homocoupled

Homocoupled refers to a product or process in which two identical reacting partners join to form a single bond between two identical fragments, producing a homodimer or symmetrical product. In organic synthesis, homocoupling is a subset of coupling reactions, distinguished from cross-coupling where two different partners are joined. It can occur under catalytic conditions with metals such as nickel, palladium, or copper, and under oxidative, reductive, or radical pathways.

Common examples include the homocoupling of terminal alkynes to give diynes (the Glaser coupling) using copper catalysts and oxygen, and the palladium- or nickel-catalyzed homocoupling of aryl halides to form biaryls, typically under reductive or oxidative conditions. Homocoupling can be an undesired side reaction during cross-coupling when two identical electrophiles react, competing with the intended cross-product. Controlling stoichiometry, catalyst, and ligands can suppress homocoupling when cross-coupling is desired, or be exploited to make symmetric biaryl or diyne motifs when appropriate.

In radical and photoredox chemistry, two identical radical species may couple to form a dimer, providing another route to homocoupled products. In materials science and polymer chemistry, deliberate homocoupling is used to construct conjugated dimers, oligomers, and polymers with defined symmetry and electronic properties.

See also: coupling reactions, biaryl synthesis, Glaser coupling, radical coupling.