2. • Coupling reactions
• Mechanism
• Reductive and beta hydride elimination
• Organometallic reagents in coupling
• Coupling with Palladium catalyst
• Reaction mechanisms
TABLE OF CONTENTS
3. A coupling reaction in organic chemistry is a general term
for a variety of reactions where two hydrocarbon
fragments are coupled with the aid of a metal catalyst.
Richard F. Heck, Ei-ichi Negishi and Akira Suzuki were
awarded the 2010 Nobel Prize in Chemistry for
developing palladium catalysed cross coupling
reactions.
Introduction
4. Types of coupling
Heterocouplings
• These type of couplings
couple two different
partners
• E.g. Heck Reaction
alkene and alkyl halide
to give a substituted
alkene.
Homocouplings
• These type of couplings
couple two identical
partners.
• E.g. Glaser Coupling of
two Acetylideo(RC≡CH)
to form a dialkyne
(RC≡C-C≡CR).
5. Reductive elimination
Reductive elimination is the reverse of Oxidative
addition. In reductive elimination reactions, a metal
centre is reduced by two electrons with the loss of two
ligands that must be cis to each other.
6. Order of rates of reductive elimination
vinyl-vinyl > phenyl-phenyl > alkynyl-alkynyl > alkyl- alkyl
Order of activation energies for reductive
elimination
vinyl-vinyl > vinyl-alkyl > alkyl-alkyl
7. Beta hydride elimination
β-Hydride elimination is a reaction in which
an alkyl group bonded to a metal centre is converted
into the corresponding metal-bonded hydride and
an alkene. The alkyl must have hydrogens on the β-
carbon.
9. Organometallic Compounds
An organic compound containing a carbon–metal bond
Organolithium compounds and organomagnesium
compounds are two of the most common organometallic
compounds
