Catalysts
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(VI)- and tungsten(VI)-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.
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