Unsupported metals

In examination of various disubstituted cyclic olefins, the following decreasing isomerization order was adduced Pd Rh, Ru, Pi > Os > r 84). At 20% conversion of 1-octene to octane, the ratio of isomerization to hydrogenation in isopropanol for various unsupported metals was Pd (2.05), Rh (0.125), Ru (0.121. Pt (0.025), Ir (0.025), Os (0.009) 82). Palladium is used frequently when migration and isomerization are wanted platinum, when they are to be avoided (2J24). 

Another example is the hydrogenation of the homoallylic eompound 4-methyl-3-cyclohexenyl ethyl ether to a mixture of 4-methylcyclohexyl ethyl ether and methylcyclohexane. The extent of hydrogenolysis depends on both the isomerizing and the hydrogenolyzing tendencies of the catalysts. With unsupported metals in ethanol, the percent hydrogenolysis decreased in the order palladium (62.6%), rhodium (23 6%), platinum (7.1%), iridium (3.9%), ruthenium (3.0%) (S3). 

Anilines have been reduced successfully over a variety of supported and unsupported metals, including palladium, platinum, rhodium, ruthenium, iridium, (54), cobalt, and nickel. Base metals require high temperatures and pressures (7d), whereas noble metals can be used under much milder conditions. Currently, preferred catalysts in both laboratory or industrial practice are rhodium at lower pressures and ruthenium at higher pressures, for both display high activity and relatively little tendency toward either coupling or hydrogenolysis,... 

Because of deformability, plastic packing is limited to a 10-15 ft depth unsupported, metal to 20-25 ft. 

Y. A. Ryndin, and Y. I. Yermakov, Reactions of organometallic compounds with surfaces of supported and unsupported metals. In Surface Organometallic Chemistry Molecular Approaches to Catalysis edited by J. -M. Basset, B. C. Gates, J.-P. Candy, A. ChopUn, M. Lecomte, F. Quignard, and C. Santini (Kluwer, Dordrecht 1998) pp. 127-141. 

A] to form [(Tab)2M][Au(CN)2] units. Two such fragments are further connected by one gold-gold aurophilic bonding interaction [Au-Au 3.0140(5) A] to form an uncommon Ag-Au-Au-Ag linear string structure with three ligand-unsupported metal-metal bonds [605]. 

Unsupported Metals under Vacuum or in a Single-Component Gas... 

Solvated metal atoms can be dispersed in excess organic solvent at low temperature and used as a source of metal particles for the preparation of both unsupported metal powders and supported metal catalysts158,161. Alternatively, metal vapor is condensed into a cold solution of a stabilizing polymer to form crystallites of the order 2-5 nm in diameters159. Equation 17 illustrates the unique activity of a colloidal Pd catalyst in the partial hydrogenation of acenaphthene. 

Hydrotreating catalysts originated in the 1920s when German researchers developed unsupported metal sulfide catalysts to liquefy coal. However, it was not until the 1970s that the structures of these catalysts and the mechanisms of their catalytic action began to be understood. It was established that under catalytic reaction conditions, most of the molybdenum in industrial... 

Unless otherwise noted, the substrate (0.10—0.15 ml) was hydrogenated over unsupported metals (7.5—40 mg) in 4-5 ml of t-BuOH at 26°C and atmospheric hydrogen pressure. 

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