NEWS OF THE WEEK
FORGING LIGANDS ORGANOMETALLICS: Custom hybrid chelating system could have many uses
two ligands that coordinate metals well on their own—a team of German chemists has created a new class of bifunctional ligands that can chelate metals while leaving an NH group available for further derivatization. These combined abilities of carboranylamidinates could prove useful for an array of applications, from catalysis to making polymer films. Carboranes are carbon-boron icosahedral cluster compounds that feature extensively in the synthesis of polymers, ceramics, catalysts, and radiopharmaceuticals. Amidinate ligands, RC(NRʹ)2–, are widely used to construct main-group, BIFUNCTIONAL The hybrid transition-metal, and f-element carboranylamidine readily forms a complexes, often as alternatives dimeric chromium complex, with to cyclopentadienyl ligands. They the NH groups available for further make possible a large degree of variaction (boron hydrogens and carbon ability through use of different subhydrogens not shown). stituents at carbon or nitrogen.
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Y COUPLING a carborane and an amidinate—
DON’T BLAME THE PILL WATER POLLUTION: Only a small fraction of the estrogen in waterways comes from oral contraceptives IRTH CONTROL PILLS often take the blame for estrogen pollution in rivers, lakes, and reservoirs. A new metastudy by researchers at the University of California, San Francisco, however, finds that oral contraceptives are not the source of most of the estrogens found in U.S. and European waterways (Environ. Sci. Technol., DOI: 10.1021/es1014482). Nearly 11 million women in the U.S. use oral contraceptives, according to the Guttmacher Institute, a nonprofit organization that researches sexual and reproductive issues. The synthetic estrogens and progestin in these pills flow into wastewater treatment systems via urine and feces. But estrogen-like chemicals also enter waterways from other sources, such as large-scale animal farms, landfills, and non-birth-control pharmaceuticals. To better understand the sources of estrogens in
B Residual estrogen in treated wastewater can disrupt the reproductive health of fish in rivers and streams.
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Peter Dröse, Cristian G. C Hrib, and Frank T. Edelmann CH of Otto von Guericke University, in Magdeburg, Germany, decided to see what would Carboranylamidine happen if the two ligands were joined (J. Am. Chem. Soc., DOI: 10.1021/ja108051u). The team treated C2B10H12 carborane with butyllithium followed by diisopropylcarbodiimide, a reaction that created an isolable lithium complex. Hydrolysis of this complex yielded the free carboranylamidine. A crystal structure of the lithium complex led to a surprise: The carborane’s unsubstituted CH is preferentially deprotonated over the amidinate’s NH, Edelmann notes. The result is bidentate C,N coordination of lithium by both the carborane and amidinate instead of the expected N,N coordination only by the amidinate. The NH remains uncoordinated and is available for further chemistry, Edelmann says. Initial experiments show that the carboranylamidinate coordinates chromium and tin to form monomeric or dimeric C,N complexes. “The simplicity of the one-pot synthesis is quite neat, and the unexpected outcome of the ligand’s reactivity is remarkable,” says M. Frederick Hawthorne of the University of Missouri, Columbia, a leading expert in carborane chemistry. Because the ligand binds chromium and tin, “it should bind many metals in the periodic table, leading to opportunities to make functional materials and catalysts,” he says.—STEVE RITTER
drinking water, UC San Francisco postdoctoral fellow Amber Wise and her colleagues reviewed 82 studies. Using the data they gathered, the researchers estimated that ethinylestradiol, the most commonly used synthetic estrogen in the birth control pill, likely accounts for less than 1% of the total estrogens excreted in the U.S. The researchers found evidence for other estrogen sources, such as hormone replacement therapy drugs, that could play an important role in contaminating surface waters. They also determined that runoff from large-scale animal farms could contribute to estrogen contamination of waterways, in part because, unlike household waste, livestock effluents are untreated. Estrogen in water has raised concerns because in laboratory and field tests, the synthetic estrogen found in birth control pills disrupts reproduction in several fish species. The hormone can trigger male fish to develop female reproductive organs and to produce eggs. And researchers have connected estrogens in drinking water to human fertility problems and cancers. Karen Kidd, a biologist at the University of New Brunswick, says that in addition to estrogens, chemicals that interfere with testosterone probably contribute to feminizing male fish in some rivers. “What happens in the fish will really depend on the total mixture that they are being exposed to,” she says.—SARA PEACH, special to C&EN
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