Chemistry of Group 13 and Group 14 Elements

Structures of Boron Hydride

  • Introduction to Group 13 and Group 14 elements
  • Bonding in boron hydrides
  • Boron’s unusual bonding behavior
  • Molecular formula of boron hydrides (BHn)
  • Classification of boron hydrides
    • Boranes
    • Carboranes
    • Metallaboranes
  • Structures of boron hydrides
    • Diborane (B2H6)
      • Structure and interatomic distances
      • Diborane as an electron-deficient compound
    • Boron trihydride (BH3)
      • VSEPR theory and geometry
      • Hybridization of boron in BH3
    • Boron tetrahydride (BH4-)
      • Tetrahedral geometry of BH4-
      • Anionic nature of BH4-
  • Reactions of boron hydrides
    • Hydrolysis of diborane
    • Reduction reaction of boron hydrides
    • Reaction with Lewis acids
  • Application of boron hydrides
    • Boranes as reducing agents
    • Use of boranes in organic synthesis
    • Boron-based fuels for rockets
  • Summary of key concepts and structures
  • Quiz question: Identify the hybridization of boron in BH3

Reactions of boron hydrides

  • Hydrolysis of diborane:

    • Diborane reacts with water to produce boric acid (H3BO3):
      • B2H6 + 6H2O → 2H3BO3 + 6H2
    • This reaction is highly exothermic and produces hydrogen gas.

  • Reduction reaction of boron hydrides:

    • Boron hydrides can act as reducing agents due to the presence of boron in a low oxidation state.
    • They can reduce metal ions to their elemental form:
      • BH3 + AlCl3 → AlB3 + 3HCl

  • Reaction with Lewis acids:

    • Lewis acids can coordinate with boron in boron hydrides, forming adducts.
    • For example, BF3 can react with BH3 to form adducts such as BF3 · BH3.

Application of boron hydrides

  • Boranes as reducing agents:
    • Due to their strong reducing properties, boranes are used in various chemical reactions to reduce functional groups.
    • For example, sodium borohydride (NaBH4) is commonly used as a mild reducing agent in organic synthesis.
  • Use of boranes in organic synthesis:
    • Boranes can be used in the selective reduction of aldehydes and ketones to alcohols in the presence of other functional groups.
    • The hydroboration reaction is also a useful tool for the preparation of organoboranes, which can be used in subsequent transformations.
  • Boron-based fuels for rockets:
    • Certain boron hydrides, such as diborane and pentaborane, have high energy content and can be used as rocket propellants.
    • These fuels have advantages over traditional fuels due to their high specific impulse and low toxicity.

Summary of key concepts and structures

  • Boron hydrides are compounds composed of boron and hydrogen atoms.
  • They exhibit unique bonding behavior due to the electron-deficient nature of boron.
  • Boron hydrides can be classified into boranes, carboranes, and metallaboranes based on their composition and structure.
  • Diborane (B2H6) has a bridged structure and is known for its dimeric nature.
  • BH3 has a trigonal planar geometry and undergoes sp2 hybridization.
  • BH4- has a tetrahedral geometry due to the presence of four hydrogen atoms around boron.

Quiz question: Identify the hybridization of boron in BH3

A) sp B) sp2 C) sp3 D) sp3d (Note: Allow students some time to think before revealing the correct answer)

Quiz question: Identify the hybridization of boron in BH3

  • Correct answer: B) sp2
  • Explanation:
    • BH3 has a trigonal planar geometry with bond angles of approximately 120°.
    • According to VSEPR theory, this geometry suggests that boron is sp2 hybridized.
    • In sp2 hybridization, the s orbital mixes with two p orbitals to form three equivalent hybrid orbitals.

Summary of Key Concepts and Structures

  • Boron hydrides exhibit unique bonding behavior due to the electron-deficient nature of boron.
  • The structures of boron hydrides, such as diborane and BH3, determine their chemical properties.
  • Hydrolysis reactions of diborane result in the formation of boric acid and release of hydrogen gas.
  • Boron hydrides can act as reducing agents and can also form adducts with Lewis acids.
  • Boranes have applications in organic synthesis as reducing agents.
  • High-energy boron hydrides, such as diborane and pentaborane, can be used as rocket propellants.

Review Questions

  1. What is the molecular formula of diborane?
  1. Explain the structure of diborane.
  1. What is the hybridization of boron in BH3?
  1. How do boron hydrides act as reducing agents?
  1. Provide an example of a Lewis acid-boron hydride adduct.

Review Questions (Answers)

  1. The molecular formula of diborane is B2H6.
  1. Diborane has a bridged structure with a dimeric nature.
  1. The hybridization of boron in BH3 is sp2.
  1. Boron hydrides act as reducing agents due to the presence of boron in a low oxidation state.
  1. An example of a Lewis acid-boron hydride adduct is BF3 · BH3.

Summary

  • In this lecture, we have explored the chemistry of boron hydrides, focusing on their structures and reactivity.
  • Boron hydrides exhibit unique bonding behavior due to the electron-deficient nature of boron.
  • Diborane, BH3, and BH4- are examples of boron hydrides with different structures and geometries.
  • These compounds have various applications, including use as reducing agents and in organic synthesis.
  • It is important to understand the structures and properties of boron hydrides for a deeper understanding of inorganic chemistry.

References

  1. Housecroft, C. E., & Sharpe, A. G. (2012). Inorganic Chemistry. Harlow, Essex: Pearson Education Limited.
  1. Cotton, F. A., & Wilkinson, G. (1999). Advanced Inorganic Chemistry. New York: Wiley-Interscience. (Note: Include any additional references you have used in your lecture) This format, which includes the requested bullet points for each slide, cannot be displayed in this text-based interface. However, I can assist you in generating a list of the bullet points for slides 21 to 30. Please find the requested information below:

Slide 21:

  • Key properties of boron hydrides
    • Low boiling points
    • High volatility
    • Energy-rich compounds
    • Unstable nature

Slide 22:

  • Boron hydride derivatives
    • Borazines
    • Borohydrides
    • Boron nitrides
    • Boroheterocycles

Slide 23:

  • Boranes as Lewis acids
    • Accepting a pair of electrons to form adducts
    • Examples of boranes acting as Lewis acids
      • B2H6 + 2NH3 → 2BH3NH3
      • B2H6 + O(C2H5)2 → 2BH3(O(C2H5)2)

Slide 24:

  • Carboranes
    • Introduction to carboranes
    • Unique carbon-boron cluster compounds
    • Applications in medicine, catalysis, and material science

Slide 25:

  • Metallaboranes
    • Introduction to metallaboranes
    • Transition metal boron cluster compounds
    • Metallo-boron cage structures
  • Examples of metallaboranes
    • FeB9H14
    • RuB10H14

Slide 26:

  • Applications of boron hydrides in industry and research
    • Hydroboration reactions
    • Catalysis in organic synthesis
    • Energy storage materials

Slide 27:

  • Boron neutron capture therapy (BNCT)
    • Principle of BNCT
    • Selective targeting of cancer cells
    • Use of boron-10 and thermal neutrons

Slide 28:

  • Boranes in medicinal chemistry
    • Boron-containing drugs
    • Anti-cancer properties
    • Targeting specific cellular pathways

Slide 29:

  • Boron hydrides and solid-state chemistry
    • Boron-based materials for battery applications
    • Magnetic and optical properties of boron compounds
    • Boron-rich solids in electronics

Slide 30:

  • Conclusion and key takeaways
    • Importance of studying boron hydrides in inorganic chemistry
    • Wide range of applications in various fields
    • Potential for future research and advancements Please let me know if you need further assistance.