Contents Palladium Compounds

Alloys based on Ag—Pd have been used for a number of years and are available from most gold alloy manufacturers (148). The palladium content is 22—50 wt % silver content is from 35 to 66 wt %. Minor amounts of Zn, In, or Sn are often present to increase fluidity. Both In and Sn form intermetaUic compounds with both Pd and Ag and, therefore, some of the commercial alloys are susceptible to age hardening (149). These alloys are somewhat difficult to fabricate and require meticulous processing. They may also produce a greenish discoloration when they are fused with porcelain veneers. Nevertheless, clinical experience generally has been satisfactory, and cost is the primary criterion for use. 

X-Ray studies confirm that platinum crystallites exist on carbon supports at least down to a metal content of about 0.03% (2). On the other hand, it has been claimed that nickel crystallites do not exist in nickel/carbon catalysts (50). This requires verification, but it does draw attention to the fact that carbon is not inert toward many metals which can form carbides or intercalation compounds with graphite. In general, it is only with the noble group VIII metals that one can feel reasonably confident that a substantial amount of the metal will be retained on the carbon surface in its elemental form. Judging from Moss s (35) electron micrographs of a reduced 5% platinum charcoal catalyst, the platinum crystallites appear to be at least as finely dispersed on charcoal as on silica or alumina, or possibly more so, but both platinum and palladium (51) supported on carbon appear to be very sensitive to sintering. 

Figure 12.24 depicts the oxidation of a silyl enol ether A to give an a,/3-unsaturated ketone B. Mechanistically, three reactions must be distinguished. The first justifies why this reaction is introduced here. The silyl enol ether A is electrophilically substituted by palladium(II) chloride. The a-palladated cyclohexanone E is formed via the intermediary O-silylated oxocarbenium ion C and its parent compound D. The enol content of cyclohexanone, which is the origin of the silyl enol ether A, would have been too low to allow for a reaction with palladium(II) chloride. Once more, the synthetic equivalence of a silyl enol ether and a ketonic enol is the basis for success (Figure 12.24). 

Kemmerer.1 On the other hand, Keller and Smith, who consider that traces of palladium are lost by this method, determined the palladium content of the compound electrolytically, as also did Amberg 2 in two series of experiments, and Woernle. Moreover, Amberg made a series of determinations in which the reduction to metal was accomplished in solution with hydrazine sulphate, while Shinn 3 effected his reductions with ammonium formate. The results of these investigations are summarised in the following table ... 

The nitric acid solution from the dissolution of the fuel rod contents is filtered [poly(propene) fleece] or centrifuged, to remove suspended solids (zirconium- or molydenum- compounds and ruthenium and palladium alloys). The thus obtained fuel solution contains uranium, plutonium and the radioactive fission products. It is, after its composition is adjusted to the extraction conditions (3 molar in nitric acid and 240 to 300 g/L uranium) subjected to multi-cyclic extraction with tributylphosphate (dissolved in dodecane). Uranium and plutonium pass into the organic phase and are thereby separated from the fission products, which remain in the aqueous phase. 

Four chiral homologous complexes were also prepared. None of the palladium complexes showed mesomorphic properties, whereas a monotropic chiral discotic nematic phase was observed for the platinum complex (Table 18). The absence of mesomorphism for the dinuclear palladium complexes may be due to the type of chiral chain used, which differed from that used for the platinum system. All of the complexes form charge-transfer complexes with TNF. A Colh phase was induced for the two halo-bridged palladium complexes and for the platinum complex, as was observed for their non-chiral analogs. Flowever, the chiral nematic phase of the platinum compound was suppressed. At low TNF content, a chiral Nq phase was stabilized for the thiocyanato-bridged compound along with a non-chiral No phase at higher concentration. 

Catalysts for total hydrocarbon and volatile organic compounds (VOC) combustion in waste gases contain noble metals supported on alumina. The noble metals are platinum, palladium, combinations of platinum and palladium, or rhodium and the typical content is 0.3-0.5 wt%. The BASF RO-25 catalyst, specified for VOC combustion, is reported to contain 0.5% palladium on 0-AI2O3 characterized by a surface area of 109 w g (428). 

The second family of compounds has a larger transition metal and/or indium content. In all of these compounds T-ln bonding is much more important than in the / -rich compounds. The transition metal atoms have broadly varying indium coordination. In compounds like Ce8Pd24ln (Gordon et al., 1996), only one indium atom is bonded to palladium. Such small fragments also occur in the rare earth metal rich compoimds. Normally, the lowest coordination number for a transition metal by indium is three. In fig. 94 we present the various Rhln c, Pdln, and Ptln monomeric units in the ternary indides with rhodium, palladium, and platinum as transition metal component. With the other late transition metals similar... 

Cyclopropane and Cyclopropene Adds.— The undesirable physiological properties of cyclopropene acids such as malvalic acid (20 R = H) and sterculic acid (21 R = H) and their presence, albeit in small amount, in cottonseed oil has aroused interest in these compounds. The content of cyclopropene acids is reduced by heating with palladium catalysts, though not with nickel or platinum catalysts. Palladium treatment cleaves the cyclopropene ring and produces methyl- and methylene-substituted acids. Hydrogenolysis of cyclopropane acids is reported to give methyl-substituted fatty acids which can be identified by their g.l.c. behaviour on capillary columns. The chemical reactions of cyclopropene acids (malvalic and sterculic) shown in Scheme 5 have been reported. ... 

The first mixed-metal cluster of Os-Pd, [Os6Pd(bipy)(CO)i8], was reported in 1994, and since then a variety of mixed-metal cluster that contain various Os Pd ratios have been created. Palladium-pyridine complexes appear to be useful reagents in the synthesis of mixed-metal clusters with osmium carbonyl compounds. " The reaction of the coordinately unsaturated cluster [Os3(yu-H)2(CO)io] with [Pd(NH3)2l2] afforded a number of Os-Pd clusters with a high hydride content. " Both palladium phosphine and bidentate phosphine complexes are useful in the preparation of high-nuclearity mixed-metal clusters. The reaction of [Os3(/i-H)2(CO)io] with [Pd2(/i-dppm)2Cl2] gave 258 and 259, in addition to 260, with the same metal core, " in which the molecule contains a twofold symmetry axis. " " ... 

The palladium content of a steel sample was determined as follows. A 16.312 g steel sample was dissolved in concentrated HCl(aq). The solution obtained was treated to remove interfering ions, to establish the proper pH, and to obtain a final solution volume of 250.0 mL. A 10.00 mL sample of this solution was then treated with dimethylglyoxime to convert all of the palladium to palladium dimethylglyoximate, a chemical compound that is 31.61% Pd (by mass), 28.54% C, 4.19% H, 19.01% O, and 16.64% N. The mass of purified, dry palladium dimethylglyoximate obtained was 0.0784 g. 

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