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In organic chemistry, a Sonogashira coupling is a coupling reaction of terminal alkynes with aryl or vinyl halides. This reaction was first reported by Kenkichi Sonogashira and Nobue Hagiwara in 1975.
Catalyst
Typically, two catalysts are needed for this reaction: a zerovalent palladium complex and a halide salt of copper(I). The palladium complex activates the organic halides by oxidative addition into the carbon-halogen bond. Phosphine-palladium complexes such as tetrakis(triphenylphosphine)palladium(0) are used for this reaction, but palladium(II) complexes are also available because they are reduced to the palladium(0) species by the consumption of terminal alkynes in the reaction medium. In contrast, copper(I) halides react with the terminal alkyne and produce copper acetylide, which acts as an activated species for the coupling reactions.
Conditions
The reaction medium must be basic to neutralize the hydrogen halide produced as the byproduct of this coupling reaction, so alkylamine compounds such as triethylamine and diethylamine are used as solvents. In addition, deaerated conditions are formally needed for Sonogashira coupling reactions because the palladium(0) complexes are unstable in the air, but the recent development of air-stable organopalladium catalysts enable this reaction to be conducted in the ambient atmosphere.
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