Iridium rhodium

Catalytic hydrogenation of tnfluoroacetic acid gives tnfluoroethanol in high yield [73], but higherperfluorocarboxybc acids and their anhydndes are reduced much more slowly over rhodium, iridium, platinum, or ruthenium catalysts [7J 74] (equation 61) Homogeneous catalysis efficiently produces tnfluoroethanol from tnfluoroacetate esters [75] (equation 61)... 

The most widely used methods for the application of coatings of gold, silver and the platinum group metals (platinum, palladium, rhodium, iridium, ruthenium, osmium) to base metals are mechanical cladding and electroplating. 

The chemistry of ruthenium, osmium, rhodium, iridium, palladium and platinum in the higher oxidation states. D. J. Gulliver and W. Levason, Coord. Chem. Rev., 1982,46,1-127 (1131). 

Advances in platinum metal carbonyls and their substituted derivatives, II. Rhodium, iridium, palladium and platinum carbonyls. S. C. Tripathi, S, C. Srivastava, R. P. Mani and A. K. Shirma), Inorg. Chim. Acta, 1976, 17, 257-290 (463). 

Plutonium-noble metal compounds have both technological and theoretical importance. Modeling of nuclear fuel interactions with refractory containers and extension of alloy bonding theories to include actinides require accurate thermodynamic properties of these materials. Plutonium was shown to react with noble metals such as platinum, rhodium, iridium, ruthenium, and osmium to form highly stable intermetallics. 

Pauling, L. Evidence from Bond Lengths and Bond Angles for Enneacovalence of Cobalt, Rhodium, Iridium, Iron, Ruthenium, and Osmium in Compounds with Elements of Medium Electronegativity Proc. Natl. Acad. Sci. (USA) 1984, 81, 1918-1921. 

Scheme 27 Synthesis of rhodium, iridium, and copper polysulfido clusters from the corresponding, u-hydrogensulfido complexes...

CO oxidation, an important step in automotive exhaust catalysis, is relatively simple and has been the subject of numerous fundamental studies. The reaction is catalyzed by noble metals such as platinum, palladium, rhodium, iridium, and even by gold, provided the gold particles are very small. We will assume that the oxidation on such catalysts proceeds through a mechanism in which adsorbed CO, O and CO2 are equilibrated with the gas phase, i.e. that we can use the quasi-equilibrium approximation. 

In the early work on the thermolysis of metal complexes for the synthesis of metal nanoparticles, the precursor carbonyl complex of transition metals, e.g., Co2(CO)8, in organic solvent functions as a metal source of nanoparticles and thermally decomposes in the presence of various polymers to afford polymer-protected metal nanoparticles under relatively mild conditions [1-3]. Particle sizes depend on the kind of polymers, ranging from 5 to >100 nm. The particle size distribution sometimes became wide. Other cobalt, iron [4], nickel [5], rhodium, iridium, rutheniuim, osmium, palladium, and platinum nanoparticles stabilized by polymers have been prepared by similar thermolysis procedures. Besides carbonyl complexes, palladium acetate, palladium acetylacetonate, and platinum acetylac-etonate were also used as a precursor complex in organic solvents like methyl-wo-butylketone [6-9]. These results proposed facile preparative method of metal nanoparticles. However, it may be considered that the size-regulated preparation of metal nanoparticles by thermolysis procedure should be conducted under the limited condition. 

IH of alkynylamines has been performed with a variety of catalytic systems based on palladium [274-281], cobalt, rhodium, iridium, ruthenium, platinum, copper, silver, zinc, cadmium, mercury [279-281], nickel [279-282], gold [279-281, 283], and molybdenum [284] derivatives. 

In recent years, the asymmetric hydrogenation of prochiral olefins have been developed in the presence of various chiral sulfur-containing ligands combined with rhodium, iridium or more rarely ruthenium catalysts. The best results have been obtained by using S/P ligands, with enantioselectivities of up to 99% ee in... 

Other metals on silica supports have been investigated less extensively than platinum and nickel, and average particle diameters have only been estimated by gas adsorption methods, supported in a few cases by X-ray line broadening data. Thus, rhodium, iridium, osmium, and ruthenium (44, 45) and palladium (46) have all been prepared with average metal particle diameters <40 A or so, after hydrogen reduction at 400°-500°C. 

