Clusters and Colloidal Metals in Catalysi

The review summarizes the results of works on the synthesis, structure, and magnetic and catalytic properties of giant palladium clusters, specifically, nanosized palladium complexes stabilized by o-phenanthroline and acetate ligands, which are objects of the colloid chemistry of palladium.     

Electrode reactions of palladium(II) in chloride solution at carbon paste electrodes modified with derivatives of N-benzoylthiourea

The study of the electrode reactions of palladium(II) at non-modified carbon paste electrodes (CPEs) in chloride solution has revealed the existence of a chloropalladate(II) complex at the electrode surface. The complex is formed during the application of anodic potentials after preceding palladium deposition. In the present paper the electrode reactions of Pd^II at CPEs modified with some N′,N′-disubstituted derivatives of N-benzoylthiourea [as selective ligands for palladium(II)] are studied in chloride solution by cyclic voltammetry. Two reduction peaks are observed in the cathodic scans recorded after deposition of palladium and anodization of the electrode. From the results it is concluded that [in addition to the chloropalladate(II) complex, observed at the non-modified electrode] a second palladium complex is formed at positive potentials. The formation of the palladium(II) complex of the N-benzoylthiourea derivatives by ligand exchange at the electrode surface is assumed. The ligand exchange itself occurs without charge transfer across the electrode|solution interface; therefore, it cannot be detected electrochemically. After palladium deposition and anodic treatment a pronounced "inverse" peak (i.e., an anodic peak in the cathodic scan) with peak currents up to 100 μA is observed at about +0.8 V. Its peak current increases with the amount of deposited palladium and the number of cycles. The reactions at the electrode surface are discussed. The results of the study reveal the existence of two different surface complexes of palladium(II) at ligand-modified CPEs, but the surface reactions could not be elucidated in detail. Electronic Publication     

Characterization of Hydrogen Adsorption on Palladium and Pd/c Using a Radiotracer

Hydrogen adsorption on palladium black and palladium supported on activated carbon was characterized by the Temperature Programmed Desorption technique (TPD) using the radiotracer tritium. It is shown that there are five energetic desorbed hydrogens with peak maxima at —50, 35, 115, 350, and 580°C. An additional peak at — 120°C hydrogen desorbed from activated carbon was observed on Pd/C. An isotopic hydrogen separation experiment was designed to demonstrate that hydrogen only dissociatively adsorbed on palladium surfaces whereas it was associatively adsorbed on activated carbon.     

Nature of the modifying action of white phosphorus on the properties of nanosized hydrogenation catalysts based on bis(dibenzylideneacetone)palladium(0)

The catalytic properties and nature of the nanoparticles forming in the system based on Pd(dba)₂ and white phosphorus are reported. A schematic mechanism is suggested for the formation of nanosized palladium-based hydrogenation catalysts. The mechanism includes the formation of palladium nanoclusters via the interaction of Pd(dba)₂ with the solvent (N,N-dimethylformamide) and substrate and the formation of palladium phosphide nanoparticles. The inhibiting effect exerted by elemental phosphorus on the catalytic process is due to the conversion of part of the Pd(0) into palladium phosphides, which are inactive in hydrogenation under mild conditions, and the formation of mainly segregated palladium nanoclusters and palladium phosphide nanoparticles. By investigating the interaction between Pd(dba)₂ and white phosphorus in benzene, it has been established that the formation of palladium phosphides under mild conditions consists of the following consecutive steps: Pd(0) → PdP₂ → Pd₅P₂ → Pd₃P. It is explained why white phosphorus can produce diametrically opposite effects of on the catalytic properties of nanosized palladium-based hydrogenation catalysts, depending on the nature of the palladium precursor.     

Extractive separation of platinum from macroamounts of palladium using triphenylphosphine oxide and its successive spectrophotometric determination by the stannous chloride method

Trialkylphosphine oxides extract more effectively chloride complexes of platinum than of palladium(II). Of the examined tributylphosphine (TBPO), trioctylphosphine (TOPO), and triphenylphosphine (TPPO) oxides the latter one makes possible best separation of these metals.The extraction of platinum with TPPO from solutions containing platinum and palladium unfavorably decreases with increasing palladium concentration. Using 0.1 M TPPO solution in dichloroethane, at HCl concentration 7.5 M, it is possible to separate 2–200 μg Pt/ml at a palladium concentration not higher than 10 mg/ml.Separation of platinum from macroamounts of palladium has been combined with spectrophotometric determination of platinum by means of stannous chloride. The method has been applied to the analysis of palladium for platinum content.     

