Carbidocarbonyl Clusters of Cobalt and Rhodium

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)]. 

The reaction of CufMeCNJJBFj with 24 results in the capping of the two trigonal faces of the prismatic Rh6C core by MeCN Cu vertices [Eq. (18)] (61). 

The oxidation of [Co6C(CO)l5]2- with ferric ion results in a similar decarbonylation, and rearrangement of the trigonal prism to an octahedron, 

With both cobalt and rhodium, clusters of higher nuclearity are accessible from the hexanuclear anions. Condensation of [Co6C(CO)l5]2- with Co4(CO)l2 in isopropanol at 60°C results in the isolation of [Co8C(CO)lg]2-[Eq. (22)] (64). 

The anion (Fig. 33) comprises two parallel rhombs of metal atoms at an interplanar distance of 2.12 A. The two layers are staggered so as to produce an antiprismatic geometry, which may be derived from the trigonal prismatic starting material by the capping of two tetragonal faces and the breaking of the Co-Co bond common to these two faces (shown as a dotted line in Fig. 33). 

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