Some second- and third-row transition metals are, for good reason, known as precious metals. These include silver, palladium, rhodium, iridium, osmium, gold, and platinum. As this is written, gold is over 900 per ounce and silver is over 15 per ounce. Some of the other metals such as rhodium, osmium, and rhenium are also extremely expensive. Most of the second- and third-row transition metals are found as minor constituents in ores of other metals. Consequendy, we will not enumerate the sources, minerals, or the processes by which these metals are obtained. Some of their most important properties are shown in Table 11.3. 

Numerous studies aimed at the understanding of the mechanism of these processes rapidly appeared. In this context, Murai examined the behavior of acyclic linear dienyne systems in order to trap any carbenoid intermediate by a pendant olefin (Scheme 82).302 A remarkable tetracyclic assembly took place and gave the unprecedented tetracyclo[6.4.0.0]-undecane derivatives as single diastereomer, such as 321 in Scheme 82. This transformation proved to be relatively general as shown by the variation of the starting materials. The reaction can be catalyzed by different organometallic complexes of the group 8-10 elements (ruthenium, rhodium, iridium, and platinum). Formally, this reaction involves two cyclopropanations as if both carbon atoms of the alkyne moiety have acted as carbenes, which results in the formation of four carbon-carbon bonds. 

The cost of the catalysts represents a major hurdle on the road to the industrial application of homogeneous catalysis, and in particular for the production of fine chemicals [1, 2], This is particularly true for chiral catalysts that are based on expensive metals, such as rhodium, iridium, ruthenium and palladium, and on chiral ligands that are prepared by lengthy total syntheses, which often makes them more expensive than the metals. In spite of this, the number of large-scale applications for these catalysts is growing. Clearly, these can only be economic if the substrate catalyst ratio (SCR) can be very high, often between 103 and 105. 

Field emission microscopy was the first technique capable of imaging surfaces at resolution close to atomic dimensions. The pioneer in this area was E.W. Muller, who published the field emission microscope in 1936 and later the field ion microscope in 1951 [23]. Both techniques are limited to sharp tips of high melting metals (tungsten, rhenium, rhodium, iridium, and platinum), but have been extremely useful in exploring and understanding the properties of metal surfaces. We mention the structure of clean metal surfaces, defects, order/disorder phenomena,... 

Keywords Carbonylation Catalysis Rhodium Iridium Mechanism... 

Indirect Reduction with Mediators Containing Palladium, Rhodium, Iridium, and Platinum... 

If a denotes C—C bond rupture in the vicinity of the substituent and b that in the next position, bja values are usually higher than unity for the four metals mentioned. This is the situation, for example, with C5 ring opening over carbon-supported 98) and unsupported (62) platinum, as well as rhodium, iridium, and palladium 42). Ring opening over nickel is also selective 42,99) much less (or even the opposite) selectivity has been found with other metals 42). 

Cyclohexane dehydrogenates rather rapidly to benzene. Its rearrangement has not been reported over pure metals until now. Cg Ring opening is negligible over platinum and palladium 48, 5i) slight hexane formation was reported over carbon supported rhodium, iridium, and, especially, osmium and ruthenium (702), as well as over nickel on alumina (99). 

The first use of a metal catalyst in the DKR of secondary alcohols was reported by Williams et al. [7]. In this work, various rhodium, iridium, ruthenium and aluminum complexes were tested. Among them, only Rh2(OAc)4 and [Rh(cod)Cl]2 showed reasonable activity as the racemization catalyst in the DKR of 1-phenylethanol. The racemization occurred through transfer-hydrogenation reactions and required stoichiometric amounts of ketone as hydrogen acceptor. The DKR of 1-phenylethanol performed with Rh2(OAc)4 and Pseudomonas Jluore-scens lipase gave (R)-l-phenylethyl acetate of 98%e.e. at 60% conversion after 72 h. 

Many transition metal complexes catalyze homogeneous activation of molecular hydrogen in solution, forming hydrido complexes. Such complexes include pentacyanocobaltate(II) anion, [Co(CN)5], many metal carbonyls, and several complexes of rhodium, iridium, and palladium. 

The initial steps are similar to any other mineral extraction process. This involves crushing mineral, froth flotation, gravity concentration and other steps to obtain platinum metal concentrates that may contain about 30 to 40 wt% of platinum group metals. The concentrate is treated with aqua regia to separate soluble metals, gold, platinum, and palladium from other noble metals such as ruthenium, rhodium, iridium, osmium, and silver that remain in... 

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