Carbide carbonyl

In 1962, Dahl had also structurally characterized Fej(CO)i5C, the first high nuclearity carbide (26). This compound was originally prepared in extremely low yields (0.5%) by the reaction of Fe3(CO)i2 with substituted acetylenes, and, probably due to the peculiarity of this synthesis, was considered for some time much more a curiosity rather than being recognized as the precursor of today s large family of carbide-carbonyl clusters. 

Finally, cobalt carbide-carbonyl clusters have recently been isolated through a two-step synthesis. First of all, the well-known Co3(CO)9CCl is prepared from Co2(CO)8 and CCh, and then the hexanuclear carbide dianion [Co6(CO)i5C]2- is obtained in good yields (9) by further reaction with Xa[(, o(CO)4] in diisopropylether [see Eqs. (18) and (19)]. Further redox condensation between [Oo6(CO)i5C]2-and Co4(CO)i2 [see Eq. (11)] gives the square antiprismatic octanuclear cluster [Cdo8(Cdt )i8 C]2- (13). Both these carbide derivatives, as well as all of the other cobalt high nuclearity clusters, are sensitive to air and react with carbon monoxide at atmospheric pressure. 

The mechanism probably involves a multistep reaction, with initial formation of [Rh7(CO)u]>, degradation to [Rh(CO)4], and condensation of this anion with the chloroform (10, 18). The [Rh6(CO)i6C]2 dianion is the precursor of a wide series of carbide-carbonyl derivatives. Scheme 6 shows the compounds so far structurally characterized and the necessary conditions for their syntheses (9,13). 

Metal Cyanides, Carbides, Carbonyls, and Alkyls Metal carbonyls Preparation and properties... 

Cluster Compounds of Co, Rh, and Ir. In addition to the above-mentioned neutral cluster compounds, there is a large number of anionic carbonyl clusters and metal carbonyl carbides. Carbonyl carbides are formed when the interstice inside the metal cluster is sufficiently large to accommodate the carbon atom. Carbonyl carbides possessing at least four metal atoms are known. The most thoroughly investigated carbides are those of rhodium because they are very stable and resist air oxidation. Carbonyl clusters of group 9 elements containing even more than 20 metal atoms are now known [M6(CO)i5] - (M = Co, Rh, Ir), lM CO)uT. [M6(CO)i5C]"-(M = Co,Rh), [Co8(CO),sC] -, [Rh,(CO)i,] -, [Rh8(CO)i,C], [Ir8(CO)22]"-,... 

It should be noted that the bibliography refers principally to organic compounds. Purely inorganic substances such as inorganic carbides, carbonyls, carbonates, cyanides, thiocyanates are excluded even though they contain carbon. Polymers and high molecular weight compounds like proteins are excluded. 

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