C O M M U N I C A T I O N S
of the reaction. The final spectrum was hardly affected by changing
the solvent to CH2Cl2 or propionitrile (Figures S7 and S8),
indicating that no solvent coordination to the metal ion took place.
Moreover, similar spectral changes were obtained in the reactions
and DꢀM. Further studies on the reaction mechanism of the aliphatic
hydroxylation process are in progress.
Acknowledgment. This work was financially supported in part
by Grants-in-Aid for Scientific Research on Priority Area (19020058,
20036044, and 20037057 for S.I.) and the Global Center of
Excellence (GCOE) Program (“Picobiology: Life Science at Atomic
Level” to T.O.) from MEXT, Japan, and by a Grant-in-Aid for
Scientific Research (20350082 to S.I.) from JSPS, Japan. The
authors also thank Asahi Glass Foundation for financial support
and JSPS for a Research Fellowship (to A.K.).
of O2 with 1OCH and 1 (Figures S9 and S10). The final spectrum
in Figure 2A is rather similar to those of copper(II) end-on (η1)
superoxo complexes reported to date17 but is significantly different
from that of the reported copper(II) side-on (η2) superoxo com-
plex.12 The dark-green species generated using 16O2 showed isotope-
sensitive resonance Raman bands at 1033 and 457 cm-1 when
excited with 406.7 nm laser light. These bands shifted to 968 and
442 cm-1, respectively, when 18O2 was used instead of 16O2 (Figure
S11). The peak positions and associated isotope shifts are similar
to those of the reported Cu(II)-superoxo complexes and can be
assignedtotheO-OandCu-Ostretchingvibrations,respectively.16,22
The same Raman bands were obtained in other solvent systems
(Figures S12 and S13), also confirming the absence of solvent
coordination to the metal center. All of these UV-vis and resonance
Raman results indicate that the generated dark-green species are
the four-coordinate mononuclear copper(II) end-on superoxo com-
plexes 2X-OO•. In support of this, the O2/copper ion stoichiometry
was found to be 1:1 by manometry in a preparative-scale reaction.23
Although the detailed geometries of 2X-OO• are not clear at
present, they may have distorted tetrahedral geometries analogous
NO2
3
Supporting Information Available: Experimental details for the
synthetic procedures, results of structure determinations (CIF), and
additional spectroscopic and kinetic data. This material is available free
References
(1) Itoh, S. Curr. Opin. Chem. Biol. 2006, 10, 115–122.
(2) Mirica, L. M.; Ottenwaelder, X.; Stack, T. D. P. Chem. ReV. 2004, 104,
1013–1046.
(3) Lewis, E. A.; Tolman, W. B. Chem. ReV. 2004, 104, 1047–1076.
(4) Rolff, M.; Tuczek, F. Angew. Chem., Int. Ed. 2008, 47, 2344–2347.
(5) Klinman, J. P. Chem. ReV. 1996, 96, 2541–2561.
(6) Francisco, W. A.; Wille, G.; Smith, A. J.; Merkler, D. J.; Klinman, J. P.
J. Am. Chem. Soc. 2004, 126, 13168–13169.
(7) Chen, P.; Solomon, E. I. J. Am. Chem. Soc. 2004, 126, 4991–5000.
(8) Yoshizawa, K.; Kihara, N.; Kamachi, T.; Shiota, Y. Inorg. Chem. 2006,
45, 3034–3041.
NO2
to those of 2NO -Cl and 2 -OAc (see Figure 1B).
2
The fine-structure ESR spectrum of 2H-OO• (Figure 2B) in an
acetone-CH3CN glass at 3 K was acquired in the parallel
microwave-excitation mode, in which weak ESR-forbidden transi-
tions in the conventional perpendicular mode become allowed,
giving evidence for the triplet state in a straightforward manner.
As Figure 2B clearly shows, the half-field absorption signal with a
salient feature of g anisotropy was observed, illustrating that
2H-OO• is a spin triplet in the ground state.24 From the observed
fine-structure spectrum, the principal g values and zero-field splitting
parameter were estimated to be (g1, g2, g3) ) (2.125, 2.033, 2.015)
and |D′| g 13.7 mT, respectively. The estimated distance between
the two unpaired electron spins was ∼2.73 Å, assuming a localized
model for the triplet state. The spin-spin distance is nearly identical
to the distance between the copper and the distal oxygen atom of
the end-on superoxide ligand in the enzyme active site (2.78 Å,
Figure 1A).11 Such a good agreement between the estimated
spin-spin distance and the Cu-Odistal distance in the enzymatic
(9) Gherman, B. F.; Heppenr, D. E.; Tolman, W. B.; Cramer, C. J. J. Biol.
Inorg. Chem. 2006, 11, 197–205.
(10) Crespo, A.; Marti, M. A.; Roitberg, A. E.; Amzel, L. M.; Estrin, D. A.
J. Am. Chem. Soc. 2006, 128, 12817–12828.
(11) Prigge, S. T.; Eipper, B. A.; Mains, R. E.; Amzel, L. M. Science 2004,
394, 836–837.
(12) (a) Fujisawa, K.; Tanaka, M.; Moro-oka, Y.; Kitajima, N. J. Am. Chem.
