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Chemical dancing: chemists choreograph molecular moves for Nobel honor.

This year's Nobel Prize in Chemistry went to three scientists for their work on a versatile strategic for synthesizing all manner of novel chemical compounds in an environmentally friendly way.

Yves Chauvin of the French Petroleum Institute in Rueil-Malmaison, Richard R. Schrock of the Massachusetts Institute of Technology, and Robert H. Grubbs of the California Institute of Technology in Pasadena will share the nearly $1.3 million award.

The three scientists focused on a reaction called metathesis, a Greek term for change in position. During metathesis, molecules that contain carbon-carbon double bonds swap groupings of atoms. Discovered in the 1950s, the mechanism behind these swaps wasn't understood until 1970, when Chauvin showed that the key is a catalyst with a metal-carbon double bond.

The Royal Swedish Academy of Sciences describes metathesis as a dance that capitalizes on the double bonds of the participants. At the beginning of the dance, a catalyst molecule joins with one starting molecule, forming a chemical ring. This primes the compound for a swap of molecular parts. The ring disbands, and the catalyst, with its new molecular part, becomes available to partner with the second starting molecule. Essentially, metathesis is a series of chemical handoffs, orchestrating the swap of atomic groupings between the two starting molecules.

By targeting the carbon-carbon double bond, which is usually difficult to break, metathesis reactions provide "a new way to link molecules together," says Ronald Breslow, a chemist at Columbia University and Grubbs' Ph.D. adviser in the 1960s. "You can make a lot of molecules that would have been hard to make before."

Once the mechanism behind metathesis was in hand, other scientists began searching for useful metal catalysts that could extend the strategy's reach. Schrock presented the first practical and effective metathesis catalyst, based on the metal molybdenum, in 1990. "Initially, it was basic research," says Schrock, who ascribes his discovery to "being in the right place at the right time."

Two years later, Grubbs introduced a ruthenium-based catalyst, which, unlike previous catalysts, is stable in air. That makes the reaction easy to do on a laboratory bench top. Grubbs made several similar catalysts, and other chemists found them to be useful for many applications. "Carbon-carbon double bonds show up everywhere," Grubbs notes, adding that this ubiquity "allows these catalysts to be plugged into many different reactions."

Metathesis reactions are also a green way to make molecules, says Charles P. Casey, an organometallic chemist at the University of Wisconsin-Madison. The reactions can yield products in fewer steps than are necessary in other synthetic routes, while producing almost no by-products, he says.

Interest in metathesis, which has begun to make its way into the pharmaceutical and polymer industries, remains intense. Says Casey: "Open almost any journal in synthetic organic chemistry, and if you don't open to a page that has one of these reactions, within 10 pages you will [find one]."
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Title Annotation:This Week
Author:Cunningham, A.
Publication:Science News
Date:Oct 15, 2005
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