Borane
Encyclopedia
In chemistry, a borane is a chemical compound of boron
and hydrogen
. The boranes comprise a large group of compounds with the generic formulae of BxHy. These compounds do not occur in nature. Many of the boranes readily oxidise on contact with air, some violently. The parent member BH3 is called borane, but it is known only in the gaseous state, and dimerises to form diborane
, B2H6. The larger boranes all consist of boron clusters
that are polyhedral, some of which exist as isomer
s. For example, isomers of B20H26 are based on the fusion of two 10-atom clusters.
The most important boranes are diborane
B2H6, pentaborane
B5H9, and decaborane
B10H14.
The development of the chemistry of boron hydrides led to new experimental techniques and theoretical concepts. Boron hydrides have been studied as potential fuels, for rockets and for automotive uses.
Over the past several decades, the scope of boron hydride chemistry has grown to include cages containing atoms other than boron, such as carbon in the carborane
s and metals in the metallaboranes, wherein one or more boron atoms are substituted by metal atoms.
There also exists a series of substituted neutral hypercloso-boranes that have the theoretical formulae BnHn. Examples include B12(OCH2Ph)12, which is a stable derivative of hypercloso-B12H12.
The naming of anions is illustrated by the following, where the hydrogen count is specified first followed by the boron count, and finally the overall charge in brackets:
Optionally closo− nido− etc. (see above) can be added:-
Understandably many of the compounds have abbreviated common names.
that are found in borane chemistry are (using the names favoured by most chemists)
One feature of these deltahedra
is that boron atoms at the vertices may have different numbers of boron atoms as near neighbours. For example, in the pentagonal bipyramid, 2 borons have 3 neighbors, 3 have 4 neighbours, whereas in the octahedral cluster all vertices are the same, each boron having 4 neighbours. These differences between the boron atoms in different positions are important in determining structure, as they have different chemical shifts in the 11B NMR
spectra.
B6H10 is a typical example. Its geometry is, in essence, a 7-boron framework (pentagonal bipyramid), missing a vertex that had the highest number of near neighbours, e.g., a vertex with 5 neighbours. The extra hydrogen atoms bridge around the open face. A notable exception to this general scheme is that of B8H12, which would be expected to have a nido- geometry (based on B9H92− missing 1 vertex), but is similar in geometry to B8H14, which is based on B10H102− .
The names for the series of boranes are derived from this general scheme for the cluster geometries:-
and pose a problem for conventional descriptions of covalent
bonding that involves shared electron pairs. BH3 is a trigonal planar
molecule (D3h molecular symmetry
). Diborane
has a hydrogen-bridged structure, see the diborane
article.
The description of the bonding in the larger boranes formulated by William Lipscomb
involved:
The styx number was introduced to aid in electron counting where s = count of 3-center B-H-B bonds; t = count of 3-center B-B-B bonds; y = count of 2-center B-B bonds and x = count of BH2 groups.
Lipscomb's methodology has largely been superseded by a molecular orbital
approach, although it still affords insights. The results of this have been summarised in a simple but powerful rule, PSEPT
, often known as Wade's rules, that can be used to predict the cluster type, closo-, nido-, etc. The power of this rule is its ease of use and general applicability to many different cluster types other than boranes.
There are continuing efforts by theoretical chemists to improve the treatment of the bonding in boranes — an example is Stone's tensor surface harmonic treatment of cluster bonding. A recent development is four-center two-electron bond
.
. They are reactive compounds and some are pyrophoric
. The majority are highly poisonous and require special handling precautions.
closo−
nido−
arachno−
Diborane
B2H6 and higher boranes
General reactivity
Boranes can react to form hetero-boranes, e.g., carborane
s or metalloboranes (clusters
that contain boron and metal atoms).
The German chemist Alfred Stock
first characterized the series of boron-hydrogen compounds. His group developed the glass vacuum line and techniques for handling the compounds. However, exposure to mercury (used in mercury diffusion pumps and float valves) caused Stock
to develop mercury poisoning, which he documented in the first scientific papers on the subject. The chemical bonding of the borane clusters
was investigated by Lipscomb and his co-workers. Lipscomb was awarded the Nobel prize
in Chemistry in 1976 for this work. PSEPT
, (Wades rules) can be used to predict the structures of boranes.
