Science Concentrates REAGENTS
Toward more versatile fluorinations Optimized Lewis acid-base approach offers a new CF3– transfer reagent made from waste fluoroform
more expensive trifluoromethyl halides (Angew. Chem. Int. Ed. 2017, DOI: 10.1002/ anie.201711316). “Szymczak’s group has developed a very clever and thoughtful approach that exUniversity of Michigan chemists have pose or irreversibly react with its Lewis ploits a Lewis acid-base combination with developed a Lewis acid-base pair strategy acid partner to limit trifluoromethyl broad utility,” says Douglas W. Stephan of to prepare and stabilize a versatile new transfer. the University of Toronto, who specializes reagent capable of adding trifluoromethyl The Michigan team found that in reactive Lewis acid-base pair chemistry. groups to molecules. The method promhexamethylborazine paired with a potas“This has wide-reaching implications, and ises to expand on current synthetic stratsium crown ether counterion provides a I expect rapid adoption of this strategy.” egies for making fluorinated pharmaceuLewis acidity sweet spot for maintaining Szymczak thinks the method could ticals and agrochemicals while lowering CF3– stability—the combination allows be applied to unstable anions other than costs and reducing chemical waste. reactions to take place at room temperaCF3– to promote nucleophilic reactions. Jacob B. Geri and Nathaniel K. ture in just a few minutes, and the boSzymczak conducted a computational razine is recyclable. Plus, he believes this is the first useful H3C CF3 study and developed an acid-base affinity Geri, Szymczak, and application of borazine as a reagent in any H3C B– CH3 scale to help identify hexamethylborabranch of synthetic chemistry. Chemical N N zine as the optimal Lewis acid—an elecsupplier Sigma-Aldrich is planning to offer B N B F C CF 3 3 H3C CH3 tron-pair acceptor—to go with trifluohexamethylborazine and the CH3 N romethyl anion as the Lewis trifluoromethyl reagent soon, CF 3 Lewis acid-base base—an electron-pair donor. he notes. Various N N Cl reagent They carried out the study “This new approach repelectrophilic Room temperature, H reagents with the aim of deriving CF3– resents a significant advantage 10 minutes O2N CuCF3 over previously used nucleofrom fluoroform (CHF3), an (CH3)3SiCF3 philic CF3-transfer reagents,” industrial waste product and potent green- Michael M. Wade CF3 Wolfe report the abilihouse gas, while also allowing for simple adds G. K. Surya Prakash of – ty to use the new reagent to functionalize the University of Southern California, who CF3 transfer from the acid-base pair to a carbonyls and imines and carry out nucodeveloped TMSCF3. But he points out range of inorganic and organic electrophilcleophilic aromatic substitutions. They ic reagents (J. Am. Chem. Soc. 2017, DOI: a few limitations to watch for, such as the can also prepare commonly used metal 10.1021/jacs.7b05408). high mass of the fluorinating reagent and trifluoromethyl transfer reagents (Cu, Chemists have previously developed the ability to easily recycle toxic borazine, Zn, Pd, Ag, Au) and synthesize commonacid-base trifluoromethylating reagents, which could pose challenges in industry ly used nucleophilic (TMSCF3), radical including the widely used trifluorowhere TMSCF3 is already established. Demethyltrimethylsilane (TMSCF3). These (KSO2CF3), and electrophilic (iodonispite those caveats, Prakash says the work “clearly can be expected to have a broad reagents are a challenge to use, however, um-CF3) trifluoromethylation reagents impact.”—STEVE RITTER because CF3– is unstable and can decomstarting from fluoroform instead of
ASTROCHEMISTRY
Low-energy electrons may spark space chemistry Low-energy electrons—rather than high-energy X-rays, gamma rays, and ions— may actually do much of the heavy lifting when it comes to forming bonds and making compounds in outer space that could be precursors to complex organic molecules. Michael A. Huels, Léon Sanche, and their groups at the University of Sherbrooke bombarded methane and oxygen ices with low-energy electrons under conditions resembling interstellar space. They detected spectroscopic signatures of ethane and ethanol, as well as carbonyl and carboxylate func-
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C&EN | CEN.ACS.ORG | JANUARY 1, 2018
tional groups (J. Chem. Phys. 2017, DOI: 10.1063/1.5003898). “We have known that significant chemistry occurs from higher-energy sources,” says Stefanie N. Milam of the National Aeronautics & Space Administration, who was not involved in the work. “Demonstrating the formation of complex species from these low-energy electrons provides even further evidence of how readily chemistry is induced and occurs within surfaces both in and out of the solar system.” The researchers say this chemistry could happen on grains of ice and dust
in nebulae, on comets, or on icy bodies in our solar system. But Huels is careful to point out that the molecules they observed are still a far cry from the ingredients for life. “We’re not making a building block of life here,” he says. “We’re making organic molecules that are more complex than the two molecules we put in there.” The next step, according to Huels, is to make more complex ices. His group has now tested ice mixtures containing methane, oxygen, and ammonia.—SAM
LEMONICK
