Cobalt compounds decarbonylation reactions

One important property of CF3-transition metal complexes became apparent almost immediately when all of the low-valent, late transition metal trifluoromethylated compounds then known were found to be significantly more thermally and oxidatively stable than the analogous methylated species. Tetracarbonyl(trifluoromethyl)cobalt(I), for example, was isolated by distillation at 91°C, whereas the hydrocarbyl Co(CO)4(CH3) decomposes at subambient temperatures (72). Additionally, while the reverse of the decarbonylation reaction, CO insertion, is commonly observed in methylated transition metal species, these reactions are essentially unknown for trifluoromethyl metal complexes (13). Prior to 1980, evidence for CO insertion into an M—CF3 bond had been reported in only one case. That reaction employed the photolysis of Mn(C05)(CF3) in an argon matrix at 17 K, and the identity of the product was not determined (14). The clear implication of the above results is that MCF3 metal—carbon bonds are significantly less reactive and thus presumably stronger than MCH3 metal—carbon bonds. 

The bridging phosphide group in bimetallic transition metal complexes appeared to participate in a transformation, rather than behave as an inert spectator ligand. This is particularly obvious in homobimetallic iron and cobalt systems.Mays et al. showed that the reactions of iron-cobalt phosphido-bridged complex 25 with both symmetrical and unsymmetrical alkynes gave five-membered ferracycle-containing compounds, such as 26, in which a CO and an alkyne were inserted regiospecifically into a Co-P bond in 25. Subsequent decarbonylation led to a set of four-membered ferracyclic species 27-30 in low yields. 

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