Organocobalt reagents

The treatment of diorganozincs or organozinc halides with cobalt bromide in THF NMP mixtures provides blue solutions of organocobalt reagents, which have a half-life of several hours at -20 °C.25,26 Carbonylation reactions with these new cobalt reagents proceed well simply by bubbling carbon monoxide... 

The intermolecular addition reactions between organocobalt reagents 44 and 38 and a variety of deactivated C=C bonds led to new alkene products 45 and 46 respectively which resulted from radical addition to the C=C bonds followed by dehydro-cobaltation from the presumed [20] organocobalt intermediates (Scheme 16). 

Addition of sodium hydroxide to a mixture of [Co"(DMG)2] and an alkylating agent in methanol-water yields up to 50% of the organocobalt product. This appears to be the most convenient method for the preparation of organocobalt(III) derivatives, provided that the maximum yield is not required 161,163). Methods involving the reaction of Co with electrophiles are, at least with DMG complexes, more convenient than the main alternative route via Co(III) and Grignard reagents. 

Organocobalt compounds may be prepared by several routes.833 The Co1 species is a useful starting point. This may be obtained by reduction of Co11 or Com compounds using hydrazine, thiols, chromium(II), borohydride and other reagents. The Co1 species will give a Com hydride species by reacting with a proton. Both the Co1 and the hydridocobalt(III) species are alkylated readily. 

The addition of hydrido complex-scavenging reagents would be expected either to reduce the reagent (19, 20) (Reaction 14) or to form a stable organocobalt complex (22) (Reaction 15), depending on the re-... 

A series of electronically and coordinatively unsaturated four-coordinate organocobalt(II) complexes, [Co(R)(PhTt Bu)] (R = Me, Et, Ph, Bn), have been prepared by reaction of [CoCl(PhTt Bu)] with the corresponding MgR2 reagent and characterized spectroscopically and structurally. [Co(r 3-allyl)(PhTt Bu)] is a low-spin species. 

Because of the toxicity and purification problems associated with tributytin hydride reactions, many ring expansions have been attempted under tin-free conditions. These include the use of reagents such as (Me3Si)3SiH [15a], 138/02 [15b] and SmI [15c], the photoinduced electronic transfer (PET) process [15d], photolysis of thiohydroxamic esters or organocobalt complexes [15e], and electroreductions of fi-keto esters [15f]. 

Hydroxy- and alkoxy-cobalt(III) complexes are also known to react with reagents which can form stabilized carbanions on loss of a proton [67], such as malononitrile, to form organocobalt complexes (Eqn. 27, R = H or CH3, R = CN, R" = CN, CONH2, etc.). 

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