Suzuki Coupling Reaction

Akira Suzuki 

Suzuki coupling reaction is another name reaction of organic chemistry which is used in formation of carbon-carbon single bonded compounds. As the name suggests it is a coupling reaction. As metal catalyst is used in the reaction so more precisely it is a cross – coupling reaction. It was given by Akira Suzuki in 1979. He got the Nobel Prize in Chemistry in 2010. This is the reason this reaction is also known as Suzuki coupling. 

What is Suzuki Coupling Reaction?

In Suzuki coupling reaction carbon – carbon single bond is formed by coupling an organoboron species with an alkyl or aryl halide in presence of Pd(0) and a base. General scheme for Suzuki coupling reaction is given below –

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Mechanism of Suzuki Coupling Reaction 

Suzuki coupling reaction takes place by following three steps –

  • Oxidative addition (its rate determining step)

  • Transmetalation

  • Reductive elimination 

Catalyst – Catalyst used in Suzuki coupling reaction is palladium which is taken in its zero-oxidation state as palladium is most reactive in its zero-oxidation state. 

Oxidative Addition – As the name of this step suggests, in this step oxidation and addition both take place. Catalyst palladium oxidized from zero to +2 oxidation state. It gets coupled with alkyl halide and yield organopalladium complex. In this step carbon-halogen bond breaks and palladium gets bonded to halogen and R-group both. As given in the reaction diagram below –

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Transmetalation – The organometallic reaction in which ligands are transferred from one species to another is called transmetalation. In this reaction the halide group of organopalladium complex gets attached to organoboron and R-group of organoboron gets attached to organopalladium complex. Thus, transmetalation takes place. Organoboron compounds do not go transmetalation in absence of base so in this step a base is used with organoboron. Exact mechanism of transmetalation is still not discovered. The reactions expected to be involved are given below –

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Reductive Elimination - As the name of this step suggests, in this step reduction and elimination both take place. It is the final step of this reaction mechanism. In this step catalyst palladium(II) gets eliminated as palladium(0) and generates carbon – carbon single bond. Thus, catalyst palladium with oxidation state zero gets regenerated. This step proceeds with retention of stereochemistry. Order of reductive elimination of organic compounds is as follows – Ar-Ar> Ar-R> R-R where Ar = aryl group, R = alkyl group.

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Complete mechanism pathway of Suzuki coupling reaction can be written as – (image will be uploaded soon)

Advantages of Suzuki Coupling Reaction 

Suzuki coupling reaction has various advantages over other old coupling reactions. Few of them are listed below –

  • Organoboron compounds are easily available.

  • It is less toxic in nature and safer for the environment.

  • This reaction is more economical and eco-friendlier than other reactions.

  • A wide range of reagents can be used for Suzuki coupling. 

  • With many different types of halides being possible for Suzuki coupling, pseudo halides can also be used.

Above stated various advantages and overall flexibility of the Suzuki coupling process makes it widely accepted for chemical synthesis. 

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