Soc. 1994, 116, 12079–12080. (b) Chen, P.; Root, D. E.; Campochiano,
C.; Fujisawa, K.; Solomon, E. I. J. Am. Chem. Soc. 2003, 125, 466–474.
(13) (a) Cramer, C. J.; Tolman, W. B. Acc. Chem. Res. 2007, 40, 601–608. (c)
Hong, S.; Huber, S. M.; Gagliardi, L.; Cramer, C. C.; Tolman, W. B. J. Am.
Chem. Soc. 2007, 129, 14190–14192.
(14) (a) Fujii, T.; Yamaguchi, S.; Funahashi, Y.; Ozawa, T.; Tosha, T.; Kitagawa,
T.; Masuda, H. Chem. Commun. 2006, 4428–4430. (b) Fujii, T.; Yamaguchi,
S.; Hirota, S.; Masuda, H. Dalton Trans. 2008, 164–170.
(15) (a) Izzet, G.; Zeitouny, J.; Akdas-Killig, H.; Frapart, Y.; Me´nage, S.;
Douziech, B.; Jabin, I.; Le Mest, Y.; Reinaud, O. J. Am. Chem. Soc. 2008,
130, 9514–9523. (b) Lande, A.; Parisel, O.; Gerard, H.; Moliner, V.;
Reinaud, O. Chem.s Eur. J. 2008, 14, 6465–6473.
(16) Wu¨rtele, C.; Gaoutchenova, E.; Harms, K.; Holthausen, M.; Sundermeyer,
J.; Schindler, S. Angew. Chem., Int. Ed. 2006, 45, 3867–3869.
(17) (a) Maiti, D.; Fry, H. C.; Woertink, J. S.; Vance, M. A.; Solomon, E. I.;
Karlin, K. D. J. Am. Chem. Soc. 2007, 129, 264–265. (b) Maiti, D.; Lee,
D.; Gaoutchenova, K.; Wu¨rtele, C.; Holthausen, M. C.; Sarjeant, A. A. N.;
Sundermeyer, J.; Schindler, S.; Karlin, K. D. Angew. Chem., Int. Ed. 2008,
47, 82–85. (c) Maiti, D.; Lee, D.; Sarjeant, A. A. N.; Pau, M. Y. M.;
Gaoutchenova, K.; Sundermeyer, J.; Karlin, K. D. J. Am. Chem. Soc. 2008,
130, 6700–6701.
(18) Jazdzewski, B. A.; Reynolds, A. M.; Holland, P. L.; Young, V. G., Jr.;
Kaderli, S.; Zuberbu¨hler, A. D.; Tolman, W. B. J. Biol. Inorg. Chem. 2003,
8, 381–393.
(19) Komiyama, K.; Furutachi, H.; Nagatomo, S.; Hashimoto, A.; Hayashi, H.;
Fujinami, S.; Suzuki, M.; Kitagawa, T. Bull. Chem. Soc. Jpn. 2004, 77,
59–72.
(20) Lanci, M. P.; Smirnov, V. V.; Cramer, C. J.; Gauchenova, E. V.;
Sundermeyer, J.; Roth, J. P. J. Am. Chem. Soc. 2007, 129, 14697–14709.
(21) Reinaud and co-workers15 observed a ligand hydroxylation reaction in the
oxygenation of a mononuclear copper(I) complex supported by the
calix[6]arene-tren ligand. They suggested that the active oxygen species
was a mononuclear copper(II)-superoxo intermediate, but direct detection
of such an intermediate was unsuccessful.
•-
system further supports the end-on binding mode of O2 in our
model system. A complete fine-structure ESR spectral simulation
and sophisticated quantum-chemical calculations for all of the
magnetic tensors, to interpret the experimentally derived parameters,
are underway.
Notably, 2X-OO• gradually decomposed even at low tempera-
tures, obeying first-order kinetics (kOMe ) 7.8 × 10-4 s-1, kH
)
2.5 × 10-4 s-1, and kNO ) 1.3 × 10-4 s-1); the kinetic isotope
2
effect kHH/kH was found to be 4.1 at -60 °C using LH-d4 with a
D
perdeuterated phenethyl sidearm. 1H NMR analysis of the modified
ligand obtained by the ordinary workup treatment of the reaction
mixture using NH4OH demonstrated that the phenethyl sidearm was
∼30% hydroxylated based on the starting material. Furthermore,
an isotope-labeling experiment using 18O2 confirmed that the origin
of the oxygen atom incorporated into the product was molecular
oxygen. In summary, this study presents mononuclear copper(II)-
superoxo complexes 2X-OO• having triplet (S ) 1) ground states
that mimic both the structure (tetrahedral geometry with an end-
on-bound O2•-) and reactivity (aliphatic hydroxylation) of PHM
(22) The spectrum taken with a mixed-isotope gas containing a 1:2:1 stoichio-
metric mixture of 16O2/16O18O/18O2 matches well the addition spectrum taken
with 16O2 and 18O2 (Figure S14), as in the case of other end-on superoxo
copper(II) complexes.16,17
(23) Reversibility of the O2 binding was demonstrated by the fact that 2X-OO•
gradually disappeared to regenerate 1X when argon gas was flashed onto
the solution at-70 °C.
(24) Bencini, A.; Gatteschi, D. EPR of Exchange Coupled Systems; Springer-
Verlag: New York, 1990; p 167.
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