![• The reaction proceeds through
oxidative addition,
transmetallation,
cis-trans isomerization and
reductive elimination.
• The purpose of the fluoride ion is to activate the conversion of silicon compound RSiR3 to
a pentacoordinate [RSiR3F]- intermediate which is more amiable to transmetallation.
• Reactions in which the fluoride ion is replaced by a strong base have also been reported.](https://image.slidesharecdn.com/coupling-reaction-pps-200805100852/85/Coupling-Reactions-6-320.jpg)
![CHEMISTRY OF PEPTIDES [M.PHARM, M.SC, BSC, B.PHARM]](https://cdn.slidesharecdn.com/ss_thumbnails/45-191219080659-thumbnail.jpg?width=560&fit=bounds)
![Homogeneous catalysis [ MPHARM, MSC, BPHARM, BSC]](https://cdn.slidesharecdn.com/ss_thumbnails/62-191219155346-thumbnail.jpg?width=560&fit=bounds)
More Related Content
What's hot (20)
Similar to Coupling Reactions (20)
Recently uploaded (20)
Coupling Reactions
- 1. COUPLING REACTIONS SHAFNA JOSE ASSISTANT PROFESSOR DEPARTMENT OF CHEMISTRY ST. MARY’S COLLEGE THRISSUR – 680020 KERALA
- 2. • Coupling reaction involves the joining of two chemical species with the help of a metal catalyst. • An important type of coupling reaction is the reaction of an organic halide with an organometallic compound which facilitates the formation of a new carbon-carbon bond. R1 and R3 denotes alkyl, alkene or alkylene groups and R2 denotes an H group or an alkyl group. X denotes the halide group. Coupling Reaction ?
- 3. hgajkgjghghghafgfahghghghagkhjg yt65Hetero coupling reactions Homo coupling reactions Two different molecules react to form one new molecule Two similar molecules react to form a new molecule COUPLING REACTIONS
- 4. • It is the Pd-catalyzed C-C bond formation between aryl, alklenyl, alkyl halides or pseudohalides and organosilanes. • This reaction is comparable to Suzuki coupling but it requires an activating agent such as fluoride ions or a base. • The polarization of the Si -C bond is important for the success of Hiyama coupling. • The first necessary step is the activation of the silane with a base or fluoride ion that leads to a pentavalent silicon compound. • The reaction rate is increased by using silanes with fluro or alkoxy group instead of alkyl. Hiyama Coupling
- 5. Catalytic cycle for Hiyama coupling
- 6. • The reaction proceeds through oxidative addition, transmetallation, cis-trans isomerization and reductive elimination. • The purpose of the fluoride ion is to activate the conversion of silicon compound RSiR3 to a pentacoordinate [RSiR3F]- intermediate which is more amiable to transmetallation. • Reactions in which the fluoride ion is replaced by a strong base have also been reported.
- 7. Advantages Hiyama coupling possesses advantages such as • low environmental impact, • high atom efficiency, • safe handling compared with the coupling reactions of organoboron, organozinc or organotin compounds. Disadvantages • Use of highly nucleophilic fluoride or hydroxide as an activator makes the transformation less chemoselective, especially for substrates with a base sensitive functionality.
- 8. • Kumada coupling or Kumada – Corriu Coupling is the Ni or Pd catalyzed cross coupling reaction between an alkyl, aryl, vinyl halide or triflate and aryl, alkenyl or alkyl Grignard reagents Kumada Coupling Reaction
- 9. Catalytic cycle for Kumada Coupling reaction
- 10. • The reactivity of the halides follows the order I> Br> Cl when Pd is used as the catalyst, whereas with certain Ni catalysts, the order is Cl> I> Br. • The reaction is important since it gives access to styrene compounds. • (Z) –Alkenyl – Grignard reagents couple non- stereospecifically with Ni catalysts, but the reaction is stereospecific with Pd catalysts. • Ni is also used to catalyse the reaction of alkyl and aryl Grignard reagents with an aryl and alkenyl halides
- 11. • It involves the Pd catalyzed substitution of the vinylic hydrogen with a vinyl, aryl or benzyl group. Heck Coupling • The coupling can be intra or intermolecular. • A base is necessary to remove the liberated acid.
- 12. Some examples are given below:
- 13. • The reaction time and temperature depend on the nature of the organic halide to be activated. • Heck reactions are useful on the inter and intra molecular level, although intermolecular reactions are more common. • Organic halides containing beta hydrogens cannot be used as they tend to form olefins at the Pd centre. • Electron rich, disubstituted or cyclic olefins are less reactive than electron deficient, monosubstituted olefins.
- 14. • Many functional groups are compatible with Heck conditions which enables the synthesis of carbo- and heterocyclic compounds and c-c bonded isomerized products including natural products. • The active form of the catalyst is a 14e Pd(0) complex with two PPh3 ligands. • 1,2 migratory insertion step is known as carbometallation in palladium based catalytic cycles.
- 15. • Discrimination in reactivity is possible in Heck reactions by controlling the reaction conditions. • In the given reaction when PPh3 is not added, only iodide is replaced by acrylate whereas upon the addition of PPh3, the bromides also react giving the tri-alkenyl substituted toluene
- 16. Catalytic cycle for Heck Reaction