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More moves with metathesis

Chemists swap substituents on C–S and C–P bonds

by Bethany Halford
June 16, 2017 | A version of this story appeared in Volume 95, Issue 25

The bonding-partner switcheroo that happens in metathesis reactions has been a boon for molecule makers. Chemists who made crucial discoveries in olefin metathesis even won the Nobel Prize in Chemistry back in 2005. But metathesis reactions in which the bonding partners on heteroatoms undergo a swap are rare. Seeking to expand their repertoire of catalytic reversible reactions, chemists at the Max Planck Institute for Kohlenforschung developed a metathesis reaction for carbon-sulfur and carbon-phosphorus bonds (Science 2017, DOI: 10.1126/science.aam9041).

A scheme showing the depolymerization of polyphenylene sulfide using the Morandi group’s metathesis chemistry.

“The key power of these reactions lies in their ability to formally rearrange the substituents on important functional groups—thioethers and phosphines—in a reversible manner,” says Bill Morandi, who led the research team. “You basically keep the same functionality while only changing the substituents.”

Morandi’s team used its new palladium-catalyzed reaction to transform thio­ridazine, an antipsychotic drug with serious side effects, into a small library of derivatives that could be safer. The researchers also used the reaction to depolymerize the commercial polymer polyphenylene sulfide (shown). Such a reaction could recycle polymers at the end of their life span back into new monomers.

Morandi points out that the metathesis reactions are particularly useful in the “rapid synthesis and discovery of new small organic molecules, with applications ranging from drug candidates to new organic materials.” He adds that they might also find use in polymer chemistry, where olefin metathesis reactions have found a number of applications.

“These C–S and C–P bond metathesis reactions add a versatile new tool for bond construction in new molecules,” comments Patrick Holland, an expert in organic synthesis and organo­metallic chemistry at Yale University. “I am particularly excited about the potential for accessing constrained functional molecules with sulfur or phosphorus.”


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