Boranes and carboranes as ligands

Many boranes and carboranes can act as very effective polyhapto ligands to form metallaboranes and metallacarboranes. Metallaboranes are borane cages containing one or more metal atoms in the skeletal framework. Metallacarboranes have both metal and carbon atoms in the cage skeleton. In contrast to the metallaboranes, syntheses of metallacarboranes via low- or room-temperature metal insertion into carborane anions in solution are more controllable, usually occurring at a well-defined C2BK open face to yield a single isomer. 

Conversion of icosahedral carborane o-C2B10H12 to nido-C2 BgU1, ido-C2BioH1, and 

A large number of metallacarboranes and polyhedral metallaboranes of s-, p-, d-, and f-block elements are known. In these compounds, the carboranes and boranes act as polyhapto ligands. The domain of metallaboranes and metallacarboranes has grown enormously and engenders a rich structural chemistry. Some new advances in the chemistry of metallacarboranes of f-block elements are described below. 

The full-sandwich lanthanacarborane [Na(THF)2] [O75 -C2B9H11 )2La(THF)2] has been prepared by direct salt metathesis between Na2[C2B9Hn] and LaCb in THF. The structure of the anion is shown in Fig. 13.4.14(a). The average La-cage atom distance is 280.4 pm, and the ring centroid-La-ring centroid angle is 132.7°. 

B-H groups from a neighboring larac/MO-iCellsCHihCiBioHio]4 ligand and one THF molecule. The average Er-B(cage) distance is 266.5 pm, and that for the Er-C(cage) is 236.6 pm. 

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