Cobalt-Catalyzed Reactions

Cobalt- and iron-catalyzed reactions lead sometimes to very similar results. Thus, Grignard reagents and organozinc compounds efficiently react with alkenyl halides under cobalt catalysis.

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However, some reactions are only possible with cobalt. As an example, 1,2-dichloroetylene gives an alkenyl chloride (monosubstitution) under cobalt catalysis and only the dialkylated product with iron. Our interest in cobalt-catalyzed reactions is directed to the discovery of such original reactivities.

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We have shown that the coupling of various heteroaryl- or aryl chlorides with Grignard reagents or functionalized organocopper compounds takes place very efficiently in the presence of cobalt salts.

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 On the other hand, Grignard reagents can be coupled with both primary and secondary alkyl halides in satisfactory yields under cobalt-catalysis. It is the first report of a chemoselective coupling between an unactivated secondary w-bromoester and a Grignard reagent.

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Aromatic Grignard reagents also react with primary and secondary alkyl halides in the presence of cobalt salts. This reaction can be performed under iron-catalysis but is then clearly less chemoselective.

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Selective Organic Synthesis and Organometallic Catalysis