Metal-containing compounds, Rhodium

Metal-containing compounds, Rhodium Compounds (Continued) Hydridotetrakis(triphenylphosphine)-rhodium(I), 144 Rhodium(II) acetate, 226, 266 Rhodium(II) carboxylates, 226, 266 Rhodium(II) trifluoroacetate, 266 Tetra-jx3-carbonyldodecacarbonylhexa-rhodium, 152, 288... 

Divalent sulfur is a poison for most noble metal catalysts so that catalytic hydrogenation of sulfur-containing compounds poses serious problems (p. 10). However, allyl phenyl sulfide was hydrogenated over tris trisphenyl-phosphine)rhodium chloride in benzene to give 93% yield of phenyl propyl sulfide [674. ... 

This preparation is an illustration of the hydroformylation of olefins (oxo synthesis). The reaction occurs in the presence of soluble catalytic complexes containing metals of Group VIII of the periodic system. Although the metal originally used by Roelen and still largely used in the industry for the production of aliphatic aldehydes and alcohols is cobalt, the most active and selective catalysts are rhodium-containing compounds. The catalytic activity of the other Group VIII metals is in... 

Supported mixed metal catalysts are also prepared by other means such as the deposition of bimetallic colloids onto a support O and the decomposition of supported bimetallic cluster compounds.208 The photocatalytic codeposition of metals onto titania was also attempted with mixed results.209 with a mixture of chloroplatinic acid and rhodium chloride, very little rhodium was deposited on the titania. With aqueous solutions of silver nitrate and rhodium chloride, more rhodium was deposited but deposition was not complete. In aqueous ammonia, though, deposition of both silver and rhodium was complete but the titania surface was covered with small rhodium crystallites and larger silver particles containing some rhodium. With a mixture of chloroplatinic acid and palladium nitrate both metals were deposited but, while most of the resulting crystallites were bimetallic, the composition varied from particle to particle.209... 

Garland M, Bor G (1989) Infrared spectroscopic studies on metal carbrniyl compounds. 24. Observation of the infrared spectrum of an acyirhodium tetracarbonyl during the hydroformylation of olefins with rhodium-containing catalyst preciusors. friOTg Chem 28(3) 410-413... 

Polynuclear anionic metal carbonyl compounds are usually prepared by reduction reactions of metal carbonyls M(CO) with such reducing agents as the alkali metals, NaBH4 in ethers, hydrocarbons, liquid ammonia, and similar solvents [see, for example, reactions (2.54), (2.55), (2.84), (2.89), (2.95>-(2.102), and (2.108)-(2.113)]. In alkali medium the metal carbonyls may be reduced by certain solvents (e.g., alcohols) or by the CO ligand itself, and in the presence of Lewis bases the carbonyls disproportionate to give anionic clusters. The mixed metal clusters containing platinum and rhodium are formed by reduction reactions of chloro complexes... 

Polymer-supported, carbon dioxide-protected NHCs were also prepared for catalysis reactions [150]. These supports were prepared using DMN-H6 with 3-(bicyclo[2.2.1]hept-2-ene-5-ylmethyl)-l-(2-propyl)-3,4,5,6-tetrahydropyrimidin-l-ium-2-carboxylate and a Schrock catalyst. They were later used for the trimerization reaction of isocyanates and for the cyanosilylation of carbonyl-containing compounds. Various metals could be immobilized through the NHC hgands including rhodium(I), iridium(l), and palladium(II). The resulting monoUths polymerized phenylacetylene and were successful catalysts for Heck-type couplings [150]. 

Methods for separating the different platinum metals are comphcated and are partly kept secret. The traditional method with dissolution in aqua regia is still used, in which platinum, palladium and gold are dissolved while the other platinum metals stay undissolved. Gold is obtained from the solution by reduction, platinum is precipitated as ammonium hexachloroplatinate and palladium as a dichlorodiammine compound. The residue after the first aqua regia treatment contains iridium, rhodium, osmium and ruthenium. They are separated in several complicated steps. 

As previously mentioned in paragraph 3.2.1., many patents on the use of palladium-based catalytic systems containing a metallic cocatalyst also mention the use of rhodium compounds (usually RhCL) in place of PdCL, but lower yields are always reported. We will not mention again here the same patents and will discuss only the systems for which a rhodium compound is explicitly mentioned as the, or the best, catalyst. Compared to the number of patents dealing with palladium compounds and metal-containing cocatalysts, the number of reports on similar rhodium-based systems is much more limited, confirming that, at least for the synthesis of carbamates and ureas, the combination of... 

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