Diborane: Definition, Properties, Formula and Structure

Diborane

Edited By Shivani Poonia | Updated on Jul 02, 2025 06:27 PM IST

A compound capable of making the sea change in its creation, would be diborane, B₂H₆, with weird chemical properties but having immense potential to be of use in a plethora of industrial and scientific applications. Diborane is an extremely reactive, colorless gas with repulsive smells, similar to sickly sweetness. Its unusual bonding and high reactivity have attracted the attention of chemists since its synthesis.

This Story also Contains

Diborane: Structure and Properties
Types and Aspects of Diborane
Relevance and Applications of Diborane
Some Solved Examples
Summary

Diborane

In organic chemistry, for example, it represents one important reagent for hydroboration, which allows complex molecules to be fabricated like those used in pharmaceuticals and agrochemicals. In the high-tech industry related to electronics, diborane is used for chemical vapor deposition to make the boron-doped silicon used when fabricating semiconductors and many other electronic devices.

Diborane: Structure and Properties

Diborane is a boron hydride chemical compound with the molecular formula B₂H₆. It has an exceedingly weird structure wherein two boron atoms are held substantially by three-center, two-electron bonds; both of the boron atoms are four-bonded: two terminal B-H bonds and two B-H-B bridging bonds. This unusual bonding arrangement gives rise to characteristic properties of diborane. It is highly reactive and acts like a reducing agent. The structure of the diborane determines its chemical behavior and thus its reactivity.

The simplest boron hydride known is diborane. B₂H₆ is prepared by the following methods:

Laboratory Method: In the laboratory, it is prepared by the reaction of sodium borohydride with iodine in a high boiling polyether solvent(CH₃OCH₂CH₂)₂O.2NaBH4+I2→ Polyether B2H6+2NaI+H2
Industrial Method: 2BF3+6LiH→450 K B2H6+LiF
From Boron Halides:4BX3+3LiAlH4→2 B2II6+3LiX+3AlX3
When boron halides and excess hydrogen undergo a reaction by passing silent electric discharge at low pressure, B₂H₆ is formed.

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Types and Aspects of Diborane

The most widely employed application of diborane is in the hydroboration reactions whereby it adds across the carbon-carbon double bond to give organoboranes. These organoboranes then convert into many useful compounds, examples of which are their reduction to alcohols, amines, and halides. Another application of diborane is in CVD for the creation of high-purity thin films containing boron species. On the other hand, pentaborane and decaborane, the derivatives of the diborane series, exist to manifest a wide range of properties and applications as BH derivatives do.

Relevance and Applications of Diborane

The applications of diborane extend far beyond a laboratory to be sure. It finds a place as a reagent in organic chemistry for the synthesis of complex molecules, like pharmaceuticals and agrochemicals. This makes it a very strong tool in the armamentarium of organic synthesis since it can selectively reduce compounds. On the other hand, semiconductor industries also make use of diborane in chemical vapor deposition processes, during which, with its help, resulting boron-doped films of silicon are formed; it is quite essential to be used in the manufacturing of electronic devices. Moreover, much attention is paid to diborane as a rocket fuel due to the large content of energy in its molecule. However, its reactivity and toxicity do not give any chance for practical application. As for academic disciplines, the study of diborane allows the development of advanced bonding theories and reaction mechanisms; therefore, research into this field is made in inorganic chemistry courses.

Some Solved Examples

Example 1

Question:

How many isomeric disubstituted borazine B₃N₃H₄X₂ are possible?

Solution:

Disubstituted borazine has 4 isomers: Ortho, meta-1, meta-2, and para isomers.

Therefore, the correct number of isomeric disubstituted borazine is 4. Hence, the correct option is (2).

Example 2

Question:

In B₂H₆, which of the following statements is correct?

1) There is a direct boron-boron bond.

2) The B-H bonds are ionic.

3) It is isostructural to C₂H₆.

4) Boron atoms are linked through hydrogen bridges.

Solution:

In B₂H₆, the structure includes three-center two-electron bonds, also known as banana bonds. There are two types of B-H bonds:

(B−Ht): Normal covalent bond (2c-2e bond)

(B−Hb): Bond between three atoms (B−Hb−B) (3c-2e bond)

B₂H₆ has two 3c-2e bonds made by bridged hydrogens between the two borons.

Therefore, the correct option is (4): Boron atoms are linked through hydrogen bridges.

Example 3

Question:

The number of 2-center-2-electron and 3-center-2-electron bonds in B₂H₆ respectively are:

1) 4 and 2

2) 2 and 4

3) 2 and 2

4) 2 and 1

Solution:

B₂H₆, or diborane, has a structure that includes three-center two-electron bonds (banana bonds). There are two types of B-H bonds in diborane:

(B−Ht): Normal covalent bond (2c-2e bond)

(B−Hb): Bond between three atoms (B−Hb−B) (3c-2e bond)

Diborane has four 2-center-2-electron bonds and two 3-center-2-electron bonds.

