Cobalt carbonyl formation

Ma.nufa.cture. Nickel carbonyl can be prepared by the direct combination of carbon monoxide and metallic nickel (77). The presence of sulfur, the surface area, and the surface activity of the nickel affect the formation of nickel carbonyl (78). The thermodynamics of formation and reaction are documented (79). Two commercial processes are used for large-scale production (80). An atmospheric method, whereby carbon monoxide is passed over nickel sulfide and freshly reduced nickel metal, is used in the United Kingdom to produce pure nickel carbonyl (81). The second method, used in Canada, involves high pressure CO in the formation of iron and nickel carbonyls the two are separated by distillation (81). Very high pressure CO is required for the formation of cobalt carbonyl and a method has been described where the mixed carbonyls are scmbbed with ammonia or an amine and the cobalt is extracted as the ammine carbonyl (82). A discontinued commercial process in the United States involved the reaction of carbon monoxide with nickel sulfate solution. 

The formation of isomeric aldehydes is caused by cobalt organic intermediates, which are formed by the reaction of the olefin with the cobalt carbonyl catalyst. These cobalt organic compounds isomerize rapidly into a mixture of isomer position cobalt organic compounds. The primary cobalt organic compound, carrying a terminal fixed metal atom, is thermodynamically more stable than the isomeric internal secondary cobalt organic compounds. Due to the less steric hindrance of the terminal isomers their further reaction in the catalytic cycle is favored. Therefore in the hydroformylation of an olefin the unbranched aldehyde is the main reaction product, independent of the position of the double bond in the olefinic educt ( contrathermodynamic olefin isomerization) [49]. 

If cobalt carbonylpyridine catalyst systems are used, the formation of unbranched carboxylic acids is strongly favored not only by reaction of a-olefins but also by reaction of olefins with internal double bonds ( contrathermo-dynamic double-bond isomerization) [59]. The cobalt carbonylpyridine catalyst of the hydrocarboxylation reaction resembles the cobalt carbonyl-terf-phos-phine catalysts of the hydroformylation reaction. The reactivity of the cobalt-pyridine system in the hydrocarboxylation reaction is remarkable higher than the cobalt-phosphine system in the hydroformylation reaction, especially in the case of olefins with internal double bonds. This reaction had not found an industrial application until now. 

Only a few other cobalt complexes of the type covered in this review (and therefore excluding, for example, the cobalt carbonyls) have been reported to act as catalysts for homogeneous hydrogenation. The complex Co(DMG)2 will catalyze the hydrogenation of benzil (PhCOCOPh) to benzoin (PhCHOHCOPh). When this reaction is carried out in the presence of quinine, the product shows optical activity. The degree of optical purity varies with the nature of the solvent and reaches a maximum of 61.5% in benzene. It was concluded that asymmetric synthesis occurred via the formation of an organocobalt complex in which quinine was coordinated in the trans position (133). Both Co(DMG)2 and cobalamin-cobalt(II) in methanol will catalyze the following reductive methylations ... 

The Co2(CO)g/pyridine system can catalyze carbomethoxylation of butadiene to methyl 3-pentenoate (Eq. 6.44) [80]. The reaction mechanism of the cobalt-catalyzed carbalkoxylation of olefins was investigated and the formation of a methoxycar-bonylcobalt species, MeOC(0)Co from a cobalt carbonyl complex with methanol as an intermediate is claimed [81, 82]. 

Rhodium and cobalt carbonyls have long been known as thermally active hydroformylation catalysts. With thermal activation alone, however, they require higher temperatures and pressures than in the photocatalytic reaction. Iron carbonyl, on the other hand, is a poor hydroformylation catalyst at all temperatures under thermal activation. When irradiated under synthesis gas at 100 atm, the iron carbonyl catalyzes the hydroformylation of terminal olefins even at room temperatures, as was first discovered by P. Krusic. ESR studies suggested the formation of HFe9(C0) radicals as the active catalyst, /25, 26/. Our own results support this idea, 111,28/. Light is necessary to start the hydroformylation of 1-octene with the iron carbonyl catalyst. Once initiated, the reaction proceeds even in the... 

Cobalt carbonyls are the oldest catalysts for hydroformylation and they have been used in industry for many years. They are used either as unmodified carbonyls, or modified with alkylphosphines (Shell process). For propene hydroformylation, they have been replaced by rhodium (Union Carbide, Mitsubishi, Ruhrchemie-Rhone Poulenc). For higher alkenes, cobalt is still the catalyst of choice. Internal alkenes can be used as the substrate as cobalt has a propensity for causing isomerization under a pressure of CO and high preference for the formation of linear aldehydes. Recently a new process was introduced for the hydroformylation of ethene oxide using a cobalt catalyst modified with a diphosphine. In the following we will focus on relevant complexes that have been identified and recently reported reactions of interest. 

A more complex carbonylation process is involved in the formation of bisbutenolides (bifurandiones) from cobalt carbonyl-catalyzed carbonylation of alkynes112 117 (Scheme 68). The trans derivative (53) is formed in good yield from acetylene,112 but yields from substituted acetylenes (e.g., propyne)... 

Subtle differences in the behavior of azoarenes toward cobalt carbonyl derivatives are observed in regard to metal-complex formation. Azobenzene is transformed by dicobalt octacarbonyl in processes of orthometallation and carbonyl insertion into 2-phenylindazolin-3-one (see Section IV,D,2). In contrast, cyclopentadienylcobalt dicarbonyl effects N—N bond cleavage, and carbonylation of the isolable complex 88a provides 1 -phenylbenzimid-azolin-2-one (Scheme 106).171... 

