Catalysis Merger Leads to Mild Arylation | November 7, 2011 Issue - Vol. 89 Issue 45 | Chemical & Engineering News
Volume 89 Issue 45 | p. 10 | News of The Week
Issue Date: November 7, 2011

Catalysis Merger Leads to Mild Arylation

Combination of photocatalysis with palladium catalysis could be broadly applicable
Department: Science & Technology
News Channels: JACS In C&EN
Keywords: C-H activation, catalysis, organometallic chemistry, photochemistry
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Sanford’s photocatalysis-palladium catalysis combo arylates even sensitive substrates.
Structure: Ru catalyst, light, Pd catalyst
 
Sanford’s photocatalysis-palladium catalysis combo arylates even sensitive substrates.

By marrying two catalytic cycles—one mediated by palladium and the other by light—chemists at the University of Michigan have developed a C–H arylation reaction that proceeds at room temperature (J. Am. Chem. Soc., DOI: 10.1021/ja208068w). The merger is “a far-reaching concept” that could extend the capabilities of C–H activation chemistry for making pharmaceuticals and materials, says chemistry professor Melanie S. Sanford, who led the Michigan team.

Aryl-aryl bonds are common motifs, but C–H activation routes to these bonds require acidic solvents, elevated temperatures, or both. To improve that state of affairs, postdoc Dipannita Kalyani and graduate students Kate B. McMurtrey and Sharon R. Neufeldt revisited a C–H arylation reaction Sanford developed in 2005. That reaction barely worked at room temperature. But after studying the reaction’s mechanism, the team realized they could fix that by changing their arylating reagent to something more reactive—aryl radicals.

To generate aryl radicals under mild conditions, the Michigan team looked to an emerging movement—combining catalytic processes (C&EN, Sept. 8, 2008, page 10). By adding a ruthenium(II) bipyridine catalyst to their palladium-catalyzed process, Sanford’s team harvested light from a compact fluorescent bulb to produce aryl radicals. The room-temperature method is compatible with functional groups, such as oximes, that don’t behave well in traditional C–H activations.

In addition to studying the reaction’s mechanism, Sanford’s team is exploring ways to extend the merger concept. “All sorts of radicals and reactive species can be generated with photocatalysis,” she says. Coupling those species with palladium-catalyzed C–C bond formations would open up many new synthetic doors, she adds.

“I am convinced that the mild nature of this transformation renders it very attractive for sophisticated applications, including C–H activations of sensitive materials like metal-organic frameworks,” says Frank Glorius, who studies C–H activation at the University of Münster, in Germany. “Moreover, I expect this work to inspire many more related processes using other catalytically active metals.”

 
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Comments
Bob Buntrock (November 15, 2011 4:37 PM)
Having done some photochemical syntheses in my PhD research, I'm impressed that a CFL was a satisfactory light source for these reactions. I'm eager to read the article (but that will require a trip to the nearby university library).
Carmen Drahl (November 17, 2011 10:17 AM)
Bob-thanks for your comment. Folks seem to be finding the right combinations of reagents and sensitizers to do chemistry with what may seem like “ordinary” light sources. You might also want to check out this article from the “related articles” section, where the authors used a bulb from Home Depot as the light source. http://pubs.acs.org/cen/science/87/8725scic5.html
Bob Buntrock (December 15, 2011 11:27 AM)
Carmen: I just checked the original article in Google Science and so far, no citations. Of course if there were, the citations would probably be for the chemistry and not the CFL light source. Guess I'll have to do some browsing for CFL photochemistry.

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