001/Accepted: 19 January 2001     

Synthesis of Pd(II) coordination complexes of (S)-4-isobutyl-2-methyl-2-oxazoline and (S)-2-(2,2-dimethylpropyl)-4-isopropyl-2-oxazoline

(S)-4-Isobutyl-2-methyl-2-oxazoline (1) was obtained from ethyl acetimidate hydrochloride and l-leucinol in 81% yield. (S)-2-(2,2-Dimethylpropyl)-4-isopropyl-2-oxazoline (2) was synthesized from 3,3-dimethylbutyryl chloride and l-valinol in two steps in a total yield of 44%. Reactions of oxazolines 1 and 2 with Pd(OAc)₂ in AcOH or MeCN at different temperatures followed by treatment with LiCl resulted in the formation of the corresponding coordination complexes PdCl₂(1)₂ and PdCl₂(2)₂ with no traces of cyclopalladated complexes.     

Effect of residual Cl− derived from metal precursors on catalytic activity in the hydrogenation of naphthalene over supported Pd catalysts

Hydrogenation of naphthalene was performed over supported Pd catalysts prepared from precursors that contained Cl⁻ and from precursors that were free of Cl⁻. The activity of catalyst prepared from PdCl₂ was much higher than that prepared from Pd(NH₃)₂(NO₂)₂. The species of Pd precursor strongly affected the activity of Pd/Al₂O₃, whereas no significant influence was observed in the effect of Pd/SiO₂, because residual Cl⁻ was easily removed by calcination and/or reduction. Catalytic activity was increased by addition of NH₄Cl to Cl⁻-free Pd/Al₂O₃. Residual Cl⁻ was concluded to enhance the catalytic activity of the supported Pd catalysts.     

Ligand transfer between hard and soft metal centres. Synthesis and X-ray characterisation of a new trinuclear Pd(II) dithiocarbamate Pd3(Et2NCS2)4Cl2

Reaction between PdCl₂(PhCN)₂ and Nb₂(μ-S₂)₂(Et₂NCS₂)₄ results in a transfer of the dithiocarbamate ligand from Nb(IV) to Pd(II) and allows isolation of the new trinuclear palladium complex Pd₃(Et₂NCS₂)₄Cl₂ for the first time. The crystal structure of the complex has been determined.     

New carbon composites containing ultrafine metal particles. 2. Synthesis by pyrolisis of pitch-organometallic blends

Air-stable new carbon composites containing uniformly dispersed ultrafine Fe, Co, Ni, Ru, Pd, Rh, or Ag particles were obtained by thermal degradation of coal pitches mixed homogeneously with 1–10% of poly(vinyl ferrocene), cobaltocene, nickelocene, (acenaphthylene) Ru₃(CO)₇, PdCl₂(COD), RhCp(COD), and AgC₆H₄CH₂NMe₂, respectively, at 400–1200°C in Ar. Carbonization yields are 45–55% and the size of metal particles varied from 5 to 65 nm depending upon the treatment temperature and identity of the metal. The carbon composites containing Fe particles showed high Vicat hardness and good electrical conductivity. Pd- and Rh-dispersed materials exhibited good catalysis in hydrogenation of 1-hexene. The composite containing ultrafine Ag particles showed excellent bacteriostatic activity forEscherichia coli, Pseudomonas aeruginosa, andBatchillus subtilis.     

Low-Pressure Carbonylation of Benzyl Bromide with Palladium Complexes Modified with PNS (PNS = Ph2PCH2CH2C(O)NHC(CH3)2CH2SO3Li) or P(OPh)3. Structural Identification of Palladium-Catalyst Intermediate

The catalytic activities of two palladium complexes with water soluble phosphine PNS (PNS = Ph₂PCH₂CH₂C(O)NHC(CH₃)₂CH₂SO₃Li) (I) and phosphite P(OPh)₃ (II) were tested in the carbonylation of benzyl bromide in methanol at 40–50°C and 1 atm of CO. The first catalyst, (I), was formed in situ from PdCl₂(cod) and PNS, the second one, (II), was based on the PdCl₂(P(OPh)₃)₂ complex. At the ratio of [NEt₃]:[PhCH₂Br] equal to 2.5 the yields of phenylacetic acid methyl ester were 83–86% in the carbonylation with PNS and 100% in the carbonylation with P(OPh)₃. The palladium catalyst with P(OPh)₃ produced under the same conditions 70% of phenylacetic acid methyl ester in the carbonylation of benzyl chloride and 60% of 2-methylphenylacetic acid methyl ester in the carbonylation of 1-bromoethylbenzene. The lower rate of carbonylation of 1-bromoethylbenzyl bromide in comparison to that of benzyl bromide was explained by the lower rate of the substrate oxidative addition step leading to palladium benzyl complexes. Two palladium benzyl complexes, cis-PdBr(PhCH₂)(P(OPh)₃)₂ and trans-PdBr(PhCH(Me))(P(OPh)₃)₂ have been isolated and characterized (X-ray, ³¹P and ¹H NMR).     