The Preparation, Characterization and Biological Activity of Palladium(II) and Platinum(II) Complexes of Tridentate NNS Ligands Derived from S-methyl- and S-benzyldithiocarbazates and the X-ray Crystal Structure of the [Pd(mpasme)Cl] Complex

New complexes of general formula, [M(NNS)Cl] (M = Pd^II, Pt^II; NNS = anionic forms of the 6-methyl-2-formylpyridine Schiff bases of S-methyl- and S-benzyldithiocarbazates) have been prepared and characterized by a variety of physico-chemical techniques. Based on conductance and spectral evidence, a square-planar structure is assigned to these complexes. The crystal and molecular structure of the [Pd(mpasme)Cl] complex (mpasme=anionic form of the 6-methyl-2-formylpyridine Schiff base of S-methyldithiocarbazate) has been determined by X-ray diffraction. The complex has a distorted square-planar geometry with the ligand coordinated to the palladium(II) ion via the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom; the fourth coordination position around the palladium(II) ion is occupied by the chloride ligand. The distortion from a regular square-planar geometry is ascribed to the restricted bite angle of the ligand. Both the Schiff bases exhibit strong cytotoxicity against the human ovarian cancer (Caov-3) cell lines, the S-methyl derivative being two times more active than the S-benzyl derivative. The [Pt(mpasme)Cl] complex is moderately active but the palladium(II) complex is weakly active against this cancer. None of the complexes of Hmpsbz are active against Caov-3. The Schiff base, Hmpasme exhibits moderate activity against the bacteria, MRSA, P. aeruginosa and S. typhimurium but is inactive against B. subtilis. Coordination of the ligand with palladium(II) substantially reduces its activity. The Schiff base, Hmpasbz and its palladium(II) and platinum(II) complexes are inactive against these bacteria. The Schiff bases and their palladium(II) and platinum (II) complexes are inactive against the pathogenic fungi, C. albican, Aspergillus ochraceous and Saccharomyces cerevisiae.     

Redox reactions in nanocomposites on a sulfated polytetraphenylcalix[4]resorcinarene matrix

Redox reactions involving hydrogen and oxygen in the presence of hybrid nanocomposites containing palladium and copper or palladium and silver in a cis-tetraphenylcalix[4]resorcinarene polymer matrix were studied. In the composites containing palladium and copper, the redox transformations involved copper. In the composites with palladium and silver, the redox reactions involved the polymer matrix. The reductions in the metal-polymer nanocomposites were catalyzed by palladium.     

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.     

Spectrophotometric Determination of Palladium with Methylthymol Blue

A new, sensitive spectrophotometric method for the determination of palladium(II) with methylthymol blue has been developed. The palladium methylthymol blue complex has an absorption maximum at 530 nm. The colour reaction has a sensitivity of 0.005 µg of palladium/cm² and obeys Beer's Law over the range 0.4 to 3.24 ppm of palladium. The effects of concentration of perchloric acid, reagent, heating, stability of colour and diverse ions have been investigated. The ratio of metal: ligand in the complex is 1:1 and the formation constant was calculated to be 1.18×10⁴.     

5-Vinylpyrimidines. Synthesis via organopalladium intermediates

Reactions of 1,3-dimethyl-5-iodouracil or 2,4-dimethoxy-5-iodopyrimidine with vinyl acetate in the presence of a catalytic amount of diacetato-bis (triphenylphosphine) palladium (II) resulted in good yields of the corresponding 5-vinylpyrimidines. The reactions are viewed as resulting from regioselective addition of an initially formed 5-pyrimidinyl palladium species to the double bond of vinyl acetate followed by elimination of a palladium acetate with regeneration of the double bond and formation of the 5-vinylpyrimidine product.     

