Metal Group VIII

Group VIII Metals.—The majority of catalysts reported for homogeneous hydration, carbonylation, and hydroformylation are compounds of these nine metals, particularly of cobalt, rhodium, and palladium. 

Alk-l-enes, ethyl acrylate, ethyl crotonate, ethyl but-3-enoate, and styrene are all carbonylated by carbon monoxide in the presence of K[FeH(CO)4] or K2[Fe(CO)4]. Vinylcyclopropanes (103) are carbonylated in the presence of Fe(CO)5 or FcaCCO), under irradiation. The initial product is (104), which can isomerize to (105). The reaction of alkenes 

Ruthenium. Cyclic secondary amines, including morpholine and piperidine, can be carbonylated to give iV-formyl derivatives in the presence of ruthenium carbonyl compounds [Ru(OaCMe)(CO)2ln or Ru3(CO)ig. With the former catalyst it is possible to isolate an intermediate [RuCOgCMe)-(amine)(CO)2]OT, where m is probably 2.  

Cobalt. The rate law for carbonylation of Schiff bases, catalysed by Co2(CO)8, has been reported. Dicobalt octacarbonyl also catalyses reaction between aldehydes, for instance formaldehyde or acetaldehyde, amides, for example acetamide or benzamide, and carbon monoxide. The products are iV-acyl-amino-acids. The main product from the reaction of acetylene with carbon monoxide in the presence of CoH(CO)4 is ethyl acrylate. Characterization of the intermediates permits suggestions to be made as to the mechanism of this reaction. Initial reactions between the acetylene and two molecules of catalyst may give (106), in equilibrium with its isomer (107) the carbon monoxide inserts into the cobalt-carbon bonds of the latter. Further information about Coa(CO)8-catalysed hydro-formylation of acrylonitrile and of 3-methyl[3- H]hex-l-ene has led 

Rhodium. The determination of the rates of conversion of alkenes to aldehydes under hydroformylation conditions, using RhH(CO)(PPh3)a as 

The Group VIII metals are active for steam reforming. The turn-over frequency, TOF, is typically 2—5 s at 500 C for steam reforming of methane on nickel (H20/CH4=4. H2O/H2=10, 1 bar abs [389]). 

Allo5Tng nickel with groups IB metals (Cu,Ag) may cause a drastic decrease in the activity [49] [389], 

Sintering of the nickel crystals results in no significant change in TOF. However, for small nickel particles (dNi 10 inn) there is a significant increase in TOF with increased dispersion as discussed in Chapter 6. 

Cobalt shows a lower activity than nickel [389] - probably attributable to the process conditions, with the H2O/H2 value being close to that causing oxidation of the metal. Iron is active for steam reforming. 

Rhodium and mthenium show TOP values about ten times higher than nickel, platinum or palladium [264] [272] [379]. Only one study [517] claimed platinum to be the most active metal. The sequence of metal activities is discussed further in Chapter 6. Rhodium is also the best catalyst for selective steam dealkylation of toluene at low temperature [213]. 

It has recently been shown that decomposition of ferrocene does not occur in the spectrometer until 900°-1000°C (165). Therefore it is reasonable to believe that the associated products observed by Schumacher and Taubenest are indeed the products of ion-molecule reactions. 

Low-voltage mass spectrometry has been used to identify ferrocene and its derivatives, for by using an ionizing voltage of 8 eV only the molecular ion peaks are observed (44,189). Reed and Tabrizi studied the mass spectra 

Following the paper by Reed and Tabrizi, Mandelbaum and Cais (135) reported the mass spectra of six monosubstituted ferrocenes having a carbonyl group in the a-position to the cyclopentadienyl ring. In addition 

However, the more interesting aspects of the fragmentation of these compounds were the formation of rearranged ions in which the group R 

Mass spectrometry has been used as a means of identification of various ferrocene derivatives, as well as in the study of specific problems such as determination of configuration and the interesting loss of formaldehyde in some methyl esters. 

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The classic catalyst consists of Co-Th02-MgO mixtures supported on Kieselguhr (see Ref. 269) group VIII metals, especially Ni, generally are active,... 

We consider next perhaps the bet understood catalyzed reaction the oxidation of CO over group VIII metal catalysts. The reaction is an important environmental one since it involves the conversion of CO to CO2 in automobile catalytic converters. The mechanism is straightforward ... 

Hydrogenation Catalysts. The key to catalytic hydrogenation is the catalyst, which promotes a reaction which otherwise would occur too slowly to be useful. Catalysts for the hydrogenation of nitro compounds and nitriles are generally based on one or more of the group VIII metals. The metals most commonly used are cobalt, nickel, palladium, platinum, rhodium, and mthenium, but others, including copper (16), iron (17), and tellurium... 

Dehalogenation of monochlorotoluenes can be readily effected with hydrogen and noble metal catalysts (34). Conversion of -chlorotoluene to Ncyanotoluene is accompHshed by reaction with tetraethyl ammonium cyanide and zero-valent Group (VIII) metal complexes, such as those of nickel or palladium (35). The reaction proceeds by initial oxidative addition of the aryl haHde to the zerovalent metal complex, followed by attack of cyanide ion on the metal and reductive elimination of the aryl cyanide. Methylstyrene is prepared from -chlorotoluene by a vinylation reaction using ethylene as the reagent and a catalyst derived from zinc, a triarylphosphine, and a nickel salt (36). 

