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September 1, 2008
Volume 86, Number 35
p. 13

Catalysis

Breaking C–F Bonds

Reaction could lead to ways to dispose of or recycle fluorocarbons

Rachel Petkewich

BRANDEIS UNIVERSITY researchers report that a robust silylium-carborane catalyst can transform notoriously strong, unreactive carbon-fluorine bonds into carbon-hydrogen bonds under mild conditions (Science 2008, 321, 1188).

8633cov3_SiGNacxd2.tif Courtesy of Oleg Ozerov
The silylium-carborane catalyst above breaks the aliphatic C–F bonds of the fluorocarbon below at room temperature. (C is black, Si is pink, Cl is green, and B is orange.)

The stable, inert C–F bonds that coat nonstick frying pans are what allow fried eggs to slip off, but the bonds are also why fluorocarbon-containing molecules cause concern as greenhouse gases and persist in the environment.

The team's results could lead to a strategy for disposal or recycling of fluorocarbons. Most of the prior work in C–F bond activation has used transition-metal catalysts or strong reducing agents with limited success.

"The key difference in our approach is in how we set out to break a C–F bond," says Oleg V. Ozerov, an associate professor of chemistry at Brandeis. Rather than delivering electrons to the C–F bond through either simple electron transfer or oxidative addition to a metal center, Ozerov and colleagues use an extremely strong silylium Lewis acid to abstract the fluoride.

The researchers previously showed that a silylium catalyst could break C–F bonds, but the catalyst didn't last very long. In the new work the catalyst turnover is "orders of magnitude higher," Ozerov says.

In the longer lived catalyst that he