One-Pot Synthesis of Symmetric and Asymmetric p-Quinone Ligands and Unprecedented Substituent Induced Reactivity in Their Dinuclear Ruthenium Complexes

Article abstract of DOI:10.1021/ic101972u

The compounds 2-[2-(trifluoromethyl)-anilino]-5-hydroxy-1, ⁴-benzoquinone (L¹), 2,5-di-[2-(trifluoromethyl)-anilino]- 1,⁴-benzoquinone (L²),2-[2-(methylthio)-anilino]-5- hydroxy-1,⁴-benzoquinone (L

Full text of DOI:10.1021/ic101972u

1150 Inorg. Chem. 2011, 50, 1150–1159
DOI: 10.1021/ic101972u
One-Pot Synthesis of Symmetric and Asymmetric p-Quinone Ligands
and Unprecedented Substituent Induced Reactivity in Their Dinuclear
Ruthenium Complexes
David Schweinfurth, Hari Sankar Das, Fritz Weisser, Denis Bubrin, and Biprajit Sarkar*
€
Institut fu€r Anorganische Chemie, Universitat Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany
Received September 27, 2010
The compounds 2-[2-(trifluoromethyl)-anilino]-5-hydroxy-1,4-benzoquinone (L1), 2,5-di-[2-(trifluoromethyl)-anilino]-
1,4-benzoquinone (L2), 2-[2-(methylthio)-anilino]-5-hydroxy-1,4-benzoquinone (L3), and 2,5-di-[2-(methylthio)-
anilino]-1,4-benzoquinone (L4) were prepared in high yields by reacting 2,5-dihydroxy-1,4-benzoquinone with the
corresponding amines in a one-pot synthesis in refluxing acetic acid. This straightforward and “green” synthesis
delivers biologically relevant asymmetric p-quinones such as L1 and L3 in a rare, simple, one-step process. The
proposed synthetic route is general and can be applied to generate a variety of such molecules with different
substituents on the nitrogen atoms. Structural characterization of L2 and L4 shows electron delocalization across the
“upper” and “lower” parts of the molecule, thus showing the importance of charge separated species in the proper
description of such molecules. Reactions of these ligands with [Cl(η6-Cym)Ru(μ-Cl)2Ru(η6-Cym)Cl] (Cym =
p-Cymene = 1-isopropyl-4-methyl-benzene) in the presence of a base result in the formation of complexes
[{Cl(η6-Cym)Ru}2(μ-L-2H1)] (1), [{Cl(η6-Cym)Ru}2(μ-L-2H2)] (2), [{Cl(η6-Cym)Ru}2(μ-L-2H3)] (3), and
[{Cl(η6-Cym)Ru}2(μ-L-2H4)] (4). Structural characterization of 2 and 4 shows a rare syn-coordination of the chloride
atoms. The SMe groups in 3 and 4 are not coordinated to the ruthenium center, and the bridging ligands thus function in
a bis-bidentate form. Abstraction of the chloride atoms in these complexes with AgClO4 in CH3CN results in the
expected formation of solvent substituted complexes [{(CH3CN)(η6-Cym)Ru}2(μ-L-2H1)][ClO4]2 (5[ClO4]2) and
[{(CH3CN)(η6-Cym)Ru}2(μ-L-2H2)][ClO4]2 (6[ClO4]2) with the ligands where there are no additional donor atoms on
the nitrogen substituents. The same chloride abstraction reaction in the cases of 3 and 4 leads to an unprecedented
substituent induced release of the Cym ligand, resulting in complexes of the form [(CH3CN)(η6-Cym)Ru(μ-
L-2H3)Ru(CH3CN)3][ClO4]2 (7[ClO4]2) and [{(CH3CN)3Ru}2(μ-L-2H4)][ClO4]2 (8[ClO4]2), where the SMe groups
are now coordinated to the metal center. In the case of complex 3, which contains an asymmetric bridging ligand, Cym
release is observed only at the side that contains an additional SMe donor, thus proving the necessity of such donor
substituents for the observed reactivity. The increase in Lewis acidity at the ruthenium center on chloride abstraction is
made responsible for SMe coordination and the rigidity of the ligand systems, and their concomitant failure to
coordinate in a “fac” manner as is required for a piano stool configuration results in the eventual Cym release. The
bridging ligand which then coordinates in a bis-meridional fashion in 8[ClO4]2 results in a bis-pincer type of
coordination. These observations were validated by a structural analysis of 8[ClO4]2. The results show the potential
hemilabile character of ligands such as L3 and L4. Electrochemical and spectroscopic investigations are reported on
8[ClO4]2, and substitution reactions of the CH3CN molecules are presented to show the use of 8[ClO4]2 as a versatile
precursor for other reactions.
Introduction
photosynthesis.1-3 Owing to their facile electron transfer
properties, they are often found in combination with transi-
tion metal centers in biological systems.3,4 They are also
usually found in the paradoxical role of mutagenic agents as
well as effective antitumor agents.5 The biological activity of
quinone molecules is often related to the presence of acidic
Quinones are ubiquitous in biological systems, being
part of vital processes such as cellular respiration and
*Email: sarkar@iac.uni-stuttgart.de.
(1) Morton, R. A. The Biochemistry of Quinones; Academic Press:
New York: 1965.
(2) Patai, S.; Rappoport, Z. The Chemistry of Quinonoid Compounds;
Wiley and Sons: New York, 1988; Vols. 1 and 2.
(3) Nohl, H.; Jordan, W.; Youngman, R. J. Adv. Free Radical Biol. Med.
1986, 2, 211.