Interest in boranes increased during World War II due to the potential of uranium borohydride
for enrichment of the uranium isotopes. In the US, a team led by Schlesinger
developed the basic chemistry of the boron hydrides and the related aluminium hydrides. Although uranium borohydride was not utilized for isotopic separations, Schessinger’s work laid the foundation for a host of boron hydride reagent
s for organic synthesis
, most of which were developed by his student Herbert C. Brown
. Borane-based reagents are now widely used in organic synthesis. For example, sodium borohydride
is the standard reagent for converting aldehyde
s and ketone
s to alcohol
s. Brown was awarded the Nobel prize
in Chemistry in 1979 for this work.
In the 1950s and early '60s, the US and USSR investigated boron hydrides as high-energy fuels
(ethylboranes, for example) for high speed aircraft, such as the XB-70 Valkyrie
. The development of advanced surface-to-air missiles made the fast aircraft redundant, and the fuel programs were terminated, although triethylborane
(TEB) was later used to ignite the engines of the SR-71 Blackbird
.
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...
and hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
. The boranes comprise a large group of compounds with the generic formulae of BxHy. These compounds do not occur in nature. Many of the boranes readily oxidise on contact with air, some violently. The parent member BH3 is called borane, but it is known only in the gaseous state, and dimerises to form diborane
Diborane
Diborane is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless gas at room temperature with a repulsively sweet odor. Diborane mixes well with air, easily forming explosive mixtures. Diborane will ignite spontaneously in moist air at room temperature...
, B2H6. The larger boranes all consist of boron clusters
Cluster chemistry
In chemistry, a cluster is an ensemble of bound atoms intermediate in size between a molecule and a bulk solid. Clusters exist of diverse stoichiometries and nuclearities. For example, carbon and boron atoms form fullerene and borane clusters, respectively. Transition metals and main group...
that are polyhedral, some of which exist as isomer
Isomer
In chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...
s. For example, isomers of B20H26 are based on the fusion of two 10-atom clusters.
The most important boranes are diborane
Diborane
Diborane is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless gas at room temperature with a repulsively sweet odor. Diborane mixes well with air, easily forming explosive mixtures. Diborane will ignite spontaneously in moist air at room temperature...
B2H6, pentaborane
Pentaborane
Pentaborane, also called pentaborane to distinguish it from B5H11, is an inorganic compound with the formula B5H9. It is one of the most common boron hydride clusters, although it is a highly reactive compound. Because of its high reactivity toward oxygen, it was once evaluated as rocket or jet fuel...
B5H9, and decaborane
Decaborane
Decaborane, also called decaborane, is the borane with the chemical formula B10H14. This white crystalline compound is one of the principal boron hydride clusters, both as a reference structure and as a precursor to other boron hydrides....
B10H14.
The development of the chemistry of boron hydrides led to new experimental techniques and theoretical concepts. Boron hydrides have been studied as potential fuels, for rockets and for automotive uses.
Over the past several decades, the scope of boron hydride chemistry has grown to include cages containing atoms other than boron, such as carbon in the carborane
Carborane
A carborane is a cluster composed of boron and carbon atoms. Like many of the related boranes, these clusters are polyhedra and are similarly classified as closo-, nido-, arachno-, hypho-, etc...
s and metals in the metallaboranes, wherein one or more boron atoms are substituted by metal atoms.
Generic formula of boranes
The four series of single-cluster boranes have the following general formulae, where "n" is the number of boron atoms:| Type | formula | notes |
|---|---|---|
| closo |
BnHn2 |
No neutral BnHn+2 boranes are known |
| nido |
BnHn+4 | |
| arachno |
BnHn+6 | |
| hypho |
BnHn+8 | only adducts established |
There also exists a series of substituted neutral hypercloso-boranes that have the theoretical formulae BnHn. Examples include B12(OCH2Ph)12, which is a stable derivative of hypercloso-B12H12.
