Applications of Carbene and Carbyne Complexes

The discussed reactions of carbene and carbyne complexes show that they have essential significance as catalysts or unstable transient intermediate compounds in such catalytic processes as metathesis of olefins and other unsaturated compounds, Fischer-Tropsch synthesis, syntheses of cyclopropanes from diazoalkanes and olefins, and polymerization of olefins and alkynes as well as in organic synthesis. Except for alkynes [reaction (5.132) ] some compounds containing double bonds react with carbon monoxide and carbene ligands to form bonds with those groups. Examples of such compounds are enamines, ynamines, and Schiff bases. The JV-vinylpyrrolidone (enamine), methoxyphenylcarbene, and excess of CO (higher pressure) react to furnish enaminoketone. 

Schiff bases give linear as well as cyclic products in reactions of carbene with CO. 

Perspectives of application of carbene complexes for natural product synthesis seem very promising. Coordination carbene compounds are utilized in the synthesis of peptides, vitamins K and E, and antibiotics.  

Owing to activation of a hydrogen atoms by heteroatoms, the enol forms of carbene complexes are relatively stable. Such carbonyl carbenes may react with carbonyl compounds to give aldols [equation (5.160)]. The reaction of the enol form with 

Metathesis reactions occurring between carbene complexes and compounds containing the C = N or N = N double bonds are interesting. Dicyclohexylcarbodiimide react with (OC)5W = CPhR according to equation (5.161).  

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