Potassium pentacyanocobaltate

The interconversion of a- and 7r-allyl complexes has been observed by Kwiatek, Mador, and Seyler in the interesting homogeneous catalytic system of potassium pentacyanocobaltate(II), K3Co(CN)5 (46). This solution absorbs molecular hydrogen to form the active hydride species, Kj[Co (CN)jH]. Addition of butadiene to the hydride results in the formation of a [Pg.36]

Potassium pentacyanocobalt hydride reduces conjugated dienes to mono-olefins (61). The reaction mechanism probably involves an addition of the hydride to the diene followed by reduction with a second molecule of hydride (61). 

Similar acetylene addition reactions take place with bis-cydopentadienylnickel carbonyl dimer (93). Changing from carbonyl to cyanide ligands seems to allow the formation of a true vinyl derivative. Thus, potassium pentacyanocobaltate, which may react as a dimer with a cobalt-cobalt bond (20), reacts with acetylene to give the adduct XV (31). The product was thought to be the trans isomer, but the data were not conclusive. 

Certain monohydride catalysts exhibit high selectivity toward hydrogenation of conjugated dienes and polyenes to give monoenes. Potassium pentacyanocobaltate prepared from CoCl2 and KCN is one of the most active catalysts, but reduces only conjugated double bonds. The reduction of dienes with nonequivalent double bonds follows the usual substitution trend noted for monoenes. 1,3-Pentadiene, for example, is converted selectively to trans-2-pentene via 1,2 addition 134... 

Potassium pentacyanocobaltate(II), derived form cobalt(II) chloride and KCN, catalyzes the hydrogenation of 1,3-dienes to monoalkenes. 1,3-Butadiene (22), isoprene and 1-phenyl-1,3-butadiene (23), have been converted to mixtures of the corresponding 1-butenes, fra s-2-butenes and cw-2-butenes. The product distribution depends highly on reaction conditions such as the cyaniderCo ratio, the concentra-... 

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