Coupling reaction

Coupling reaction is the generic term for certain reactions in organic chemistry . In the narrower sense, these are organometallic reactions in which two hydrocarbons are formally linked to one another via a new carbon-carbon bond with the aid of a catalytically active metal complex. In a broader sense, it also refers to peptide synthesis , cross-linking and molecular labeling .

A distinction is made between homocoupling reactions and cross-coupling reactions . In the first type, two identical hydrocarbons react to form a new product, the second type involves the coupling of two different hydrocarbons.

• Homocoupling reaction of aryl iodides (e.g. Ullmann reaction )

${\displaystyle \mathrm {Ar-I\quad +\quad Ar-I\quad {\xrightarrow[{-CuI_{2}}]{Cu}}\quad Ar-Ar} }$

• Cross -coupling reaction (e.g. Stille coupling )

${\displaystyle \mathrm {R_{1}-X\quad +\quad R_{2}Sn(R_{3})_{3}\quad {\xrightarrow[{-(R_{3})_{3}Sn-X}]{Pd^{0}}}\quad R_{1}-R_{2}} }$

A commonly used metal in this type of reaction is palladium , very often as tetrakis (triphenylphosphine) palladium (0) . This is converted in situ into the complex then required in the special coupling reaction.

Since most reactions are very sensitive to traces of water or oxygen, a reaction under an inert gas atmosphere is necessary. This sensitivity is primarily due to the fact that the reactions often result in intermediately unsaturated metal complexes (less than 18 valence electrons) that would be able to take up oxygen and thus initiate side reactions.

The most important coupling reactions are:

• Heck reaction
• Suzuki clutch
• Hiyama clutch
• Sonogashira coupling
• Wurtz synthesis
• Ullmann reaction
• Silence coupling
• Kumada coupling (based on Grignard reagents )
• Negishi clutch