Naming conventions
The naming of neutral boranes is illustrated by the following examples, where the Greek prefix shows the number of boron atoms and the number of hydrogen atoms is in brackets:- B5H9 pentaborane(9)
- B6H12 hexaborane(12)
The naming of anions is illustrated by the following, where the hydrogen count is specified first followed by the boron count, and finally the overall charge in brackets:
- B5H8
− octahydropentaborate(1− )
Optionally closo
- B5H9, nido
− pentaborane(9) - B4H10TetraboraneTetraborane, or to be more precise tetraborane or arachno-B4H10 was the first boron hydride compound to be classified by Stock and Messenez in 1912 and was first isolated by Alfred Hock. It has a relatively low boiling point at 18°C and is liquid at room temperature. Tetraborane gas is foul...
, arachno− tetraborane(10) - B6H62
− , hexahydro− closo− hexaborate(2− )
Understandably many of the compounds have abbreviated common names.
Cluster types
It was realised in the early 1970s that the geometry of boron clusters are related and that they approximate to deltahedra or to deltahedra with one or more vertices missing. The deltahedraDeltahedron
A deltahedron is a polyhedron whose faces are all equilateral triangles. The name is taken from the Greek majuscule delta , which has the shape of an equilateral triangle. There are infinitely many deltahedra, but of these only eight are convex, having 4, 6, 8, 10, 12, 14, 16 and 20 faces...
that are found in borane chemistry are (using the names favoured by most chemists)
| deltahedron | vertices |
|---|---|
| Trigonal bipyramid | 5 |
| Octahedron | 6 |
| Pentagonal bipyramid | 7 |
| Dodecahedron (see Snub disphenoid Snub disphenoid In geometry, the snub disphenoid is one of the Johnson solids . It is a three-dimensional solid that has only equilateral triangles as faces, and is therefore a deltahedron. It is not a regular polyhedron because some vertices have four faces and others have five... ) |
8 |
| Tricapped trigonal prism | 9 |
| Bicapped square antiprism | 10 |
| Octadecahedron | 11 |
| Icosahedron | 12 |
One feature of these deltahedra
Deltahedron
A deltahedron is a polyhedron whose faces are all equilateral triangles. The name is taken from the Greek majuscule delta , which has the shape of an equilateral triangle. There are infinitely many deltahedra, but of these only eight are convex, having 4, 6, 8, 10, 12, 14, 16 and 20 faces...
is that boron atoms at the vertices may have different numbers of boron atoms as near neighbours. For example, in the pentagonal bipyramid, 2 borons have 3 neighbors, 3 have 4 neighbours, whereas in the octahedral cluster all vertices are the same, each boron having 4 neighbours. These differences between the boron atoms in different positions are important in determining structure, as they have different chemical shifts in the 11B NMR
NMR spectroscopy
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is a research technique that exploits the magnetic properties of certain atomic nuclei to determine physical and chemical properties of atoms or the molecules in which they are contained...
spectra.
B6H10 is a typical example. Its geometry is, in essence, a 7-boron framework (pentagonal bipyramid), missing a vertex that had the highest number of near neighbours, e.g., a vertex with 5 neighbours. The extra hydrogen atoms bridge around the open face. A notable exception to this general scheme is that of B8H12, which would be expected to have a nido- geometry (based on B9H92
The names for the series of boranes are derived from this general scheme for the cluster geometries:-
- hypercloso- (from the Greek for "over cage") a closed complete cluster, e.g., B8Cl8 is a slightly distorted dodecahedron
- closo- (from the Greek for "cage") a closed complete cluster, e.g., icosahedral B12H122
− - nido- (from the Latin for "nest") B occupies n vertices of an n+1 deltahedron, e.g., B5H9 an octahedron missing 1 vertex
- arachno- (from the Greek for "spiders web") B occupies n vertices of an n+2 deltahedron e.g. B4H10 an octahedron missing 2 vertices
- hypho- (from the Greek for "net") B occupies n vertices of an n+3 deltahedron possibly B8H16 has this structure, an octahedron missing 3 vertices
- conjuncto- 2 or more of the above are fused together, eg., the edge or two vertex fused B19H221
− , face or three vertex fused B21H181− , and four vertex fused B20H16
Bonding in boranes
Boranes are electron-deficientElectron deficiency
Electron deficiency occurs when a compound has too few valence electrons for the connections between atoms to be described as covalent bonds. Electron deficient bonds are often better described as 3-center-2-electron bonds...
and pose a problem for conventional descriptions of covalent
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....
bonding that involves shared electron pairs. BH3 is a trigonal planar
Trigonal planar
In chemistry, trigonal planar is a molecular geometry model with one atom at the center and three atoms at the corners of a triangle, called peripheral atoms, all in one plane. In an ideal trigonal planar species, all three ligands are identical and all bond angles are 120°. Such species belong to...
molecule (D3h molecular symmetry
Molecular symmetry
Molecular symmetry in chemistry describes the symmetry present in molecules and the classification of molecules according to their symmetry. Molecular symmetry is a fundamental concept in chemistry, as it can predict or explain many of a molecule's chemical properties, such as its dipole moment...
