Octacarbonyl-dicobalt transformation

The octacarbonyl-dicobalt transformation scheme in these conditions takes the form... 

The dicobalt octacarbonyl-catalyzed transformation of azoarenes into 2-arylindazolin-3-ones by carbonylation has been known for many years157 high pressures of carbon monoxide are required and under more forcing conditions the products are quinazoline-2,4-diones (Scheme 92). Reactions... 

A combination of Co-mediated amino-carbonylation and a Pauson-Khand reaction was described by Pericas and colleagues [286], with the formation of five new bonds in a single operation. Reaction of l-chloro-2-phenylacetylene 6/4-34 and dicobalt octacarbonyl gave the two cobalt complexes 6/4-36 and 6/4-37 via 6/4-35, which were treated with an amine 6/4-38. The final products of this domino process are azadi- and azatriquinanes 6/4-40 with 6/4-39 as an intermediate, which can also be isolated and separately transformed into 6/4-40 (Scheme 6/4.11). 

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... 

An interesting cyclization reaction was reported that involved the reaction of dienes, diynes, or ene-ynes with transition metals to form cyclopentenone derivatives in the presence of carbon monoxide.363 in a simple example, ene-yne 444 was heated with dicobalt octacarbonyl and CO to give a 68% yield of 445.364 jjjj transformation has become an important synthetic tool known as the Pauson-Khand reaction.365 jhe mechanism probably involves insertion of the alkene (or alkyne) into the transition metal bond, which is why it is presented in this section. Formally, it is a [2+2+l]-cycloaddition, but the accepted mechanism is the one proposed by Magnus,364 and shown in Figure 13.8.366 n has been stated that further study is required to... 

Acetylenes with one bulky substituent are transformed into symmetrically or unsymmetrically substituted cyclopentadienones by the combined action of dicobalt octacarbonyl and carbon monoxide see, for example, equation 55. ... 

Group 9 metals (Co, Rh, Ir) have been the subject of much interest because of their known catalytic properties. Dicobalt octacarbonyl, Co2(CO)s, can be trapped in zeolites and undergoes various transformations leading to polynuclear Co4(CO)i2, anionic [Co(CO)4] and other species [259-263]. Thermal decarbonylation of 7 -C5H5Co(CO)2 [264] and (CO)4CoSnMe3 [265, 266] in zeolites has also been investigated. 

All the named compounds form cobalt carbonyls under the reaction conditions applied in the oxo reaction. These carbonyls are in equilibrium with cobalt hydrocarbonyl [823] which is the active catalyst in the oxo reaction [30,108,109, 760] see also page 4—6. Since dicobalt octacarbonyl is readily transformed into cobalt hydrocarbonyl, it is often used as a promoter in combination with other cobalt compounds. 

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