Therefore, the correct option is (1): 4 and 2.

Summary

Amongst such compounds, as an extraordinary structure with wide applications in the range of hydroboration reactions to CVD processes, stands that of diborane in organic synthesis and materials science. Indeed, this proves to be very challenging since it is highly reactive and toxic. Still, it is the potential that keeps researchers on track through research and innovation. The understanding of diborane will not only improve our knowledge about boron chemistry but also give way to new technological perspectives.

Frequently Asked Questions (FAQs)

1. What is diborane?

It is a chemical compound made of boron and hydrogen atoms. Its formation holds a unique structure, wherein it has two boron atoms and six hydrogen atoms. It will then confer three-center two-electron bonds, otherwise spelled as Banana bonds.

2. Use of diborane in organic chemistry:

Diborane, for example, used in hydroboration reactions, adds across the carbon-carbon double bond to create organoboranes. The organoboranes can then be turned into useful materials like alcohols and amines.

3. Industrial Applications of Diborane

Uses for this gas include chemical vapor deposition to form high-purity, boron-containing thin films required by the semiconductor industry. It is also under study as a high-energy rocket fuel.

4. Why is diborane important in academic research?

Studies of diborane demonstrate higher-order bonding theories and reaction mechanisms. Diborane is a constituent interest in most inorganic chemistry courses and represents a compound of interest to researchers wishing to study the behavior of boron-hydrogen compounds.

5. What are the safety concerns of the use of diborane?

Diborane is a highly toxic and very reactive compound; therefore, it should be handled and stored with due care. It is hazardous in that it produces fires and explosions, while its exposure has serious effects on health conditions. Proper care must be taken while handling diborane.

6. What is diborane and why is it considered unusual?

Diborane (B2H6) is a colorless, highly reactive gas composed of boron and hydrogen. It's considered unusual because it doesn't follow the octet rule and has a unique structure with three-center two-electron bonds, unlike most covalent compounds.

7. How does the structure of diborane differ from what we might expect?

Instead of having two separate BH3 units, diborane forms a bridge-like structure. Two hydrogen atoms bridge between the boron atoms, creating two three-center two-electron bonds. This results in a structure with two terminal and four bridging hydrogen atoms.

8. Why can't diborane form a simple Lewis structure like other molecules?

Diborane can't form a simple Lewis structure because boron only has three valence electrons, making it electron-deficient. To achieve a stable structure, it forms three-center two-electron bonds, which can't be represented by conventional Lewis dot structures.

9. What is the hybridization of boron in diborane?

The boron atoms in diborane are sp3 hybridized. This hybridization allows for the formation of four bonds: two terminal B-H bonds and two three-center two-electron B-H-B bonds.

10. Why is diborane so reactive?

Diborane is highly reactive due to its electron-deficient nature and the presence of three-center two-electron bonds. These factors make it unstable and prone to react with electron-rich species to achieve a more stable electron configuration.

11. What is the significance of diborane in the study of chemical bonding?

Diborane is significant in the study of chemical bonding because it demonstrates the existence of electron-deficient compounds and three-center two-electron bonds. This challenges traditional bonding theories and expands our understanding of how atoms can share electrons.

12. How does diborane react with water?

Diborane reacts vigorously with water, producing boric acid and hydrogen gas:

13. Why is diborane considered a reducing agent?

Diborane is a strong reducing agent due to its electron-deficient nature. It readily donates electrons or hydride ions to other compounds, reducing them in the process. This property makes it useful in various organic and inorganic synthesis reactions.

14. How does diborane behave as a Lewis acid?

Diborane acts as a Lewis acid because of its electron-deficient boron atoms. It can accept electron pairs from Lewis bases, forming adducts or undergoing reactions where it gains electrons to achieve a more stable electronic configuration.

15. How does the reactivity of diborane compare to that of other hydrides in the p-block?

Diborane is generally more reactive than other p-block hydrides due to its electron-deficient nature and unique bonding. It reacts more readily with water, oxygen, and other electron-rich species compared to hydrides like methane (CH4) or silane (SiH4).

16. What type of bonding is present in diborane?

Diborane exhibits two types of bonding: conventional two-center two-electron (2c-2e) bonds for the terminal B-H bonds, and three-center two-electron (3c-2e) bonds for the bridging B-H-B bonds.

17. How does the three-center two-electron bond in diborane work?

In a three-center two-electron (3c-2e) bond, two electrons are shared among three atoms (two boron atoms and one hydrogen atom). This allows for electron-deficient bonding, where fewer than two electrons are shared between each pair of atoms.

