Dmitry I. Kochubey

Giant palladium clusters: synthesis and characterization

A series of palladium clusters containing from four to several hundred Pd atoms in the metal skeleton has been prepared and characterized with respect to structure and chemical properties, including catalytic activity. For smaller clusters good agreement was observed. between single-crystal X-ray and EXAFS structural data. Giant clusters approximating to Pd561L60(OCOCH3)180(L = phen, bipy) and Pd561phen60O60X60(X = PF6, ClO4, BF4, CF3CO2), were characterized with TEM, SAXS, EXAFS, NMR and magnetic succeptibility data. These clusters contain a closepacked metal core and ligands L and X that are located at the periphery of a cluster. They are very soluble in water and polar organic solvents and can be considered as a bridge between low molecular clusters and particles of colloidal metals. Giant Pd clusters were found to be active homogeneous catalysts for various organic reactions, e.g. oxidative acetoxylation of alkenes and alkylarenes; oxidation of alkenes, formic acid and alcohols; dehydration of alcohols and formation of acetals. The kinetics and mechanism of the homogeneous oxidation of alkenes and HCO2H in solutions of giant clusters were elucidated.

First trigonal-antiprismatic tris-dichloroglyoximate iron(II) clathrochelate and its reactivity in nucleophilic substitution reactions

Tris-dichloroglyoximate clathrochelate [Fe(Cl2Gm)3(SnCl3)2]2− dianion has been synthesized by a procedure differing from those described earlier for boron-capped analogs. The co-ordinately saturated SnCl62− dianion is now used as the capping agent instead of boron-containing Lewis acids. The tris-dichloroglyoximate tin-capped product obtained is far less reactive than its boron-capped analogs, and only in the case of a thiophenolate anion was the “regular” hexafunctionalized clathrochelate obtained. The complexes synthesized have been characterized by elemental analysis, PD and MALDI-TOF mass, IR, UV-vis and 1H, 13C and 119Sn NMR spectra, cyclic voltammetry, and X-ray crystallography for the clathrochelate [Fe(Cl2Gm)3(SnCl3)2]2− dianion. The geometry of the functionalized complex (the distortion angle φ and main bond lengths in the clathrochelate framework) has been deduced from the quadrupole splitting value in the 57Fe Mossbauer spectrum and EXAFS data, respectively.

A novel giant palladium cluster

Electron microscopy, electron diffraction, EXAFS, and ultracentrifuging data show that a new catalytically active cluster prepared by reduction of Pd(OAc)2 by H2 in the presence of L = 1,10-phenanthroline, or 2,2′-bipyridine, followed by O2 treatment, contains a close-packed metal nucleus (570 ± 30 Pd atoms) bearing 60 ± 3 co-ordinated L and 180 ± 10 OAc– in the outer sphere of the cluster.

Synthesis and characterization of platinum and palladium clusters with phosphide ligands

Abstract Clusters of composition [Pt(PPh 2 )] n , n = 6−10, have been synthesized by reduction of a series of Pt II complexes [(PPh 3 )Pt (OAc)G] m (G = (OAc) 2 · PdC 3 H 5 , m = 1; G = Cl, OAc, (OAC) 2 Ag, m = 2) with H 2 , HCOOH and Na-amalgam. A hydridophosphide Pd II complex [Pd 2 (PPh 2 )H x ] n was obtained in an analogous manner by reduction of [(PPh 3 )Pd(OAc) 2 ] 2 with HCOOH. Additionally a complex with diphenylphosphonic acid as a ligand [Pd(μ-O 2 PPh 2 )(C 6 H 5 )(PPh 3 )] 2 was obtained and characterized with X-ray data. The formation of O 2 PPh 2 anion under strictly anaerobic reductive conditions implies the transfer of an O atom from the carboxylic ligand to the P atom of the phosphorus-containing ligand. Cleavage of the CPh bond seems to be a common process for the reductive reactions of both Pd and Pt phosphine complexes. Phosphide clusters of compositions [Pt(PPh 2 ) n , and [Pd 2 (PPh 2 )H x ] n were characterized with IR, SAXS, EXAFS and NMR data and molecular mass measurements.

Formation of active catalysts in the system: chlorocuprates-CCl4-n-C10H22.

Transformations of anionic Cu(II) chlorocomplexes have been studied under conditions of catalytic exchange reactions between carbon tetrachloride and n-alkanes. It was shown that chlorocuprates are just precursors and are easily reduced to the genuine catalysts, that is, to the respective Cu(I) complexes. Both the composition and the geometric structure of the precursor (CuCl(4)(2-)) and, probably, the active site (CuCl(3)(2-)) have been investigated by several techniques (UV-vis spectroscopy, electron spin resonance (ESR), extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), and static magnetic measurements). The dependence of the metathesis velocity on the [Cl-]/[Cu] ratio was found to exhibit a maximum most likely corresponding to the highest content of trichlorocuprite CuCl(3)(2-).