(4) Thompson, S. D. Naturally Occuring Quinones IV; Springer: The
Netherlands, 1996.
(5) Lin, A. J.; Cosby, L. A.; Sartorelli, A. C. Cancer Chemother. Rep. Part
2 1974, 4, 23.
r
pubs.acs.org/IC
Published on Web 01/07/2011
2011 American Chemical Society

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 1151
Scheme 1
Figure 1. Quinone containing -OH substituent.
protons in these molecules.6-8 Quinones of the form L
(Figure 1) containing an OH substituent play an important
role as inhibitors of tumors9 and of hydroxyphenyl pyruvate
dioxygenase.10 Despite intensive research efforts in that
direction, straightforward one-pot and green synthetic routes
for access to such molecules are, to the best of our knowledge,
nonexistent in the literature, with the existing procedures
requiring multistep synthesis, extraction from natural pro-
ducts, or involved purification steps.9-17
Coordination compounds with quinone ligands have been
studied for a variety of reasons, such as their interesting
electron transfer properties,18-22 magnetic behavior,23,24 use
in supramolecular chemistry,25,26 as well as homogeneous
catalysis.27,28 Ligand noninnocence is a well-known phenom-
enon in metal complexes of quinones,29-32 and recently
valence ambiguities arising out of such a process have been
extensively studied for diruthenium complexes containing
potentially bridging quinone ligands.20,33-35 Valence ambi-
guity as well as mixed valency are widely researched fields for
di- and multiruthenium complexes with a variety of ligands.36-43
Hemilability of ligands is an important phenomenon in
catalysis.44 Efforts at synthesizing potentially bridging qui-
none ligands with additional donor atoms capable of show-
ing hemilability have been rare until now.28 In view of our
interest in developing easy, straightforward, and green routes
for synthesizing various quinone ligands and exploring
their use in coordination and organometallic chemistry, we
ventured onto this present project.45-49 We present here a one-
pot synthesis of the ligands 2-[2-(trifluoromethyl)-anilino]-5-
hydroxy-1,4-benzoquinone (L1), 2,5-di-[2-(trifluoromethyl)-
anilino]-1,4-benzoquinone (L2), 2-[2-(methylthio)-anilino]-5-
hydroxy-1,4-benzoquinone (L3), and 2,5-di-[2-(methylthio)-
anilino]-1,4-benzoquinone (L4). L1 and L3 are rare examples
of asymmetric p-quinones containing an additional OH
group and are directly related to molecules of the form L
(Scheme 1). L3 and L4 combine additional SMe donors at the
nitrogen substituents, thus making these ligands potentially
hemilabile, with L3 having this feature only on one side of the
molecule. These ligands were usedto form complexes [{Cl(η6-
Cym)Ru}2(μ-L-2H1)] (1), [{Cl(η6-Cym)Ru}2(μ-L-2H2)] (2),
[{Cl(η6-Cym)Ru}2(μ-L-2H3)] (3), and [{Cl(η6-Cym)Ru}2(μ-
L-2H4)] (4) that contain the “[Ru(Cym)]” (Cym = p-Cymene =
1-isopropyl-4-methyl-benzene) fragment popularized
(6) Inbaraj, J. J.; Gandhidasan, R.; Murugesan, R. Free Radical Biol.
Med. 1999, 26, 1072.
(7) Frigaard, N. U.; Tokita, S.; Matsuura, K. Biochim. Biophys. Acta
1999, 1413, 108.
(8) Bachur, N. R.; Gordon, S. L.; Gee, M. V. Cancer Res. 1978, 1745.
(9) Stahl, P.; Kissau, L.; Matzischek, R.; Giannis, A.; Waldmann, H.
Angew. Chem., Int. Ed. 2002, 41, 1174.
(10) Meazza, G.; Scheffler, B. E.; Tellez, M. R.; Rimando, A. M.;
Romagni, J. G.; Duke, S. O.; Nanayakkara, D.; Khan, I. A.; Abourashed,
E. A.; Dayan, F. E. Phytochemistry 2002, 59, 281.
(11) Ling, T.; Poupon, E.; Rueden, E. J.; Kim, S. H.; Theodorakis, E. A.
J. Am. Chem. Soc. 2002, 124, 12261.
(12) Aguilar-Martinez, M.; Bautista-Martinez, J. A.; Macias-Ruvalcaba,
N.; Gonzalez, I.; Tovar, E.; Alizal, T. M. d.; Collera, O.; Cuevas, G. J. Org.
Chem. 2001, 66, 8349.
(13) Subbarayudu, N.; Satyanarayana, Y. D.; Vankata-Rao, E.; Venkata-Rao,
D. Ind. J. Pharm. Sc. 1978, 40, 173.
(14) Joshi, B. S.; Kamat, V. S. Indian J. Chem. 1975, 13, 795.
(15) Manthey, M. K.; Pyne, S. G.; Trusscot, R. J. W. Aust. J. Chem. 1989,
42, 365.
(16) Mize, P. D.; Jeffs, P. W.; Boelkelheide, K. J. Org. Chem. 1980,
45, 3540.
(17) Braunstein, P.; Siri, O.; Taquet, J.-P.; Yang, Q.-Z. Chem.;Eur. J.
2004, 10, 3817.
(18) Lever, A. B. P. Coord. Chem. Rev. 2010, 254, 1397.
(19) Pierpont, C. G. Coord. Chem. Rev. 2001, 216-217, 95.
(20) Ward, M. D. Inorg. Chem. 1996, 35, 1712.
(21) Leschke, M.; Melter, M.; Lang, H. Inorg. Chim. Acta 2003, 350, 114.