New palladium (II) complexes containing phosphine‐nitrogen ligands and their use as catalysts in aminocarbonylation reaction

Aminocarbonylation of aryl halides, homogeneously catalysed by palladium, is an efficient method that can be employed for obtaining amides for pharmaceutical and synthetic applications. In this work, palladium (II) complexes containing P^N ligands were studied as catalysts in the aminocarbonylation of iodobenzene in the presence of diethylamine. Two types of systems were used: a palladium (II) complex formed in situ; and one prepared prior to the catalytic reaction. In general, the palladium complexes studied achieved high conversions in an average reaction time of less than 2 hr, which is less than that for the standard system (Pd (II)/PPh₃) used. The pre‐synthesized complexes were faster than their in situ counterparts, as the latter require an induction time to form the Pd/P^N species. The structure and electronic properties of the ligand P^N can influence both the activity and the selectivity of the reaction, stabilizing the acyl‐palladium intermediates formed in a better manner.     

Synthesis and characterization of palladium amido complexes containing pincer CNO ligands through nitrene insertion

Catellani reactions of aryl iodides allow the double functionalization at the ortho and ipso positions in one pot. Catellani reactions involving a nitrene intermediate are not yet known. In this paper, a few palladium amino complexes were prepared from PdCl₂, anthranil and iodoarenes, and their structures were determined by X‐ray single‐crystal diffraction. These complexes are supported by a pincer C,N,O tridentate ligand forming fused six‐membered palladacycles. The high stability of the palladium complexes inhibits their reductive elimination.     

Synthesis and Characterization of Bis(azido)bis(2‐chloropyridine)palladium(II), Bis(azido)bis(3‐chloropyridine)palladium(II), Bis(azido)bis(quinoline)palladium(II), and the Crystal Structure of Bis(azido)bis(quinoline)palladium(II)

Three new monomeric complexes of palladium(II) azide with 2‐chloropyridine ( 1 ), 3‐chloropyridine ( 2 ), and quinoline ( 3 ), have been synthesized by reaction of palladium nitrate and the respective Lewis‐base with sodium azide in a water/acetone mixture. All three compounds were characterized by IR, Raman, and multinuclear NMR spectroscopy. The composition of the complexes were confirmed by elemental analysis. The spectroscopic investigations confirm terminal azide ligands in trans position. Complex 3 was also characterized by crystallographic methods. Each palladium atom of 3 is surrounded in a distorted square planar fashion by 4 nitrogen atoms. The terminal azide ligands are in trans position.     

Palladium(0)‐Catalyzed Si—Si Bond Insertion by the Terminal Nitrogen of Diazo Compounds

The palladium(0)‐catalyzed nitrogen insertion into cyclic Si—Si bonds has been realized by using N‐tosylhydrazones/diazo compounds as the nitrogen source. The palladium(II) nitrene formation and subsequent migratory insertion process are proposed as the key steps for this reaction.     

Mikrotitrationen mit äthylendiamintetraessigsäure. vii

Zusammenfassung Durch Umsetzung von Palladiumsalzen mit Kaliumnickeltetracyanid wird eine dem Palladium äquivalente Nickelmenge in Freiheit gesetzt und kann in ammoniakalischer Lösung gegen Murexid titriert werden. Bei Verwendung von 0,01-m Komplexonlösungen ergeben sich maximale Fehler von±20g Palladium.

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Summary By treating palladium salts with potassium nickel tetracyanide, a quantity of nickel equivalent to the palladium is liberated and can be titrated in an ammoniacal solution with murexide. Maximum errors of±20 g palladium are obtained when 0.01 M solutions of complexone are used.

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Résumé En traitant des sels de palladium avec le nickelotétracyanure de potassium une quantité de nickel équivalente au palladium est mise en liberté et peut être titrée en solution ammoniacale avec la murexide comme indicateur. Par emploi d'une solution 0,01 m de complexone, on obtient une erreur maximum de±20g sur le palladium.

