Cobalt blue carbonyls

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 mixture is allowed to cool to room temperature and then is suction filtered in air to obtain a bright-blue residue (cobalt salts, which are discarded) and an intensely purple-colored filtrate. The latter is treated with 1500 mL of 10% aqueous hydrochloric acid to destroy remaining noncluster cobalt carbonyl. The product ester is extracted into 500 mL of pentane. The extracts are washed several times with equal portions of water. The organic layer is dried over anhydrous magnesium sulfate. Filtration is followed by evaporation of the filtrate at reduced pressure (rotary evaporator). The solid that remains is sublimed at 50° and 0.1 torr to yield 38.79 g (53%) of purple crystals of /j3-[(ethoxycar-bonyl)methylidyne]-tris(tricarbonylcobalt), mp 45-46°,2 Anal. Calcd. for CuHjOuCoj C, 30.38 H, 0.98. Found C, 30.30 H, 0.96. 

Under a nitrogen atmosphere, cobalt carbonyl probably experiences disproportionation by base (Scheme 5) to give Co(CO)4. One of the disproportionation by-products is the Co(II) ion which gives a blue color in aqueous NaOH due to the presence of small amounts of the Co(OH)42-ion. The subsequent reaction of the cobalt tetracarbonyl anion with 14 is probably a displacement (path a), giving the cr-allyl complex 16. However, the possibility of an electron-transfer pathway (path b), either as an alternative to, or concurrent with, the displacement pathway cannot be dismissed at this time. 

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