(22) Siri, O.; Taquet, J.-P.; Collin, J.-P.; Rohmer, M.-M.; Benard, M.;
Braunstein, P. Chem.;Eur. J. 2005, 11, 7247.
(23) Ye, S.; Sarkar, B.; Lissner, F.; Schleid, T.; Slageren, J. v.; Fiedler, J.;
Kaim, W. Angew. Chem., Int. Ed. 2005, 44, 2103.
(24) Carbonera, C.; Dei, A.; Letard, J.-F.; Sangregorio, C.; Sorace, L.
Angew. Chem., Int. Ed. 2004, 43, 3136.
(25) Kitagawa, S.; Kawata, S. Coord. Chem. Rev. 2002, 224, 11.
(26) Yang, Q.-Z.; Siri, O.; Braunstein, P. Chem.;Eur. J. 2005, 11, 7237.
(27) Taquet, J.-P.; Siri, O.; Braunstein, P.; Welter, R. Inorg. Chem. 2004,
43, 6944.
(28) Yang, Q.-Z.; Kermagoret, A.; Agostinho, M.; Siri, O.; Braunstein, P.
Organometallics 2006, 25, 5518.
(29) Ward, M. D.; McCleverty, J. A. J. Chem. Soc., Dalton Trans.
2002, 275.
(34) Kar, S.; Sarkar, B.; Ghumaan, S.; Janardanan, D.; Slageren, J. v.;
Fiedler, J.; Puranik, V. G.; Sunoj, R. B.; Kaim, W.; Lahiri, G. K. Chem.;
Eur. J. 2005, 11, 4901.
(35) Kumbhakar, D.; Sarkar, B.; Maji, S.; Mobin, S. M.; Fiedler, J.;
Urbanos, F. A.; Aparicio, R.-J.; Kaim, W.; Lahiri, G. K. J. Am. Chem. Soc.
2008, 130, 17575.
(36) Das, A. K.; Sarkar, B.; Fiedler, J.; Zalis, S.; Hartenbach, I.; Strobel,
S.; Lahiri, G. K.; Kaim, W. J. Am. Chem. Soc. 2009, 131, 8895.
(37) Creutz, C. Prog. Inorg. Chem. 1983, 30, 1.
(38) Crutchley, R. J. Adv. Inorg. Chem. 1994, 41, 273.
(39) Salsman, J. C.; Kubiak, C. P.; Ito, T. J. Am. Chem. Soc. 2005, 127, 2382.
(40) Londergan, C. H.; Salsman, J. C.; lear, B. J.; Kubiak, C. P. Chem.
Phys. 2006, 324, 57.
(41) Salsman, J. C.; Ronco, S.; Londergan, C. H.; Kubiak, C. P. Inorg.
Chem. 2006, 45, 547.
(42) Fabre, M.; Bonvoisin, J. J. Am. Chem. Soc. 2007, 129, 1434.
(43) Fabre, M.; Jaud, J.; Hliwa, M.; Launay, J.-P.; Bonvoisin, J. Inorg.
Chem. 2006, 45, 9332.
(44) Braunstein, P.; Naud, F. Angew. Chem., Int. Ed. 2001, 40, 680.
(45) Braunstein, P.; Bubrin, D.; Sarkar, B. Inorg. Chem. 2009, 48, 2534.
(46) Das, H. S.; Das, A. K.; Pattacini, R.; Huebner, R.; Sarkar, B.;
Braunstein, P. Chem. Commun. 2009, 4387.
(30) Herebian, D.; Boethe, E.; Neese, F.; Weyhermueller, T.; Wieghardt,
K. J. Am. Chem. Soc. 2003, 125, 9116.
(31) Bhattacharya, S.; Gupta, P.; Basuli, F.; Pierpont, C. G. Inorg. Chem.
2002, 41, 5810.
(32) Patra, S.; Sarkar, B.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. Inorg.
Chem. 2003, 42, 6469.
(33) Masui, H.; Freda, A. L.; Zerner, M. C.; Lever, A. B. P. Inorg. Chem.
2000, 39, 141.
(47) Paretzki, A.; Pattacini, R.; Huebner, R.; Braunstein, P.; Sarkar, B.
Chem. Commun. 2010, 46, 1497.
(48) Das, H. S.; Weisser, F.; Schweinfurth, D.; Su, C.-Y.; Bogani, L.;
Fiedler, J.; Sarkar, B. Chem.;Eur. J. 2010, 16, 2977.
(49) Sarkar, B.; Huebner, R.; Pattacini, R.; Hartenbach, I. Dalton Trans.
2009, 4653.

1152 Inorganic Chemistry, Vol. 50, No. 3, 2011
Schweinfurth et al.
Figure 3. ORTEP plot of L4. Ellipsoids are drawn at 50% probability.
high yields after just a one-step chromatographic purifica-
tion. This route is general and can be extended to include all
possible aliphatic and aromatic amines. The synthesis of L4
shows the possibility of building in additional donor atoms
at the nitrogen substituents in such ligands, which can be
crucial for hemilabile behavior and catalysis. To our sur-
prise, repeating the same reactions with equimolar amounts
of 2,5-dihydroxy-1,4-benzoquinone and the corresponding
amine under the same conditions as stated above resulted in
the formation of asymmetric p-quinone compounds L1 and
L3 (Scheme 1). There are no reports in the literature of the
synthesis of such compounds in m-cresol, as has been
mentioned above for symmetrically amino-substituted
p-quinones. Such compounds containing an additional OH
group are very closely related to many biologically active p-
quinones which function as bioinhibitors, and a simple and
straightforward synthesis of such molecules has been rare
and elusive up to now, to the best of our knowledge. L1 and
L3 could be obtained in high yields with our method of using
acetic acid as a solvent. L3 contains an additional SMe
donor on only one side of the molecule. L1-L4 were
Figure 2. ORTEP plot of L2. Ellipsoids are drawn at 50% probability.
