Carboranes isomers

Garboranes. The term carborane is widely used in American Hterature as a contraction of the lUPAC approved nomenclature carbaborane. The first carboranes, isomers of C2B2H, and were prepared in the mid-1950s at Olin Mathiesen. These carboranes were obtained as a mixture... 

The three isomeric icosahedral carboranes (76-78) are unique both in their ease of preparation and their great stability in air, and consequently their chemistry has been the most fully studied. The 1,2-isomer in particular is available on the multikilogram scale. It is best prepared in bulk by the direct reaction of ethyne with decaborane in the presence of a Lewis base, preferably Et2S ... 

Carboranes are also called o-carboranes, while the 1,7- and 1,12-isomers are m- and / -car-boranes respectively. Chemical Abstracts uses the sequence C-H-B-N (etc.) in the Formula Index, whereas inorganic textbooks prefer B - C - H - N. 

The discovery of polyhedral boranes and polyhedral heteroboranes, which contain at least one atom other than in the cage, initiated a new era in boron chemistry.1-4 Most commonly, of the three commercially available isomeric dicarba-closo-dodecaborane carboranes(l,2-, 1,7-, and 1,12-), the 1,2-isomer 1 has been used for functionalization and connection to organic molecules. The highly delocalized three-dimensional cage bonding that characterizes these carboranes provides extensive thermal and kinetic stabilization as well as photochemical stability in the ultraviolet and visible regions. The unusual icosahedral geometry of these species provides precise directional control of all exopolyhedral bonds. 

Nomenclature for the carboranes is discussed by R. Adams, Inorg. Chem., 2, 1087 (1963). Briefly, the accepted name for the isomer of Bi0C2Hi2 containing adjacent carbon atoms is... 

One well-known derivative of the B12H122 ion is the carborane, B10C2H12. Note that this species is neutral because each carbon atom has one more electron than does a boron atom. Because the carbon atoms can be located in any two positions in an icosahedron, there are three isomers of B10C2H12 that differ in the location of the two carbon atoms in the structure. These isomers have the structures shown in Figure 13.6. 

C2B9H12, the isomers m- and p-carborane (see Chapter 3.2), the cioso-dodecaborate system B,2H,22 (see Chapter 2.1.5.6), and an arachno-azanonaborane system BXN H n (see Chapter 3.4.4.3). All these dusters have in common the fact that they are stable in aqueous solution, and thereby would allow administration to patients via the blood stream. Their chemistry, and thus the way in which they can be attached to organic molecules, as well as their physiologically relevant parameters of hydrophobicity, vary considerably, however. For a review of the chemistry of BNCT, see Refs. [9-11]. 

It turned out that the [B-H]-catalyzed condensation of two molecules of the intermediate 24 proceeds slowly with elimination of BEt3, when compared with bis(diethylboryl)-substituted hydrocarbons. Thus, a route to the arachno-carboranes 27 is provided [36] by heating the in situ formed 24 and 26 in the "hydride bath . The carboranes 27 were obtained as mixtures of isomers (Scheme 3.2-14). 

---