NEWS OF THE WEEK
BORON-OXYGEN TRIPLE PLAY MULTIPLE BONDING: First isolable
compound with a B≡O bond, thanks to platinum coordination
B
Y USING PLATINUM as a stabilizing influence, a
team of inorganic chemists led by Holger Braunschweig of Germany’s University of Würzburg has created just the right set of electronic conditions to achieve one of chemistry’s few remaining bonding feats: creating an isolable compound with a boron-oxygen triple bond (Science 2010, 328, 345). Besides being the first metal complex with a boron monoxide ligand, the platinum oxoboryl comP plex and others like it could be useful as S Pt B O chemical building blocks or in catalysis. Boron is known for its electron defiP ciency and its propensity to compensate by participating in multicentered bonds that let it draw electron density from neighboring atoms. But chemists have rarely enticed boron to participate in Oxoboryl thiophenyl complex double or triple bonds.
TARGETING TRICLOSAN
SHUTTERSTOCK
CHEMICALS: Regulators question safety, effectiveness of antibacterial ingredient
F
EPA and FDA plan to take another look at the safety of triclosan in products such as liquid soap.
EDERAL REGULATORS are worried about the
potential for antibiotic resistance and endocrine disruption from human exposure to triclosan, an antibacterial ingredient found in numerous consumer products, including soaps, body washes, cutting boards, and toys. “Existing data raise valid concerns about the effects of repetitive daily human exposure” to triclosan, the Food & Drug Administration wrote in a letter to Rep. Edward J. Markey (D-Mass.), which he released on April 8. The agency was responding to a January inquiry from Markey, who sent letters to both FDA, which regulates the chemical in soaps and hand washes, and the Environmental Protection Agency, which regulates it in other products. Markey believes that antibacterial consumer products are ineffective and unsafe for human health and the environment. EPA reassessed the safety of triclosan in 2008 and WWW.CEN-ONLINE.ORG
8
Lai-Sheng Wang of Brown University and coworkers previously found that fleeting gas-phase species such as Au2B≡O− have a B≡O bond that is as strong as the triple bonds in electronically equivalent CN− and CO complexes. “We wondered why no metal complexes with oxoboryl ligands had been synthesized when CN− and CO are ubiquitous ligands in inorganic chemistry,” Wang says. Braunschweig’s team shows that “the trick appears to be stabilization of B≡O through significant platinum-boron covalent bonding,” he says. Braunschweig’s group previously showed how a metal center can be used to stabilize the B≡N bond in iminoboryl complexes. Building on that work, Braunschweig, Krzysztof Radacki, and Achim Schneider made the B≡O complex by treating Pt(PR3)2, where R is cyclohexyl, with Br2BOSi(CH3)3 in toluene at room temperature. The resulting intermediate eliminates BrSi(CH3)3, leaving behind B≡O as a novel ligand in (PR3)2BrPtB≡O. The complex is unusually stable to heat and light, and even when the team treated it with ammonium thiophenylate, the thiophenyl group bypassed the B≡O ligand and opted to exchange with the bromine ligand, forming an oxoboryl thiophenyl complex. Armin Berndt of Philipps University, in Marburg, Germany, an expert on multiple bonding and aromaticity in boron compounds, says achieving the B≡O bond is like a “Sahnehäubchen”—getting whipped cream “on top of a masterful series of studies on the stabilization of unusual boron species by metal complexation.”—STEVE RITTER
concluded that “human exposure resulting from the use of triclosan in cutting boards, kitchen utensils, toys, and other products did not pose unacceptable risks to human health, including risks to infants and children.” But since then, work by EPA researchers has shown that triclosan has potential estrogenic effects in rats. “EPA plans to reexamine the potential risks to human health in light of the new and planned research on the effects of triclosan on the endocrine system,” the agency wrote in its letter to Markey, which he also released on April 8. FDA is in the midst of rule-making and is considering a petition from environmental groups related to the use of triclosan, according to its letter. It is also working closely with EPA’s Endocrine Disruptor Screening Program to assess the endocrine effects of triclosan, the letter said. In response to FDA’s letter, Markey is now calling on regulators to ban triclosan in consumer soaps and hand washes, as well as other products that contact food or are intended for children. And on April 13, he sent letters to 13 manufacturers, urging them to voluntarily stop using triclosan in their products. The Soap & Detergent Association, an industry trade group, continues to emphasize the benefits of antibacterial soaps. In a statement responding to FDA’s concerns, the group claims that soaps containing triclosan are safe and more effective at reducing the risk of bacterial infection than nonantibacterial soaps.—BRITT ERICKSON
AP RI L 1 9, 20 10