because of its anticancer properties and the catalytic activity
of many of its metal complexes.50,51 These complexes were
further reacted with silver salts in acetonitrile to produce
[{(CH3CN)(η6-Cym)Ru}2(μ-L-2H1)][ClO4]2 (5[ClO4]2), [{(CH3-
CN)(η6-Cym)Ru}2(μ-L-2H2)][ClO4]2 (6[ClO4]2), [(CH3CN)-
(η6-Cym)Ru(μ-L-2H3)Ru(CH3CN)3][ClO4]2 (7[ClO4]2), and
[{(CH3CN)3Ru}2(μ-L-2H4)][ClO4]2 (8[ClO4]2). In the follow-
ing, a detailed synthetic, spectroscopic, and crystallographic
study on these ligands and complexes is presented. Reactivity
studies are reported to determine the potential hemilabile
character of ligands such as L3 and L4. Reasons for the
unprecedented coordination induced release of Cym in com-
plexes 3 and 4 to form 7[ClO4]2 and 8[ClO4]2 are stated and
explained. Finally, electrochemical and spectroscopic investi-
gations on 8[ClO4]2 as well as the use of this compound as a
versatile precursor are explored.
Results and Discussion
1
characterized by H and 13C NMR spectroscopy and ele-
Synthesis of Ligands and Crystal Structures of L2 and L4.
One of the reports on the synthesis of (aromatic)amino-
substituted p-quinones deals with the reaction of the com-
mercially available and relatively inexpensive 2,5-dihy-
droxy-1,4-benzoquinone with aromatic amines in m-cresol
under reflux at temperatures of over 100 °C in the presence
of catalytic amounts of trifluoroacetic acid.52 This reaction,
which is often used in the literature even up to now,53 deals
with m-cresol as a solvent, a substance that is highly toxic,
and whose health hazards are well documented.54 Addi-
tionally, polymer formation is often a problem while using
the above-mentioned synthetic method.52 In trying to unveil
the possible mechanism of this reaction, we reasoned that
the critical points in its functioning are relatively high
temperatures and acid catalysis. Similar acid catalyzed
reactions are found in several enzymatic processes which
function in water.55 Hence, we carried out the same reaction
with nontoxic and environmentally benign acetic acid as a
solvent. Gratifyingly, the reaction in acetic acid worked
as good as or even better than that using m-cresol. No
problems with polymer formation were observed, and we
were able to isolate compounds L2 and L4 (Scheme 1) in
mental analyses. Whereas L2 and L4 show only one signal
corresponding to the p-quinone ring C-H protons in their
1H NMR spectra owing to symmetry equivalence, L1 and
L3 show two different signals for the now inequivalent
p-quinone ring C-H protons (see the Experimental
Section), and this was the first indication for the formation
of such asymmetrically substituted p-quinones. In the 13C
NMR spectra for L2 and L4, only one signal is seen for the
“CdO” carbon; for L1 and L3 two different signals are
observed owing to their inequivalence. In addition, the
presence of the -CF3 groups in L1 and L2 makes the
assignment of signals in their 13C NMR spectra convenient
because of coupling to the 19F nuclei (Experimental
Section).
The ligand L2 could be crystallized from a dichloro-
methane/n-hexane (1/5, diffusion) solution and L4 from
the slow evaporation of a CHCl3/MeOH (4/1) solution at
ambient temperatures (Figures 2 and 3). L2 and L4
crystallized in the C2/c and P1h space groups, respectively
(Table 1). Analysis of bond lengths within the six-mem-
bered p-quinone ring shows that the C1-O distances for
2
4
˚
L and L are 1.237(2) and 1.233(2) A, respectively, and
˚
the C3-N distances are 1.337(2) and 1.344(2) A, respec-
(50) Peacock, A. F. A.; Habtemariam, A.; Fernandez, R.; Walland, V.;
Fabbiani, F. P. A.; Parsons, S.; Aird, R. E.; Jodrell, D. I.; Sadler, P. J. J. Am.
Chem. Soc. 2006, 128, 1739.
(51) Ikariya, T.; Blacker, A. J. Acc. Chem. Res. 2007, 40, 1300.
(52) Ueda, M.; Sakai, N.; Imai, Y. Makromol. Chem. 1979, 180, 2813.
(53) Zhang, D.; Jin, G.-X. Organometallics 2003, 22, 2851.
(54) Sigma Aldrich Safety Data Sheet (MSDS), Regulation (EC) No. 1907/
2006, version 3.0, Revision Date Dec. 28, 2008; Sigma Aldrich: St. Louis, MO.
(55) Klinman, J. P. Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 14766.
tively. Accordingly, the C1-C2 distances are 1.418(2)
˚
and 1.432(2) A, and the C2-C3 distances are 1.366(2) and
2
4
˚
1.365(2) A respectively for L and L . These distances that
are between those of typical single and double bonds
point to electron delocalization and imply the formula-
tion of these compounds as two C-C connected W-like
merocyanine subunits (Scheme 1). The C1-C3 distances

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 1153
Table 1. Crystallographic Details
L2
L4
2
4
8[ClO4]2
formula
Mr
C20H12F6N2O2
426.32
monoclinic
C2/c
9.961(2)
11.829(2)
15.068(3)
90
93.10(3)
90
1772.9(6)
4
1.597
C20H18N2O2S2
382.48
triclinic
P1
3.8774(1)
9.3734(3)
11.8747(4)
93.894(2)
97.976(2)
95.969(2)
423.60(2)
1
C40H38Cl2F6N2O2Ru2
965.76
monoclinic
P21/c
17.592(4)
12.234(2)
19.212(4)
90
107.35(3)
90
3946.8(1)
4
1.625
100(2)
0.711
1936
C43H51Cl2N3O3Ru2S2
995.03
monoclinic
C2/c
36.128(4)
11.652(1)
23.099(3)
90
96.245(9)
90
9666.0(2)
8
1.367
173(2)
0.711
4064
C35.5H37.5Cl2N8O10Ru2S2
1073.40
triclinic
P1
8.0825(5)
12.4651(7)
12.4812(8)
100.619(3)
101.953(3)
107.976(4)
1127.7(1)
1
cryst syst
space group
˚
a (A)
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
V (A )
Z
Dcalc (g cm-3
T (K)
)
1.499
100(2)
0.711
200
1.580
100(2)
0.711
541
100(2)
0.711
864
μ Mo KR (mm-1
F(000)
)
measd/ ind. reflns
obsd. [I > 2σ(I)] reflns
R (int)
4072/2165
1673
0.026
0.042
0.119
3665/2058
1865
0.022
0.034
0.084
15417/8011
4924
0.075
0.078
0.175
10790/9317
5553
0.106
0.109
0.255
8432/4407
3511
0.045
0.062
0.150
R [F2 > 2σ(F2)]
wR (F 2)
S
1.308
0.327, -0.248
1.107
0.348, -0.299
1.286
2.677, -0.972
1.319
2.076, -2.237
1.133
1.049, -0.935
-3
˚
ΔFmax, ΔFmin (e A
)
Scheme 2
Figure 4. ORTEP plot of 2. Ellipsoids are drawn at 50% probability.
Hydrogen atoms are omitted for clarity.
conditions. Additionally, 1H NMR spectroscopy as well
as mass spectrometry showed the presence of two Cym
groups in all of the complexes, including 3 and 4, that
have additional thioether donor groups on the substituent
on nitrogen atoms (Experimental Section).
Compounds 2 and 4 could be crystallized from the slow
evaporation of a dichloromethane solution and slow
diffusion of ether into a CH3CN/MeOH (1/1) solution,
respectively, at ambient temperatures. ORTEP plots are
presented in Figures 4 and 5, and selected bond lengths
and bond angles are given in Tables 2 and 3.
2
4
˚
of 1.519(2) and 1.524(2) A respectively for L and L are
typical C-C σ-bond distances, showing the presence of
authentic single bonds that connect the merocyanine
subunits. These data corroborate earlier observations
and show the importance of charge separated species
which must be invoked in order to explain the complete
physicochemical properties of such color systems.48,56
The trifluoromethyl(phenyl) substituents on the nitrogen
atoms of L2 are almost perpendicular to the p-quinone
plane.
Synthesis of 1-4 and Crystal Structures of 2 and 4.
Reactions of L1-L4 with [Cl(η6-Cym)Ru(μ-Cl)2Ru(η6-
Cym)Cl] in the presence of a base resulted in the forma-
tion of 1-4, respectively, in excellent yields (Scheme 2).
The analytical purity of these complexes was determined
by 1H NMR spectroscopy, elemental analyses, and mass
spectrometry. Of the possible syn- and anti- isomers that
can form for such dinuclear compounds depending on
the orientation of the chloro ligands with respect to the
p-quinone plane, 1H NMR spectroscopy showed the pre-
ferential formation of only one isomer under our reaction
Compound 2 crystallized in the P21/c and 4 in the C2/c
space group. The quality of the crystallographic data for 4
is not very high, and despite several attempts of growing
better crystals, we were not successful in improving their
quality. However, the connectivity of the atoms can be
stated with full confidence, confirming the presence of the
chloride groups as well as the η6-Cym ligands in 4. From
the crystal structure, we were also able to unambiguously
identify the configuration of the complexes. To our
surprise, the chloro ligands in 2 as well as 4 turned out to
be in the synorientation. This is in contrast to what hasbeen
reported in the literature for dinuclear complexes with
similar ligands with the “Ir(Cp*)Cl” or “Rh(Cp*)Cl”
(56) Daehne, S.; Leopold, D. Angew. Chem., Int. Ed. 1966, 5, 984.

1154 Inorganic Chemistry, Vol. 50, No. 3, 2011
Schweinfurth et al.
has always been formulated as anti on the basis of compar-
ison with related structures (for example, Ir(III)).58,59 We
found the reverse in our case from structural analyses. The
chloride ions possibly adopt a syn orientation in order to
avoid repulsive interactions with the -CF3 or -SMe groups
on the phenyl substituents of the bridge. The Ru-O, Ru-N,
and Ru-Cl distances are typical for values reported in the
literature for such complexes (Table 3). The η6 coordination
mode of the Cym ligand is seen in the similar Ru-C bond
distances for all six carbon atoms of the arene ring. Thus, the
ruthenium centers have a piano-stool-type configuration in
these complexes. Analyses of the bond lengths within the
p-quinone ring in 2 show a tendency toward localization of
the double bonds in contrast to the free ligands (Table 2).34,48
Thus, the C1-O1 and C3-N2 distances in 2 are 1.281(8)
˚
Figure 5. ORTEP plot of 4. Ellipsoids are drawn at 50% probability.
