Olefin metathesis

Olefin metathesis or transalkylidenation (in some literature, a disproportionation) is an organic reaction which involves redistribution of olefinic (alkene) bonds. Since its discovery, olefin metathesis has gained widespread use in research and industry for making products ranging from medicines and polymers to enhanced fuels. Its advantages include the creation of fewer sideproducts and hazardous wastes. Yves Chauvin, Robert H. Grubbs, Richard R. Schrock shared the 2005 Nobel Prize in Chemistry for "the development of the metathesis method in organic synthesis".

Metathesis chemistry

The complete family of metathesis chemistry:

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• Cross-metathesis (CM)
• Ring-closing metathesis (RCM)
• Enyne metathesis (EM)
• Ring-opening metathesis (ROM)
• Ring-opening metathesis polymerization (ROMP)
• Acyclic diene metathesis (ADMET)
• Alkyne metathesis (AM)
• Alkane metathesis
• Alkene metathesis

Like most organometallic reactions, the metathesis pathway is usually driven by a thermodynamic imperative; that is, the final products are determined by the energetics of the possible products, with a distribution of products proportional to the exponential of their respective energy values.

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Alkene metathesis is generally driven by the evolution of gaseous ethylene; and alkyne metathesis is driven by the evolution of acetylene. These are both dominated by the entropy gained by the net release of gas. Enyne metathesis cannot evolve a simple gas, and for that reason is disfavored. Ring-opening metathesis usually involves a strained alkene (often a norbornene) and the release of ring strain drives the reaction. Ring-closing metathesis, conversely, usually involves the formation of a five- or six-membered ring which is highly energetically favorable; although these reactions tend to also evolve ethylene. RCM has been used to close larger macrocycles, in which case the reaction may be kinetically controlled by running the reaction at extreme dilutions.

Related Topics:
Ethylene - Acetylene - Ring-opening metathesis - Norbornene - Ring-closing metathesis

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Alkane metathesis is synthetically equivalent to ozonolysis followed by the Wittig reaction (or vice versa).

Related Topics:
Ozonolysis - Wittig reaction

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