C O M M U N I C A T I O N S
Supporting Information Available: Experimental details (PDF)
and X-ray crystallographic data (CIF). This material is available free
References
(1) Solomon, E. I.; Chen, P.; Metz, M.; Lee, S.-K.; Palmer, A. E. Angew.
Chem., Int. Ed. 2001, 40, 4570.
(2) For example: Higashimura, H.; Kubota, M.; Shiga, A.; Fujisawa, K.;
Moro-oka, Y.; Uyama, H.; Kobayashi, S. Macromolecules 2000, 33, 1986.
(3) Recent reviews: (a) Kopf, M.-A.; Karlin, K. D. In Biomimetic Oxidations
Catalyzed by Transition Metal Complexes; Meunier, B., Ed.; Imperial
College Press: London, 2000; pp 309-362. (b) Blackman, A. G.; Tolman,
W. B. Struct. Bonding (Berlin) 2000, 97, 179. (c) Mahadevan, V.; Klein
Gebbink, R. J. M.; Stack, T. D. P. Curr. Opin. Chem. Biol. 2000, 4, 228.
(d) Schindler, S. Eur. J. Inorg. Chem. 2000, 2311. (e) Que, L., Jr.; Tolman,
W. B. Angew. Chem., Int. Ed. 2002, 41, 1114.
Figure 3. X-ray crystal structure of (4c)(O3SCF3), showing all non-
hydrogen atoms as 50% thermal ellipsoids.
indicates that there are indeed precisely four pairs of unshared d
electrons on copper.
(4) For example: (a) Karlin, K. D.; Wei, N.; Jung, B.; Kaderli, S.; Niklaus,
P.; Zuberbu¨hler, A. D. J. Am. Chem. Soc. 1993, 115, 9506. (b) Becker,
M.; Heinemann, F. W.; Schindler, S. Chem.-Eur. J. 1999, 5, 3124.
Removal of free O2 from solutions of 3 at -80 °C did not result
in degradation of its UV-vis spectral features, thus setting the stage
for its potential use as a building block in reactions with Cu(I)
complexes that would otherwise bind O2 if it were present. We
injected solutions of the Cu(I) reagents [L′Cu(MeCN)]n+ (L′ )
H(Me2LMe2)-, n ) 0; L′ ) TMPDA, n ) 1; L′ ) Me3TACN, n )
1)18 into degassed green solutions of 3a at -80 °C.19 The solutions
remained EPR silent, but rapidly became yellow-brown, with growth
of an intense UV-vis absorption at λmax ≈ 400-430 nm (Table
S1). Titration data for the reaction with [(TMPDA)Cu(MeCN)]-
O3SCF3 showed that maximum absorbance was reached when the
ratio of reactants was 1:1. Raman data were acquired on solutions
(5) Karlin, K. D.; Tolman, W. B.; Kaderli, S.; Zuberbu¨hler, A. D. J. Mol.
Catal. A 1997, 117, 215.
(6) Fujisawa, K.; Tanaka, M.; Moro-oka, Y.; Kitajima, N. J. Am. Chem. Soc.
1994, 116, 12079. TptBu,iPr ) tris(3-tert-butyl-5-isopropyl)hydroborate.
(7) Chaudhuri, P.; Hess, M.; Weyhermu¨ller, T.; Wieghardt, K. Angew. Chem.,
Int. Ed. 1999, 38, 1095.
(8) Jazdzewski, B. A.; Reynolds, A. M.; Holland, P. L.; Young, V. G., Jr.;
Kaderli, S.; Zuberbu¨hler, A. D.; Tolman, W. B., submitted for publication.
(9) Spencer, D. J. E.; Aboelella, N. W.; Reynolds, A. M.; Holland, P. L.;
Tolman, W. B. J. Am. Chem. Soc. 2002, 124, 2108.
(10) Spencer, D. J. E.; Reynolds, A. M.; Holland, P. L.; Jazdzewski, B. A.;
Duboc-Toia, C.; Le Pape, L.; Yokota, S.; Tachi, Y.; Itoh, S.; Tolman, W.
B., submitted for publication.
(11) Raman data (ref 9, cm-1): 3a, ν(16O16O) ) 968, ∆ν(16O18O,18O18O) )
25, 51. 3b, ν(16O16O) ) 961, ∆ν(16O18O,18O18O) ) 24, 49.
derived from 3a that had been prepared with 16O2 or 18O2 (λex
)
413.1 or 457.9 nm, -196 °C). Resonance enhanced 18O-isotope
sensitive features were observed in the 600-650 cm-1 region (∆18O
) 23-28 cm-1; Table S1). The spectral data are consistent with
formulation of the products as bis(µ-oxo) complexes,20 although
the Raman shifts for the monocationic species are anomalously high
(∼650 cm-1).21 Importantly, formation of the “asymmetric” species
4 is indicated by spectral features that are distinct from those
associated with the “symmetric” bis(µ-oxo) species that would result
from reaction of the added Cu(I) reagent with free O2.10,22,23
To prove this assignment, we obtained the X-ray crystal structure
of (4c)(O3SCF3) (Figure 3). The [Cu2(µ-O)2]2+ core parameters are
similar to others reported previously (cf., Cu-Cu ) 2.8492(5) Å).3e
Despite differences in Cu-N distances (avg. 1.89 Å for the
â-diketiminate versus 1.99 for TMPDA), the Cu-O bond distances
are essentially equivalent (1.817-1.819 Å). A significant interaction
between the triflate counterion and Cu2 is indicated by the Cu2-
O3 distance of 2.614(2) Å. Similar triflate interactions to yield five-
coordinate centers in [(TMPDA)2Cu2(µ-O)2](O3SCF3)2 were iden-
tified previously by EXAFS (Cu-O ) 2.32 Å).22
(12) X-ray data for 3b‚3THF: orthorhombic, space group Imm2, a ) 15.464(4)
Å, b ) 17.324(4) Å, c ) 8.763(2) Å, V ) 2348(1) Å3, Z ) 2, Fcalcd
)
1.151 g/cm3.
