Heck reaction

Also known as: Heck coupling

Schematic of the Heck reaction. Reagents: organohalide, alkene with vinyl hydrogen, Palladium(0) catalyst, Ligands, base. Product: substituted alkene.

The Heck reaction is a cross-coupling reaction of an organohalide with an alkene to make a substituted alkene using palladium as a catalyst and a base. The reaction begins by oxidative addition of the aryl halide to the palladium, which is followed by coordination and migratory insertion of the olefin to the palladium. Bond rotation then places the two groups trans to each other to relieve the steric strain and subsequent β-hydride elimination results in a trans final product. Base mediated reductive elimination regenerates the palladium(0) catalyst.[1][2][3]

Mechanism

Mechanism of the Heck reaction. Note: For simplisity we have shown the mechanism using iodobenzene, styrene, and n-Bu3N, the reagents in one of the original Heck papers from 1972. The Heck Reaction Catalytic Cycle reductive elimination. The two phenyl groups are facing opposite sides of the page wich results in a trans product after β-hydride elimination.

References:

1.
Heck, R. F. J. Am. Chem. Soc. 1968, 90, 5518–5526.
2.
Heck, R. F.; Nolley, J. P. J. Org. Chem. 1972, 37, 2320–2322.
3.
Dieck, H. A.; Heck, R. F. J. Am. Chem. Soc. 1974, 96, 1133–1136.