Boron monohydride

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Boron monohydride
Boron monohydride.png
IUPAC name
  • BH:13766-26-2
3D model (JSmol)
PubChem CID
  • InChI=1S/BH/h1H
  • DB:InChI=1S/BH/h1H/i1D
  • TB:InChI=1S/BH/h1H/i1T
  • BH:[BH]
  • DB:[2H][B]
  • TB:[3H][B]
Molar mass 11.82 g·mol−1
Thermochemistry [1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Borane(1), boron monohydride, hydridoboron or borylene is the molecule with the formula BH. It exists as a gas but rapidly degrades when condensed. By contrast, the cluster [[B<sub>12</sub>H<sub>12</sub>]]2- (dodecaborate), which has very similar empirical formula, forms robust salts.



Boron monohydride can be formed from borane carbonyl exposed to ultraviolet light. BH3CO → BH + CH2O [2]

Boron monohydride is formed when boron compounds are heated to a high temperature in the presence of hydrogen. [3]

Boron monohydride is formed when the boron anion B reacts with a hydrogen ion H+. It is also formed when atomic boron reacts with hydrogen. B + H2 → BH + H. There is too much energy in the reaction for BH2 to be stable. [4]

Boron monohydride probably exists in sunspots, [5] but as of 2008 has not been detected. [6]


The ionization potential is around 9.77  eV. [7] The dissociation energy for the ground state molecule is 81.5 kcal/mol. [8] The electron affinity is roughly 0.3 eV, and the HB ion is formed. [9]

The dipole moment of the molecule in its ground state is 1.27 debye and for the first excited electronic state A1Π is 0.58 debye. [10]

The spectrum of boron monohydride includes a molecular band for the lowest electronic transition X1Σ+ → A1Π with a band head at 433.1 nm (for 0→0) and 437.1 (for 0→1) [3] The spectrum contains P, Q, and R branches. [10]

Although BH is a closed shell molecule, it is paramagnetic independent of temperature. [11]


Boron monohydride is unstable in bulk and disappears quickly on a timescale of 20 ns when at a pressure of 20 Torr. [12] Boron monohydride reacts with oxygen, probably forming HBO. [2] Boron monohydride shows no reaction with methane, but reacts with propane to give C3H7BH2. With nitric oxide (NO) it probably yields HBO and HBNO. Boron monohydride appears to add onto double bonds in unsaturated organic compounds. It also reacts with water. [2]

Boron monohydride can take on the form of solid poly-borane(1) which spontaneously inflames in air. [13]

Solid BH is predicted to take on an Ibam phase at pressures over 50 GPa and then become a metallic P6/mmm phase over 168 GPa. [14]


Both a cation and a dication are known. The dication HB2+ can be supported by a σ-donating ligand framework with two links. [15] The dianion can also be stabilized by an amine. [16]

Related Research Articles


Boranes is the name given to compounds with the formula BxHy and related anions. Many such boranes are known. Most common are those with 1 to 12 boron atoms. Although they have few practical applications, the boranes exhibit structures and bonding that differs strongly from the patterns seen in hydrocarbons. Hybrids of boranes and hydrocarbons, the carboranes are also well developed.

Hydroboration–oxidation reaction is a two-step hydration reaction that converts an alkene into an alcohol. The process results in the syn addition of a hydrogen and a hydroxyl group where the double bond had been. Hydroboration–oxidation is an anti-Markovnikov reaction, with the hydroxyl group attaching to the less-substituted carbon. The reaction thus provides a more stereospecific and complementary regiochemical alternative to other hydration reactions such as acid-catalyzed addition and the oxymercuration–reduction process. The reaction was first reported by Herbert C. Brown in the late 1950s and it was recognized in his receiving the Nobel Prize in Chemistry in 1979.

Diborane Chemical compound

Diborane(6), generally known as diborane, is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless, pyrophoric gas with a repulsively sweet odor. Synonyms include boroethane, boron hydride, and diboron hexahydride. Diborane is a key boron compound with a variety of applications. It has attracted wide attention for its electronic structure. Its derivatives are useful reagents.

