THEORISTS WIN WELCH AWARD ACCOLADES: Two chemists are
honored for achievements in electron transfer, reaction dynamics
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HEMISTRY PROFESSORS Noel S. Hush of the University of Sydney, in Australia, and William H. Miller of the University of California, Berkeley, have won the 2007 Welch Award in Chemistry for their work in chemical theory. The Welch Foundation, based in Houston, grants the $300,000 award to honor achievements in basic chemical research. Hush is most known for his work on electron transfer. In particular, he provided a description of electron donation by a complex, taking into account both solvent reorganization and the inner structure of the complex. Hush also investigated electron transfer between species covalently linked by a bridging molecule. He now focuses on the theoretical foundation of electrode-molecule-electrode conduction in nanoscale electronics. "It's a wonderful thing to see Hush get this recogni-
ARENES HOOK UP SYNTHESIS: Catalytic
reaction selectively couples benzene and an indole
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AKING CERTAIN pharmaceuticals and electronic chemicals could get much simpler, thanks to a new catalytic reaction for coupling two different arenes together. Coupling one aromatic molecule to another usually requires elaborate functionalization of one or both aromatics beforehand to ensure the compounds react efficiently and selectively with one another. Now, the University of Ottawa's Keith Fagnou and David R. Stuart have devised a way to stick benzene and an Nacetylindole together without functionalizing them first. The reaction proceeds in high yields with high regioselectivity and, most important, produces no selfcoupled by-products (Science 2007,316,1131). "The waybiaryls are made commercially today, you have to preactivate everything. You can't just couple two carbon atoms together at their C-H bonds," Fagnou explains. The problem is that until now, coupling
tion," says Henry F. Schaefer, director of the Center for Computational Chemistry at the University of Georgia. "Hush and Rudolph Marcus looked at the problem of electron transfer in rather different ways, and the work of each of them, being utterly independent and motivated in different ways, has added greatly to the richness of our understanding of electron-transfer processes." Marcus, professor of chemistry at California Institute of Technology, won the Nobel Prize in Chemistry in 1992. Miller's research focuses on chemical reaction dynamics. His achievements include developing a semiclassical scattering theory (the classical S-matrix theory) for chemical reactions, as well as a rigorous quantum theory of reaction rates. He is currently investigating a method for adding quantum effects to classical molecular dynamics simulations of complex chemical processes. Miller, an ACS member, directs the Kenneth S. Pitzer Center for Theoretical Chemistry at UC Berkeley. "Miller showed first that it was possible to solve dynamical problems in terms of semiclassical mechanics, and I don't think that was obvious before," Schaefer says. "Miller's work stood between the quantum real world and the classical world that is easy to simulate and really was the Rosetta stone that unleashed the power of classical dynamics and made it believable for chemical systems."—JYLLIAN KEMSLEY
reactions haven't been selective enough to avoid the stew of homocoupled biaryls that are produced along with the desired cross-coupled biaryl. "How do you get two things to react only with the other coupling partner and not with itself?" Fagnou says. "That was the trick that needed to be solved." Fagnou and Stuart realized that by selecting aromatic compounds based on nucleophilicity and C-H acidity, they could get one arene to react selectively with the catalyst. The catalyst/arene complex then reacts exclusively with the other arene. It took a lot of optimization to get the crosscoupling to work, Fagnou and Stuart acknowledge. They had to employ a palladium trifluoroacetate catalyst, along with copper (II) acetate for catalyst regeneration. Critical to the reaction's success were two additives, 3-nitropyridine and cesium pivalate, and the pivalic acid solvent. The new process "could have immense practical importance for the synthesis of materials, electronic devices, and drugs," writes Jonathan A. Ellman of the University of California, Berkeley, in a Science commentary. "However, further advances will be required to enhance reaction efficiency, for example, by reducing catalyst and terminal oxidant loading levels."—BETHANY HALFORD
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MAY 28, 2007
Hush
Miller
CROSS-COUPLED New synthesis gives no homocoupled by-products.