). Diborane
Diborane
Diborane is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless gas at room temperature with a repulsively sweet odor. Diborane mixes well with air, easily forming explosive mixtures. Diborane will ignite spontaneously in moist air at room temperature...
has a hydrogen-bridged structure, see the diborane
Diborane
Diborane is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless gas at room temperature with a repulsively sweet odor. Diborane mixes well with air, easily forming explosive mixtures. Diborane will ignite spontaneously in moist air at room temperature...
article.
The description of the bonding in the larger boranes formulated by William Lipscomb
William Lipscomb
William Nunn Lipscomb, Jr. was a Nobel Prize-winning American inorganic and organic chemist working in nuclear magnetic resonance, theoretical chemistry, boron chemistry, and biochemistry.-Overview:...
involved:
- 3-center 2-electronThree-center two-electron bondA three-center two-electron bond is an electron-deficient chemical bond where three atoms share two electrons. The combination of three atomic orbitals form three molecular orbitals: one bonding, one non-bonding, and one anti-bonding. The two electrons go into the bonding orbital, resulting in a...
B-H-B hydrogen bridges - 3-center 2-electron B-B-B bonds
- 2-center 2-electron bonds (in B-B, B-H and BH2)
The styx number was introduced to aid in electron counting where s = count of 3-center B-H-B bonds; t = count of 3-center B-B-B bonds; y = count of 2-center B-B bonds and x = count of BH2 groups.
Lipscomb's methodology has largely been superseded by a molecular orbital
Molecular orbital
In chemistry, a molecular orbital is a mathematical function describing the wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of finding an electron in any specific region. The term "orbital" was first...
approach, although it still affords insights. The results of this have been summarised in a simple but powerful rule, PSEPT
Polyhedral skeletal electron pair theory
In chemistry the polyhedral skeletal electron pair theory provides electron counting rules useful for predicting the structures of clusters such as borane and carborane clusters. The electron counting rules were originally formulated by Kenneth Wade and were further developed by D. M. P. Mingos and...
, often known as Wade's rules, that can be used to predict the cluster type, closo-, nido-, etc. The power of this rule is its ease of use and general applicability to many different cluster types other than boranes.
There are continuing efforts by theoretical chemists to improve the treatment of the bonding in boranes — an example is Stone's tensor surface harmonic treatment of cluster bonding. A recent development is four-center two-electron bond
Four-center two-electron bond
A four-center two-electron bond is a type of chemical bond in which four atoms share two electrons in bonding which is unusual because in ordinary chemical bonds two atoms share two electrons . This type of bonding is postulated in certain cluster compounds...
.
Properties and reactivity trends
Boranes are all colourless and diamagneticDiamagnetism
Diamagnetism is the property of an object which causes it to create a magnetic field in opposition to an externally applied magnetic field, thus causing a repulsive effect. Specifically, an external magnetic field alters the orbital velocity of electrons around their nuclei, thus changing the...
. They are reactive compounds and some are pyrophoric
Pyrophoricity
A pyrophoric substance is a substance that will ignite spontaneously in air. Examples are iron sulfide and many reactive metals including uranium, when powdered or sliced thin. Pyrophoric materials are often water-reactive as well and will ignite when they contact water or humid air...
. The majority are highly poisonous and require special handling precautions.
closo
- There is no known neutral closo borane. Salts of the closo anions, BnHn2
− are stable in neutral aqueous solution, and their stabilities increase with size. The salt K2B12H12 is stable up to 700o.
nido
- Pentaborane(9)PentaboranePentaborane, also called pentaborane to distinguish it from B5H11, is an inorganic compound with the formula B5H9. It is one of the most common boron hydride clusters, although it is a highly reactive compound. Because of its high reactivity toward oxygen, it was once evaluated as rocket or jet fuel...
and decaborane(14)DecaboraneDecaborane, also called decaborane, is the borane with the chemical formula B10H14. This white crystalline compound is one of the principal boron hydride clusters, both as a reference structure and as a precursor to other boron hydrides....
are the most stable nido− boranes, in contrast to nido− B8H12 that decomposes above -35o.
arachno
- Generally these are more reactive than nido
− boranes and again larger compounds tend to be more stable.
