Question

What are coupling reactions?

Answer 1

The term coupling reaction is widely used in organic chemistry to classify a variety of reactions where two fragments or chemical species are joined together with the aid of a metal catalyst.The metal catalyst helps in speeding up the reaction to a great extent.

Complete answer:
In coupled reactions it is observed that there is always a presence of common intermediate and energy gets transferred from one side of the reaction to the other side.The presence of metal catalyst is considered as very important.The metal catalyst speeds up the reaction without disturbing the thermodynamic of the reactants involved.Transition elements are often used as catalyst in coupling reactions.
Depending upon the type of chemical species involved,coupling reactions can be classified into two distinct categories.
1)Homo-couplings reaction-The term homo means the same.When two similar chemical species undergo coupling reaction to form a new compound then the reaction is known as Homo-coupling reaction.
Eg:Wurtz reaction,Glaser coupling reaction,Ullmann reaction etc
2)Hetero-coupling reaction- The term hetero means different.When two dissimilar chemical species undergo coupling reaction to form a new compound then the reaction is known as Homo-coupling reaction.
Eg:Suzuki reaction,Kumada coupling,Heck reaction etc

Note:
Coupling reactions are routinely employed in many industrial processes.It is used for preparation of conjugated polymers.Pharmaceutical companies use coupling reactions frequently for developing life saving drugs.Caparratriene which is highly effective for treatment of leukemia is synthesized using Suzuki reaction. Many natural products can be obtained by certain coupling reactions. For example, benzylisoquinoline alkaloids are also synthesized with the help of the Sonogashira cross-coupling reaction.