Approaches to bi- and trimetallic platinum and palladium complexes using the DPPEPM ligand

Bis{(diphenylphosphinoethyl)phenylphosphino}methane (DPPEPM) reacts with [PtR₂(cod)] in 1:1 ratio to give [PtR₂(DPPEPM-PP)] (2a, R=Me; 2b, R=Ph), whereas with [PtCl₂(cod)] or [PdCl₂(cod)] it yields the ionic species [M(DPPEPM-PP)₂]²⁺ (3 and 4). With [MClMe(cod)], the product is [MMe(DPPEPM-PPP)]⁺ (5, M=Pt; 6, M=Pd), in which one of the internal P atoms of the ligand is uncoordinated. These complexes undergo oxidation of the free P atom to give 7 and 8 on standing in solution. Complexes 2–4 may be used to construct bimetallic and trimetallic mixed metal complexes. The molecular structures of 7 and [PtMe₂(μ-DPPEPM)PdCl₂] (11) are reported.     

Long-Chain-Amine Metal Complexes as Hydrogenation Catalysts. Heterogenisation on Activated Carbon

The catalytic activity of [PdCl₂(NH₂(CH₂)₁₂CH₃)₂] (named [Pd(TDA)]) and [RhCl(NH₂(CH₂)₁₂CH₃)₃] (named [Rh(TDA)]) complexes for the hydrogenation of cyclohexene has been analysed both in homogeneous phase and heterogenised on activated carbon. The [Rh(TDA)] complex has been found to be more active than the [Pd(TDA)], both homogeneous and heterogenised. Experimental and modelled results indicate that these complexes follow a similar reaction mechanism, but with different rates. A clear positive effect of the carbon support has been found in the case of the complex [Rh(TDA)], which has been related to the anchorage of the aliphatic chains of the amine ligands on the activated carbon pores. Experiments in consecutive catalytic runs show that the heterogenised complexes can be used several times giving an acceptable conversion level.     

Transfer hydrogenation and transfer hydrogenolysis. X. Selective hydrogenation of methyl linoleate by indoline and isopropyl alcohol

The selective hydrogenation of methyl linoleate was studied using indoline and isopropyl alcohol as hydrogen sources. Many transition metal compounds and metallic palladium were examined as catalysts. High selectivity to monoenes and little formation oftrans isomers were realized under mild conditions in some reaction systems. For example, the system in which isopropyl alcohol and RuCl₂(PPh₃)₃ were used as hydrogen donor and catalyst was excellent. Also in the hydrogen transfer from indoline to the linoleate catalyzed by PdCl₂ and (NH₄)₂PdCl₄, high selec-tivity was realized. In the RuCl₂(PPh₃)₃-isopropyl alcohol, (NH₄)₂PdCl₄-indoline and PdCl₂-indoline system, methylcis- trans conjugated octadecadienoate was reduced rapidly with complete selectivity, where-as the same hydrogen transfer systems resulted in little if any reaction with methyl oleate. High selec-tivity in the reduction of linoleate is presumed to be realized through prior conjugation of the substrate.     

An efficient catalyst system for the carbonylation to esters of α-arylpropionic acids

The polymer-supported bimetallic catalyst system PVP–PdCl₂–CuCl₂/PPh₃ has good conversion and regioselectivity to carbonylation of α-(6′-methoxy-2′-naphthyl)ethanol under mild conditions. The effects of temperature, CO pressure, reaction time and P/Pd ratio have been studied to obtain optimum reaction conditions. The carbonylation of various α-arylethanols and styrene derivatives are also investigated with the same catalyst. X-ray photoelectron spectroscopy (XPS) and transmission electron micrograph (TEM) show that the polymer would protect palladium particles against aggregation and serve as a ligand.     

Reactivity of mononuclear dithiolato palladium and platinum metalloligands towards the formation of homo- and heterobimetallic complexes

The reactivity of mononuclear platinum and palladium dithiolato species as building blocks for homo- and heterobimetallic complexes is described. The heterobimetallic cationic complex [(PPh₃)₂Pt(μ-S(CH₂)₂S)Pd(dppb)](BF₄)₂ was obtained by reaction of [Pt(S(CH₂)₂S)(PPh₃)₂] with [PdCl₂(Ph₂P(CH₂)₄PPh₂)] in presence of AgBF₄.     