Acetylation occurs at the 2-position of allene systems (Scheme 8.14). The intermediate 7t-allyl complex breaks down via the nucleophilic displacement of the cobalt carbonyl group by the hydroxide ion to produce the hydroxyketone (7) [ 11 ]. An alternative oxygen-initiated radical decomposition of the complex cannot, however, be totally precluded. The formation of a second major product, the divinyl ketone (8), probably arises from direct interaction of the dicobalt octacarbonyl with the allene and does not require the basic conditions. 

Desulphurization of thiols has been accomplished in high yield under phase-transfer conditions using tri-iron dodecacarbonyl (or dicobalt octacarbonyl). The mechanism proposed for the formation of the alkanes and the dialkyl sulphide byproducts involves a one electron transfer to the thiol from the initially formed quaternary ammonium hydridoiron polycarbonyl ion pair [14], Similar one electron transfers have been postulated for the key step in the cobalt carbonyl promoted reactions, which tend to give slightly higher yields of the alkanes (Table 11.18). 

One final interesting isomerization achieved in the cobalt carbonyl system should be mentioned. Heck and Breslow (22b) found that acylcobalt tetracarbonyl compounds undergo alcoholysis with the formation of HCo(CO)4. With methanol, the reaction proceeds at 50° ... 

Cobalt carbonyl complexes react with 1,3-diynes to give a variety of complexes in which two molecules of diyne have coupled to form y-cyclobutadiene ligands slightly different conditions result in formation of cluster complexes (see Section VILE.2). In the mixture of complexes obtained from the reaction... 

On an alumina support, independently of the cobalt carbonyl precursor used, complex cobalt sub-carbonyls compounds, [Co(CO)4] and hydrogencarbonate species formed [143, 149]. However, the reactivity of the alumina surface depends on the degree of hydroxylation highly hydroxylated alumina is more reactive against Co2(CO)g and facilitates decarbonylation, whereas dehydroxylated alumina favors the formation of high nuclearity species like [Co6(CO),5] , which would need higher temperatures than the initial Co2(CO)8 to be decarbonylated [149]. 

Regarding the function of the cobalt component, we find for different iodide charges (at fixed Ru, Co) there is a close parallel between HOAc productivity and the presence of the cobalt carbonyls, and a linear relationship between lOAc and [Co(CO)4] anion content (see Figure 6). This linear correspondence, taken together with the [Co], HOAc selectivity correlation of Figure 3, is indicative of cobalt carbonyl—or a derivative thereof- being responsible for the formation of the desired acetic acid. 

To achieve, then, high acetic acid selectivity directly from synthesis gas (eq. 1) it is necessary to balance the rates of the two consecutive steps of this preparation - ruthenium-carbonyl catalyzed methanol formation (10) (Figures 2 and 5) and cobalt-carbonyl catalyzed carbonylation to acetic acid (Figure 6) - such that the instantaneous concentration of methanol does not build to the level where competing secondary reactions, particularly methanol homologation (7, H), ester homologation (12, 13), and acid esterification (1 ), become important. 

As highly reactive heterocycles, the thietes are well suited for the formation of metal complexes. Takahashi and Dittmer both individually and in collaboration have been involved with the interaction of thietes and iron or cobalt carbonyls. During the thermally or photochemically induced complexation process, ring opening takes place so that the resultant thioacrolein is the actual ligand in the organometallic compound (Scheme i7)/ 3-203,204... 

Meantime, several independent modifications have been introduced to circumvent this inconvenience. The bottom line in devising the catalytic PKR is to develop the way to discourage the formation of higher cobalt clusters, and allow enough time to the unsaturated cobalt carbonyl species for binding the new substrates before making aggregated clusters (Scheme 4). 

Evidence was presented that cobalt precursors under the reaction conditions are transformed into cobalt carbonyls.31 Additives such as Lewis bases accelerate the formation of the catalyst.11 [CoH(CO)4] the key catalytic species was shown by infrared (IR) spectroscopy to be formed under hydroformylation conditions32 and was isolated in the reaction of [Co(CO)4]2 and hydrogen.33 [CoH(CO)4] dissociates carbon monoxide to create [CoH(CO)3] [Eq. (7.2)], which is capable of olefin com-plexation because of a ligand vacancy ... 

The metal hydride mechanism was first described for the cobalt-carbonyl-catalyzed ester formation by analogy with hydroformylation.152 It was later adapted to carboxylation processes catalyzed by palladium136 153 154 and platinum complexes.137 As in the hydroformylation mechanism, the olefin inserts itself into the... 

In the classical oxo process the catalyst cohalt carbonyl is formed in situ by introducing divalent cobalt into the reactor. High temperature is required for this catalyst formation that gives a mixture of aldehydes and alcohols containing only 60-70% of linear product. A new BASF process using cobalt carbonyl hydride shows improved selectivity and efficient catalyst recovery. The catalyst is prepared by passing an aqueous solution of cobalt salt over a promoter and extracting the catalyst from the water phase with olefin. 

T,he hydroformylation reaction or oxo synthesis has been used on an industrial scale for 30 years, and during this time it has developed into one of the most important homogeneously-catalyzed technical processes (I). A variety of technical processes have been developed to prepare the real catalyst cobalt tetracarbonyl hydride from its inactive precursors, e.g., a cobalt salt or metallic cobalt, to separate the dissolved cobalt carbonyl catalyst from the reaction products (decobaltation) and to recycle it to the oxo reactor. The efficiency of each step is of great economical importance to the total process. Therefore many patents and papers have been published concerning the problem of making the catalyst cycle as simple as possible. Another important problem in the oxo synthesis is the formation of undesired branched isomers. Many efforts have been made to keep the yield of these by-products at a minimum. 

---