Coupling reaction
A coupling reaction in organic chemistry is a general term for a variety of reactions where two fragments are joined together with the aid of a metal catalyst. In one important reaction type, a main group organometallic compound of the type R-M reacts with an organic halide of the type R'-X with formation of a new carbon-carbon bond in the product R-R'. The most common type of coupling reaction is the cross coupling reaction.
Richard F. Heck, Ei-ichi Negishi, and Akira Suzuki were awarded the 2010 Nobel Prize in Chemistry for developing palladium-catalyzed cross coupling reactions.
Broadly speaking, two types of coupling reactions are recognized:
- Heterocouplings combine two different partners, such as in the Heck reaction of an alkene and an alkyl halide to give a substituted alkene. Heterocouplings are called cross-couplings.
- Homocouplings couple two identical partners, as in the Glaser coupling of two acetylides to form a dialkyne.
Homo-coupling types
Coupling reactions are illustrated by the famous Ullmann reaction:
An illustrative cross-coupling reaction is the Heck coupling of an alkene and an aryl halide:
Applications
Coupling reactions are routinely employed in the preparation of pharmaceuticals. Conjugated polymers are prepared using this technology as well.
