The boron hydrides were first systematically synthesized and characterized during the period 1912 to roughly 1937 by the German chemist Alfred Stock. He called them boranes in analogy to the alkanes (saturated hydrocarbons (hydrocarbon)), the hydrides (hydride) of carbon (C), which is the neighbour of boron in the periodic table. Because the lighter boranes were volatile, sensitive to air and moisture, and toxic, Stock developed high-vacuum methods and apparatus for studying them. American work on boranes began in 1931, carried out by Hermann I. Schlesinger and Anton B. Burg. Boranes remained primarily of academic interest until World War II, when the U.S. government supported research to find volatile uranium compounds (borohydrides) for isotope separation, and the 1950s, when it supported programs to develop high-energy fuels for rockets and jet aircraft. (Boranes and their derivatives have much higher heats of combustion than hydrocarbon fuels.) William Nunn Lipscomb (Lipscomb, William Nunn, Jr.), Jr., received the 1976 Nobel Prize for Chemistry “for his studies on the structure of boranes illuminating problems of chemical bonding,” while one of Schlesinger's students, Herbert Charles Brown (Brown, Herbert Charles), shared the 1979 prize for his hydroboration reaction (1956), the remarkably easy addition of BH₃ (in the form of BH₃ · S) to unsaturated organic compounds (i.e., alkenes and alkynes) in ether solvents (S) at room temperature to yield organoboranes quantitatively (that is, in a reaction that proceeds wholly, or almost wholly, to completion). The hydroboration reaction in turn opened up new avenues of research in the area of stereospecific organic synthesis.

One of several systems of nomenclature suggested by the International Union of Pure and Applied Chemistry (IUPAC) employs characteristic structural prefixes: (1) closo- (a corruption of “clovo,” from Latin clovis, meaning “cage”), deltahedrons of n boron atoms; (2) nido- (from Latin nidus, meaning “nest”), nonclosed structures in which the B_n cluster occupies n corners of an (n + 1)-cornered polyhedron—i.e., a closo-polyhedron with one missing vertex; (3) arachno- (Greek, meaning “spider's web”), clusters that are even more open, with boron atoms occupying n contiguous corners of an (n + 2)-cornered polyhedron—i.e., a closo-polyhedron with two missing vertices; (4) hypho- (Greek, meaning “to weave” or “a net”), the most open clusters, with boron atoms occupying n corners of an (n + 3)-cornered closo-polyhedron; and (5) klado- (Greek, meaning “branch”), n vertices of an n + 4-vertex closo-polyhedron occupied by n boron atoms. Members of the hypho- and klado- series are currently known only as borane derivatives. Linkage between two or more of these polyhedral borane clusters is indicated by the prefix conjuncto- (Latin, meaning “join together”). For example, conjuncto-B₁₀H₁₆ is produced by joining the B₃H₈ units from two B₆H₉ molecules via a B−B bond.

One of the reasons for the great interest in boranes is the fact that they possess structures different from any other class of compounds. Because the bonding in boranes involves multicentre bonding, in which three or more atoms share a pair of bonding electrons (electron), boranes are commonly called electron-deficient substances. Diborane(6) has the following structure:

This structure involves three-centre bridge bonding, in which one electron pair is shared between three (rather than two) atoms—two boron atoms and one hydrogen atom. (See chemical bonding: Advanced aspects of chemical bonding: Boranes (chemical bonding) for a discussion of the three-centre bond.) The ability of boron to form such bonds in addition to normal covalent bonds (covalent bond) leads to the formation of complex polyhedral boranes.

Although the simplest boranes—e.g., B₂H₆—are spontaneously flammable in air (burning with a characteristic green flame) and very reactive toward solvents containing replaceable protons (proton), reactivity generally decreases with increasing molecular weight. Some of the higher-molecular-weight polyhedral anions, such as B₁₀H₁₀²⁻ and B₁₂H₁₂²⁻, are remarkably stable in air, water, and heat. Arachno-boranes are generally more reactive and less thermally stable than nido-boranes, which in turn are more reactive and less thermally stable than closo-boranes. Alfred Stock first obtained mixtures of boranes in low yield by treating magnesium boride (Mg₃B₂) with hydrochloric acid (HCl). Diborane is more easily prepared in high yield by reaction of iodine (I₂) with sodium tetrahydroborate (NaBH₄, commonly called sodium borohydride) in diglyme as a solvent,

The commercially available borohydrides, which are also important owing to their wide use as inorganic reducing agents, are the most commercially significant series of borane derivatives and the primary starting materials for preparing boranes on both a laboratory and an industrial scale. The stereospecific hydroboration reaction mentioned above,