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Advanced Photon Source was supported by the U.S. Depart-
ment of Energy, Office of Science, Office of Basic Energy
Sciences, under Contract No. DE-AC02-06CH11357. MRCAT
operations are supported by the Department of Energy and the
MRCAT member institutions. Partial funding for J.T.M. was
provided by the Chemical Sciences, Geosciences and
Bioscience Division, U.S. Department of Energy, under
Contract No. DE-AC0-06CH11357. This work was also funded
by the Chemical Sciences and Engineering Division, Argonne
National Laboratory.
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Coordination of C−C triple bonds to Cu(II) leads to activation
of the C−H bond and thus facilitates the deprotonation in the
presence of base and formation of Cu−C bonds. The
subsequent innersphere electron transfer breaks the Cu−C
bonds and forms the C−C bond. The attack of Cl− to Cu(I)
releases the homocoupling product and forms [(TMEDA)-
CuCl]2.
In conclusion, X-ray absorption spectroscopy and in situ
electron paramagnetic resonance provided evidence for the
reduction of Cu(II) to Cu(I) species by terminal alkynes in the
presence of TMEDA. A wide range of aromatic and aliphatic
terminal alkynes could be coupled in the presence of Cu(II)
and TMEDA, where TMEDA plays dual roles as both ligand
and base. The structures of the starting Cu(II) species and the
obtained Cu(I) species were determined by EXAFS spectros-
copy as (TMEDA)CuCl2 and [(TMEDA)CuCl]2 dimer
complex, respectively. Given the extensive application of Cu/
TMEDA/alkyne system, the oxidation state and structural
information provided in the present work could shed light on
Cu/acetylene chemistry.
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(b) He, C.; Zhang, G.; Ke, J.; Zhang, H.; Miller, J. T.; Kropf, A. J.; Lei,
A. J. Am. Chem. Soc. 2013, 135, 488.
ASSOCIATED CONTENT
* Supporting Information
The experimental procedure; XANES/EXAFS fitting results.
This material is available free of charge via the Internet at
■
S
(8) FT range of the EXAFS spectra are listed below. CuCl2
+
TMEDA: 2.85−10.34 Å−1; CuCl2 + PhCCH: 2.80−10.98 Å−1; CuCl2
(solid): 2.87−11.93 Å−1.
(9) (a) Kau, L. S.; Spirasolomon, D. J.; Pennerhahn, J. E.; Hodgson,
K. O.; Solomon, E. I. J. Am. Chem. Soc. 1987, 109, 6433. (b) DuBois, J.
L.; Mukherjee, P.; Stack, T. D. P.; Hedman, B.; Solomon, E. I.;
Hodgson, K. O. J. Am. Chem. Soc. 2000, 122, 5775.
AUTHOR INFORMATION
Corresponding Author
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(10) The pre-edge of the Cu(II) XANES spectra originates from the
1s−3d electron transition. 3d orbitals are directly related to the
oxidation state of Cu, so the pre-edge energy is usually used to
determine the oxidation state of Cu species. Cu(I) species usually have
a d10 electronic configuration, so no pre-edge could be observed.
(11) Kirchhoff, J. R.; McMillin, D. R.; Robinson, W. R.; Powell, D. R.;
McKenzie, A. T.; Chen, S. Inorg. Chem. 1985, 24, 3928.
Author Contributions
§G. Zhang and H. Yi contributed equally.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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This work was supported by the “973” Program
(2012CB725302) and the National Natural Science Founda-
tion of China (21025206, 21272180). The authors also thank
the support from “the Fundamental Research Funds for the
Central Universities”, Program for New Century Excellent
Talents in University (NCET), the Research Fund for the
Doctoral Program of Higher Education of China
(20120141130002) and Program for Changjiang Scholars and
Innovative Research Team in University (IRT1030). Use of the
C
dx.doi.org/10.1021/ja410756b | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX