Article
Inorganic Chemistry, Vol. 49, No. 22, 2010 10265
coupling in the mixed-valence state.5,6 It is noteworthy that
few examples of coordination compounds feature ligands
rather than metal ions as electron donors and acceptors.
Tetra- or hexa-Re(I) complexes with either bipyridyl or
triazine ligand-centered MV systems are prime candidates
for realizing direct through space electronic communication.5
Electron transfer via superexchange may be the dominant
mechanism, provided the energy of the lowest unoccupied
molecular orbital of the bridging ligand is close to that of the
donor and acceptor moieties, since the comparable energies
of the bridge and metal redox centers would act to reduce the
activation barrier to electron tunneling.6,7 Therefore, dinu-
clear ruthenium(II) complexes bridged by o- and p-quinonoid
molecules in combination with different coligands and mixed-
valence systems have been scrutinized in detail.1a,b,7 However,
the subtleties of quinonoid-rhenium(I) behavior, which un-
derlie the importance of these compounds, have yet to be
explored.
produced via the reduction of neutral dirhenium(I) metalla-
cycles show the following features: (1) quinone ligand-centered;
two well-separated, single-electron, reversibly accessible 0,
-1, -2 redox states. The benziimidazolate ligand appears to
be redox innocent within the solvent window: (2) small-to-
negligible g-factor anisotropy in the ESR signal, signifying
a e 5% metal-centered spin in the singly reduced states, and
(3) highly stable, noncommunicating, localized, quinonoid-
centered radical complexes, as evidenced by combined SEC
and ESR data. The electronic characteristics of the radical-
anionic and dianionic states of such biologically relevant
quinonoid ligands in the forms of free and Re(I) complexes
are described for the first time.
Experimental Section
Materials. All starting materials and products were stable toward
moisture and air. Commercial grade reagents, Re2(CO)10, 6,11-
dihydroxy-5,12-naphthacenedione (H2-dhnq), and 1,4-dihydroxy-
9,10-anthraquinone (H2-dhaq), were used as received. The solvents
used in this study were of spectroscopic grade.
Herein, we report on the synthesis (in a one step assembly)
of the chair-shaped, neutral dirhenium(I) metallacycles, [(CO)3-
ReI(μ-L)(μ-L0)ReI(CO)3], (1, L = dhnq2-; 2, L = dhaq2-
;
Physical Measurements and Procedures. Elemental analyses
for carbon, hydrogen, and nitrogen were recorded with a Perkin-
Elmer 2400 CHN elemental analyzer. Infrared spectra were
measured on a Perkin-Elmer PARAGON 1000 FT-IR spectrom-
H2dhnq = 6,11-dihydroxy-5,12-naphthacenedione; H2dhaq =
1,4-dihydroxy-9,10-anthraquinone) and a ditopic semirigid
N-donor ligand, 1,4-bis(5,6-dimethylbenzimidazol-1-ylmethyl)-
naphthalene (L0=p-NBimM). The ligand valence state distri-
bution in 1n and 2n, where n=0, -1, and -2, was assessed
via CV and UV-vis-NIR SEC. Type C quinone-containing
1
eter. H NMR spectra were recorded on Bruker AC 300 and
AMX-400 FT-NMR spectrometers. FAB-MS data were ob-
tained using a JEOL JMS-700 double focusing mass spectrom-
eter. The electronic absorption spectra were obtained on a
Hewlett-Packard 8453 spectrophotometer at room temperature
in a 1 cm quartz cell. Fluorescence spectra were recorded on a
Hitachi F4500 spectrometer. Excited-state lifetimes were mea-
sured as described previously.5d Cyclic voltammograms (CV) and
differential pulse voltammograms (DPV) were measured in an-
hydrous DMSO/0.1 M Bu4NClO4 as a supporting electrolyte
at 298 K. CVs were carried out at a 100 mV/s scan rate, using a
three-electrode configuration (Pt working electrodes, Pt wire
counter electrode, and saturated calomel electrode (SCE) refer-
ence electrode) and a CHI Electrochemical Workstation 611A
under deaerated conditions. UV-vis-NIR spectroelectrochem-
istry was performed with an airtight, optically transparent thin-
layer electrochemical cell (OTTLE) constructed with a 100 mesh
platinum gauze working electrode in a 1 mm quartz cell.8 UV-
vis-NIR spectra were recorded with a JASCO V-570 UV-vis-
NIR spectrophotometer. Both electrolysis cells were assembled
under an inert atmosphere in a glovebox equipped with a drytrain
to exclude moisture and oxygen.
radical complexes, [(CO)3ReI(μ-L3•-)(μ-L0)ReI(CO)3]•-
,
(3) (a) Robert, R.; David, S.; Annemarie, S.; Eskouhie, T.; Andrea, F.
Nature 2005, 433, 7025. (b) Hiroshi, S.; Knapp, E.-W. J. Am. Chem. Soc. 2005,
127, 14714. (c) Fufezan, C.; Gross, C. M.; Sjodin, M.; Rutherford, A. W.; Krieger-
Liszkay, A.; Kirilovsky, D. J. Biol. Chem. 2007, 282, 12492. (d) Davidson, V. L.
In Principles and Applications of Quinoproteins; Marcel Dekker: New York,
1993. (e) Klinman, J. P.; Mu, D. Annu. Rev. Biochem. 1994, 63, 299. (f) Dooley,
D. M. J. Biol. Inorg. Chem. 1999, 4, 1. (g) Duine, J. A. Eur. J. Biochem. 1991,
200, 271. (h) Duine, J. A. J. Biosci. Bioeng. 1999, 88, 231. (i) Goodwin, P. M.;
Anthony, C. Adv. Microb. Physiol. 1998, 40, 1. (j) Duine, J. A.; Jongejan, J. A. In
Bioinorganic Catalysis; Reedijk, J., Ed.; Marcel Dekker: New York, 1993; p 447.
