Carborane skeletons beyond the icosahedron

Recent synthetic studies have shown that carborane skeletons larger than the icosahedron can be constructed by the insertion of additional BH units. The reaction scheme and structure motifs of these carborane species are shown in Fig. 13.4.15. Treatment of 1,2-(CH2)3-1,2-C2BioHio (1) with excess lithium metal in THF at room temperature gave [(CH2)3-l,2-C2BioHio][Li4(THF)s] 2 (2) in 85% yield. X-ray analysis showed that, in the crystalline state, both the hexagonal and pentagonal faces of the carbon-atoms-adjacent arachno-carborane tetra-anion in 2 are capped by lithium ions, which may in principle be substituted by BH groups. 

Quite different from the planar open faces in mdo BgHj2- and nido-C2BioH122-, the open faces of the 13- and 14-vertex nido cages in 5 and 6 are 

Synthesis of carbon-atoms-adjacent 13- and 14-vertex c/oso-carboranes and n fo-carborane anions. From L. Deng, H.-S. Chan and Z. Xie, Angew. Chem. Int. Ed. 44, 2128—31 (2005). 

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