Carboranes open-cage

Tetraborane(lO) reacts with RC=CR (R=H, CH3) to produce mixtures of small w io-(open cage) or c/oso-(closed cage) carboranes 163> however, with C2H4, 2,4-dimethylenetetraborane(10) is formed 164>. This compound is properly classified as an alkyl substituted tetraborane(lO). 

One of the most important features of a carborane system is its ability to enter into substitution reactions at both the carbon and boron atoms without degradation of the carborane cage. The susceptibility for removal of the most electrophilic boron atom in closed-cage carborane such as 1,2-dicarba-cZoso-dodecaborane is an added advantage for its transformation into open cage form... 

Reduction of the pentaalkyl-1,5-dicarba-closo-pentaboranes(5) 44 with elemental K opens the cluster and subsequent reaction with I2 enforces oxidative fusion of two C2B3 units to give a C4B6 cage (Scheme 3.2-36). The peralkylated hexaboraadamantane derivatives 70 (R = Me, Et X-ray structure analysis for R = Me [89]) rearrange irreversibly into the carboranes 71 with a wido-C4B6 framework [89] (X-ray structural analysis for R = Et [90]). The structure of the nido-C Bf, cluster is fluxional in solution [91]. 

However, separation of the carborane cage from The phos-phazene ring or chain by a methylene spacer group allows metals to be Inserted into the open face of the carborane. These syntheses were accomplished by the reaction routes shown in Schemes 3 and A. High polymeric analogues of these transformations have also been accomplished following polymerization of XXX. The rhodium-bound cyclophosphazenes and polyphosphazenes are catalysts for the hydrogenation of 1-hexene. In this, they show a similar behavior to metallocarboranes linked to polystyrene... 

Ru3(CO)i2] and 7,8-Me2-Kfframework bridges a triangular arrangement of ruthenium or osmium atoms with the open CBBBlf or CCBBB faces, respectively, coordinated in a pentahapto fashion to one metal atom while the carborane cage forms two exo-polyhedral B-H M bonds with the other two metal atoms. 

The alkaline degradation of closo-carboranes, used to prepare smaller carboranes from icosahedral starting materials, also occurs by closo- to nido-, possibly even arachno-, cage opening, e.g. 107),... 

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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