Synthesis and general reactivity
Borane BH3- This is an important intermediate in the pyrolosis of diborane to produce higher boranes.
Diborane
Diborane
Diborane is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless gas at room temperature with a repulsively sweet odor. Diborane mixes well with air, easily forming explosive mixtures. Diborane will ignite spontaneously in moist air at room temperature...
B2H6 and higher boranes
- DiboraneDiboraneDiborane is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless gas at room temperature with a repulsively sweet odor. Diborane mixes well with air, easily forming explosive mixtures. Diborane will ignite spontaneously in moist air at room temperature...
is made industrially by the reduction of BF3Boron trifluorideBoron trifluoride is the chemical compound with the formula BF3. This pungent colourless toxic gas forms white fumes in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds.-Structure and bonding:...
, and is the starting point for preparing the higher boranes. It has been studied extensively.
General reactivity
- Typical reactions of boranes are
-
- electrophilicElectrophileIn general electrophiles are positively charged species that are attracted to an electron rich centre. In chemistry, an electrophile is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile...
substitution - nucleophilic substitution by Lewis bases
- deprotonationDeprotonationDeprotonation is the removal of a proton from a molecule, forming the conjugate base.The relative ability of a molecule to give up a proton is measured by its pKa value. A low pKa value indicates that the compound is acidic and will easily give up its proton to a base...
by strong bases - cluster building reactions with borohydrides
- reaction of a nido-borane with an alkyneAlkyneAlkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC nomenclature...
to give a carborane clusterCluster chemistryIn chemistry, a cluster is an ensemble of bound atoms intermediate in size between a molecule and a bulk solid. Clusters exist of diverse stoichiometries and nuclearities. For example, carbon and boron atoms form fullerene and borane clusters, respectively. Transition metals and main group...
- electrophilic
- Boranes can act as ligandLigandIn coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
s in coordination compounds. HapticitiesHapticityThe term hapticity is used to describe how a group of contiguous atoms of a ligand are coordinated to a central atom. Hapticity of a ligand is indicated by the Greek character 'eta', η. A superscripted number following the η denotes the number of contiguous atoms of the ligand that are bound to...
of η1 to η6 have been found, with electron donation involving bridging H atoms or donation from B-B bonds. For example, nido-B6H10 can replace ethene in Zeise's saltZeise's saltZeise's salt, potassium trichloroplatinate, is the chemical compound with the formula KPtCl3]·H2O. The anion of this air-stable, yellow, coordination complex contains an η2-ethylene ligand. The anion features a platinum atom with a square planar geometry.-Preparation:This compound is commercially...
to produce Fe(η2-B6H10)(CO)4.
Boranes can react to form hetero-boranes, e.g., carborane
Carborane
A carborane is a cluster composed of boron and carbon atoms. Like many of the related boranes, these clusters are polyhedra and are similarly classified as closo-, nido-, arachno-, hypho-, etc...
s or metalloboranes (clusters
Cluster chemistry
In chemistry, a cluster is an ensemble of bound atoms intermediate in size between a molecule and a bulk solid. Clusters exist of diverse stoichiometries and nuclearities. For example, carbon and boron atoms form fullerene and borane clusters, respectively. Transition metals and main group...
that contain boron and metal atoms).
