closocarborane

Closo-carboranes are a family of polyhedral boron–carbon clusters in organoboron chemistry. They arise from the closo-B12H12(2−) framework by substituting two adjacent boron atoms with carbon, yielding neutral C2B10H12 species. The three common isomers are ortho-, meta-, and para-carborane, named for the relative positions of the two carbon atoms on the icosahedral cage.

The core structure of closo-carboranes is an icosahedral B10C2 skeleton with hydrogen atoms attached to boron vertices. They follow Wade’s rules for closo polyhedral boranes, contributing to their high thermochemical stability and resilience to many chemical conditions. The carbon substitutions influence reactivity and electronic properties, enabling selective functionalization at carbon or remaining boron–hydrogen vertices to introduce substituents or complexation partners.

Synthesis and chemistry of closo-carboranes typically involve transformations of boron-hydride clusters, followed by carbon introduction and cage rearrangements to furnish the C2B10H12 framework. Once prepared, a wide range of derivatives can be obtained by substituting B–H or C–H bonds, or by attaching substituents to the cage carbons. Functionalization enables tuning of properties and reactivity for subsequent applications.

Applications of closo-carboranes include use as ligands in organometallic chemistry, boron delivery agents for boron neutron capture therapy (BNCT), and building blocks for materials, polymers, and boron-rich pharmaceuticals. Their thermal and chemical stability, as well as the ability to tailor electronic and steric properties through functionalization, underlie these uses.