Metallacarborane anions

Many novel cluster compounds have now been prepared in this way, including mixed metal clusters. Further routes involve the oxidative fusion of dicarbon metallacarborane anions to give dimetal tetracarbon clusters such as (103) and (104) O (jjg insertion of isonitriles into inetallaborane clusters to give monocarbon meiallacarboranes such as (105) and the reaction of small ii/t/o-carboranes with alane adducts such as Et3NAlH3 to give the commo species (106) ... 

The fact that the metallacarborane aggregates can rather be interpreted as temporal fluctuations of small subunits is partly supported by quantum mechanics calculations, which suggest that a mutual attraction of metallacarborane anions in the implicit solvent model is relatively weak and it only slightly beats a contribution of electrostatic repulsion (Matijfdek, 2009). 

The stability of the liquid carboranes depends on the substituents R at carbon and boron. The axial (endo) hydrogen atom is acidic and involved in 3c2e bonding to one of the basal boron atoms. In the 1H NMR it exhibits a high field shift near S = —1.4. Deprotonation of 55 with potassium or Bu Li leads to the anion (55-H)-, which is isolobal with C5H5. Reactions of 55 and (55-H) with appropriate metal complexes lead to metallacarboranes with sandwich structures [67, 69],... 

In addition to that said above, complexes with closopolyhedral hydroborate metal-containing fragments are known, for example 564, obtained through the interaction of tetramethylammonium salt of nido-B9H12 anion and nickelocene [957], An up-to-date covering of carborane and metallacarborane structures and properties is given in Ref. 184f. 

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. 

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