Dicobalt hexacarbonyl fragments

When an alkyne reacts with [Co2(CO)g], the two C = C —C angles in the formed (n-acetylene)dicobalt hexacarbonyl complex are reduced to a value of =140° [26] therefore, dicobalt hexacarbonyl fragments have been used as protecting groups to allow geometrictilly disfavored cyclization reactions by bending an alkyne moiety [27]. Since the alkyne can be... 

Scheme 2.14 Synthesis of (+)-fostriecin (Co, dicobalt hexacarbonyl fragment BOM, benzy-loxymethyl and NMO, N-methylmorpholine N-oxide).

The loss of CO from the hexacarbonyl dicobalt fragment is a key step in the mechanism of the reaction (see section 2.2) the majority of additives are employed to affect this stage of the pathway. Other chemical additives include Lewis bases such as //-butyl methyl sulfide and cyclohexylamine, while molecular sieves have also been employed in order to trap CO out of the reaction mixture.13-16... 

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