Any of a class of organometallic compounds containing carbon, boron, and hydrogen. The general carborane chemical formula is C2Bmath.nHmath.n + 2, in which math.n is an integer; carboranes with math.n ranging from 3 to 10 have been described. Carboranes can form three-centre bonds (one pair of electrons is shared between three atoms) and classical two-centre bonds (one pair of electrons is shared between two atoms). As a result, carboranes can form complex polyhedral structures that are based on networks of boron and carbon atoms. Carboranes are generally prepared by reaction of acetylene or acetylene derivatives with boron hydrides.
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A carborane is a cluster composed of boron and carbon atoms. Like many of the related boranes, these clusters are polyhedra and are similarly classified as closo-, nido-, arachno-, hypho-, etc. based on whether they represent a complete (closo-) polyhedron, or a polyhedron that is missing one (nido-), two (arachno-), or more vertices.
A prominent example is the charge-neutral C2B10H12 or o-carborane with the prefix o derived from ortho, which has been explored for use in a wide range of applications from heat-resistant polymers to medical applications. This compound is called super aromatic because it obeys Huckel's rule and exhibits high thermal stability. At 420 °C o-carborane converts to the meta isomer. In comparison, benzene requires a >1000 °C to induce skeletal rearrangement. Like arenes, carboranes also undergo electrophilic aromatic substitution.
Another important carborane is the negatively charged CHB11H12−, which has been used to make solid superacids.
The carborane superacid H(CHB11Cl11) is one million times stronger than sulfuric acid. The reason for this high acidity is that the acid anion CHB11Cl11- is very stable and substituted with electronegative substituents. H(CHB11Cl11) is the only acid known to protonate C60 fullerene without decomposing it. .
Heating the reaction mixture to 35 °C releases carboryne, which can subsequently be trapped with suitable dienes:
Carborynes react with alkynes to benzocarboranes in an adaptation of the above described procedure. O-carborane is deprotonated with n-butyllithium as before and then reacted with dichloro-di(triphenylphosphino) nickel to a nickel coordinated carboryne. This compound reacts with 3-hexyne in an alkyne trimerization to the benzocarborane.
Design of carborane molecular architectures with electronic structure computations: from endohedral and polyradical systems to multidimensional networks.(Report)
Apr 01, 2009; INTRODUCTION The discoveries of carboranes  were first disclosed in the 1960s ; since then, many synthetic [3,4],...