Metal clusters carbidocarbonyls

The first carbidocarbonyl transition metal cluster to be recognized was Fe5C(CO),5 (1), which was isolated in very low yield from the reaction of triiron dodecacarbonyl with methylphenylacetylene and characterized by X-ray diffraction by Dahl and co-workers (2). The molecule (Fig. 1) comprises a square pyramidal Fe5 core with the carbide situated. 08 A below the center of a square face. Each iron atom bears three terminal carbonyls. Improved syntheses of 1 by protonation (5) or oxidation of [Fe6C(CO)l6]2-... 

An additional significance for carbidocarbonyl clusters has appeared more recently with the discovery of the fascinating reactivity of carbon atoms in clusters when they are exposed to reactive molecules in low nuclearity carbidocarbonyl clusters. These observations followed on the heels of the recognition of the crucial role played by surface bound carbon atoms in metal-catalyzed carbon monoxide hydrogenation, and so a new area of overlap between cluster chemistry and surface chemistry has arisen. Moreover, in this case the comparisons between organometallic and surface chemistry may lie in reactivity and not merely structural similarities. 

Iron is so far unique in that it alone forms carbidocarbonyl clusters containing only four metal atoms, and the discovery of this class of compounds and the reactivity of its members has provided one of the most... 

In the case of rhodium, however, it was demonstrated early that in the synthesis of [Rh6C(CO)l5]2 the encapsulated carbon atom originated as chloroform, which had reacted with the rhodium carbonyl anion [Rh7(CO)l6]3- (59). In the cobalt analog, [Co6C(CO)l5]2-, the carbon atom is derived indirectly from carbon tetrachloride [via Co3(CO)9CCl] (60) Both these syntheses are performed under mild conditions, and there are apparently no examples of carbidocarbonyl clusters of cobalt or rhodium prepared directly from the metal carbonyls under pyrolysis conditions. 

The hexanuclear iron cluster (37) in the salt [Me4N]s[Fe (CO)uC] is regarded as the first known anionic carbidocarbonyl complex of any metal, ... 

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