2005

Olefin Metathesis

Yves Chauvin (1930–2015), Robert Howard Grubbs (b. 1942), Richard Royce Schrock (b. 1945)

Metathesis, also called double decomposition, is a reaction between two compounds in which both compounds appear to be broken in half and switched to form two new combinations. In olefin (alkene) metathesis two carbon-carbon double bonds get reordered and rearranged, in a process that can unzip rings, form new ones, and stitch carbon chains together. A simple example is two molecules of propylene (the three-carbon alkene) going into the reaction, to emerge as a fifty-fifty mixture of two-carbon and four-carbon alkenes. The same number of carbons and double bonds are present, but in a new combination. The reaction provides a unique way to form carbon-carbon bonds, and that’s a topic that will never fail to attract the attention of synthetic-organic chemists.

Metathesis has its origins in the Ziegler-Natta catalysis, since both chemists, Germany’s Karl Waldemar Ziegler and Italy’s Giulio Natta, separately observed reactions that we now know to have been part of this chemistry. Industrial groups at companies like Shell, Phillips, Goodyear, and DuPont also discovered new reactions with olefins, which began to fit into an overall pattern, and French chemist Yves Chauvin suggested in the early 1970s that these reactions involved a four-membered ring intermediate containing a metal atom from the catalyst. American chemist Robert Howard Grubbs proposed a five-membered metallocycle intermediate, but his own isotope-labeling experiments showed that Chauvin was probably right. American chemist Richard Royce Schrock developed a series of metal catalysts for the transformation containing tungsten and molybdenum, and Grubbs found easy-to-handle ruthenium complexes that helped make the reaction popular among the wider organic community. It’s now being applied even to biomolecules, creating new cross-linked varieties with different biological activities.

Olefin metathesis went from a curiosity to an industrial processing route—where millions of tons of ethylene are turned into longer-chain compounds that are used as feedstocks for plastics and detergents—to a technique used in even the most delicate total synthesis reactions. As such, Chauvin, Grubbs, and Schrock were awarded the Nobel Prize in 2005.

A crystal structure of a first-generation Grubbs catalyst. The blue atom in the middle is a ruthenium, with two green chlorines flanking it. It’s also coordinated to two bulky substituted orange phosphorus atoms.