Propargyl complexes, cationic dicobalt

Complexation of dicobalt octacarbonyl to aUcynes not only protects the triple bond against a number of reagents, but stabilization of propargylic cations, anions, and radicals is also observed. The carbocations are readily obtained as dark red, thermally stable sohds by treatment of propargylic alcohols,... 

IJ-Enynes.1 (Propargyl)dicobalt hexacarbonyl cations (8, 148-149) couple with allylsilanes to give complexes of 1,5-enynes, generally in satisfactory yields. A typical reaction is formulated in equation (I). 

The chemistry and synthetic utility of cobalt complexed propargyl cations have been demonstrated by Nicholas in an impressive series of papers, and the area was reviewed in 1987.72 More recently, reviews of cluster-stabilized cations73 and propargylium complexes74 have appeared. Two general routes for the synthesis of dicobalt-propargylium complexes have been developed. The most commonly used method is the treatment of an alkynic ether or alkynic alcohol-hexacarbonyldicobalt complex with a Lewis or Bronsted acid [Eq. (7)]. 

Cationic complexes formed from acyclic diene iron complexes react in a fashion very similar to dicobalt hexacarbonyl stabilized propargylic cations. The cations can... 

Nicholas, K. M. Chemistry and synthetic ntility of cobalt-complexed propargyl cations. (1987). Acc. Chem. Res., 20, 207-214. Teobald, B. J. (2002). The Nicholas reaction the use of dicobalt hexacarbonyl-stabilised propargylic cations in synthesis. Tetrahedron, 58, 4133 170. 

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