Hydrogen atoms are omitted for clarity.
and 1.311(9) A, respectively. The corresponding distances in
2
L are 1.237(2) and 1.337(2) A, respectively. Similarly, the
˚
˚
C1-C2 and C2-C3 distances in 2 are 1.34(1) and 1.39(1) A,
˚
respectively, and the corresponding distances in L2 are
Table 2. Selected Bond Lengths (A)
˚
1.418(2) and 1.366(2) A, respectively. These results point
to a localization of double bonds within the p-quinone ring
L2
L4
2
4
8[ClO4]2
C1-O1
C4-O2
C3-Na
C6-N1
C1-C2
1.237(2) 1.233(2) 1.281(8) 1.30(1) 1.287(7)
1.294(8) 1.31(1)
1.337(2) 1.344(2) 1.311(9) 1.34(1) 1.336(7)
1.313(9) 1.32(1)
2
and the concomitant binding of L-2H through O- and
imine nitrogen atoms. These observations corroborate pre-
vious studies on dinuclear systems with similar ligands.34,48
1.418(2) 1.432(2) 1.34(1)
1.39(1) 1.384(8)
˚
The C1-C6 and C3-C4 distances at about 1.5 A remain
C1-C3/C1-C6b 1.519(2) 1.524(2) 1.511(9) 1.50(1) 1.503(8)
authentic C-C σ bonds in both the free ligands and the
metal complexes (Table 2). Although the bond lengths in 4
cannot be discussed with confidence because of the poor
quality of the crystal data, the trends seem to match those
described above for 2, as one would intuitively expect. The
C2-C3
C3-C4
C4-C5
C5-C6
1.366(2) 1.365(2) 1.39(1)
1.43(1) 1.393(8)
1.498(9) 1.49(1)
1.34(1)
1.41(1)
1.36(1)
1.43(1)
a C3-N refers to C3-N2 for 2 and 4 and C3-N1 for 8[ClO4]2. b The
bond C1-C6 in 2 and 4 is the same as the bond C1-C3 in the other
molecules. A uniform numbering is not possible because certain mole-
cules are centrosymmetric and others are not.
˚
Ru-S distance of more than 4 A in case of 4 clearly shows
that the SMe group does not coordinate to the metal centers
in this case. The Ru-Ru intramolecular distances are
7.964(2) and 8.051(1) A respectively for 2 and 4.
˚
˚
Table 3. Selected Bond Lengths (A) and Bond Angles (deg) for 2 and 4
Synthesis of 5-8 and Crystal Structure of 8. Reactions
of 1 or 2 with two equivalents of AgClO4 in acetonitrile
resulted in chloride abstraction and the expected forma-
tion of 5[ClO4]2 or 6[ClO4]2, respectively, where the
chloro ligands have been substituted by acetonitrile mo-
lecules (Experimental Section). Such reactions have been
observed before, and compounds related to 5[ClO4]2 or
6[ClO4]2 are often intermediates in the formation of
supramolecular systems.58,59 While carrying out the same
reaction under identical conditions with 4, we observed
that the 1H NMR spectrum of the formed product
(8[ClO4]2) showed no signals corresponding to the Cym
group (Scheme 3). Since there are reports in the literature
of Cym release from such molecules either through
excitation by light or because of the presence of an
oxidizing agent, we carried out the same reaction with 4
first in the dark and then by substituting AgClO4 with
NaClO4 as a chloride abstracting agent. In both of these
bond lengths
2
4
bond angles
2
4
Ru1-O1
Ru1-N1
Ru1-Cl1
Ru1-Ca
Ru2-O2
Ru2-N2
Ru2-Cl2
Ru2-Cb
Ru1-S1
Ru2-S2
Ru1-Ru2
2.083(4) 2.078(7) O1-Ru1-N1 76.2(2) 76.7(3)
2.083(5) 2.091(8) O1-Ru1-Cl1 83.2(1) 85.9(2)
2.414(2) 2.437(3) N1-Ru1-Cl1 85.0(2) 85.1(2)
1.669(8) 1.67(1)
2.065(5) 2.064(7) O2-Ru2-Cl2 83.6(2) 85.4(3)
2.092(6) 2.070(8) N2-Ru2-Cl2 85.0(2) 83.8(2)
2.403(2) 2.430(3)
1.669(8) 1.66(1)
4.304(4)
4.275(4)
7.964(2) 8.051(1)
O2-Ru2-N2 76.2(2) 77.4(3)
a Ru1-C refers to the distance between the Ru centerand the centroid
of the p-Cym ring. b Ru2-C refers to the distance between the Ru center
and the centroid of the p-Cym ring.
(Cp*=pentamethylcyclopentadienyl) fragments, where
X-ray crystallography showed the presence of the chloro
ligands in an anti configuration.57 To the best of our knowl-
edge, there are no reports of crystal structures of dinuclear
complexes with substituted p-quinone ligands that have
“Ru(Cym)Cl” fragments as in the present case. In cases where
such complexes have been synthesized, the configuration
1
cases, there was again no sign of the Cym signals in H
NMR spectrum of the product. At this point, we thought
of the possible importance of the SMe groups in the side
arm of the ligand L-2H4 in Cym release. In order to verify
this hypothesis, we carried out the chloride abstraction
reaction with 3 in acetonitrile. In keeping with our
hypothesis, the product 7[ClO4]2 formed in this case
showed the presence of only one Cym group per molecule
of 7[ClO4]2, thus proving the importance of the SMe
(57) Jia, W.-G.; Han, Y.-F.; Lin, Y.-J.; Weng, L.-H.; Jin, G.-X. Organo-
metallics 2009, 28, 3459.