(13) Calculations employed the mPWPW91 functional (Adamo, C.; Barone,
V. J. Chem. Phys. 1998, 108, 664) with the mixed basis set: H (STO-
3G), C (6-31G), N and O (6-311G(d)), and Cu (CEP-31g). This level
was validated against structural and Raman spectroscopic data for
experimentally well-characterized binuclear copper species and found to
be highly accurate. For instance, the computed Cu-O and Cu-Cu
distances for [(TMPDA)2Cu2(µ-O)2]2+ are 1.837 and 2.869 Å, and the
[Cu2(µ-O)2]2+ Ag breathing vibration is predicted to be 608 cm-1 (∆18O
) 28 cm-1). These data closely agree with previously reported (ref 22b)
experimental values of 1.81 Å, 2.85 Å, and 608 cm-1 (∆18O ) 26 cm-1).
All closed-shell KS wave functions were checked for stability.
(14) DFT predicted Raman data for 3b (cm-1): ν(16O16O)
) 1013,
∆ν(16O18O,18O18O) ) 28, 57.
(15) The O-O bond distances in the few reported (η2-superoxo)metal
complexes are: (a) TptBu,iPrCuO2, 1.22(3) Å, ref 6. (b) TptBu,MeCoO2,
1.262(8) Å: Egan, J. W., Jr.; Haggerty, B. S.; Rheingold, A. L.; Sendlinger,
S. C.; Theopold, K. H. J. Am. Chem. Soc. 1990, 112, 2445. (c) (TpMe2)2-
SmO2, 1.319(5) Å: Zhang, X.; Loppnow, G. R.; McDonald, R.; Takats,
J. J. Am. Chem. Soc. 1995, 117, 7828. (d) TptBu,MeCr(pzH)O2, 1.327(5)
Å: Qin, K.; Incarvito, C. D.; Rheingold, A. L.; Theopold, K. H. Angew.
Chem., Int. Ed. 2002, 41, 2333.
(16) Gubelmann, M. H.; Williams, A. F. Struct. Bonding (Berlin) 1983, 55, 1.
(17) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. ReV. 1988, 88, 899.
(18) For the cases where n ) 1, the counterion is O3SCF3-. Abbreviations
In sum, a novel electronic structure for a structurally defined
1:1 Cu/O2 adduct that features significant Cu(III)-(O22-) character
is indicated by DFT calculations. Reaction of this adduct with Cu(I)
reagents leads to unique asymmetric bis(µ-oxo) complexes identified
by spectroscopy and X-ray diffraction. This demonstration of the
use of an isolable 1:1 Cu/O2 adduct as a synthon for building
multicopper species in stepwise fashion provides important prece-
dent for future applications of the methodology to other systems,
including those containing alternative metal ions.
-
used: H(Me2LMe2
)
) L with R ) H, R′ ) R′′ ) Me; TMPDA )
N,N,N′,N′-tetramethyl-1,3-propanediamine; Me3TACN ) 1,4,7-trimethyl-
1,4,7-triazacyclononane.
(19) Because of sluggish reactivity in initial experiments, similar reactions of
3b have not yet been studied.
(20) (a) Holland, P. L.; Cramer, C. J.; Wilkinson, E. C.; Mahapatra, S.; Rodgers,
K. R.; Itoh, S.; Taki, M.; Fukuzumi, S.; Que, L., Jr.; Tolman, W. B. J.
Am. Chem. Soc. 2000, 122, 792. (b) Henson, M. J.; Mukherjee, P.; Root,
D. E.; Stack, T. D. P.; Solomon, E. I. J. Am. Chem. Soc. 1999, 121, 10332.
(21) Theoretical studies to address this issue are in progress.
(22) (a) Mahadevan, V.; Hou, Z.; Cole, A. P.; Root, D. E.; Lal, T. K.; Solomon,
E. I.; Stack, T. D. P. J. Am. Chem. Soc. 1997, 119, 11996. (b) Mahadevan,
V.; DuBois, J. L.; Hedman, B.; Hodgson, K. O.; Stack, T. D. P. J. Am.
Chem. Soc. 1999, 121, 5583.
Acknowledgment. We thank the NIH (GM47365 to W.B.T.)
and NSF (CHE-9876792 to C.J.C.; predoctoral fellowships to
N.W.A. and A.M.R.) for financial support, Profs. L. Que, Jr., and
J. Lipscomb for access to Raman and EPR facilities, and Prof. K.
McNeill for helpful discussions.
(23) A small amount of [(TMPDA)2Cu2(µ-O)2](O3SCF3)2 is evident in the
Raman spectra for the TMPDA case (Figure S4), which we suspect is
due to adventitious O2. Experiments to test this notion are in progress.
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J. AM. CHEM. SOC. VOL. 124, NO. 36, 2002 10661