Dimer (chemistry) Oligomer consisting of two monomers joined by bonds of any kind

A dimer is an oligomer consisting of two monomers joined by bonds that can be either strong or weak, covalent or intermolecular. The term homodimer is used when the two molecules are identical and heterodimer when they are not. The reverse of dimerisation is often called dissociation. When two oppositely charged ions associate into dimers, they are referred to as Bjerrum pairs, after Niels Bjerrum.

Ammonia borane Chemical compound

Ammonia borane (also systematically named amminetrihydridoboron), also called borazane, is the chemical compound with the formula H3NBH3. The colourless or white solid is the simplest molecular boron-nitrogen-hydride compound. It has attracted attention as a source of hydrogen fuel, but is otherwise primarily of academic interest.

Tris(pentafluorophenyl)borane Chemical compound

Tris(pentafluorophenyl)borane, sometimes referred to as "BCF", is the chemical compound (C6F5)3B. It is a white, volatile solid. The molecule consists of three pentafluorophenyl groups attached in a "paddle-wheel" manner to a central boron atom; the BC3 core is planar. It has been described as the “ideal Lewis acid” because of its high thermal stability and the relative inertness of the B-C bonds. Related fluoro-substituted boron compounds, such as those containing B−CF3 groups, decompose with formation of B-F bonds. Tris(pentafluorophenyl)borane is thermally stable at temperatures wide over 200 °C, resistant to oxygen and water-tolerant.

In chemistry, a frustrated Lewis pair (FLP) is a compound or mixture containing a Lewis acid and a Lewis base that, because of steric hindrance, cannot combine to form a classical adduct. Many kinds of FLPs have been devised, and many simple substrates exhibit activation.

Chromium(I) hydride Chemical compound

Chromium(I) hydride, systematically named chromium hydride, is an inorganic compound with the chemical formula (CrH)
. It occurs naturally in some kinds of stars where it has been detected by its spectrum. However, molecular chromium(I) hydride with the formula CrH has been isolated in solid gas matrices. The molecular hydride is very reactive. As such the compound is not well characterised, although many of its properties have been calculated via computational chemistry.

Iron(I) hydride Chemical compound

Iron(I) hydride, systematically named iron hydride and poly(hydridoiron) is a solid inorganic compound with the chemical formula (FeH)
. It is both thermodynamically and kinetically unstable toward decomposition at ambient temperature, and as such, little is known about its bulk properties.

Trihydridoboron, also known as borane or borine, is an unstable and highly reactive molecule with the chemical formula BH
. The preparation of borane carbonyl, BH3(CO), played an important role in exploring the chemistry of boranes, as it indicated the likely existence of the borane molecule. However, the molecular species BH3 is a very strong Lewis acid. Consequently it is highly reactive and can only be observed directly as a continuously produced, transitory, product in a flow system or from the reaction of laser ablated atomic boron with hydrogen.

Calcium monohydride Chemical compound

Calcium monohydride is a molecule composed of calcium and hydrogen with formula CaH. It can be found in stars as a gas formed when calcium atoms are present with hydrogen atoms.

Magnesium monohydride Chemical compound

Magnesium monohydride is a molecular gas with formula MgH that exists at high temperatures, such as the atmospheres of the Sun and stars. It was originally known as magnesium hydride, although that name is now more commonly used when referring to the similar chemical magnesium dihydride.

1,2-Dimethyldiborane Chemical compound

1,2-Dimethyldiborane is an organoboron compound with the formula [(CH3)BH2]2. Structurally, it is related to diborane, but with methyl groups replacing terminal hydrides on each boron. It is the dimer of methylborane, CH3BH2, the simplest alkylborane. 1,2-Dimethyldiborane can exist in a cis- and a trans arrangement. 1,2-Dimethyldiborane is an easily condensed, colorless gas that ignites spontaneously in air.