(58) Therrien, B.; Fink, S.-G.; Govindaswamy, P.; Renfrew, A. K.;
Dyson, P. J. Angew. Chem., Int. Ed. 2008, 47, 3773.
(59) Han, Y.-F.; Jia, W.-G.; Lin, Y.-J.; Jin, G.-X. Organometallics 2008,
27, 5002.
3
group since the bridging ligand L-2H in this case has a
SMe group on only one side of the molecule (Scheme 3).

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 1155
Scheme 3
bonds within the p-quinone ring, as has been pointed out
above for 2 and 4.34,48
The bis-tridentate coordination mode of the bridging
4
ligand L-2H as confirmed by X-ray crystal structure
raises some interesting points about binding modes and
the resulting reactivity observed. Ruthenium complexes
of η6-arene ligands are text book examples of piano-stool
complexes, and this has been observed in our case for 2
and 4.60 The η6-arene ligand in a piano-stool complex
“dictates” the facial coordination of the other three donor
atoms at the metal center. In cases where ligand rigidity
together with strong donation force a meridional coordi-
nation, a direct Cym release has been observed in the
literature previously,61 with bis(imino) pyridine ligands
being an important example showing such an effect.62
Substitution of one arene ring with another has also been
studied in the context of hemilability.63 In our case, the
isolation of 4 proves that such a direct Cym release does
not occur. The abstraction of chloride atoms from 4
certainly increases the Lewis acidity at the metal center.
However, this increase of Lewis acidity alone is not
sufficient for the binding of SMe and concomitant release
of Cym, as has been proven by the observation of the [M-
2Cl-]2þ peak for 42þ in mass spectrometry experiments in
the gas phase (Experimental Section). This probably has
to do with the need of finding suitable coordinating atoms
for substituting the Cym ligand. On carrying out these
chloride abstraction reactions in a coordinating solvent
such as acetonitrile, we believe there are several phenom-
ena that occur simultaneously. Chloride abstraction in-
creases the Lewis acidity at the metal center, and this
facilitates the binding of the SMe group, which stays
otherwise uncoordinated in the chloro complex 4. The
Figure 6. ORTEP plot of 8[ClO4]2. Ellipsoids are drawn at 50% prob-
ability. Hydrogen atoms and perchlorate ions are omitted for clarity.
Final proof of the structure came from the successful
growth of suitable single crystals of 8[ClO4]2 as a toluene
solvate (Figure 6). This compound crystallizes in the P1h
space group. Each ruthenium center is in a distorted
octahedral environment, the distortion being imposed
by the two chelating rings formed at each of the ruthe-
nium centers by the bridging ligand. Accordingly, the
O1-Ru-N1 and S1-Ru-N1 angles of 79.7(2)° and
86.0(1)° are smaller than the 90° angle expected for a
perfect octahedron. The bridging ligand now binds in a
bis-tridentate fashion with the SMe group also coordi-
nated to the metal centers. The additional coordination
sites are taken up by acetonitrile molecules. The Ru-O1,
Ru-N1, and Ru-S1 distances to the donor atoms of the
ligands L-2H4 are in the typical range for such distances
(Table 4). The Ru-N distances to the two acetonitrile
molecules that are trans to each other are rather similar
(Table 4). This is contrast to the Ru-N200 distance of
4
rigidity of the ligand L-2H because of partial double
bond character of the bonds around the donor atoms
prevents the facial binding mode of the O,N,S atoms and
˚
2.051(6) A to the acetonitrile molecule that is trans to the
imine N atom of the bridging ligand. The longer Ru-N
distance in this case compared to the Ru-N distances to
the two trans acetonitrile molecules is because of the
better trans influence of the imine N atoms of the bridging
ligand. The elongation of the C1-O1 distance and the
shortening of the C1-C2 distance on complexation
(Table 2) also points to a possible localization of double
(60) Elschenbroich, C. Organometallics; Wiley-VCH: Weinheim, Germany,
2006; pp 543.
(61) Braunstein, P.; Naud, F.; Pfaltz, A.; Rettig, S. J. Organometallics
2000, 19, 2676.
(62) Cetinkaya, B.; Cetinkaya, E.; Brookhart, M.; White, P. S. J. Mol.
Cat. A: Chem. 1999, 142, 101.
(63) Ozdemir, I.; Demir, S.; Cetinkaya, B.; Toupet, L.; Castarlenas, R.;
Fischmeister, C.; Diexneuf, P. H. Eur. J. Inorg. Chem. 2007, 2862.

1156 Inorganic Chemistry, Vol. 50, No. 3, 2011
Schweinfurth et al.
˚
Table 4. Selected Bond Lengths (A) and Bond Angles (deg) for 8[ClO4]2
bond lengths
bond angles
bond angles
Ru-O1
2.077(4)
2.016(5)
2.289(2)
2.007(5)
2.051(6)
2.014(5)
7.8534(8)
O1-Ru-N1
79.7(2)
88.3(2)
95.9(2)
89.6(2)
86.0(1)
87.9(2)
98.4(2)
93.9(2)
N1-Ru-N100
N1-Ru-N300
N100-Ru-N200
N200-Ru-N300
O1-Ru-S1
N1-Ru-N200
N100-Ru-N300
86.7(2)
91.9(2)
93.3(2)
87.9(2)
165.4(1)
175.6(2)
177.7(2)
Ru-N1
O1-Ru-N100
O1-Ru-N200
O1-Ru-N300
S1-Ru-N1
Ru-S1
Ru-N100
Ru-N200
Ru-N300
Ru-Ru
S1-Ru-N100
S1-Ru-N200
S1-Ru-N300
Figure 7. Cyclic voltammogram of 82þ in CH2Cl2/0.1 M Bu4NPF6 at
295 K. Scan rate: 100 mV/s. The ferrocene/ferrocenium couple was used
as an internal standard.
the simple substitution of the Cl- atom with the SMe
group. The Lewis acidic metal center, however, now wants to
bind the SMe group, which is possible only in a meridional
fashion. This meridional coordination is incompatible with a
piano-stool-type structure and the η6-binding mode of the
arene ligands. This leads to arene release, which is now aided
by the coordination of the acetonitrile molecules which take
up the other three meridional positions of the octahedron
Figure 8. EPR spectrum of in situ generated 83þ in CH2Cl2/0.1 M
Bu4NPF6 at 110 K with simulation (top) and 8þ in CH2Cl2/0.1 M
Bu4NPF6 at 295 K (bottom).
