Clusters palladium

Colchero J, Marti O, Mlynek J, Humbert A, Henry C R and Chapon C 1991 Palladium clusters on mica a study by scanning force microscopy J. Vac. Sc/. Technol. B 9 794... 

In pyridinium chloride ionic liquids and in l,2-dimethyl-3-hexylimida2olium chloride ([HMMIMjCl), where the C(2) position is protected by a methyl group, only [PdClJ was observed, whereas in [HMIMjCl, the EXAFS showed the formation of a bis-carbene complex. In the presence of triphenylphosphine, Pd-P coordination was observed in all ionic liquids except where the carbene complex was formed. During the Heck reaction, the formation of palladium was found to be quicker than in the absence of reagents. Overall, the EXAFS showed the presence of small palladium clusters of approximately 1 nm diameter formed in solution. 

The catalytic applications of Moiseev s giant cationic palladium clusters have extensively been reviewed by Finke et al. [167], In a recent review chapter we have outlined the potential of surfactant-stabilized nanocolloids in the different fields of catalysis [53]. Our three-step precursor concept for the manufacture of heterogeneous egg-shell - nanocatalysts catalysts based on surfactant-stabilized organosols or hydrosols was developed in the 1990s [173-177] and has been fully elaborated in recent time as a standard procedure for the manufacture of egg-shell - nanometal catalysts, namely for the preparation of high-performance fuel cell catalysts. For details consult the following Refs. [53,181,387]. 

Palladium clusters deposited on amorphous carbon have been studied by XPS and UPS [28] and both techniques show broadening of the d-band peak as cluster size increases. The d-threshold shifts towards Ep as cluster size increases. In UPS studies the d-emission of the single atom has its peak at 3.0 eV below Ep, whereas the d-threshold is 2eV below Ep. Palladium clusters evaporated onto Si02 have been studied by UPS [38]. At large coverages of the Pd metal evaporated (> 10 atoms/cm ), a high emission intensity at Ep excited with photons of 21.2 eV (He(I)) or 40.8 eV (He(II)) as excitation source, is observed. This feature is characteristic in the spectra from bulk Pd samples. At the lowest metal coverage (3 x 10 atoms/cm ),... 

Vargafdk MN, Moiseev II, Kochubey DI, Zamaraev KI. 1991. Giant palladium clusters— S3mthesis and characterization. Earaday Discuss 92 13-29. 

Fig. 51. Scanning electron microscope image of different stages of metalization of DNA. (a) Linear chain of separated palladium clusters connecting two gold contacts (b) magnification of (a) showing clusters with diameter > 40 nm (c) continuous coated DNA strand after one development step with a diameter larger than 40 nm. Reproduced with permission from Ref. (175). Copyright 2001, American Institute of Physics.

Figure 9.8 Relative reactivities (a) and selectivities (b) of palladium cluster size in the formation of C6H6, C4H8 and C4H6 in the polymerisation of acetylene. (Reproduced from Ref. 29).

A review21 with 45 references has topics on syntheses, characterization, structures, bonding, and reactivity of palladium cluster compounds. 

Os4Pd6(CO)8(//-CO)8(/x-dppm)2] in low yields, while the reaction of [Os5(/u5-C)(CO)i5] with [Pd2(/u-dppm)2Cl2] afforded [Os5Pd4(/u6-C)(CO)12(/u-CO)3(/u-dppm)2] and [Os5(/X5-C)(CO)13(/r-dppm)] in moderate yields.289 The electron counts found in these osmium-palladium clusters do not always agree with those predicted by skeletal electron counting rules. This may simply be ascribed to the ability of Pd to be satisfied with both 16- and 18-electron counts.289... 

Moiseev, I. I. Vargaftik, M. N. Catalysis with palladium clusters. In Catalisis by Di- and Polynuclear Metal Cluster Complexes Adams, R. D. Cotton, F. A. Eds. Wiley VCH New York, 1998, p 395. 

The reaction of these platinum or palladium clusters with transition metal compounds has also been studied and many cluster derivatives have been prepared for this method, which included reactions with gold,3 02-3306 silver, 302,33 3,3307-3310 copper 3302,3303,3309-3311 Qr mercury com ... 

Oleshko, V. et al., High resolution electron microscopy and electron energy-loss spectroscopy of giant palladium clusters, Z. Phys. D., 34, 283, 1995. 

Reetz, M.T., Breinbauer, R., and Wanninger, K., Suzuki and heck reactions catalyzed by performed palladium clusters and palladium/nickel bimetallic clusters, Tetrahedron Lett., 37, 4499, 1996. 

Schmid, G. et al., Synthesis and catalytic properties of large ligand stabilized palladium clusters, J. Mol. Catal. A, 107, 95, 1996. 

Reetz, M.T. and Dugal, M., Entrapment of Nanostructured Palladium Clusters in Hydrophobic Sol-Gel Materials, Catal. Lett., 58, 207, 1999. 

Structure and Magnetism of Neutral and Anionic Palladium Clusters. 

Palladium clusters [51], solubilized by tetra-n-alkylammonium salts, are effective in the Suzuki coupling of phenylborinic acid with bromoarenes to produce biaryls... 

Figure 15.5. Giant palladium cluster in Wacker reactions...

X. L. Bai and W. M. H. Sachtler, Methylcyclopentane conversion catalysis by zeolite encaged palladium clusters and palladium-proton adducts, J. Catal. 129, 121-129 (1991). 

In contrast to the usual Wacker-conditions, optimum rates and catalyst stability in the Pd/batophenanthroHne-catalyzed olefin oxidations was observed in the presence of NaOAc (pH s 11.5). Under such conditions, the catalyst-containing aqueous phase could be recycled with about 2-3 % loss of activity in each cycle. In the absence of NaOAc precipitation ofPd-black was observed after the second and third cycles. Nevertheless, kinetic data refer to the role of a hidroxo-bridged dimer (Scheme 8.1) rather than the so-called giant palladium clusters which could easily aggregate to metallic palladium. 

Okamoto K, Akiyama R, Yoshida H, Yoshida T, Kobayashi S. Formation of nanoarchitectures including subnanometer palladium clusters and their use as highly active catalysts. J Am Chem Soc 2005 127 2125-2135. 

Reetz MT, Helbig W, Quaiser SA, Slimming U, Breuer N, Vogel R (1995) Visualization of Surfactants on Nanostructured Palladium Clusters by a Combination of STM and High-Resolution TEM. Science 267 367-369... 

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