Trialkylborane

Definition

Trialkyboranes are a class of organoborane compounds containing three alkyl groups bonded to a central boron atom. These compounds play a crucial role in the hydration of alkenes through the process of hydroboration-oxidation, which is a key reaction in organic chemistry.

5 Must Know Facts For Your Next Test

1. Trialkyboranes are formed as intermediates during the hydroboration-oxidation reaction of alkenes.
2. The boron atom in a trialkylborane has a trigonal planar geometry with an empty p-orbital, making it an electrophilic species.
3. The hydroboration step involves the addition of the borane reagent (BH3) across the carbon-carbon double bond of an alkene, forming the trialkylborane intermediate.
4. The oxidation step converts the trialkylborane intermediate into an alcohol, with the alkyl group from the borane becoming the alcohol's alkyl group.
5. Trialkyboranes are highly reactive and must be handled with care due to their pyrophoric nature (tendency to spontaneously ignite in air).

Review Questions

• Explain the role of trialkyboranes in the hydration of alkenes through the hydroboration-oxidation reaction.
  • Trialkyboranes are key intermediates in the hydroboration-oxidation reaction, which is a two-step process for the hydration of alkenes. In the first step, the borane reagent (BH3) adds across the carbon-carbon double bond of the alkene, forming a trialkylborane intermediate. This trialkylborane is then oxidized in the second step, converting the alkyl group from the borane into an alcohol group, effectively adding water (H2O) across the alkene.
• Describe the reactivity and structural features of trialkyboranes that make them suitable for the hydroboration-oxidation reaction.
  • Trialkyboranes have a trigonal planar geometry around the boron atom, with an empty p-orbital that makes the boron center electrophilic. This allows the borane reagent to readily add across the carbon-carbon double bond of an alkene, forming the trialkylborane intermediate. The reactive nature of the boron-carbon bonds in trialkyboranes also facilitates the subsequent oxidation step, where the alkyl group is converted into an alcohol group.
• Evaluate the importance of trialkyboranes in the context of organic synthesis and their potential limitations or safety concerns.
  • Trialkyboranes are invaluable intermediates in organic synthesis, as they enable the hydration of alkenes through the hydroboration-oxidation reaction, a powerful tool for introducing alcohol functional groups. However, the high reactivity and pyrophoric nature of trialkyboranes require careful handling and storage, as they can spontaneously ignite in air. Additionally, the use of borane reagents and the generation of trialkyboranes must be considered in the context of atom economy and environmental impact, as the boron-containing waste products may require special disposal methods. Despite these limitations, the utility of trialkyboranes in organic synthesis continues to make them an important topic of study in organic chemistry.

Related terms

Hydroboration:

The addition of a borane (BH3) reagent to an alkene, resulting in the formation of an organoborane intermediate.

Oxidation:

The process of increasing the oxidation state of an atom or molecule, often by the addition of oxygen or the removal of hydrogen.

Alkene:

An unsaturated hydrocarbon containing a carbon-carbon double bond.