Synthesis and Interconversion Reactions

Although the main concern of this book is to survey the structures and bonding of hypercarbon systems, it is appropriate to note briefly the routes by which carboranes have been synthesized, and methods by which one carborane can be converted into another. Section 3.7 outlines the types of reaction that can occur at the highly coordinated carbon atoms of carboranes. 

Cage closure from nido or arachno to closo commonly occurs on heating, though disproportionation may occur simultaneously [Eq. (3.4)]. Reaction with diborane can be used to effect cage expansion [Eq. (3.5)]  

Successive deboronation reactions make intermediate-sized carboranes accessible from C2B10H12. 

Tlie steps by which deboronation of orz/io-carborane occurs have been established by the isolation and characterization of key intermediates in systems in which the deboronating nucleophile was the iminophosphorane HNP(NMe2)3 [Eq. (3.6), or pyridine [Eq. (3.6), Nir. rhc structure 

Isomerization reactions, whereby adjacent carbon atoms in carborane polyhedra move apart, allow more stable isomers to be prepared from the less stable by heating [Eqs. (3.7) and (3.8)]  

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