Tetramethyldiborane Chemical compound

Dimethylborane, (CH3)2BH is the simplest dialkylborane, consisting of a methyl group substituted for a hydrogen in borane. As for other boranes it normally exists in the form of a dimer called tetramethyldiborane or tetramethylbisborane or TMDB ((CH3)2BH)2. Other combinations of methylation occur on diborane, including monomethyldiborane, trimethyldiborane, 1,2-dimethylborane, 1,1-dimethylborane and trimethylborane. At room temperature the substance is at equilibrium between these forms. The methylboranes were first prepared by H. I. Schlesinger and A. O. Walker in the 1930s.

Trimethyldiborane Chemical compound

Trimethyldiborane, (CH3)3B2H3 is a molecule containing boron carbon and hydrogen. It is an alkylborane, consisting of three methyl group substituted for a hydrogen in diborane. It can be considered a mixed dimer: (CH3)2BH2BH(CH3) or dimethylborane and methylborane. called 1,2-dimethyldiborane. Other combinations of methylation occur on diborane, including monomethyldiborane, 1,2-dimethyldiborane, tetramethyldiborane, 1,1-dimethylborane and trimethylborane. At room temperature the substance is at equilibrium between these forms, so it is difficult to keep it pure. The methylboranes were first prepared by H. I. Schlesinger and A. O. Walker in the 1930s.

Methyldiborane Chemical compound

Methyldiborane, CH3B2H5, or monomethyldiborane is the simplest of alkyldiboranes, consisting of a methyl group substituted for a hydrogen in diborane. As with other boranes it exists in the form of a dimer with a twin hydrogen bridge that uses three-center two-electron bonding between the two boron atoms, and can be imagined as methyl borane (CH3BH2) bound to borane (BH3). Other combinations of methylation occur on diborane, including 1,1-dimethylborane, 1,2-dimethyldiborane, trimethyldiborane, tetramethyldiborane, and trimethylborane (which is not a dimer). At room temperature the substance is at equilibrium between these molecules.


A borylene is the boron analogue of a carbene. The general structure is R-B: with R an organic residue and B a boron atom with two unshared electrons. Borylenes are of academic interest in organoboron chemistry. A singlet ground state is predominant with boron having two vacant sp2 orbitals and one doubly occupied one. With just one additional substituent the boron is more electron deficient than the carbon atom in a carbene. For this reason stable borylenes are more uncommon than stable carbenes. Some borylenes such as boron monofluoride (BF) and boron monohydride (BH) the parent compound also known simply as borylene, have been detected in microwave spectroscopy and may exist in stars. Other borylenes exist as reactive intermediates and can only be inferred by chemical trapping.

1,1-Dimethyldiborane Chemical compound

1,1-Dimethyldiborane is the organoboron compound with the formula (CH3)2B(μ-H)2BH2. A pair of related 1,2-dimethyldiboranes are also known. It is a colorless gas that ignites in air.

Silylidyne Chemical compound

Silylidyne is a chemical substance occurring as a molecule found in stars and probably existing in interstellar space, or as a monolayer on the surface of solid silicon. The SiH molecule is a radical, and can be made experimentally by striking an electric arc to silicon on a low pressure hydrogen gas.


The triboracyclopropenyl fragment is a cyclic structural motif in boron chemistry, named for its geometric similarity to cyclopropene. In contrast to nonplanar borane clusters that exhibit higher coordination numbers at boron (e.g., through 3-center 2-electron bonds to bridging hydrides or cations), triboracyclopropenyl-type structures are rings of three boron atoms where substituents at each boron are also coplanar to the ring. Triboracyclopropenyl-containing compounds are extreme cases of inorganic aromaticity. They are the lightest and smallest cyclic structures known to display the bonding and magnetic properties that originate from fully delocalized electrons in orbitals of σ and π symmetry. Although three-membered rings of boron are frequently so highly strained as to be experimentally inaccessible, academic interest in their distinctive aromaticity and possible role as intermediates of borane pyrolysis motivated extensive computational studies by theoretical chemists. Beginning in the late 1980s with mass spectrometry work by Anderson et al. on all-boron clusters, experimental studies of triboracyclopropenyls were for decades exclusively limited to gas-phase investigations of the simplest rings (ions of B3). However, more recent work has stabilized the triboracyclopropenyl moiety via coordination to donor ligands or transition metals, dramatically expanding the scope of its chemistry.


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