Olefin Metathesis
Olefin metathesis is a versatile and powerful chemical reaction that involves the redistribution of fragments of alkenes (olefins) by the scission and recombination of carbon-carbon double bonds. This reaction has found widespread applications in organic synthesis, polymer chemistry, and the petrochemical industry due to its ability to efficiently form carbon-carbon bonds. The development of highly active and selective catalysts has significantly expanded the scope and utility of olefin metathesis.
Mechanism
The generally accepted mechanism for olefin metathesis involves the formation of a metallacyclobutane intermediate through the interaction of an olefin with a metal carbene catalyst. This process was first proposed by Yves Chauvin and is known as the Chauvin mechanism[1][3][5][10][17]. The cycle begins with the coordination of an olefin to a metal carbene species, leading to the formation of a metallacyclobutane intermediate. This intermediate then undergoes cycloreversion, generating a new olefin and a new metal carbene species, which can enter another catalytic cycle. The overall effect is the exchange of substituents between olefins, without the formation of byproducts other than the desired metathesis products.
Catalysts
The development of well-defined, highly active, and stable catalysts has been crucial for the advancement of olefin metathesis. Two major classes of catalysts dominate the field: Schrock catalysts and Grubbs catalysts[1][3][5][7][18].
- Schrock Catalysts: These are based on high-valent molybdenum(VI) and tungsten(VI) centers supported by alkoxide and imido ligands. They are known for their high activity and ability to catalyze the metathesis of sterically hindered substrates. However, they are generally more sensitive to air and moisture compared to Grubbs catalysts.
- Grubbs Catalysts: These are ruthenium-based carbene complexes that exhibit high functional group tolerance, stability in air, and ease of handling. The first-generation Grubbs catalyst was a breakthrough, but the second-generation catalyst, featuring a more electron-rich N-heterocyclic carbene (NHC) ligand, offers even higher activity and stability[1][3][5][7].
Types of Olefin Metathesis Reactions
Olefin metathesis encompasses several reaction types, each with its own set of applications[1][3][5][12][15]:
- Cross Metathesis (CM): The intermolecular reaction of two different olefins.
- Ring-Closing Metathesis (RCM): The intramolecular reaction of dienes to form cyclic olefins.
- Ring-Opening Metathesis Polymerization (ROMP): The polymerization of cyclic olefins to produce polymers with unique properties.
- Enyne Metathesis: The reaction between an alkene and an alkyne to form a diene.
- Acyclic Diene Metathesis Polymerization (ADMET): The polymerization of dienes to form linear polymers.
Applications
Olefin metathesis has found applications across a wide range of fields[1][2][3][5][6][16]:
- Synthesis of Complex Molecules: It is used in the synthesis of natural products, pharmaceuticals, and other complex molecules.
- Materials Science: ROMP and ADMET are used to create novel polymers with unique properties for materials science applications.
- Petrochemical Industry: Olefin metathesis is employed in processes such as the Shell Higher Olefin Process (SHOP) for the production of higher olefins from ethylene and propylene[2][5].
The versatility, efficiency, and broad applicability of olefin metathesis make it a cornerstone of modern synthetic chemistry. The ongoing development of new catalysts and reaction conditions continues to expand its utility in creating new materials and synthesizing complex organic molecules.
Citations:
[1] https://www.organic-chemistry.org/namedreactions/olefin-metathesis.shtm
[2] https://www.sciencedirect.com/science/article/pii/S1381116903007830
[3] https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_and_Websites_%28Inorganic_Chemistry%29/Catalysis/Catalyst_Examples/Olefin_Metathesis
[4] https://chemistry.illinois.edu/system/files/inline-files/CHEM535_Final_Abstract_Pulin_Wang.pdf
[5] https://en.wikipedia.org/wiki/Olefin_metathesis
[6] https://www.mdpi.com/1420-3049/28/4/1680
[7] https://www.sigmaaldrich.com/US/en/products/chemistry-and-biochemicals/catalysts/olefin-metathesis
[8] https://courses.cs.washington.edu/courses/cse154/cp/19su/cp1/ipswich/about.html
[9] https://pubs.acs.org/doi/10.1021/ja010624k
[10] https://thesis.library.caltech.edu/1517/2/1_introduction.pdf
[11] https://www.nature.com/articles/s41929-022-00793-4
[12] http://www.ilpi.com/organomet/olmetathesis.html
[13] https://www.masterorganicchemistry.com/reaction-guide/olefin-metathesis/
[14] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6369983/
[15] https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_%28Morsch_et_al.%29/Chapter_31:_Synthetic_Polymers/31.5:_Olefin_Metathesis_Polymerization
[16] https://pubs.acs.org/doi/abs/10.1021/acs.oprd.7b00319
[17] https://hwpi.harvard.edu/files/myers/files/31-the_olefin_metathesis_reaction.pdf
[18] https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_and_Websites_%28Inorganic_Chemistry%29/Advanced_Inorganic_Chemistry_%28Wikibook%29/01:_Chapters/1.28:_Olefin_Metathesis
[19] https://www.youtube.com/watch?v=XjNqNY_nxB4
[20] https://pubs.acs.org/doi/10.1021/acs.accounts.0c00495