Science Concentrates INORGANIC CHEMISTRY
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Organoboron compounds offer a direct route for synthesizing nitrogen chains sor via standard methods and then reducDinitrogen tends to be a loner. Extreme ing it with a solution of KC8 in the presconditions, such as intense radiation in the ionosphere, are needed to coerce two ence of dinitrogen at roughly 4 bar (four or more N2 molecules to form chains. times atmospheric pressure) and –30 °C. The group determined the product’s strucVarious pharmaceuticals and explosives ture using X-ray diffraction and various made by humans contain three- and spectroscopy methods. By teaming up with four-atom nitrogen chains. To make these theoreticians at Goethe University Frankcompounds, chemists have to use an infurt, the chemists studied the molecule’s direct route. They first split dinitrogen unusual bonding. They found that the through a high-temperature borylene moieties bind dinitrogen and high-pressure industrial similar to how process to produce ammotransition metals nia and amines. Then they do—by forming stitch together those N1 end-on N2-bridgcompounds into the nitrogen chains. ing complexes— A new study yet the boron describes a direct compound’s reacand gentle way tivity is like that to make comof main-group pounds with elements. nitrogen chains Légaré says the group is using dinitrogen. now working to incorporate Marc-André the nitrogen chains into Légaré and organic molecules for use in An N4 chain sits Holger Braunsynthesizing pharmaceutical compounds. sandwiched between schweig of “The beauty of this study is the simtwo borylene Julius-Maximilplicity of the transformation, in which one moieties. C = gray. ians University N = blue. B = green. reduced boron species can lead to spontaWürzburg and neous coupling of N2 under fairly mild concoworkers report that an organoboron ditions,” says Frédéric-Georges Fontaine, a compound can stitch together two N2 catalysis specialist at Laval University. Fontaine remarks that chemists might molecules under near-ambient conditions expect such a transformation to be medito form a complex in which an N4 chain ated by a transition metal complex or alkabridges two boron moieties (Science 2019, line earth species, but this one is done by a DOI: 10.1126/science.aav9593). fairly simple boron molecule. He describes The study follows work published last the work as an important step in the trend year by the Würzburg group in which to develop metal-free they succeeded in binding transformations. This trend a single dinitrogen molehas shown that main group cule between organoboron elements, used under the ligands. This general area right set of conditions, can of research, known as ni2 replace conventional cattrogen fixation, seeks ways alysts, which can be costly to use highly abundant and challenging to prepare. atmospheric nitrogen in “The prospect of eventually chemical synthesis. including N2 as a reagent in The team made the new nitrogen-chain complex —Frédéric-Georges metal-free catalysis is really by first synthesizing a diFontaine, a catalysis exciting,” he adds.—MITCH haloorganoborane precurspecialist at Laval University JACOBY
“The prospect of eventually including N as a reagent in metalfree catalysis is really exciting.”
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C&EN | CEN.ACS.ORG | MARCH 25, 2019
ASTROCHEMISTRY
Asteroid Ryugu is dark and dry Spectroscopic analysis by the Japanese spacecraft Hayabusa2 reveals that the asteroid 162173 Ryugu is unusually dark in color and has little water, though there’s evidence that its rocks were once wet (Science 2019, DOI: 10.1126/science.aav7432). These were the first observations of Ryugu in the 1.8–3.2 µm range, where OH stretching and H2O bending modes are visible. Diamond-shaped and a kilometer across, Ryugu orbits the sun mostly between Earth and Mars and is thought to contain materials left from the early solar system. Hayabusa2 measurements show that it is quite dark, reflecting less than 2% of light at 2.0 µm. The new results confirm that, as was previously suggested, the asteroid is rich with carbonaceous minerals. According to the researchers, a weak but consistent 2.72 µm signal points to a homogeneous composition that includes magnesium minerals thought to derive from hydrated clays. But the group saw no evidence of water ice or water-containing minerals. Study coauthor Ralph E. Milliken of Brown University said in a press conference that the group hasn’t matched Ryugu with any other space objects quite like it. The asteroid is most similar to previously studied celestial bodies that were once wet and then were heated to the point that the water was lost. Ryugu may have formed from the debris of a collision, which could have darkened, dehydrated, and dehydroxylated the rocks. But these results apply only to Ryugu’s surface, and Milliken said other Hayabusa2 experiments that will excavate and capture subsurface rocks could reveal something new.—SAM LEMONICK
C R E D I T: MA RC -A N D R É LÉGA R É /J UL IU S - MAX I MI LI A N S UN IV E RS I T Y W ÜRZB URG (B O RY L E N E ); JAXA (H AYA B U SA 2 )
Boron helps to gently couple dinitrogen
