Караборандар: құрамы, қасиеттері және синтезі

Class of chemical compounds

Carboranes (or carbaboranes) are electron delocalized (non classically bonded) clusters composed of boron, carbon and hydrogen atoms. Like many of the related boron hydrides, these clusters are polyhedra or fragments of polyhedra. Carboranes are one class of heteroboranes. In terms of scope, carboranes can have as few as 5 and as many as 14 atoms in the cage framework. The majority have two cage carbon atoms. The corresponding C alkyl and B alkyl analogues are also known in a few cases.

Carboranes and boranes adopt 3 dimensional cage (cluster) geometries in sharp contrast to typical organic compounds. Cages are compatible with sigma—delocalized bonding, whereas hydrocarbons are typically chains or rings. Like for other electron delocalized polyhedral clusters, the electronic structure of these cluster compounds can be described by the Wade–Mingos rules. Like the related boron hydrides, these clusters are polyhedra or fragments of polyhedra, and are similarly classified as closo , nido , arachno , hypho , hypercloso , iso , klado , conjuncto and megalo , based on whether they represent a complete (closo ) polyhedron or a polyhedron that is missing one (nido ), two (arachno ), three (hypho ), or more vertices. Carboranes are a notable example of heteroboranes. The essence, these rules emphasize delocalized, multi centered bonding for B B, C C, and B C interactions. Structurally, they can be considered to be related to the icosahedral (Ih) |[B12H12](2–) via formal replacement of two of its |BH– fragments with CH.

Geometrical isomers of carboranes can exist on the basis of the various locations of carbon within the cage. Isomers necessitate the use of the numerical prefixes in a compound's name. The closo dicarbadecaborane can exist in three isomers: 1,2 , 1,7 , and 1,12 |C2B10H12.

Carboranes have been prepared by many routes, the most common being addition of alkynyl reagents to boron hydride clusters to form dicarbon carboranes. For this reason, the great majority of carborane have two carbon vertices.

Monocarboranes are clusters with |B {n}C cages. The 12 vertex derivative is best studied, but several are known. Typically they are prepared by the addition of one carbon reagents to boron hydride clusters. One carbon reagents include cyanide, isocyanides, and formaldehyde. For example, monocarbadodecaborate (|[CB11H12]−) is produced from decaborane and formaldehyde, followed by addition of borane dimethylsulfide. Monocarboranes are precursors to weakly coordinating anions.

Dicarbaboranes can be prepared from boron hydrides using alkynes as the source of the two carbon centers. In addition to the closo |C2B {n}H {n+2}| series mentioned above, several open cage dicarbon species are known including nido |C2B3H7 (isostructural and isoelectronic with |B5H9) and arachno |C2B7H13. Syntheses of icosahedral closo dicarbadodecaborane derivatives (|R2C2B10H10) employ alkynes as the |R2C2 source and decaborane (|B10H14) to supply the |B10 unit.

The following classification is adapted from Grimes's book on carboranes. 1,2 and 1,3 |C2B9H13.

Dicarbollide complexes have been investigated for many years, but commercial applications are rare. The bis(dicarbollide) |[Co(C2B9H11)2]− has been used as a precipitant for removal of |^{137}Cs+ from radiowastes. The medical applications of carboranes have been explored. C functionalized carboranes represent a source of boron for boron neutron capture therapy. The compound |H(CHB11Cl11) is a superacid, forming an isolable salt with protonated benzene cation, |[C6H7]+ (benzenium cation). The formula of that salt is |[C6H7]+[CHB11Cl11]−. The superacid protonates fullerene, |C60.