     

Synthesis and characterization of N-heterocyclic carbene–PdCl2–1H-benzotriazole complexes and their catalytic activities toward Mizoroki–Heck and Sonogashira reactions

Four heteroleptic palladium complexes containing both N-heterocyclic carbenes and 1H-benzotriazole were synthesized and characterized. The solid-state structures show mononuclear carbene palladium complexes with each palladium coordinated by an NHC, the 3-position nitrogen of 1H-benzotriazole and two trans chlorides. The catalytic performance of the complexes for Mizoroki–Heck and Sonogashira reactions were further investigated. The results reveal that the complexes show high catalytic activities for coupling of aryl bromides with alkenes and alkynes.     

Norbornene/n‐Butyl methacrylate copolymerization over α‐Diimine nickel and palladium catalysts supported on multiwalled carbon nanotubes

The covalently immobilized multiwalled carbon nanotubes (MWNTs) supported three‐dimensional geometry α‐diimine nickel, palladium catalysts are prepared by corresponding α‐diimine nickel, palladium complexes and activated MWNTs. The molecular structures of the catalysts have been confirmed by X‐ray single‐crystal analyses, NMR and XPS, as well as elemental analysis. Compared with nickel, palladium catalysts without modification and physical mixing of nickel, palladium catalysts with MWNTs, the MWNTs supported nickel, palladium catalysts show improved activity and productivity in norbornene homopolymerization and copolymerization with polar monomer. The morphology of the resulting polymers obtained from MWNTs‐supported nickel(II) complex reveals that the MWNTs are dispersed uniformly in polymer and wrapped by polymers to squeeze out of spherical particles, leading to the enhanced processability and mechanical properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3213–3220     

Reduction of palladium(II) monoglycinate complexes at rotating disc palladium electrode in acid media

Reduction of palladium(II) glycinate complexes in strongly acid 0.5 M NaClO₄ solutions (pH 0.6 and 1.0) with variable palladium(II) complex and free glycine concentration was studied by the taking of cyclic voltammograms at palladium rotating disc electrode. It is shown that it was a chelate monoglycinate palladium(II) complex that was present in all studied solutions and underwent the reduction. The diffusion coefficient of the chelate monoglycinate palladium(II) complex D = (6.5 ± 0.5) × 10⁻⁶ cm²/s was determined from the limiting diffusion current of the complex reduction. The monoglycinate palladium(II) complex reduction occurred in the double-layer segment of the palladium charging curve; it was not complicated by hydrogen adsorption at electrodes. The palladium(II) complex reduction half-wave potential was determined (E _1/2 = ∼0.300 to 0.330 V (SCE)). It is shown that the decreasing of the number of ligands coordinated by palladium via nitrogen atom facilitates the complex reduction process. In particular, the reduction potentials of palladium(II) complexes with different ligand number at palladium electrode shifted markedly toward negative potentials in the series: Pdgly⁺ < Pd(gly)2 < Pd(gly)₄²⁻.     

Palladium‐Catalyzed Cascade Double C—N Bond Activation: A New Strategy for Aminomethylation of 1,3‐Dienes with Aminals

A new palladium‐catalyzed selective aminomethylation of conjugated 1,3‐dienes with aminals via double C—N bond activation is described. This simple method provides an effective and rapid approach for the synthesis of linear α,β‐unsaturated allylic amines with perfect regioselectivity. Mechanistic studies disclosed that one palladium catalyst cleaved two distinct C—N bond to furnish a cascade double C—N bond activation, in which an allylic 1,3‐diamine and allylic 1,2‐diamine were initially formed as key intermediates through the palladium‐catalyzed C—N bond activation of aminal and the α,β‐unsaturated allylic amine was subsequently produced via palladium‐catalyzed C—N bond activation of the allylic diamines.     

Silica-supported polymeric palladium (0) complexes as catalysts for Heck reaction in organic synthesis

Silica-supported palladium (0) complexes have been prepared from γ-chloropropyl triethoxysilica and γ-aminopropyl triethoxysilica via immobilization on fumed silica, followed by reacting with ethylenediamine and salicylaldehyde, and then the reaction with palladium chloride in ethanol and reduction with KBH₄ in ethanol. They are efficient catalysts for Heck reaction of aryl iodides with alkene at 90^oC. These polymeric palladium (0) catalysts can be recovered and reused without loss in activity. This revised version was published online in June 2006 with corrections to the Cover Date.