Metallocarboranes polyhedral subrogation

Synthetic polyhedral subrogation for the preparation of polymetallo-carboranes from monometallocarboranes is an offshoot of polyhedral contraction in that, after degradative removal of a BH vertex, a transition metal ion is reacted with the m do-metallocarborane produced rather than with an oxidizing agent. In this way, a new transition metal vertex is incorporated into the polyhedral framework without a change in the number of vertices between reactant and product (Fig. 6) ... 

Degradation of the icosahedral 1,2- and 1,7-C2Bi0Hi2 isomers with strong base to produce the nido eleven-vertex anions 7,8- and 7,9-CoB9Hi2-has been previously discussed and is an important route to the preparation of twelve-vertex monometallocarboranes. The discovery that similar reactions could be performed on metallocarboranes led to the isolation of novel chains of metal atoms bridged by carborane groups and to the development of the polyhedral contraction and polyhedral subrogation reactions. 

Examples of bimetallic twelve-vertex metallocarboranes have been provided by various synthetic efforts. The preparation of bi- and trimetallic chain complexes by polyhedral subrogation of (1,2-C2B9Hn)2Co has been mentioned earlier (38, 34), and the Co(C2B8Hi0)Co fragment present therein may be considered as an example of this type of bimetallic complex. 

There are now at least a dozen synthetic routes to metallocarboranes including (i) coordination using nido-carborane anions as ligands, (ii) polyhedral expansion reactions, (iii) polyhedral contraction reactions, (iv) polyhedral subrogation and (v) thermal metal transfer reactions. These first five routes were all devised by... 

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