page_title: Cross-coupling reaction
section_title: Mechanism
hierarchical_section_title: Cross-coupling reaction / Mechanism
caption_attribution_description: Katalysezyklus der Kumada-Kupplung
context_page_description: A cross-coupling reaction in organic chemistry is a reaction 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'. Cross-coupling reaction are a subset of coupling reactions. It is often used in arylations.
  Richard F. Heck, Ei-ichi Negishi, and Akira Suzuki were awarded the 2010 Nobel Prize in Chemistry for developing palladium-catalyzed cross coupling reactions.
context_section_description: The mechanism generally involves reductive elimination of the organic substituents R and R' on a metal complex of the type LₙMR(R') (where L is some arbitrary spectator ligand). The crucial intermediate LₙMR(R') is formed in a two step process from a low valence precursor Lₙ. The oxidative addition of an organic halide (RX) to LₙM gives LₙMR(X). Subsequently, the second partner undergoes transmetallation with a source of R'⁻. The final step is reductive elimination of the two coupling fragments to regenerate the catalyst and give the organic product. Unsaturated organic groups couple more easily in part because they add readily.  The intermediates are also less prone to beta-hydride elimination.
caption: Mechanism proposed for Kumada coupling (L = Ligand, Ar = Aryl).
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