Most of the carborane derivatives of the icosahedral (C2B10) or small cage (C2B4) systems are formed by varying the groups on the cage carbons. This is usually accomplished in the original carborane synthesis by reacting substituted acetylenes with either the decaborane(14) or pentaborane(9) precursors. These reactions led directly to the �carbons adjacent� carboranes in which the carbon atoms occupy adjacent positions in the cage. The larger cages are obtained as closo-icosahedra, while the small cage, C2B4-carboranes, have nido- structures. In the small cage system there is another cage geometry in which the carbon atoms are separated by a boron atom. Although these �carbons apart� or nido-2,4-(CR)2B4H6 species are thermodynamically more stable and are more symmetric than the �carbons adjacent� isomers, they are not as well studied. The main reason for the relative scarcity of information on the �carbons apart� systems lies in their method of preparation; they must be synthesized from their �carbons adjacent� analogues through a sequential series of oxidative cage closure/reductive cage opening reactions. In light of complete destruction of pentaborane stockpile at the US Edwards Airforce Base, we have also directed our attention to the development of a safe, bench-scale preparation of the small-cage carboranes, that does not require isolating and handling dangerous, volatile and toxic borane precursors, such as pentaborane(9). The historic perspective of the chemistry of carboranes and metallacarboranes along with the latest findings in our research involving boron nanomaterials    will be presented in detail.

Dendrimer-and nanostructure-supported carboranes and metallacarboranes: Historic perspective

247th National Meeting (2014)

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