Journal of the American Chemical Society
COMMUNICATION
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nance at 4.04 ppm was established in an 1HÀ N HSQC
15
experiment. The 29Si NMR spectrum of the 15N isotopologue
5-15N contained a triplet centered at À10.62 ppm (1JSiÀN
=
9.0 Hz).
The assembly of coordinated formamide from N2, silane, and
CO prompted us to explore its release from the dihafnium core.
Addition of Brønsted acids such as gaseous HCl to a benzene-d6
solution of 4 resulted in liberation of free formamide, NH4Cl,
and the hafnocene dichloride (η5-C5H2-1,2,4-Me3)2HfCl2. The
NH4Cl product likely arose from initial formation of silylamine,
which was then cleaved and protonated under the acidic condi-
tions to yield ammonium chloride.
In summary, silylation of a hafnocene complex with a strongly
activated, side-on bound dinitrogen ligand has been achieved,
opening a pathway for subsequent N2 functionalization and
cleavage chemistry. Cleavage of the NÀN bond was accom-
plished by thermal silyl migration or carbonylation under ambient
conditions. The latter reaction allowed the synthesis of an
organic nitrogen compound, formamide, from N2, CO, an
organosilane, and protons. The new chemistry observed herein
likely derives from the accessibility of side-on or end-on, side-
on intermediates resulting from a less hindered hafnocene
derivative.
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’ ASSOCIATED CONTENT
(18) Hirotsu, M.; Fontaine, P. P.; Zavalij, P. Y.; Sita, L. R. J. Am.
Chem. Soc. 2007, 129, 12960.
(19) Nikiforov, G. B.; Vidyaratne, I.; Gambarotta, S.; Korobkov, I.
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(20) Bernskoetter, W. H.; Olmos, A. V.; Lobkovsky, E.; Chirik, P. J.
Organometallics 2006, 25, 1021.
S
Supporting Information. Complete experimental details,
b
representative NMR spectra, and crystallographic data (CIF) for
[(η5-C5H2-1,2,4-Me3)2Hf]2(μ2,η2,η2-N2), 2, 3, and 4. This material
(21) (a) Chirik, P. J. Dalton Trans. 2007, 16. (b) Pool, J. A.; Chirik,
P. J. Can. J. Chem. 2005, 83, 286.
’ AUTHOR INFORMATION
Corresponding Author
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’ ACKNOWLEDGMENT
We thank the Director, Office of Basic Energy Sciences,
Chemical Sciences Division, of the U.S. Department of Energy
(DE-FG02-05ER15659) for financial support. S.P.S. thanks the
Natural Sciences and Engineering Research Council of Canada
for a predoctoral fellowship (PGS-D). We also thank Dr. Ivan
Keresztes (Cornell University NMR Facility) for assistance with
spectral acquisition and assignment and Professor Seth Brown
(Notre Dame) for helpful discussions.
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