Palladium structural analyses

Harada M, Asakura K, Toshima N (1993) Catalytic activity and structural analysis of polymer-protected gold/palladium bimetallic clusters prepared by the successive reduction of hydrogen tetrachloroaurate(ffl) and palladium dichloride. J Phys Chem 97 5103-5114... 

For the unsubstituted compound 197a-Me the 2R/2S ratio was only 5.6 1 [ 10b, c], yet in this case the absolute configuration was checked by X-ray crystal structure analysis. The a-azidoesters 197-R were converted to the a,)3-diamino acids 198-R as described above, i.e. by catalytic hydrogenation over palladium on charcoal and hydrolysis of the ester group (Scheme 58) [10b, c, 62]. Saponification was not necessary for the benzyl esters 197a,b,i-Bn. 

Other compounds of Pd + show a similar mixed valency behaviour-There is a striking similarity between the ionic radii of Pd + and Pd +, that has been proved by means of structure analysis of the chloro-complexes of two- and four-valent palladium (30). This is the reason, why the formulation Pd2+(Pd4+Fe) is not contradictory to the equivalence of the Pd sites found in the PdFs-structure (139). On the other hand it seems quite reasonable to assume a LiSbFe-type structure of compounds like Pd2+(PtFe), containing cations of different sizes. 

The crystal structure analysis of palladium-exchanged zeolite allows the determination of initial cation positions in the dehydrated porous framework. Similar studies after reduction by hydrogen at various temperatures should permit the observation of palladium removal from the cation sites and thus the estimation of the reduction level. Moreover, the presence of metal on the external surface is easily detected. Hence, x-ray diffraction techniques should give a good picture of hydrogen reduction of palladium in Y zeolites. 

Catalytic hydrogenation of 1 9, over palladium catalyst gave a practically quantitative yield of the crystalline disaccharide derivative 2 2, the constitution, and configurations at all chiral centers, of which have been verified by x-ray crystal structure analysis ( 1 5). De- 0-silylation of the 5,8-diol 2 2. 

Manceau et al. [ 129] studied the application of X-ray absorption fine-structure analysis (EXAES) to the speciation and quantification of the forms of trace metals in solid materials. Palladium was studied in particular. 

Although the number of tetrafluorides reported is as large as the number of di- and trifluorides (see Table III), this group of compounds is the least well characterized structurally of the transition metal fluorides. The synthesis of most of the expected tetrafluorides has been reported, with examples from titanium to manganese in the first, from zirconium to palladium (except for technetium) in the second, and from hafnium to platinum (except for tantalum) in the third series. Many of them have been little studied and, in general, they have not proved amenable to crystallographic structural analysis. 

The remarkable cyclotetramerization of phenylacetylene under conditions of palladium (II) catalysis has been reported.231 An X-ray crystal structure analysis has been performed on 151. 

In 1958, the fluoride long known[l] as OsFg was shown by Weinstock and Malm [2] to be OsFg and, in 1965, the fluoride of iridium, reported [3,4] on two occasions to be a tetraflu.oride was shown [5] by Bartlett and Rao to be a pentafiuoride. New hexafluorides [4,6-8] and pentafiuorides[9-ll] (in addition to RuFj which had long been known) have now established hexafluorides and pentafluorides for all of the platinum metals other than palladium. Moreover, the trifluorides, RuFj, RhFr, PdFi and IrFr have been established by X-ray crystal structure analysis [12] although that of palladium has been shown [13] to be the mixed oxidation state compound Pd(II) Pd(IV)F6. So far only one di-fluoride of the platinum metals, PdF2, has been reported[14-16]. 

In view of the successful palladium-catalyzed [2 + 2 + 2] assembly of a cyclo-hexa-1,3-diene derivative from one molecule of norbornene and two molecules of /i-bromostyrene [30 a], a rationally designed synthesis of dihydrotrifoliaphane 33 as a precursor to 29 appeared to be plausible. However, when a 1 2 mixture of [2.2]paracyclophane-l-ene (32) and its 1-bromo derivative 4 was subjected to the reported conditions, the novel hydrocarbon 34 with a different array of three [2.2]paracyclophane units was obtained in 62% yield [30b]. Trifoliaphane 29, arising from oxidation of the primarily formed dihydro derivative 33, was obtained as a minor by-product (2 % yield) in this coupling. The constitution of 34 was established by an X-ray crystal structure analysis. 

Halo-6-halomagnesio-9-alkyl-9H-carbazoles can be coupled with palladium catalysts, in the manner of a Grignard reaetion. The structural analysis of the polymers showed that earbazole repeating units are linked ex-elusively at the 3,6-positions. 

The regiochemistry of this carbopalladation has been further confirmed by the X-ray crystal structure analysis of complex 10, which was formed by the reaction of the methyl-palladium chloride complex 9 with propadiene (Scheme... 

We were delighted to find that the NHCP ligands with a direct N-P hnkage R-34 form stable chelating complexes with metals of the nickel triade and ruthenium, featuring very small bite angles between 65 and 70 as determined by X-ray crystal structure analysis of all new compounds made (Scheme 10.10) [44]. The NHCP palladium dimethyl complexes 45 show reactivity toward electron-poor... 

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