Cobalt, viii

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... 

Catalysts. The methanation of CO and C02 is catalyzed by metals of Group VIII, by molybdenum (Group VI), and by silver (Group I). These catalysts were identified by Fischer, Tropsch, and Dilthey (18) who studied the methanation properties of various metals at temperatures up to 800°C. They found that methanation activity varied with the metal as follows ruthenium > iridium > rhodium > nickel > cobalt > osmium > platinum > iron > molybdenum > palladium > silver. 

Cu -> Ni and consequently Pt or Ni II (CO), but this explanation was rather unsatisfying (although widely spread and still being popular). Cobalt caused namely the same kind of effect as Cu and yet it could be hardly suspected of donating electrons to Ni. Indeed, it appeared that the reason for a lower v(VIII grp., CO) value with alloys is simply the dilution of the CO-layer. The following experiments elucidated the problem. 

The coordination modes of the nitrate ligand in the complexes [TpBut]M(N03) (M = Cu, Ni, Co, Zn) are summarized in Fig. 46. (171, 184). Evidently, the coordination mode varies from unidentate for Zn to symmetric bidentate for Ni and Cu, with the cobalt derivative exhibiting an anisobidentate coordination mode. Moreover, the related cadmium derivative [TpBut,Me]Cd(N03) also exhibits bidentate coordination of the nitrate ligand, with Cd-0 bond lengths of2.272(6) A and 2.295(7) A (91). Such symmetric bidentate coordination contrasts with the significantly different Zn-0 interactions [1.978(3) A and 2.581(3) A] in unidentate [TpBut]Zn(N03). The coordination modes for a variety of [TpRR ]M(N03) complexes are summarized in Table VIII. 

The first reported work on the kinetics of hydrogenolysis reactions of simple hydrocarbons appears to be that of Taylor and associates at Princeton (2-4, 14, 15), primarily on the hydrogenolysis of ethane to methane. The studies were conducted on nickel, cobalt, and iron catalysts. More recently, extensive studies on ethane hydrogenolysis kinetics have been conducted on all the group VIII metals and on certain other metals as well (16,28-83). 

In the hydrogenolysis of the higher alkanes on the nonnoble group VIII metals (i.e., iron, cobalt, and nickel), the mode of cracking is very different from that observed on the noble metals of group VIII (49, 50). On nickel,... 

The successive demethylation scheme of hydrogenolysis just discussed for iron, cobalt, and nickel clearly does not apply to the noble metals of group VIII. This can be seen by examining the product distribution data in Table IV. The amounts of methane observed are much lower than would be expected if the hydrogenolysis occurred by successive demethylation steps. Thus, we have another indication that the noble and nonnoble metals of group VIII behave as two separate classes with regard to their catalytic properties in the hydrogenolysis of hydrocarbons. 

VIII. Catalysts Other Than Cobalt and Rhodium. 53... 

The need for higher product specificity and milder reaction conditions (see also Section IX) has led to extensive research in hydroformylation technology. This research, as reported in technical journals, patent literature, and commercial practice has been primarily concerned with catalysis by rhodium, in addition to the traditional cobalt, and with catalyst modification by trialkyl or triaryl phosphines. These catalyst systems form the basis for the major portion of the discussion in this chapter some other catalyst systems are discussed in Section VIII. 

The results from our work on the reaction of propylene oxide with cobalt carbonyl and base in methanol are given in Table VIII. Several base/metal oxide combinations were evaluated under mild reaction conditions. The difference in activity between the bases was not as pronounced as that observed in the reaction with benzyl halides with the exception of potassium methoxide which, when used alone, gave exclusively the hydroxy ether resulting from methoxide addition to the epoxide ring. However, the activity of sodium... 

In this connection, a recent article by Phillipson and Wells 44) dealing with the isomerization of butenes is of interest. The Group VIII metals catalyze both the hydrogenation and isomerization of butenes, cobalt... 

Rhodium is a hard shiny-white metal that resists corrosion from oxygen, moisture, and acids at room temperatures. As a member of group 8 (VIII), Rh shares many chemical and physical properties with cobalt (j Co) just above it and iridium ( ylr) below it in the vertical group. Therefore, it is considered one of the elements that are transitory between metals and nonmetals. It is rare and only found in combination with platinum ores. 

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... 

