Cobalt carbidocarbonyl clusters

The chemistry of the carbidocarbonyl clusters of cobalt and rhodium (none is known for iridium) is predominantly the work of Italian school of the late Paolo Chini and colleagues. The first rhodium cluster of this type to be reported was [Rh6C(CO)ls]2, 24 (59), isolated as a minor by-product in the synthesis of [Rh7(CO)t6]3- (and originally misformulated as [Rh3(CO)l0]-). The formation of 24 resulted from the reaction of [Rh7(CO)l6]3- with chloroform (the source of the carbon atom), present as an impurity in the reaction solvent, and 24 is now synthesized by this reaction [Eq. (17)]. 

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. 

Since the completion of this review (mid-1982), the chemistry of carbidocarbonyl clusters has continued to expand rapidly. The task of the reviewer is made even more difficult as fascinating results continue to appear. In resisting the temptation to make a comprehensive update of the field, it would be remiss of me not to direct the reader s attention to the continued investigations of Lewis, Johnson, and co-workers in the chemistry of ruthenium and osmium carbidocarbonyls (89), the report by Longoni and coworkers (90) of the syntheses of the first nickel carbide clusters and some mixed nickel-cobalt carbides, the syntheses by Shapley of a new ruthenium dicarbide cluster [Ru,oC2(CO)24]- (91) and of Os6C(CO)l7 (92), and the work of Shriver which implies the existence of a very reactive tri-iron carbide cluster (93). 

Cluster Compounds.—The reported preparation of the first carbidocarbonyl derivative of the cobalt triad, namely [Rh6(CO)i5C] -, involves the action of... 

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