F3C I
O
RF
Te
X R1 R2
Togni’s reagent
Togni’s tellurium analogs RF = CF3, CF2H, C6F5 X = O or N donor R1, R2 = various groups
bor tellurium (Organometallics 2017, DOI: 10.1021/acs.organomet.7b00535). Hypervalent compounds are those that contain a group 13 to 18 element bearing more than eight valence electrons. Because iodine(III) with 10 valence electrons fits that bill, Togni and Pietrasiak thought tellurium(II) compounds with a similar electronic structure might work as fluorinating reagents as well. The researchers made a series of fluorinated tellurium(II) compounds (shown), including ones with CF2H and C6F5 groups that aren’t known for the iodine reagents, and studied their hypervalent nature via structural and spectroscopic data. The team is now testing the tellurium derivatives for their ability to function as perfluoroalkyl transfer reagents.—STEVE RITTER
CATALYSIS
C R E D I T: PAU LO Z A RAGOZ A
▸ Tuning singleatom catalysts with ionic liquids Isolated metal atoms dispersed on the surface of a support material offer unique opportunities in heterogeneous catalysis. For example, this class of single-site catalysts uses precious metals with maximum efficiency. In addition, because of their relative simplicity compared with standard multiatom nanoparticle catalysts, single-atom supported catalysts allow researchers to deduce valuable mechanistic details far more easily. But the single-atom variety is tough to tailor. And although modifying catalyst synthesis methods sometimes improves performance, it’s not always clear why. A team led by Alper Uzun of Koç University and Bruce C. Gates of the University of California, Davis, reports that treating single-atom iridium complexes supported on γ-alumina with 1,3-dialkylimidazolium ionic liquids improves the complexes’ catalytic properties for reasons the team quantifies via high-resolution X-ray absorption spectroscopy (ACS Catal. 2017, DOI: 10.1021/acscatal.7b02429). Specifically, the team prepared atomically dispersed
INFECTIOUS DISEASE
Mutation in Zika virus protein linked to microcephaly Even though Zika virus was first identified in 1947, the infectious disease remained obscure until a 2015 outbreak in Central and South America. That’s when doctors noted a dramatic rise in infants with underdeveloped heads and brains (a condition known as microcephaly) born to women who were infected with the virus when pregnant. Now, researchers have found that mutation of a single amino acid in one of the Zika virus’s structural proteins, known as prM, may be responsible for causing microcephaly by enabling the virus to kill developing brain cells (Science 2017, DOI: 10.1126/science.aam7120). A team led by Cheng-Feng Qin of the Beijing Institute of Microbiology & Epidemiology and Zhiheng Xu of the Chinese Academy of Sciences compared three recent strains of Zika virus with one from 2010 and found the more recent versions to be deleterious or deadly to neonatal and fetal mice, whereas the 2010 virus was not. Biochemical sleuthing led them to discover that a serine residue in prM of the 2010 virus had mutated to an asparagine in the more recent strains. When the researchers made this single mutation to a virus that was otherwise identical to the 2010 strain, it was dramatically more deadly to neonatal mice than the unmutated version. When the researchers modified this asparagine to a serine in a 2016 version of the virus, it proved to be less deadly.—BETHANY HALFORD
then rebounds—the hydroxyl group moves onto the carbon radical and the metal is reduced by one electron. Although plenty of circumstantial evidence suggests this is what happens, observing the rebound step in this reaction has been impossible because it is fast compared with the hydrogen atom removal step. Now, chemists led by David P. Goldberg of Johns Hopkins University have created the first model system in which the rebound reaction can be observed (J. Am. Chem. Soc. 2017, DOI: 10.1021/jacs.7b07979). The system features Fe–OH ensconced in a tris(triphenyl) phenyl corrole ligand, which stabilizes the high redox level of the Fe complex and has sufficient steric bulk to prevent dimerization—a problem that often plagues FeOH systems. “In our case, the rebound reaction is best described as a concerted process as opposed to a stepwise process,” Goldberg says. Such mechanistic insight, he adds, could be used to engineer an enzyme or synthetic catalyst This model system to facilitate or inhibit the makes it possible to rebound step and thereby observe the radical influence the efficiency rebound reaction and selectivity of the hy(C is gray, H is white, droxylation.—BETHANY N is blue, O is red,
Ir(CO)2 complexes on alumina, coated them with various ionic liquids, and used them to catalyze partial hydrogenation of 1,3-butadiene, an important industrial process. The team found that the ionic liquids significantly increased selectivity for butenes—in some cases, from roughly 50% to 80%. They attribute the enhancement to electron donation from the ionic liquid to iridium, a process they examined in detail spectroscopically.—MITCH JACOBY
REACTION MECHANISMS
▸ Radical reaction caught on the rebound For more than 40 years, chemists and biologists have used the radical rebound mechanism to describe what happens when enzymes with transition metals, such as cytochrome P450, hydroxylate C–H bonds. Such enzymes first remove a hydrogen atom from a C–H bond using a high-valent metal-oxo species. This produces a carbon radical and a metal-OH intermediate that
Fe is orange).
HALFORD OCTOBER 2, 2017 | CEN.ACS.ORG | C&EN
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