Cobalt carbonyl derivatives halides

Benzyl- and phenylacetyl derivatives of tetracarbonylcobalt(I) are believed to be important intermediates in the cobalt-catalyzed carbonylation of benzyl halides to phenylacetic acidi2twi and to phenylpyruvic acid ", carried out under phase transfer catalysis in the presence of catalytic amounts of a cobalt-carbonyl derivative. The carbonylation to phenylacetic acid proceeds as follows ... 

Both Co2(CO)g and Co4(CO),2 are oxidized by air even in the solid state, and by halogens. With the latter, complete decomposition to CO and Co(II) halides occurs. Reaction of cobalt carbonyl derivatives with I2 in pyridine is frequently used for analyses by gas volumetry of CO evolved. Octacarbonyldicobalt, Co2(CO)g, is attacked by organic substances that contain active protons and converted to the corresponding Co(II) salts , as in reactions for Fe(CO)j [equations (1) and (m), 14.6.2.3.2]. Included here is reaction of Co2(CO)g with cyclopentadiene to give dicarbonylcyclopentadienylcobalt(I) as a dark red oil (b.p. 75 C/22 torr) ... 

Metal derivatives of cobalt carbonyl hydride such as Tl[Co(CO)4], Zn[Co(CO)4]2, or Cd[Co(CO)4]2 are formed upon reaction of cobalt octacarbonyl with these metals in the presence of carbon monoxide under pressure. Reaction with halogens (X) produces cobalt carbonyl halides, Co(CO)X2. 

The mercury compounds HgFe(CO)4 and Fe(CO)4(HgX)2 (X = C1, Br, I), which were the first representatives of non-ionic metal derivatives of iron carbonyl hydrides, were discovered by Hock and Stuhlmann (V, 36). During investigations into the preparation of cobalt carbonyls from cobalt halides under CO pressure, in the presence of another metal as a halogen acceptor, we discovered the mixed metal carbonyls M[Co(CO)4]2 (M = Zn, Cd, Hg, Sn) and M[Co(CO)4]3 (M = In, Tl) (44), e.g.,... 

Carbon monoxide evolution and formation of perfluoroalkyl derivatives directly is also observed when alkali metal salts of cobalt carbonyl are treated with perfluoroacyl halides or anhydrides at ambient temperatures (95,100, 101). 

In a similar manner, Jt-allyl complexes of manganese, iron, and molybdenum carbonyls have been obtained from the corresponding metal carbonyl halides [5], In the case of the reaction of dicarbonyl(r 5-cyclopentadienyl)molybdenum bromide with allyl bromide, the c-allyl derivative is obtained in 75% yield in dichloromethane, but the Jt-allyl complex is the sole product (95%), when the reaction is conducted in a watenbenzene two-phase system. Similar solvent effects are observed in the corresponding reaction of the iron compound. As with the cobalt tetracarbonyl anion, it is... 

Not unexpectedly, alkylation of the double carbonylated complex proceeds via a base-catalysed interfacial enolization step, but it is significant that the initial double carbonylation step also involves an interfacial reaction, as it has been shown that no pyruvic acid derivatives are obtained at low stirring rates. Further evidence comes from observations of the cobalt-catalysed carbonylation of secondary benzyl halides [8], where the overall reaction is more complex than that indicated by Scheme 8.3. In addition to the expected formation of the phenylacetic and phenylpyruvic acids, the reaction with 1-bromo-l-phenylethane also produces 3-phenylpropionic acid, 2,3-diphenylbutane, ethylbenzene and styrene (Scheme 8.4). The absence of secondary carbonylation of the phenylpropionylcobalt tetracarbonyl complex is consistent with the less favourable enolization of the phenylpropionyl group, compared with the phenylacetyl group. 

Ruthenium, cobalt and halogen are the key elements of this catalysis (2), although ruthenium in combination with halogen-containing zirconium and titanium derivatives is also effective (3). In the case of the Ru-Oo couple, the highest yields of acetic acid may generally be achieved with ruthenium oxide, carbonyls and complex derivatives in combination with various cobalt halides dispersed in low-melting quaternary phosphonium halide salts (2). 

Under conditions of photostimulation [Co2(CO)g] in aqueous alkali will catalyze carbonylation of aryl and vinyl halides, including the normally less reactive aryl chlorides, at low pressures and with high efficiency. The active catalyst under these conditions is [Co(CO)4] and this can be generated in situ from simple cobalt salts such as CoCl2 6H20, thus avoiding any need to handle the highly air sensitive [Co2(CO)s] or its derived anion (equation 22). ... 

The double carbonylation reaction (i.e. a-insertion of two carbon monoxide molecules on a single substrate molecule) was discovered by R. Perron in 1975 [42]. Phenylpyruvic acid derivatives were then directly prepared from benzyl halides using cobalt catalysts (Table VI). 

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