By Rhodium and Nickel Catalysts

While hydrosilylation of imines is known to be effected by rhodium catalysts3, nickel catalysts prepared in situ from Ni(0Ac)2 4H20 and thiosemicarbazones are also found to promote the reactions of iV-substituted imines with HSiEt3 in dry DMSO at 35 °C, giving the corresponding secondary amines in excellent yields after basic work-up (equation 77)185. 

Riesz and Weber compared the selectivities of commercial platinum, palladium, rhodium, and nickel catalysts for hydrogenation of linolenic components in soybean oil.110 Representative results are summarized in Table 3.8. Certain platinum metal catalysts showed higher selectivities than nickel catalysts, as indicated by the values of SL (A in Scheme 3.13) = 2.4-2.7. Generally, nickel catalysts showed selectivities... 

Cobalt-catalyzed cyclocotrimerization of alkynes and nitriles was pioneered by Wakatsuki, Bonneman, and co-workers [55], Highly selective intramolecular versions of this powerful pyridine-ring annulation were developed further using cobalt, rhodium, and nickel catalysts by Vollhardt, and others [53], These reactions include... 

The metal-catalysed hydrogenation of cyclopropane has been extensively studied. Although the reaction was first reported in 1907 [242], it was not until some 50 years later that the first kinetic studies were reported by Bond et al. [26,243—245] who used pumice-supported nickel, rhodium, palladium, iridium and platinum, by Hayes and Taylor [246] who used K20-promoted iron catalysts, and by Benson and Kwan [247] who used nickel on silica—alumina. From these studies, it was concluded that the behaviour of cyclopropane was intermediate between that of alkenes and alkanes. With iron and nickel catalysts, the initial rate law is... 

Nakahara and Nishimura studied the selectivities of copper-chromium oxides, nickel, palladium, rhodium, and ruthenium catalysts in the hydrogenation of phenan-threne, 9,10-dihydrophenanthrene (DHP), and 1,2,3,4-tetrahydrophenanthrene (THP), usually in cyclohexane at 80°C (150°C for copper-chromium oxide) and an initial hydrogen pressure of 11 MPa (5 MPa for platinum metals). The hydrogenations over Os-C, Ir-C, and Pt-C were very slow and not investigated further. The varying compositions of the reaction mixture versus reaction time have been analyzed on the basis of the reaction sequences shown in Scheme 11.20 by means of a computer simulation, assuming the Langmuir-Hinshelwood mechanism.262 The results are summarized in Table 11.23. 

Recently, our group has found that functionalized ethylene oligomers can be used as ligands to prepare recoverable, reusable homogeneous catalysts from both transition metals like rhodium and nickel and from lanthanide salts. In complimentary studies of polyethylene functionalization, we have found that ethylene oligomers of My > 1200 are quantitatively entrapped in polyethylene precipitates when a solution of polyethylene and a functionalized ethylene oligomer is cooled to room temperature or when polyethylene and the functionalized oligomer are co-precipitated by addition of a second solvent such as methanol Suitably... 

There has been a review of palladium-catalysed carbonylative coupling reactions of aryl halides with carbon nucleophiles in the presence of carbon monoxide. It has been shown that rhodium is an efficient catalyst for the homocoupling reaction of arylzinc compounds in the presence of 1 atm of carbon monoxide to give diaryl ketones. Under similar conditions, palladium and nickel catalysts yield biaryls. The beneficial catalysis by rhodium is likely to derive from the ease of migration of the aryl ligand to carbon monoxide in the rhodium(III) intermediate. A rhodium catalyst has also been used in the formation of indole-3-carboxylates by reaction of indoles with alcohols in the presence of carbon monoxide. The catalytic cycle. Scheme 5, is likely to involve metallation of the indole at the 3-position, followed... 

Ethanol steam reforming catalysts were developed by Men et al. [24]. Nickel, rhodium and ruthenium catalysts on different carrier materials such as alumina, silica, magnesia and zinc oxide were tested at a S/C ratio of 1.5 and WHSV 90 Lh g J in the temperature range 400-600 °C. All the monometallic catalysts were mainly selective for acetaldehyde and ethylene. Over the rhodium catalyst, a reaction temperature of 600 °C was required to achieve 80% hydrogen selectivity. 

A similar insertion of ethylene into a C—M bond of a w-butenyl complex seems to occur in the industrial synthesis of hexadienes from butadiene and ethylene, at least with rhodium and nickel compounds. These catalysts give tra f-l,4-hexadiene as the initial product 178). Cobalt and iron catalysts give the cis isomer 179,180), probably by a different mechanism. 

As mentioned in the chapter on the reaction mechanism, the anion, especially of Ni-salts, is important in affecting the reaction course. The catalytic efficiency of the nickel halides strongly increases in the series fluoride, chloride, bromide, iodide [374—376]. The molar ratio of cobalt or nickel to iodine is also very important [414]. As in the hydroformylation reaction, metal carbonyls substituted by phosphine ligands are very reactive [377, 1009], and especially modified rhodium and palladium catalysts [1021, 1045] allow reactions under mild conditions. Thus, the nickel bromide triphenylphosphine allyl bromide complex shows an increased reactivity in the carbonylation of acetylenes. On the other hand, carbonyls substituted by phosphine ligands are also readily soluble in the reaction mixture [345, 377]. 

HDPE resias are produced ia industry with several classes of catalysts, ie, catalysts based on chromium oxides (Phillips), catalysts utilising organochromium compounds, catalysts based on titanium or vanadium compounds (Ziegler), and metallocene catalysts (33—35). A large number of additional catalysts have been developed by utilising transition metals such as scandium, cobalt, nickel, niobium, molybdenum, tungsten, palladium, rhodium, mthenium, lanthanides, and actinides (33—35) none of these, however, are commercially significant. 

Earlier catalysts were based on cobalt, iron, and nickel. However, recent catalytic systems involve rhodium compounds promoted by methyl iodide and lithium iodide (48,49). Higher mol wt alkyl esters do not show any particular abiUty to undergo carbonylation to anhydrides. 

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