Carbide-centered carbonyl clusters

The relationship between boranes and metal-carbonyl clusters can be extended by considering the compound Fe5(CO)i5C, which has the square-based pyramidal structure shown in Fig. 13, with the carbide carbon atom just below the center of the Fe square, clearly contributing all its valence shell electrons to the cluster 24). The metal-carbonyl residue FeB(CO)i4 formally left by removal of this carbon as has the nido structure appropriate for a cluster with 5 skeletal atoms and seven skeletal bond pairs. 

The carbide-centered polynuclear transition-metal carbonyl clusters exhibit a rich variety of structures. A common feature to this class of carbide complexes is that the naked carbon is wholly or partially enclosed in a metal cage composed of homo/hetero metal atoms, and there is also a subclass that can be considered as tetra-metal-substituted methanes. The earliest known compound of this kind is FesC(CO)i5, in which the carbon atom is located at the center... 

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-... 

The octahedral cluster ruthenixnn carbonyl carbide (Ru0(CO)i7C) has been known for a longer time and thus has been studied in somewhat more detail. Pyrolysis of Ru3(CO)i2 about 150°C in hydrocarbon solvents was reported to give a deep red, air-stable solid, first (319) mistakenly called Ru0(CO)i0 but later (357) correctly identified as Ru0(CO)i7C on the basis of its x-ray crystal structure. The single carbon atom in RU0(CO)i7C is imbedded in the center of a ruthenium octahedron with ruthenium-ruthenium bonds along the... 

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