Iron, Cobalt and Nickel Carbide--Carbonyl Clusters by CO Scission

A new approach to the synthesis in good yields of known cobalt and iron carbide--carbonyl clusters by CO cleavage in mild conditions is reported. Cleavage of CO results from attaching an acetyl or benzoyl carbocation to the oxygen atom, and by transfer of electrons from an external source. This synthetic approach to carbide molecular clusters may be of some significance with respect to the formation of carbide atoms on to metal crystallites. Attempts to synthesize nickel carbide clusters with the same approach have only been partly successful. The new [Ni$_{9}$C(CO)$_{17}$]$^{2-}$ and [Ni$_{8}$C(CO)$_{16}$]$^{2-}$ have been obtained more conveniently from the reaction of [Ni$_{6}$(CO)$_{12}$]$^{2-}$ with CCl$_{4}$. The related reaction of [Ni$_{6}$(CO)$_{12}$]$^{2-}$ with Co$_{3}$(CO)$_{9}$CCl results in the formation of the mixed-metal carbide cluster [Co$_{3}$Ni$_{9}$C(CO)$_{20}$]$^{3-}$. This compound is degraded under a carbon monoxide and hydrogen mixture (25 degrees C, 1 atm) to Ni(CO)$_{4}$, [Co(CO)$_{4}$]$^{-}$ and ethane. Intermediate formation of [Co$_{3}$Ni$_{7}$(C-C)(CO)$_{15}$]$^{3-}$, in which the two carbide atoms show an interatomic separation of 1.43 angstrom, or of a related species, would provide a possible pathway for C-C bond formation.