Boranes

Boranes are compounds composed of boron and hydrogen, ranging from electron-deficient molecules to polyhedral clusters with multicenter bonds.

Three-center two-electron bond: A covalent bond in which two electrons are shared among three atoms. B–H–B bridges use this bonding pattern to stabilize electron-deficient boranes.
Electron-deficient compound: A compound with too few valence electrons for conventional two-center, two-electron bonds between all bonded atoms. Boranes are a major family of compounds whose bonding resolves this deficiency.
Hydroboration: The addition of a boron–hydrogen bond across a carbon–carbon multiple bond. Borane reagents deliver boron and hydrogen across alkenes in a foundational organic reaction.
Pentaborane(9): B₅H₉, a volatile borane with a square-pyramidal boron framework. Its open cluster structure contrasts with the closed polyhedra predicted by closo electron counts.
Borohydride: An anion or salt containing hydrogen bonded to boron, commonly the tetrahydroborate ion BH₄⁻. Tetrahedral borohydride has conventional four-coordinate bonding, unlike electron-deficient neutral boranes.
Wade's rules: Electron-counting rules that relate skeletal electron pairs to the shapes of many borane and related clusters. They predict cluster geometry from the number of skeletal electrons.
Hydride: A chemical compound containing hydrogen bonded to another element, or an anion in which hydrogen carries negative charge. Boranes are covalent hydrides in which hydrogen bonds to boron.
Borane–tetrahydrofuran complex: A Lewis acid–base adduct in which borane is coordinated by tetrahydrofuran. This liquid reagent makes reactive borane easier to handle in hydroboration.
Decaborane(14): B₁₀H₁₄, a stable borane with an open, nido cluster framework. It is a well-studied example linking borane formulas to cluster geometry.
Alanes: Compounds composed of aluminum and hydrogen, including electron-deficient molecular species. Alanes share electron-deficient bonding patterns but replace boron with aluminum.

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