Heck coupling
Palladium inserts into the aryl-halide bond, the alkene inserts into the aryl-palladium bond, and the hydride is eliminated to leave the alkene where it started, now carrying the ring.
What it needs, and what it gives
- Reaction class
- Cross-coupling
- A palladium source and a base, warm. The hydrogen and the palladium leave from the same face, and the conformation that arranges that with the two substituents apart is the lower one, so the trans alkene is what is isolated.
- balanced — the co-products are written out, not dropped
- Mechanism
- Heck coupling (catalytic cycle), 4 steps
How it is thought to happen
The metal inserts into the aryl-halide bond, the alkene inserts into the aryl-metal bond, the metal takes back a hydrogen and leaves, and a base strips it so the metal can start again.
- The metal inserts into the aryl-halide bond
- The alkene inserts into the aryl-metal bond
- The metal takes a hydrogen back and lets go
- A base strips the acid and the metal starts again
Try it on your own structures
Enter your reactants in the Reaction Lab. If this transformation matches what you drew, it is applied and the outcome is shown next to the records that back it — with the count of documented reactions doing the same thing on substrates like yours, rather than a confidence score.
Other cross-coupling transformations
Suzuki coupling
Palladium inserts into the aryl-halide bond, the boron hands its carbon to the metal, and the two organic groups are joined as the metal lets go.
Sonogashira coupling
A terminal alkyne is joined to an aromatic ring. The alkyne loses its hydrogen to a base, copper carries it to the palladium, and the two are joined there.
Buchwald-Hartwig amination
Palladium joins an amine to an aromatic ring, on rings that are not activated and would not react on their own.
Copper-catalysed ether coupling
Copper joins an alcohol or a phenol to an aromatic ring that would not accept it on its own.