Cyclopentadiene itself has been used as a feedstock for carbon fiber manufacture (76). Cyclopentadiene is also a component of supported metallocene—alumoxane polymerization catalysts in the preparation of syndiotactic polyolefins (77), as a nickel or iron complex in the production of methanol and ethanol from synthesis gas (78), and as Group VIII metal complexes for the production of acetaldehyde from methanol and synthesis gas (79). 

The results used for a subsequent comparison of catalytic activity of all group VIII metals are related by Mann and Lien to palladium studied at a temperature of 148°C. At this temperature the appearance of the hydride phase and of the poisoning effect due to it would require a hydrogen pressure of at least 1 atm. Although the respective direct experimental data are lacking, one can assume rather that the authors did not perform their experiments under such a high pressure (the sum of the partial pressures of both substrates would be equal to 2 atm). It can thus be assumed that their comparison of catalytic activities involves the a-phase of the Pd-H system instead of palladium itself, but not in the least the hydride. 

G.L. Haller, and D.E. Resasco, Metal-Support Interaction Group VIII Metals and Reducible Oxides, Advances in Catalysis 36, 173-235 (1989). 

H. Bdnnemann, C. Girard, W. Kopp, and G. Wilke Homogeneous reactions catalysed by Group VIII metal systems, pp. 265-296 (25). 

From chemisorption theory we know that adatom adsorption energies wiU decrease in a row of the periodic system of the group VIII metals when the position of the element moves to the right. The rate of hydrogenation of Cads vviU decrease with increasing adsorption energy of Cads and hence wiU decrease in the same order with element position in the periodic system. 

Platinum-rhenium catalysts have been reduced in one atmosphere of flowing hydrogen and then examined, without exposure to the atmosphere, by ESCA. The spectra indicate that the Group VIII metal is present in a metallic state in the reduced catalyst and that the majority of the rhenium is present in a valence state higher than Re(0). 

To Illustrate the utility of the technique, we have addressed the question of the anomalous chemlsorptlve behavior of tltanla-supported group VIII metals reduced at high temperatures. The suppression of strong H2 chemisorption on these catalysts has been ascribed to a strong-metal-support Interaction (SMSI) ( ). It has also been found that the reaction activity and selectivity patterns of the catalysts are different In normal and SMSI states... 

M. Current evidence Indicates that the effect may be ascribed to the formation of a TIO film on the surface of the group VIII metal particles (6,7) Whatever the cause of the SMSI state. It Is certainly the case that It has altered site energetics and possibly their density on the catalysts. The extraction of site... 

We plan to make studies on palladium-copper, iridium-copper, and platinum-copper catalysts to extend our investigation of the effect of varying miscibility of the components on the structural features of the bimetallic clusters present. With these additional systems, the whole range from complete immiscibility to total miscibility of copper with the Group VIII metal will be encompassed. 

A full discussion of the reactions of molecular oxygen involved in dioxygen adducts would require a separate review. Moreover, the reactions of co-ordinated molecular oxygen are discussed elsewhere l-8) dioxygen adducts of biological systems (7) and synthetic group VIII metal complexes 1,3) being of particular interest. 

Bayer and Schretzmann 25) came to the conclusion that reversible oxygenation is a characteristic property of group VIII metals. However, work has shown that the cadmium complex CdEt2 can take up dioxygen reversibly in the ratio 1 2 (Cd O2). But it was found that the oxygenated complex (II(P) or 11(G) orientation) can undergo spontaneous catalytic oxidation to form bis(ethylperoxy) cadmium ... 

Raney Type and Supported Group VIII Metal Catalysts. Effect of Metal on Selectivity... 

Supported Co, Ni, Ru, Rh, Pd and Pt as well as Raney Ni and Co catalysts were used for the hydrogenation of dodecanenitrile to amines in stirred SS autoclaves both in cyclohexane and without a solvent. The reaction temperature and the hydrogen pressure were varied between 90-140 °C and 10-80 bar, respectively. Over Ni catalysts NH3 and/or a base modifier suppressed the formation of secondary amine. High selectivity (93-98 %) to primary amine was obtained on Raney nickel, Ni/Al203 and Ru/A1203 catalysts at complete nitrile conversion. With respect to the effect of metal supported on alumina the selectivity of dodecylamine decreased in the order Co Ni Ru>Rh>Pd>Pt. The difference between Group VIII metals in selectivity can be explained by the electronic properties of d-band of metals. High selectivity to primary amine was achieved on base modified Raney Ni even in the absence of NH3. 

While the desired product of the hydrogenation of nitriles is often the primary amines, the proportion of primaiy/secondary/tertiary amines in the product is strongly affected by the nature of metal. In the hydrogenation of nitriles on Group VIII metals, the selectivity of primary amine decreases in the order Co>Ni>Ru>Rh>Pd>Pt [1], The difference between Group VIII metals in selectivity to primary amine is explained by the difference in the electronic... 

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