18. What happens when diborane is heated?

When heated, diborane decomposes to form higher boranes and hydrogen gas. The decomposition begins around 200°C:

19. How is diborane synthesized in the laboratory?

Diborane can be synthesized in the laboratory by reacting sodium borohydride (NaBH4) with boron trifluoride (BF3) in diethyl ether:

20. What safety precautions should be taken when handling diborane?

Diborane is highly toxic, flammable, and reactive. Safety precautions include:

21. How does the bonding in diborane compare to that in borane (BH3)?

While borane (BH3) is a theoretical molecule with a trigonal planar structure and sp2 hybridization, diborane (B2H6) actually exists with a different structure. Diborane forms through the dimerization of BH3 units, resulting in a more stable compound with three-center two-electron bonds.

22. Why does diborane form a dimer instead of existing as separate BH3 molecules?

Diborane forms a dimer because individual BH3 molecules are highly unstable due to their electron deficiency. By forming a dimer with three-center two-electron bonds, the compound achieves greater stability through electron sharing between two boron atoms.

23. How does the shape of diborane affect its polarity?

Despite its seemingly symmetrical structure, diborane is slightly polar. The terminal B-H bonds are more polar than the bridging B-H-B bonds, creating a small dipole moment. However, the overall polarity is relatively low due to the near-symmetrical arrangement of these bonds.

24. What are some industrial applications of diborane?

Diborane has several industrial applications, including:

25. How does the boiling point of diborane compare to other similar-sized molecules?

Diborane has a surprisingly low boiling point (-92.5°C) compared to other molecules of similar size. This is due to the weak intermolecular forces between diborane molecules, resulting from its unique structure and electron-deficient nature.

26. How does diborane interact with ammonia?

Diborane reacts with ammonia to form borazine (B3N3H6), often called "inorganic benzene":

27. Why is diborane sometimes called a "proton sponge"?

Diborane is not typically called a "proton sponge." This term is usually reserved for certain organic bases. However, diborane does react readily with proton donors (acids) due to its Lewis acidic nature, which might lead to confusion with the term.

28. How does the molecular orbital theory explain the bonding in diborane?

Molecular orbital theory explains diborane's bonding through the formation of multicentered molecular orbitals. The three-center two-electron bonds are described by molecular orbitals that span three atoms (two boron and one hydrogen), allowing for electron delocalization across these centers.

29. What is the relationship between diborane and boranes?

Diborane is the simplest stable borane (boron hydride compound). It serves as a precursor for the synthesis of higher boranes, which are compounds with more complex structures containing multiple boron atoms and varying numbers of hydrogen atoms.

30. How does diborane contribute to the concept of electron-deficient compounds?

Diborane is a classic example of an electron-deficient compound. Its structure and bonding demonstrate how atoms can form stable molecules even when they don't have enough electrons to form conventional two-center two-electron bonds, leading to the concept of three-center two-electron bonds.

31. What is the geometry around each boron atom in diborane?

Each boron atom in diborane has a distorted tetrahedral geometry. It is bonded to four hydrogen atoms: two terminal hydrogens and two bridging hydrogens. The angles between the bonds are not exactly 109.5° (as in a perfect tetrahedron) due to the unique three-center two-electron bonding.

32. How does diborane react with oxygen?

Diborane reacts spontaneously and vigorously with oxygen, often resulting in ignition:

33. What is the significance of diborane in rocket propellants?

Diborane has been investigated as a potential rocket propellant due to its high energy density and low molecular weight. However, its extreme reactivity, toxicity, and difficulty in handling have limited its practical use in this application.

34. How does the electron count in diborane compare to what we might expect?

In diborane, there are 12 valence electrons (3 from each boron and 1 from each hydrogen) instead of the 14 we might expect for two separate BH3 units. This electron deficiency is what leads to the formation of three-center two-electron bonds.

35. What is the role of diborane in organic synthesis?

In organic synthesis, diborane is used as a powerful reducing agent. It can reduce various functional groups, including aldehydes, ketones, and carboxylic acids, to alcohols. It's particularly useful for selective reductions in the presence of other functional groups.

36. How does the reactivity of diborane change at different temperatures?

At low temperatures, diborane is relatively stable. As temperature increases, its reactivity increases significantly. It becomes more prone to decomposition and reactions with other substances. At very high temperatures (above 200°C), it decomposes into higher boranes and hydrogen.

37. What is the relationship between diborane and boron trifluoride?

Both diborane and boron trifluoride (BF3) are electron-deficient compounds containing boron. While diborane forms three-center two-electron bonds, BF3 maintains a trigonal planar structure with an empty p orbital. BF3 is often used in the synthesis of diborane.

