Olefin metathesis industry
Depending on the catalytic system used, trans- or cis-polymers were obtained by polymerization of cyclopentene and tungsten leading to the trans compound. Two types of ligands can be considered, those which will be involved in the catalytic cycle and those which are only spectators such as oxo, alkoxo, amido, or imido groups.
Sherwood, M. Then in researchers at the Goodyear Tire and Rubber Company described a novel catalyst system for the metathesis of 2-pentene based on tungsten hexachlorideethanoland the organoaluminum compound EtAlMe2.
Olefin metathesis applications
The Goodyear group demonstrated that the reaction of regular 2-butene with its all- deuterated isotopologue yielded C4H4D4 with deuterium evenly distributed. Chemical Week , 20 November, p. The preparation of systems containing a higher amount of active sites could lead to more active and easily regenerated systems and could allow a better characterization and mechanistic study of the initiation and deactivation steps and their rationalization in terms of classical organometallic chemistry. Two mechanisms were proposed explaining the formation of the carbenic ligand. The good knowledge of the structure of the active site allows to propose a reasonable catalytic cycle and to determine how deactivation and regeneration will proceed. Oxo carbenic complexes synthesized by Schrock et al. Casey et al. Ligands such as 2,6-mesitylphenoxy, 2,6-diadamantyl-methylphenoxy, thio-2,6-masitylphenoxy, or tris tert-butoxy siloxy were used and the corresponding carbenes were synthesized Figure 25 [ 34 , 89 , 90 , 91 ]. Systems based on the combination of nitrosyl complexes of molybdenum or tungsten with alkylaluminum species were developed for the metathesis of terminal olefins pentene, octene [ 16 , 17 , 18 , 19 ]. No double bond migrations are observed; the reaction can be started with the butene and hexene as well and the reaction can be stopped by addition of methanol. Upon rearrangement this cycle will lead to the formation of a new olefin and restore the metal carbene species Figure 3. They are less active and less selective. Shell Chemicals Limited. Buchmeiser et al.
Cross-metathesis of ethylene and methyl oleate. For example, propylene C3 forms in a reaction of 2-butene C4 with tungsten hexachloride and tetramethyltin C1.
Olefin metathesis industry
At the end of the s, there were many studies in industrial laboratories on the catalytic effects of systems containing transition metal ions on unsaturated hydrocarbons. Google Scholar 5. Two mechanisms were proposed explaining the formation of the carbenic ligand. The main application of these heterogeneous systems is in petrochemistry and their use in other domains such as organic synthesis, oleochemistry, or polymerization remains very limited, mainly due to the drastic conditions which are required and to their intolerance of functional groups. Mechanism proposed for the formation of the oxo hydride tungsten species on alumina. This proves that the two species were activated by propene and led to the formation of carbene species with elimination of oxygen from the coordination sphere of tungsten Figure Figure 6 [ 26 ]. Google Scholar 9. Kantorowicz, S.
Possible mechanisms for the activation of the di-oxo tungsten species by propene. Conversion of the mono-oxo tungsten VI species into the di-oxo one. At the end of the s, there were many studies in industrial laboratories on the catalytic effects of systems containing transition metal ions on unsaturated hydrocarbons.
Wachs et al. Both materials gave only metathesis products equimolar amounts of ethylene and 2-butenes. In the case of oxides, the complex can be linked to the support by one or more bonds with surface oxygen atoms.
The first postulated surface species was a pentacoordinated tungsten complex but no experimental justification was given [ 44 ].
During last years, the development of highly active homogeneous and heterogeneous catalysts made the olefin metathesis reaction a powerful tool in numerous domains such as petrochemistry, polymers synthesis, fine chemistry, and synthesis of natural products.
We will review here only those containing the oxo ligand as they could be considered as models of the industrial heterogeneous catalysts.
based on 39 review