Alkyne complexes of cobalt

Similar to the alkene complexes, the alkyne complexes of cobalt were amply described in COMC (1982) and COMC (1995). We shall therefore report in this section the most remarkable examples that have been published since 1993. 

Another important intermediate in the trimerization of alkynes that was never isolated is the cobaltacyclopenta-diene unit to which an alkyne is if - bound to Co. Vollhardt e( succeeded in obtaining a series of such 

The structure of compound 223 was ascertained by a crystal structure analysis. Whereas the thermal treatment of 223 afforded the expected phenylene 224, under UV irradiation, a cyclobutadiene ring was formed, 225. The UV light was most probably responsible for the dissociation of the alkyne -bound to Co in 223, thus producing a coordinatively unsaturated Co derivative which is well known to lead to such cyclobutene compounds via reductive elimination (see Section 7.01.4.3). 

There have been relatively few studies on either 77 -cyclopropenyl- or allylcobalt derivatives during the last decade as compared with the if - or 77 -hydrocarbyl-Co complexes. 

Basolo et al. studied the kinetics of the CO substitution in j -cyclopropenyl complexes of Co with phosphine ligands.They showed that the reaction occurred via a dissociation of the CO ligand rather than via association of the phosphine to the Co center. This would have led to the slippage of the cyclopropenyl unit, leading thus to a transient 77 -cyclopropenyl unit of a 16-electron Co species. 

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