(k) Klinman, J. P. Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 705. (l) Mure, M.;
Mills, S. A.; Klinman, J. P. Biochemistry 2002, 41, 9269. (m) Bollinger, J. A.;
Brown, D. E.; Dooley, D. M. Biochemistry 2005, 44, 11708. (n) Mure, M.; Wang,
S. X.; Klinman, J. P. J. Am. Chem. Soc. 2003, 125, 6113.
(4) (a) Shimazaki, Y.; Stack, T. D. P.; Storr, T. Inorg. Chem. 2009, 48,
8383. (b) Kaim, W.; Lahiri, G. K. Angew. Chem., Int. Ed. 2007, 46, 1778.
ꢀ
(5) (a) Dinolfo, P. H.; Coropceanu, V.; Bredas, J.-L.; Hupp, J. T. J. Am.
Chem. Soc. 2006, 128, 12592. (b) Dinolfo, P. H.; Williams, M. E.; Stern, C. L.;
Hupp, J. T. J. Am. Chem. Soc. 2004, 126, 12989. (c) Dinolfo, P. H.; Lee, S. J.;
Crystallographic Determination. Suitable single crystals of
1 C7H8 and 2 C7H8 with dimensions of 0.30 ꢀ 0.30 ꢀ 0.15
ꢀ
Coropceanu, V.; Bredas, J. L.; Hupp, J. T. Inorg. Chem. 2005, 44, 5789. (d)
3
3
Bhattacharya, D.; Sathiyendiran, M.; Luo, T.-T.; Chang, C.-H.; Cheng, Y.-H.; Lin,
C.-Y.; Lee, G. H.; Peng, S.-M.; Lu, K.-L. Inorg. Chem. 2009, 48, 3731. (e) Kaim,
W.; Schwederski, B.; Dogan, A.; Fiedler, J.; Kuehl, C. J.; Stang, P. J. Inorg. Chem.
2002, 41, 4025.
(6) (a) Hush, N. S. Prog. Inorg. Chem. 1967, 8, 391. (b) Piepho, S. B.;
Krausz, E. R.; Schatz, P. N. J. Am. Chem. Soc. 1978, 100, 2996. (c) Hartmann,
H.; Berger, S.; Winter, R.; Fiedler, J.; Kaim, W. Inorg. Chem. 2000, 39, 4977. (d)
Ernst, S.; Hanel, P.; Jordanov, J.; Kaim, W.; Kasack, V.; Roth, E. J. Am. Chem.
Soc. 1989, 111, 1733. (e) Pratt, R. C.; Stack, T. D. P. J. Am. Chem. Soc. 2003,
125, 8716. (f) Chang, H.-C.; Mochizuki, K.; Kitagawa, S. Inorg. Chem. 2002, 41,
4444. (g) Pierpont, C. G. Coord. Chem. Rev. 2001, 219, 415. (h) Kaim, W.;
Schwederski, B. Pure Appl. Chem. 2004, 76, 351. (i) Ray, K.; Petrenko, T.;
Wieghardt, K.; Neese, F. Dalton Trans. 2007, 1552.
(7) (a) Ghumaan, S.; Sarkar, B.; Maji, S.; Puranik, V. G.; Fiedler, J.;
Urbanos, F. A.; Jimenez-Aparicio, R.; Kaim, W.; Lahiri, G. K. Chem.;Eur.
J. 2008, 14, 10816. (b) Ye, S.; Sarkar, B.; Duboc, C.; Fiedler, J.; Kaim, W. Inorg.
Chem. 2005, 44, 2843. (c) Kaim, W.; Sarkar, B. Coord. Chem. Rev. 2007, 251,
584. (d) Ghumaan, S.; Sarkar, B.; Patra, S.; van Slageren, J.; Fiedler, J.; Kaim, W.;
Lahiri, G. K. Inorg. Chem. 2005, 44, 3210. (e) Hendrickson, D. N.; Pierpont,
C. G. Top. Curr. Chem. 2004, 234, 63. (f) Dei, A.; Gatteschi, D.; Pardi, L. Inorg.
Chem. 1990, 29, 1442. (g) Haga, M.; Dodsworth, E. S.; Lever, A. B. P. Inorg.
Chem. 1986, 25, 447.
mm and 0.25 ꢀ 0.20 ꢀ 0.15 mm, respectively, were selected for
indexing and the collection of intensity data. Measurements
were performed using graphite-monochromatized Mo KR ra-
diation (λ = 0.71073 A) on a Nonius Kappa CCD diffracto-
meter. Intensity data were collected at 150(2) K within the
limits 1.59° < θ < 27.49° for 1 C7H8 and 1.38° < θ < 27.50°
3
for 2 C7H8. The structures were solved by direct methods and
3
refined on F2 by full-matrix least-squares calculations using
SHELX-97 program packages.9 Because of the disordered
syndrome of guest molecules, the carbon atoms of the toluene
molecules in 2 C7H8 were refined isotropically. Other non-
3
hydrogen atoms were refined anisotropically, and all hydrogen
atoms were assigned by geometrical calculation and refined as
riding models. Details of the structure determinations are given
(8) (a) Lin, C.-Y.; McGlashen, M. L.; Hu, S.; Shim, Y. K.; Smith, K. M.;
Spiro, T. G. Inorg. Chim. Acta 1996, 252, 179. (b) Krejcik, M.; Danek, M.;
Hartl, F. J. Electroanal. Chem. Interfacial Electrochem. 1991, 317, 179.
(9) Sheldrick, G. M. SHELX-97 (including SHELXS and SHELXL);
€
€
University of Gottingen: Gottingen, Germany, 1997.