Alkyl-cobalt tetracarbonyl derivative

The 2-methylenecyclopentanone initially formed presumably rearranges into 2-methyl-2-cyclopentenone under the reaction conditions. The final step of the mechanism, elimination of the cobalt carbonyl group, is not well understood but the same kind of elimination and reduction reactions occur with known 3-ketocobalt complexes. As mentioned above, crotonaldehyde, acrolein (27), and glyddaldehyde (38) react rapidly with cobalt hydrocarbonvl under similar conditions to give reduction products, rather than forming stable alkyl- or acyl-cobalt tetracarbonyl derivatives. 

Alkali Metal Derivatives of Metal Carbonyls, 2, 1S7 Alkyl and Aryl Derivatives of Transition Metals, 7, 1S7 Alkyl cobalt and Acylcobalt Tetracarbonyls, 4, 243 Allyl Metal Complexes, 2, 32S... 

As briefly indicated in the Introduction (see p. 64), alkyl and acyl halides have been converted into cobalt derivatives by replacing the halide ion with cobalt tetracarbonyl anion. The cobalt derivatives were also cleaved by methanol, resulting in compounds in which carbon monoxide had been inserted. Although application of Heck s procedure to the glycosyl halides failed, use of the modification described next enabled the reactions to be carried out successfully. 

These findings differ from the cobalt system, where alkyltetracarbonyl derivatives of cobalt(I), synthesized from Na[Co(CO)4] and the appropriate alkyl iodide under hydroformylation conditions, gave the expected aldehyde without skeletal rearrangement. This shows that under hydroformylation conditions, (i.e., under CO/H2), alkyl- and acyl-tetracarbonyl derivatives of cobalt do not undergo isomerization. 

Alkyl- and aryl-cobalt tetracarbonyls also react readily with phosphines forming acyl derivatives RCOCo(CO)3PR 3. Phosphite ligands are found to replace carbon monoxides successively forming RCOCo(CO)2L2 [193]. The replacement of two carbon monoxide ligands by phosphites under conditions where phosphine ligands will only replace one carbon monoxide, is therefore found for both cobalt and manganese complexes. Both... 

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. 

Acylcobalt carbonyl derivatives are cleaved by sodium methoxide to esters and sodium salts of the corresponding carbonyl anions. By means of this reaction, acetyl[bis(trimethylolpropane phosphite)]cobalt dicarbonyl has been converted into sodium [bis(trimethylolpropane phosphite)]cobalt dicarbonyl. The latter compound is readily alkylated by methyl iodide to form the methylcobalt derivative and this compound in turn reacts with another mole of the phosphite ester, in the same way that methylcobalt tetracarbonyl does, to form acetyl[tris(trimethylolpropane phosphite)]-cobalt carbonyl ... 

The mass of this work lies beyond the scope of this review, but a few prominent points may be cited. In most cases, treatment of either an alkyl or an acyl tetracarbonyl cobalt complex with triphenylphosphine gives only the acyl derivative, [Co(COR)(CO)3P(C6H5)3] (304, 306). The reactions of acyl, allyl, and hydridocobalt tetracarbonyl or acetylenedicobalt hexa-carbonyl complexes with phosphines are first order in the cobalt complex, so a dissociation mechanism prevails (64, 65, 66). However, the reaction between [Co(CO)3NO] and P(C6H5)3 is second order (66). 

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