Boranes

Boranes are chemical compounds composed of boron and hydrogen. The term covers simple boron hydrides such as diborane, B2H6, as well as larger boron-hydrogen clusters and their derivatives. Many boranes are polyhedral clusters that exhibit electron-deficient bonding and multicenter interactions, distinguishing them from conventional covalent molecules.

Bonding and structure in boranes are characterized by electron deficiency and three-center two-electron (3c–2e) bonds. In diborane, for example, two hydrogen atoms bridge between boron atoms via B–H–B 3c–2e bonds. The boron-hydrogen cluster family is commonly described using Wade’s rules, which classify clusters as closo (closed polyhedron), nido (one vertex missing), or arachno (two or more vertices missing). Classic closo boranes include certain boron hydride clusters such as B12H12^2−, while higher boranes and carboranes expand the scope of these skeletal types.

Representative examples range from small molecules like B2H6 and BH3 to larger boranes such as B5H9, B10H14, and B12H14. Carboranes, which incorporate carbon atoms into boron-hydrogen clusters (e.g., B10C2H12), are particularly well known for their thermal and chemical stability. These clusters have found use as scaffolds in materials science and medicine due to their boron-rich content and robust frameworks.

Reactivity and applications: hydroboration chemistry is a central pillar, with borane reagents (such as BH3 or BH3•THF) adding to alkenes and alkynes, enabling anti-Markovnikov hydroboration followed by oxidation to alcohols. Beyond classic organic synthesis, boranes and carboranes are explored as catalysts, ligands, and boron sources in materials science and, in some cases, in medical contexts such as boron neutron capture therapy.

Safety and handling vary by compound; many boranes are moisture-sensitive and some are pyrophoric, requiring inert atmosphere techniques and proper precautions.