Platinum occurrence

For organometailic compounds, the situation becomes even more complicated because the presence of elements such as platinum, iron, and copper introduces more complex isotopic patterns. In a very general sense, for inorganic chemistry, as atomic number increases, the number of isotopes occurring naturally for any one element can increase considerably. An element of small atomic number, lithium, has only two natural isotopes, but tin has ten, xenon has nine, and mercury has seven isotopes. This general phenomenon should be approached with caution because, for example, yttrium of atomic mass 89 is monoisotopic, and iridium has just two natural isotopes at masses 191 and 193. Nevertheless, the occurrence and variation in patterns of multi-isotopic elements often make their mass spectrometric identification easy, as depicted for the cases of dimethylmercury and dimethylplatinum in Figure 47.4. 

Referring first of all to the reactions over 0.2% platinum/alumina (Table V) the major features of the product distributions may be explained by a simple reaction via an adsorbed C5 cyclic intermediate. For instance, if reaction had proceeded entirely by this path, 2-methylpentane-2-13C would have yielded 3-methylpentane labeled 100% in the 3-position (instead of 73.4%) and would have yielded n-hexane labeled 100% in the 2-position (instead of 90.2%). Similarly, 3-methylpentane-2-I3C would have yielded a 2-methylpentane labeled 50% in the methyl substituent (instead of 42.6%), and would have yielded n-hexane labeled 50% in the 1- and 3-positions (instead of 43.8 and 49% respectively). The other expectations are very easily assessed in a similar manner. On the whole, the data of Table V lead to the conclusion that some 80% or so of the reacting hydrocarbon reacts via a simple one step process via an adsorbed C5 cyclic intermediate. The departures from the distribution expected for this simple process are accounted for by the occurrence of bond shift processes. It is necessary to propose that more than one process (adsorbed C6 cyclic intermediate or bond shift) may occur within a single overall residence period on the catalyst Gault s analysis leads to the need for a maximum of three. The number of possible combinations is large, but limitations are imposed by the nature of the observed product distributions. If we designate a bond shift process by B, and passage via an adsorbed Cs cyclic intermediate by C, the required reaction paths are... 

Farkas and Farkas (32) examined the kinetics of the exchange and hydrogenation of benzene catalyzed by platinized platinum foil at room temperature. The occurrence of isotope exchange was detected by the thermal conductivity technique. They reported (i) that the exchange reaction was only a little faster than hydrogenation and (ii) that exchange... 

Direct Cg cyclization of alkanes into cyclohexane-type rings. The occurrence of this process is claimed under the effect of unreduced surface platinum complexes which have no metallic properties (24). 

The signs and symptoms of hypersensitivity include urticaria, contact dermatitis of the skin, and respiratory disorders ranging from sneezing, shortness of breath, and cyanosis to severe asthma. The latency period from the first contact with platinum to the occurrence of the first symptoms varies from a few weeks to several years. ... 

The element was discovered in 1925 by Walter Noddack, Ida Tacke Noddack, and 0. Berg. They detected it by x-ray examination of platinum ores. X-ray studies also showed its occurrence in columbite and other minerals. It was named after the German river Rhine, called Rhenus in Latin. In 1929, Walter and Ida Noddack produced Ig of rhenium metal from 660 kg of Norwegian molybdenite. 

Cisplatin (dx-Diamminedichloroplatinum) is a divalent water-soluble platinum containing complex. It reacts directly with DNA, resulting in both intra-and inter-strand cross-links. It also causes DNA breaks and it inhibits DNA replication and RNA transcription. A mechanism for the occurrence of resistance appears to be an increased of the levels of DNA-excision repair enzymes. Cisplatin is used in combination therapies with other anticancer drugs in the treatment of testicular and ovarian cancers and it has also shown high activity against cancers of the bladder, head, neck and endometrium. It is administered intravenously by rapid injection or by continuous infusion. It is for more that 90% bound to... 

In 1809 Wollaston demonstrated the presence of grains of native palladium and native platinum in a Brazilian alluvial gold ore presented to him by the Portuguese ambassador, H. E. Chev. de Souza Coutinho. Wollaston was led to this discovery by the observation that some of the grains, although they looked like platinum, dissolved faster in aqua regia (44, 122, 123). In 1825 Alexander von Humboldt also reported the occurrence of native palladium in Brazil (109). 

In 1866 Friedrich Wohler discovered a ruthenium mineral. When he analyzed the shining black grains of what seemed to be an unusual platinum mineral which Herr Waitz of Cassel had brought back from Borneo, he found it to be a sulfide of ruthenium and osmium. Wohler stated that this mineral, which he named laurite, presented the first example of the natural occurrence of sulfur compounds of the platinum metals (129). 

We discussed this catalysis recently (141st National Meeting of the American Chemical Society, March 1962) in terms of an olefin insertion reaction involving a Pt(II) olefin complex (3). We found that catalysis was only accomplished by platinum compounds capable of coordinating olefins. For example, substitution by tertiary phosphines blocks coordination by olefins and greatly reduces the catalytic activity of Pt(II). The substitution by phosphines does not affect the ability of the complexes to cleave the Si—H bond, however. The hindering of a catalytic reaction by blocking coordination sites is a common occurrence and is, I think, a persuasive... 

For example, in 1963 the photochemistry of magnesium phthalocyanine with coordinated uranium cations was studied in pyridine and ethanol and indicated the occurrence of PET to the uranium complex . A rapid photoinduced electron transfer (2-20 ps) followed by an ultrafast charge recombination was shown for various zinc and magnesium porphyrins linked to a platinum terpyridine acetylide complex . The results indicated the electronic interactions between the porphyrin subunit and the platinum complex, and underscored the potential of the linking para-phenylene bisacetylene bridge to mediate a rapid electron transfer over a long donor-acceptor distance. 

The occurrence of the redox-driven reversible assembling-disassembling process involving copper complexes of 16 has been verified through cyclic voltammetry experiments at a platinum electrode in a MeCN solution. Figure 2.17 shows the CV profile obtained with a solution of the double-strand helicate complex [ Cu 21 (16)212 +. 

Although t/3-allyl complexes of platinum(II) are not rare, their occurrence is not as frequent as for -alkene complexes. This situation is reversed for palladium(II) where r 3-allyl complexes are very common, and much of modern organopalladium chemistry is becoming dominated by the reactivity of j)3-allyl complexes. 

Although complexes with these ligands are common in palladium(II) chemistry, their occurrence is more scarce in platinum(II) compounds. Nevertheless these complexes can be prepared, examples being platinum(II) complexes of the optically active quadridentate Schiff base of salicylaldehyde and (R)-l, 2-diamines.1212 An alternative synthesis involves formation of the Schiff base by reaction of a complexed amino ligand on platinum(II) with amide acetates (equation 372).1213... 

Rocks consisting essentially of olivine alone are known as dunites, the name coming from the occurrence of this rock in the Dun mountains of New Zealand. In the United States, this mineral is found in North Carolina, South Carolina, and Georgia, where corundum is associated wtith the dunite in commercial quantities. The olivine of peridotites alters readily to the mineral serpentine, often to such an extent that the rock itself is called a serpentine. As mentioned above, the pendotites may contain chromite or other valuable minerals, often to such an extent that they may be commercially exploited, for nickel, platinum, and precious garneL... 

---