Interaction of platinum and molybdophosphoric heteropoly acid under conditions of catalyst preparation for benzene oxidation to phenol with an O2-H2 gas mixture

The transformations of platinum and a heteropoly acid (HPA) in binary systems prepared from H2PtCl6 or H2PtCl4 and H3PMo12O40 were studied using IR and UV-VIS spectroscopy, elemental analysis, XPS, EXAFS, TPR, and HREM. The calcination of platinum chloride with the HPA to 450°C resulted in the formation of a platinum salt of the HPA along with decomposition products (mixture I). The reduction of calcined samples containing Pt: HPA = 1: 1 with hydrogen at 300°C (mixture II) followed by exposure to air resulted in the regeneration of the HPA structure. The resulting solid samples of Pt1−n0PtnIIClmOxHy) (H3+pPMo12−pVIMopVO40) (III) contained platinum and molybdenum in both oxidized and reduced states. The following association species were isolated from mixtures I and II by dissolving in water: [PtnIIPMo12O40] (Is) (n = 0.3−0.8) and [Ptn0PMo12red O40] (IIs) (n ≈ 1). Under exposure to air, the solutions of Is were stable (pH ∼2), whereas Ptmet was released from IIs. After the drying of Is, the solid association species (PtnIIClmOxHy). (H3PMo12O40), where n = 0.3−0.8, m = 0.2−1, and x = 3−0, (Isolid) were obtained. The Isolid/SiO2 supported samples were prepared by impregnating SiO2 with a solution of Is and drying at 100°C. Platinum metal particles of size ∼20 Å and a mixed-valence association species of platinum with the HPA were observed after the reduction of Isolid/SiO2 with hydrogen at 100–250°C. These samples were active in the gas-phase oxidation of benzene to phenol at 180°C with the use of an O2-H2-N2 mixture.

Porous Pd-Containing Polypropylene Membranes for Catalytic Water Deoxygenation

Water deoxygenation has been studied in a catalytic membrane reactor in which oxygen is reduced with hydrogen fed into the hollow fiber of a porous polypropylene membrane containing palladium metal on its outer surface. Palladized fibers obtained by different methods and the initial fibers have been characterized by dynamic desorption porosimetry, gas permeability measurements, X-ray structure determination, and light microscopy. The possibility of efficient water deoxygenation at room temperature is demonstrated.

Palladium carbene cluster : synthesis, structure and reactivity

Abstract The first palladium carbene cluster, μ-tetrakis(diphenylmethyliden)-μ-tetraacetato-quadro-tetrapalladium (4Pd-Pd) Pd 4 (μ-CPh 2 ) 4 (μ-OAC) 4 (I), has been synthesized by substitution of diphenylcarbene ligands for CO-groups in μ-tetrakis(carbonyl)-μ-tetraacetato-quadro-tetrapalladium (4Pd-Pd) Pd 4 (μ-CO) 4 (μ-OAc) 4 (II) and characterized with EXAFS data. Reactivity of I, II and related clusters is discussed. Thermolysis of the clusters has been found to involve inner-sphere oxidation of carbene or carbonyl ligands during which an oxygen atom is transferred from the carboxylate group to the carbene or carbonyl ligand. Thermolysis of carbonyl clusters in benzene or toluene solutions gives rise to the products of CO 2 insertion into the CH bond of the solvent forming benzoic acid from benzene and a mixture of phenylacetic and tolyl acids from toluene.

Genesis of the active-component precursor in the synthesis of Pt/Al2O3 catalysts: I. Transformation of the [PtCl6]2− complex in the interaction between chloroplatinic acid and the γ-Al2O3 surface

Gradient elution experiments have revealed the difference between platinum complexes in terms of the strength of their interaction with the alumina surface. A considerable part (30–40%) of the supported platinum is nondesorbable via competitive ion exchange reactions or upon changes in the charge state of the support surface. The surface platinum complexes can be divided into ion-exchangeable and coordinatively fixed species according to the nature of their bonding with aluminum oxide. Combining desorption and spectroscopic methods (EXAFS and diffuse reflectance spectroscopy) has made it possible to characterize the surface complexes. The strongest metal-support interaction takes place in the fixation of hydrolyzed platinum species.

The effect of supports (Al2O3, Al2O3-CeO2 and Al2O3-CeZrO2) on the nature of gold-species in supported gold catalysts

This work is concerned with the study of Au specimens produced by gold deposition on nanosized mixed oxides (alumina, ceria, zirconia) prepared by the sol-gel method using organometallic precursors. According to X-ray absorption near edge structure, extended X-ray absorption fine structure, transmission electron microscopy data, and ultraviolet-visible and X-ray photoelectron spectroscopy measurements, mixed Al-Ce-Zr oxides are quite effective for stabilization of different gold specimens. The samples pre- treated in hydrogen at 150°C are characterized by the presence of gold Au3+ cations located on the surface in slightly disordered octahedral oxygen coordination. Metallic gold nanoparticles with a size of about 2 nm and gold clusters were found in the samples treated in hydrogen at 300°C.