Beta Hydride Elimination Reaction

β-Hydride Elimination Reaction

β-hydride elimination is an reaction in which an alkyl group bonded to a metal atom is converted into the corresponding metal-bonded hydride and alkene. β-hydride elimination reaction is generally an intramolecular β-hydrogen abstraction by the metal.


Beta-hydride elimination reaction is facilitated by the following four conditions-
1. The metal should be capable of increasing its coordination number by one unit.
2. A substituent attached to the β- atom should be readily transferred to the metal center.
3. The β- atom should be able to form multiple bond with the α- carbon atom.
4. β- hydride elimination is facile when β- position carbon is sp³ hybridized.

Factors Retarding the Beta Hydride Elimination Reaction

1. Metal alkyls having less bulky ligands will be coordinatively saturated. Hence they are expected to be more stable and do not undergo this fragmentation.
2. Fragmentation process may also be prevented by designing the alkyl in such a way that the transfer of a fragment group to the metal is no longer feasible. Since the transfer of groups other than hydrogen from the β- carbon atom to the metal is very unlikely, alkyl groups having no β-hydrogens will retard this fragmentation process.
3. Multiple bonding between the α and β skeletal atoms may be prevented by the presence of a β-atom having no tendency to π-bond.
a-Hydrogen abstraction in which an a-hydrogen of an alkyl ligand is abstracted to give an alkylidene or carbene complex is not common.

Which of the following is most unstable species

1. Ti(C₂H₅)₄   ✓
2. Ti(C₂Ph)₄
3. Pb(CH₃)₄
4. Pb(C₂H₅)₄

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