History
The development of the chemistry of boranes posed two challenges to chemists. First, new laboratory techniques had to be developed to handle these very reactive compounds; second, the structures of the compounds challenged the accepted theories of chemical bonding.The German chemist Alfred Stock
Alfred Stock
Alfred Stock was a German inorganic chemist. He did pioneering research on the hydrides of boron and silicon, coordination chemistry, mercury, and mercury poisoning...
first characterized the series of boron-hydrogen compounds. His group developed the glass vacuum line and techniques for handling the compounds. However, exposure to mercury (used in mercury diffusion pumps and float valves) caused Stock
Alfred Stock
Alfred Stock was a German inorganic chemist. He did pioneering research on the hydrides of boron and silicon, coordination chemistry, mercury, and mercury poisoning...
to develop mercury poisoning, which he documented in the first scientific papers on the subject. The chemical bonding of the borane clusters
Cluster chemistry
In chemistry, a cluster is an ensemble of bound atoms intermediate in size between a molecule and a bulk solid. Clusters exist of diverse stoichiometries and nuclearities. For example, carbon and boron atoms form fullerene and borane clusters, respectively. Transition metals and main group...
was investigated by Lipscomb and his co-workers. Lipscomb was awarded the Nobel prize
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...
in Chemistry in 1976 for this work. PSEPT
Polyhedral skeletal electron pair theory
In chemistry the polyhedral skeletal electron pair theory provides electron counting rules useful for predicting the structures of clusters such as borane and carborane clusters. The electron counting rules were originally formulated by Kenneth Wade and were further developed by D. M. P. Mingos and...
, (Wades rules) can be used to predict the structures of boranes.
Interest in boranes increased during World War II due to the potential of uranium borohydride
Uranium borohydride
Uranium borohydride U4 is a volatile uranium complex with borohydride. This green-coloured compound is polymeric in the solid but evaporates to a tetrahedral monomer.-Preparation:...
for enrichment of the uranium isotopes. In the US, a team led by Schlesinger
Hermann Irving Schlesinger
Hermann Irving Schlesinger was an American inorganic chemist, working in boron chemistry.He and Herbert C. Brown discovered sodium borohydride in 1940 and both were involved in further development of borohydride chemistry....
developed the basic chemistry of the boron hydrides and the related aluminium hydrides. Although uranium borohydride was not utilized for isotopic separations, Schessinger’s work laid the foundation for a host of boron hydride reagent
Reagent
A reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction, or added to see if a reaction occurs." Although the terms reactant and reagent are often used interchangeably, a reactant is less specifically a "substance that is consumed in the course of...
s for organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
, most of which were developed by his student Herbert C. Brown
Herbert C. Brown
Herbert Charles Brown was a chemist and Nobel Prize in Chemistry laureate for his work with organoboranes....
. Borane-based reagents are now widely used in organic synthesis. For example, sodium borohydride
Sodium borohydride
Sodium borohydride, also known as sodium tetrahydridoborate, is an inorganic compound with the formula NaBH4. This white solid, usually encountered as a powder, is a versatile reducing agent that finds wide application in chemistry, both in the laboratory and on a technical scale. Large amounts are...
is the standard reagent for converting aldehyde
Aldehyde
An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....
s and ketone
Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...
s to alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
s. Brown was awarded the Nobel prize
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...
in Chemistry in 1979 for this work.
In the 1950s and early '60s, the US and USSR investigated boron hydrides as high-energy fuels
Zip fuel
Zip fuel, also known as high energy fuel , is any member of a family of jet fuels containing additives in the form of hydro-boron compounds, or boranes. Zip fuels offered higher power density than conventional fuels, helping extend the range of jet aircraft, a major problem for the military...
(ethylboranes, for example) for high speed aircraft, such as the XB-70 Valkyrie
XB-70 Valkyrie
The North American Aviation XB-70 Valkyrie was the prototype version of the proposed B-70 nuclear-armed deep-penetration strategic bomber for the United States Air Force's Strategic Air Command...
. The development of advanced surface-to-air missiles made the fast aircraft redundant, and the fuel programs were terminated, although triethylborane
Triethylborane
Triethylborane , also called triethylborine and triethylboron, is an organoborane , a near-colorless to yellowish transparent liquid with pungent ether-like odor. Its chemical formula can be written as C6H15B, or 3B, or 3B, or Et3B.Triethylborane is strongly pyrophoric, igniting spontaneously in...
(TEB) was later used to ignite the engines of the SR-71 Blackbird
SR-71 Blackbird
The Lockheed SR-71 "Blackbird" was an advanced, long-range, Mach 3+ strategic reconnaissance aircraft. It was developed as a black project from the Lockheed A-12 reconnaissance aircraft in the 1960s by the Lockheed Skunk Works. Clarence "Kelly" Johnson was responsible for many of the...
.