Figure D shows some olefin insertion reactions. Hydride additions to olefins have been known for a long while. Among these many examples, manganese hydrocarbonyl, and cobalt hydrocarbonyl, magnesium hydride, diborane, alkylalu-minum hydrides, germanium and tin hydrides all add quite readily to olefins. These last two cases are questionable because the mechanism is not clear. Some of these additions occur without a catalyst some are speeded up by ultraviolet light some are catalyzed by Group VIII metals. So it is not clear whether all these reactions are the same or whether there are several different mechanisms.

Although iron, cobalt, and nickel occur in the same triad in Group VIII., the three elements differ considerably in their ability to form addition compounds with ammonia. Iron forms few ammino-salts, most of which are unstable, and its tendency to complex-salt formation of the ammine type appears in the complex cyanides and not in the ammines themselves. 

All Group VIII metals, as well as Mn, Cr, and Cu, exhibit some activity in hydroformylation.6 11 Cobalt, the catalyst in the original discovery, is still used mainly in industry rhodium, introduced later, is one of the most active and studied catalysts. The metal catalysts may be applied as homogeneous soluble complexes, heteroge-nized metal complexes, or supported metals. 

One of the characteristic features of the metal-catalysed reaction of acetylene with hydrogen is that, in addition to ethylene and ethane, hydrocarbons containing more than two carbon atoms are frequently observed in appreciable yields. The hydropolymerisation of acetylene over nickel—pumice catalysts was investigated in some detail by Sheridan [169] who found that, between 200 and 250°C, extensive polymerisation to yield predominantly C4 - and C6 -polymers occurred, although small amounts of all polymers up to Cn, where n > 31, were also observed. It was also shown that the polymeric products were aliphatic hydrocarbons, although subsequent studies with nickel—alumina [176] revealed that, whilst the main products were aliphatic hydrocarbons, small amounts of cyclohexene, cyclohexane and aromatic hydrocarbons were also formed. The extent of polymerisation appears to be greater with the first row metals, iron, cobalt, nickel and copper, where up to 60% of the acetylene may polymerise, than with the second and third row noble Group VIII metals. With alumina-supported noble metals, the polymerisation prod-... 

Throughout these studies, no product other than propane was observed. However, subsequent studies by Sinfelt et al. [249—251] using silica-supported Group VIII metals (Co, Ni, Cu, Ru, Os, Rh, Ir, Pd and Pt) have shown that, in addition to hydrogenation, hydrocracking to ethane and methane occurs with cobalt, nickel, ruthenium and osmium, but not with the other metals studied. From the metal surface areas determined by hydrogen and carbon monoxide chemisorption, the specific activities of... 

As a measure of accuracy, we checked our method against NBS standards and mixtures of elements of known concentration and also participated in a round-robin analysis with NBS and EPA. We analyzed four NBS standards containing 60 elements in glass. Comparisons of results are given in Table VIII. With the exception of the cobalt result in the NBS 610 Standard, agreement is generally within 25% of the NBS value. 

Mercury-transition metal bonds have been described for all members of Groups V-VIII of the transition series except, apparently, technetium. They commonly involve a low oxidation state of the transition element and are particularly numerous for the chromium, iron and cobalt families.1 In addition, mercury-titanium bonded species have been postulated as unstable reaction intermediates.2... 

These complexes can exist in a triangular peroxo form (7a) for early d° transition metals, or in a bridged (7b) or linear (7c) form for Group VIII metals. They can be obtained from the reaction of alkyl hydroperoxides with transition metal complexes (equations 9 and 10),42-46 from the insertion of 02 into a cobalt-carbon bond (equation ll),43 from the alkylation of a platinum-peroxo complex (equation 12),44 or from the reaction of a cobalt-superoxo complex with a substituted phenol (equation 13).45 Some well-characterized alkylperoxo complexes are shown (22-24). 

All Group VIII, IX and X transition metals show some catalytic activity for hydroformylation, although cobalt and rhodium are the most active, rhodium catalysts being 104 times more reactive. More recently, platinum catalysts containing the trichlorostannate ligand have been shown to be selective catalysts that effect hydroformylation under mild conditions.6... 

The hydrocarboxylation reaction of alkenes and alkynes is one which utilizes carbon monoxide to produce carboxylic acid derivatives. The source of hydrogen is a protic solvent (equation 35) dihydrogen is not usually added to the reaction. There are a number of variations to this reaction, since the solvent can be water, alcohols, amines, acids, etc. The catalysts can be Group VIII-X transition metals, but cobalt, rhodium, nickel, palladium and platinum have found the most use. 

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