NEWS OF THE WEEK
SYNTHESIS: Hafnium complex enables
reaction with carbon monoxide
(CH3)2Si
(CH3)2Si
Hf
N N
Hf
Si(CH3)2
C
ORNELL UNIVERSITY chemists
have devised a new method to cleave and functionalize dinitrogen CO at room temperature and pressure. N2 is cheap and abundant. But it’s tough to use as a reactant because it is virtually inert, due O C N largely to its very strong triple bond and Hf Hf Si(CH3)2 nonpolarity, Cornell’s Paul J. Chirik N C O notes. Instead, most nitrogen compounds are derived from ammonia produced via the Haber-Bosch process, which uses N2 as a Excess HCl feedstock and requires energy-intensive conditions of high temperature and pressure. Chirik and Donald J. Knobloch avoided these probO O lems by forming a complex between nitrogen and a C C hafnium reagent with an ansa-bis(cyclopentadienyl) H2N NH2 ligand. Formation of the complex lengthens and weakens the N2 bond enough that it can be cleaved under Oxamide mild conditions when carbon monoxide, another abun-
STRADIVARI’S SECRET
F
OR DECADES, scientists scrutinizing violins
made by the famous instrument maker Antonio Stradivari have proposed that the instruments’ extraordinary sound may have come from special chemicals used in the varnish or as a base layer. But now a five-year study on five Stradivari violins at the Museum of Music in Paris—the largest Stradivari study to date—finds that the varnish used by the instrument maker was composed of widely available mundane oils, pigments, and resins. The work challenges established ideas that Stradivari violin varnishes held unusual music-making additives and reopens the mystery of how exactly the Stradivari instruments achieve such a superior sound. A 12-person team led by Jean-Philippe Echard, a conservation chemist at the J.-P. ECHARD ©CITÉ DE LA MUSI QUE
The linseed oil varnish on Stradivarius violins seeps into the top layer of the instruments’ wood cells, as seen by optical microscopy.
CONSERVATION CHEMISTRY: Famous violins had mundane varnish, reviving the mystery of why they sound so good
WWW.CEN-ONLINE.ORG
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dant feedstock, is added. At the same time, the reaction creates new nitrogen-carbon and carbon-carbon bonds. Subsequently adding an acid produces the fertilizer oxamide, “which demonstrates that an important agrochemical can be synthesized directly from N2 and CO,” the researchers write (Nat. Chem., DOI: 10.1038. nchem.477). “This work represents a whole new kind of reactivity for coordinated dinitrogen,” comments University of British Columbia chemist Michael D. Fryzuk, who also studies coordination complexes for activating N2. “Not only are N–C bonds being formed, but the cleavage of the N–N bond by addition of carbon monoxide is really exciting. Anytime someone finds a new chemical transformation for dinitrogen, we get closer to solving one of chemistry’s long-standing grand challenges, that of utilization of N2 as a feedstock for producing organonitrogen compounds.” In addition to fertilizers, such compounds are used in products ranging from pharmaceuticals to nylon. Chirik previously used a similar hafnium reagent to react N2 with CO2 to form a substituted hydrazine (C&EN, Jan. 15, 2007, page 45) and a zirconium complex to cleave and hydrogenate N2 to form ammonia. Chirik is now evaluating alternative metal and ligand combinations to determine whether the latest reaction can be extended to the synthesis of more elaborate organic molecules.—SOPHIE ROVNER
Museum of Music, used a combination of micro-Raman, micro-Fourier transform infrared, and X-ray spectroscopies to tease out the microchemical composition of five violins that span 30 years of Stradivari’s career in the late 1600s and early 1700s (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200905131). The team found that Stradivari laid down a layer of linseed oil, similar to that used by artists of the time, to seal the wood, followed by an oil resin that contained red iron oxide and other common crimson pigments, also used by artists of that era. Joseph Nagyvary, a professor emeritus at Texas A&M University who has studied Stradivari violins, calls the new report “startling” because it disagrees with well-established research from the 1970s, which concluded that “all Stradivari violins have a solid mineral ground layer.” If the varnish is really just linseed oil, as the new research suggests, then Nagyvary wonders how the violins achieved their exceptional sound. “If Echard is right, the minimum one can say is that the varnish is not important, and the secret was in the wood,” Nagyvary adds.—
DECEMBER 14, 2009
SARAH EVERTS
A. GI ORDAN © CITÉ DE LA MUSI QUE
N2 CLEAVED, FUNCTIONALIZED
