Olefin Metathesis

The olefin metathesis reaction refers to a process of cutting and recombining a carbon-carbon heavy bond under metal catalysis. The olefin metathesis reaction is of great significance in polymer material chemistry and organic synthesis chemistry. The general formula of olefin metathesis reaction is shown in figure 1.

Figure 1. The schematic diagram of olefin metathesis reaction

Applications:

The olefin metathesis reaction is widely used in the chemical industry and is mainly used to develop drugs and advanced polymer materials.

Chemical production:

• Phillips triene and olefin conversion technology. This process allows propylene to be converted to each other with ethylene and 2-butene under the action of a helium or molybdenum catalyst. In the industry, it mainly converts ethylene and 2-butene into propylene. The reaction process is simple and quick, the production efficiency is higher, the by-products are less, the harmful waste generated is less, and the environment is friendly. Therefore, it has great application potential in the chemical, pharmaceutical, biotechnology and daily necessities industries.
• An advanced olefin process produces (alpha-olefins) for conversion to detergents. Certain olefin fractions produced by this process can be recovered by metathesis.
• Production of new hexene. A commonly used catalyst is derived from tungsten trioxide supported on SiO₂ and MgO.
• Preparation of 1,5-hexadiene and 1,9-decadiene. Both are useful cross-linking agents and synthetic intermediates which are obtained by the decomposition of 1,5-cyclooctadiene and cyclooctene by vinyl alcohol under the action of the catalyst Re₂O₇.

Drug synthesis: Some scientists are using the method of olefin metathesis to develop new drugs for the treatment of cancer, Alzheimer's disease and AIDS.

Catalysts:

Catalysts for olefin metathesis reactions can be classified into two categories: heterogeneous catalysts and homogeneous catalysts. Commercially available olefin metathesis reactions use heterogeneous catalysts.

• Heterogeneous catalysts: Heterogeneous catalysts are typically prepared by in situ activation of metal halides using organoaluminium or organotin compounds. For example, a combination of WCl₆-EtOH-EtAlCl₂. A typical catalyst support is alumina. Commercial catalysts are usually based on molybdenum and rhodium.
• Homogeneous catalysts: Homogeneous catalysts are generally classified as schrock catalysts and grubbs catalysts.

1) Schrock catalysts: The Schrock catalyst is characterized by a molybdenum (VI)- and tungsten (VI)-based center supported by an alkoxide and an imino ligand.

Figure 2. The schematic diagram of schrock catalysts

2) Grubbs catalysts: The catalyst for Grubbs is a ruthenium (II) carotenoid complex. A portion of the chelatable isopropoxystyrene ligand is modified to form the associated Hoveyda-Grubbs catalyst.

Figure 3. The schematic diagram of grubbs catalysts

Classification:

Some important olefin metathesis classes include:

• Cross metathesis (CM)
• Ring-opening metathesis (ROM)
• Ring-closing metathesis (RCM)
• Ring-opening metathesis polymerization (ROMP)
• Acyclic diene metathesis (ADMET)
• Ethenolysis

References

1. Astruc D. (2005). 'The metathesis reactions: from a historical perspective to recent developments' (abstract). New J. Chem. 29 (1): 42-56.
2. R.R. Schrock (1986). 'High-oxidation-state molybdenum and tungsten alkylidene complexes'. Acc. Chem. Res. 19 (11): 342-348.
3. Ghashghaee, Mohammad (2018). 'Heterogeneous catalysts for gas-phase conversion of ethylene to higher olefins'. Rev. Chem. Eng. 34 (5): 595-655.