38. How does diborane behave in acidic and basic solutions?

In acidic solutions, diborane reacts to form boric acid and hydrogen gas:

39. What is the importance of diborane in understanding the periodic trends of hydrides?

Diborane's unique structure and properties highlight the differences between hydrides of different elements. It demonstrates how boron's electron deficiency leads to unexpected bonding arrangements, contrasting with the simple covalent bonds found in hydrides of carbon or nitrogen.

40. How does the dipole moment of diborane compare to other molecules?

Diborane has a small dipole moment (0.38 D) due to its near-symmetrical structure. This is lower than many other polar molecules like water (1.85 D) but higher than completely symmetrical molecules like carbon dioxide (0 D).

41. What is the relationship between diborane and boron nitride?

While not directly related, both diborane and boron nitride showcase boron's ability to form unique structures. Diborane demonstrates electron-deficient bonding, while boron nitride forms strong covalent networks similar to carbon in graphite or diamond.

42. How does diborane interact with transition metal complexes?

Diborane can act as a ligand in transition metal complexes, forming metal-borane adducts. It can also serve as a reducing agent, transferring hydride ions to metal centers. These interactions are important in catalysis and organometallic chemistry.

43. What is the significance of diborane in understanding Lewis acid-base theory?

Diborane exemplifies the concept of Lewis acidity in compounds other than typical proton donors. Its electron-deficient boron atoms can accept electron pairs from Lewis bases, demonstrating that Lewis acid-base interactions extend beyond traditional acid-base concepts.

44. How does the bond angle in diborane compare to that in water?

The H-B-H bond angle in diborane for the terminal hydrogens is approximately 120°, while the bridging B-H-B angle is about 97°. This differs significantly from water's H-O-H angle of 104.5°, reflecting the unique bonding in diborane compared to simple covalent molecules.

45. What role does diborane play in the synthesis of organoboron compounds?

Diborane is a key precursor in the synthesis of many organoboron compounds. It can react with alkenes in a process called hydroboration, forming organoboranes. These compounds are valuable intermediates in organic synthesis, particularly in carbon-carbon bond-forming reactions.

46. How does the electron affinity of boron relate to the formation of diborane?

Boron's relatively low electron affinity contributes to its tendency to form electron-deficient compounds like diborane. Instead of gaining electrons to complete its octet, boron shares electrons through unusual bonding arrangements, leading to the unique structure of diborane.

47. What is the relationship between diborane and boron trichloride in terms of Lewis acidity?

Both diborane and boron trichloride (BCl3) are Lewis acids due to their electron-deficient boron atoms. However, BCl3 is generally a stronger Lewis acid because the chlorine atoms are more electronegative than hydrogen, making the boron in BCl3 more electron-deficient.

48. How does the presence of diborane affect the pH of a solution?

When diborane dissolves in water, it forms boric acid (H3BO3), which is a weak acid. This causes a decrease in the pH of the solution. However, the reaction is vigorous and produces hydrogen gas, so the pH change is accompanied by potentially dangerous gas evolution.

49. What is the significance of diborane in understanding molecular symmetry?

Diborane's structure provides an interesting case study in molecular symmetry. Despite its seemingly symmetrical appearance, it belongs to the C2v point group due to the different nature of its terminal and bridging hydrogen atoms, illustrating the subtleties of symmetry in molecules.

50. How does the reactivity of diborane compare with that of aluminum hydride?

Both diborane and aluminum hydride (AlH3) are strong reducing agents, but diborane is generally more reactive. This is due to diborane's unique electron-deficient structure, while aluminum hydride tends to form polymeric structures that somewhat reduce its reactivity.

51. What is the role of diborane in the production of semiconductors?

Diborane is used in the production of boron-doped semiconductors. When introduced during the growth of silicon crystals, it provides boron atoms that act as p-type dopants, crucial for creating p-n junctions in electronic devices.

52. How does the concept of hypervalency relate to diborane?

Diborane is not considered hypervalent because boron does not exceed its normal valence of three. However, the three-center two-electron bonds in diborane demonstrate how atoms can share electrons in ways that don't fit traditional bonding models, which is conceptually related to hypervalency.

53. What is the relationship between diborane and the boron hydride clusters known as boranes?

Diborane is the simplest stable borane and serves as a precursor for synthesizing larger boron hydride clusters. When heated, diborane can rearrange and combine to form these more complex structures, which have fascinating polyhedral geometries and bonding arrangements.

54. How does the ionization energy of boron influence the properties of diborane?

Boron's relatively high ionization energy contributes to its tendency to form covalent rather than ionic compounds. In diborane, this leads to the formation