[PdCl2(NH2(CH2)12CH3)2] supported on γ-Al2O3 as catalyst for selective hydrogenation

The [PdCl₂(NH₂(CH₂)₁₂CH₃)₂] complex supported on -Al₂O₃ has proved to be a considerably more active, selective and sulfur-resistant catalyst in the selective hydrogenation of styrene to ethylbenzene than a traditional catalyst obtained from acid solutions of PdCl₂, and even than the same complex unsupported. The active species is the complex itself and it is stable under the reaction conditions. Hydrogen treatments above 353K destroy the complex, at least partially, leading to a less active and sulfur resistant catalyst. The higher sulfur resistance, when compared to a conventional Pd/Al₂O₃ catalyst, can be attributed to electronic and geometrical effects.     

EQUILIBRIUM OF PALLADIUM(II) EXTRACTION WITH 1-OCTYLTHEOBROMINE

ABSTRACT

1-Octyltheobromine was synthesized to study extraction equiliburium of palladium(II). To evaluate its efficiency as an extractant, the extraction of palladium(II) from acidic chloride media was studied at 303K using toluene. The extraction of palladium(II) from hydrochloric acid media by 1-octyltheobromine exhibited high selectivity for palladium(II) over the platinum group metals. The stoichiometrics of the extraction of palladium(II) with 1-octyltheobromine was elucidated by examining the effects of hydrochloric acid, chloride ion, hydrogen ion, extractant and metal ion concentrations on its extractability. Palladium(II) was found to be extracted as two molecules of 1-octyltheobromine reacted with PdCl₂ as follows: PdCl₂ +{2}¯RN ? ¯PdCl₂(RN)₂. The extraction equilibrium constant was K=2.72?×?10⁸(mol?dm^?3)^?2. The complex of 1-octyltheobromine with PdCl₂ was confirmed by mass spectrometric analysis. The stripping of palladium(II) was performed over 60% by a single batchwise treatment with an aqueous solution of thiourea or ammonia.     

Synthesis,Characterization and Properties of One-dimensional Complexes of <Emphasis Type="Italic">cis-syn-cis</Emphasis>-Dicyclohexyl-18-crown-6 with K<Subscript>2</Subscript>[M(mnt)<Subscript>2</Subscript>] (M==Ni,Pd, Pt)

Three complexes [K(DC18C6-A)]₂[M(mnt)₂] (DC18C6-A=cis-syn-cis-dicyclohexyl-18-crown-6, isomer A; M=Ni, 1; Pd, 2; Pt, 3; mnt = 1,2-dicyanoethene-1,2-dithiolate, maleonitriledithiolate, [C₂S₂(CN)₂]²⁻) have been synthesized and characterized by elementary analysis, UV–vis, FT-IR spectroscopy and X-ray single crystal diffraction. They are isomorphous and all display infinite one-dimensional chain-like structure formed by [K(DC18C6-A)]⁺ complex cations and [M(mnt)₂]²⁻ (M=Ni, Pd, Pt) complex anions through K–N interactions. Thermal analysis indicates that three complexes are all thermal stable under 260 °C and experience the same decomposition process of dissociation and evaporation of crown ether molecules. Their electrochemical behaviors have been studied by cyclic voltammetry.     

Competitive oxidation of formaldehyde and formate on amorphous copper-palladium-zirconium alloy electrodes in alkaline media

Raney-type Cu–Pd alloy electrodes were prepared from amorphous Cu–Pd–Zr ternary alloys by treatment with aq. HF, and competitive anodic oxidation reactions of HCHO and HCOO^– were studied on these electrodes in alkaline media. The initial HCHO oxidation product was HCOO^– even on Pd or Pd-rich alloy electrodes which should be more active to the HCOO^– oxidation than to HCHO. The product HCOO^– was oxidized only after a large decrease of the HCHO concentration in the electrolyte. The oxidation rate of HCOO^– was considerably lowered by the existence of even a small amount of HCHO, as well as by the introduction of CO. These results suggest that the HCHO electro-oxidation is accompanied by production of a surface contaminant such as adsorbed CO. The optimum nominal Pd atomic fraction in the Cu–Pd alloy electrodes suitable for the steady simultaneous oxidation of HCHO and HCOO^– in mixed solution was shown to be 0.25 and 0.4 in 1.0 M NaOH (M=moldm^–3) and 0.5 M K₂CO₃, respectively.