Ring-opening metathesis
Olefin metathesis is an organic reaction that entails the redistribution of fragments of alkenes (olefins) by the scission and regeneration of carbon-carbon double bonds. Catalysts for this reaction have evolved rapidly for the past few decades. Because of the relative simplicity of olefin metathesis, it often creates fewer undesired by-products and hazardous wastes than alternative organic reactions. For their elucidation of the reaction mechanism and their discovery of a variety of highly efficient and selective catalysts, Yves Chauvin, Robert H. Grubbs, and Richard R. Schrock were collectively awarded the 2005 Nobel Prize in Chemistry.
The reaction is catalyzed by metal complexes. Traditional catalysts are prepared by a reaction of the metal halides with alkylation agents, for example WCl6–EtOH–EtAlCl2. The traditional, industrial catalysts are ill-defined and used mainly for Petroleum products. Modern catalysts are well-defined organometallic compounds that come in two main categories, commonly known as Schrock catalysts and Grubbs' catalysts. Schrock catalysts are molybdenum(IV)- and tungsten(IV)-based, and are examples of Schrock alkylidenes.
Grubbs' catalysts, on the other hand, are ruthenium(II) carbenoid complexes. Grubbs' catalysts are often modified with a chelating isopropoxystyrene ligand to form the related Hoveyda–Grubbs catalyst.
Olefin metathesis was first commercialized in petroleum reformation for the synthesis of higher olefins from the products (alpha-olefins) from the Shell higher olefin process (SHOP) under high pressure and high temperatures.
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