Journal of the American Chemical Society
Communication
Sc3+ to the [CuNTs]+ core, which may help reduce the strong
electron repulsion between the electron-rich nitrene and copper
centers, presumably by lowering the electron density at the
nitrene nitrogen. In other words, the binding of Sc3+ may help to
lessen the H-atom abstraction ability of 3, thereby preventing its
spontaneous decay to the copper(II)−amide species 2 (Scheme
1). Consistent with the above explanation, the use of weaker
Lewis acids such as Y3+, Zn2+, and Ca2+ instead of Sc3+ resulted in
a significantly lower yield of the copper−nitrene intermediate
and increased formation of 2.12 Sufficient stability of 3-Sc at
−90 °C enabled its characterization using a variety of
spectroscopic methods, which helped to establish its electronic
structure as CuII−N•(Sc)Ts with a copper-bound nitrene radical.
Additionally, the vibrational modes of the CuII−N•(Sc)Ts core
have been established through rR and DFT studies, which should
help in their elucidation under catalytic turnover conditions.
Finally, the present report of the stabilization of the CuII−N•Ts
core may validate the existence of the elusive isoelectronic CuIII−
O/CuII−O• units, which have been proposed as reactive
intermediates in a number of chemical and biological oxidation
reactions.21 In particular, the ability of 3-Sc to attack the strong
C−H bonds of cyclohexane is extraordinary in the context of the
known oxidizing capabilities of copper−dioxygen species.22 With
the assumption that the reactivity of the CuII−N•Ts core can be
extended to the CuIII−O/CuII−O• core, the present study
therefore suggests the possible involvement of CuIII−O/CuII−
O• active species in the catalytic cycle of mononuclear copper
monooxygenases.
(b) Fructos, M. R.; Trofimenko, S.; Diaz-Requejo, M. M.; Perez, P. J. J.
Am. Chem. Soc. 2006, 128, 11784.
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Templeton, J. L. Organometallics 1997, 16, 4399.
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X. P.; de Bruin, B. J. Am. Chem. Soc. 2011, 133, 12264. (c) Waterman, R.;
Hillhouse, G. L. J. Am. Chem. Soc. 2008, 130, 12628.
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G.; Cundari, T. R. J. Chem. Theory Comput. 2009, 5, 2959. (d) Cundari,
T. R.; Dinescu, A.; Kazi, A. B. Inorg. Chem. 2008, 47, 10067.
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K. R.; Kaderli, S.; Zuberbuhler, A. D.; Rheingold, A. L.; Solomon, E. I.;
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Chem. Soc. 1999, 121, 7164.
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Garcia-Granda, S.; Bernardo, J. M. M. J. Inorg. Biochem. 2004, 98, 189.
(b) Macias, B.; Villa, M. V.; Gomez, B.; Borras, J.; Alzuet, G.; Gonzalez-
Alvarez, M.; Castineiras, A. J. Inorg. Biochem. 2007, 101, 444.
(10) Que, L. Jr. Physical Methods in Bioinorganic Chemistry: Spectroscopy
and Magnetism; University Science Books: Sausalito, CA, 2000.
(11) Pfaff, F. F.; Kundu, S.; Risch, M.; Pandian, S.; Heims, F.;
Pryjomska-Ray, I.; Haack, P.; Metzinger, R.; Bill, E.; Dau, H.; Comba, P.;
Ray, K. Angew. Chem., Int. Ed. 2011, 50, 1711.
(12) Other metal ions could also be used to generate the formal CuIII
purple intermediate; however, the yields (Figure S12 and Table S6)
decreased in the order Sc3+ (90%) > Y3+ (54%) > Zn2+ (28%) > Ca2+
(0%), which follows the order of decreasing Lewis acidity of the metal
ions. See: Fukuzumi, S.; Ohkubo, K. J. Am. Chem. Soc. 2002, 124, 10270.
(13) Donoghue, P. J.; Tehranchi, J.; Cramer, C. J.; Sarangi, R.;
Solomon, E. I.; Tolman, W. B. J. Am. Chem. Soc. 2011, 133, 17602.
(14) King, A. E.; Huffman, L. M.; Casitas, A.; Costas, M.; Ribas, X.;
Stahl, S. S. J. Am. Chem. Soc. 2010, 132, 12068.
ASSOCIATED CONTENT
* Supporting Information
■
S
Additional syntheses and characterization data (UV−vis, EPR,
NMR), kinetic data, experimental X-ray diffraction parameters
and crystal data, computational data, and a figure and an
animation showing the vibrational modes arising from the Cu−
NTs core. This material is available free of charge via the Internet
(15) The formation of CuI was inferred from EPR studies (it was EPR-
silent) and UV−vis studies (no CuII d−d bands were observed).
(16) Fukuzumi, S.; Morimoto, Y.; Kotani, H.; Naumov, P.; Lee, Y.-M.;
Nam, W. Nat. Chem. 2010, 2, 756.
(17) Kau, L. S.; Spira-Solomon, D. J.; Penner-Hahn, J. E.; Hodgson, K.
O.; Solomon, E. I. J. Am. Chem. Soc. 1987, 109, 6433.
AUTHOR INFORMATION
Corresponding Author
■
(18) DuBois, J. L.; Mukherjee, P.; Stack, T. D. P.; Hedman, B.;
Solomon, E. I.; Hodgson, K. O. J. Am. Chem. Soc. 2000, 122, 5775.
Notes
The authors declare no competing financial interest.
(19) Lu, C. C.; George, S. D.; Weyhermuller, T.; Bill, E.; Bothe, E.;
̈
Wieghardt, K. Angew. Chem., Int. Ed. 2008, 47, 6384.
ACKNOWLEDGMENTS
(20) Luo, Y.-R. Comprehensive Handbook of Chemical Bond Energies;
CRC Press: Boca Raton, FL, 2007.
■
We gratefully acknowledge financial support of this work from
the Cluster of Excellence “Unifying Concepts in Catalysis” (EXC
314/1), Berlin. XAS data were obtained on Beamline X3B of the
National Synchrotron Light Source (NSLS, Brookhaven Na-
tional Laboratory, Upton, NY). Beamline X3B is operated by the
Case Western Reserve University Center for Synchrotron
Biosciences, supported by NIH Grant P30-EB-009998. NSLS
is supported by the U.S. Department of Energy, Office of Science,
Office of Basic Energy Sciences, under Contract DE-AC02-
98CH10886. We also thank Dr. E. Bill, Prof. F. Neese, and Prof.
(21) (a) Yoshizawa, K.; Kihara, N.; Kamachi, T.; Shiota, Y. Inorg. Chem.
2006, 45, 3034. (b) Crespo, A.; Marti, M. A.; Roitberg, A. E.; Amzel, L.
M.; Estrin, D. A. J. Am. Chem. Soc. 2006, 128, 12817. (c) Hong, S.;
Huber, S. M.; Gagliardi, L.; Cramer, C. C.; Tolman, W. B. J. Am. Chem.
Soc. 2007, 129, 14190.
(22) (a) Lewis, E. A.; Tolman, W. B. Chem. Rev. 2004, 104, 1047.
(b) Himes, R. A.; Karlin, K. D. Curr. Opin. Chem. Biol. 2009, 13, 119.
R. Stoßer for access to the EPR instruments and Prof. C. Limberg
̈
for access to the GC−MS instrument.
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