4
around the ruthenium centers. The bridging ligand L-2H
now has a bis-pincer-type coordination (Figure 6). Metal
complexes of pincer ligands have found use in a variety of
interesting and demanding chemical transformations in
recent times.64,65 The present reaction probably occurs in a
concerted step that includes simultaneous chloride abstrac-
tion, acetonitrile coordination, and Cym release. We believe
that the Cym ligand changes its denticity in this reaction
before being finally displaced. However, attempts at identi-
fying a defined intermediate via NMR spectroscopy were
not successful. Thus, we have here an example of coordina-
tion “on demand” and concomitant reactivity associated with
that. Such potentially hemilabile behavior can be extremely
useful for various catalytic processes. Strong proof of our
hypothesis of the need for chloride abstraction, donating
solvent molecules, as well as an additional donor atom in a
rigid bridging ligand also comes from the observation of the
formation of 7[ClO4]2 from 3 (Scheme 3). The bridging
ligand L-2H3 has an additional SMe donor only on one side,
and concomitantly Cym release is observed also from one
side.
and -0.06 V vs ferrocene/ferrocenium at 295 K in
CH2Cl2/0.1 M Bu4NPF6 and a reversible reduction
at -1.96 V (Figure 7). For comparison, the free ligand
L4 shows an irreversible oxidation at 1.01 V and a
reversible reduction process at -1.29 V under identical
conditions. Further ill defined irreversible reduction pro-
cesses were also observed for L4. The chloro precursors
1-4 as well as the complexes 5 and 6 showed only
irreversible responses in their cyclic voltammogram.
The UV-vis spectrum of 8[ClO4]2 shows a metal to
ligand charge transfer (MLCT) band at 708 nm. A further
band is observed at 371 nm, which can be assigned to a
πfπ* transition based on the bridge. The in situ gener-
ated one-electron oxidized species 83þ is EPR silent at
room temperature and shows a signal with rhombic
symmetry at 110 K in CH2Cl2/0.1 M Bu4NPF6 which
could be simulated with g1 = 2.143, g2 = 2.074, and g3 =
1.975 (Figure 8). The g anisotropy (Δg = g1-g3) of 0.168
and the gav of 2.065 points to a metal-centered spin and
the presence of a predominantly metal centered SOMO
(singly occupied molecular orbital) on one-electron oxi-
dation to 83þ. In contrast to this, the one-electron reduced
species 8þ shows an isotropic EPR spectrum at 295 K with
g = 1.998 (Figure 8), the closeness of which to the free
electron g factor of 2.0023 points to a predominantly
bridging ligand centered reduction. The hyperfine cou-
pling expected from the 14N (I = 1) nuclei was unfortu-
nately not resolved, possibly due to unfavorable line
width to hyperfine coupling constant ratios.
Electrochemistry, Spectroscopic Properties, and Substi-
tution Reactions of 8. The presence of two Ru(II) centers
and a redox-active quinone ligand as a bridge prompted
us to investigate the electrochemical properties of 82þ. 82þ
shows two reversible oxidation processes at -0.46
(64) B.-Ari, E.; Leitus, G.; Shimon, L. J. W.; Milstein, D. J. Am. Chem.
Soc. 2006, 128, 15390.
(65) Kohl, S. W.; Weiner, L.; Schwartsburd, L.; Konstantinovski, L.;
Shimon, L. J. W.; David, B.-Y.; Iron, M. A.; Milstein, D. Science 2009,
324, 74.

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 1157
Scheme 4
Initial attempts at substituting the CH3CN groups in
subsequent reactions, and initial success in that direction has
been observed with the substitution of CH3CN molecules
with PPh3. In view of the observed coordination on demand
behavior of the SMe groups and the ease of synthesizing such
ligands with our new method, we will concentrate our future
efforts in building up ligands with various additional donor
atoms with different amounts of flexibility and probe their
reactivities. In addition, compound 82þ provides a unique
opportunity of getting at systems with the potential of
multielectron reservoirs because of its inherent redox-rich
nature as well as the possibility of building in additional
redox-active components in place of the labile acetonitrile
ligands. Our current research is focused in that direction.
8[ClO4]2 for other ligands met with success. The reaction
of 8[ClO4]2 with excess PPh3 under refluxing conditions
leads to the coordination of two PPh3 molecules per ruthe-
nium center, resulting in 9[ClO4]2 (Scheme 4 and the Experi-
mental Section). The product was characterized by 1H and
31P NMR spectroscopy as well as mass spectrometry. At-
tempts at substituting the third acetonitrile molecule from
each ruthenium center did not meet with success even under
forcing conditions. We believe this to be because of the steric
bulk of the PPh3 ligands. The presence of doublets in the 31
P
NMR spectrum also confirmed the formation of a cis
product. This would be expected on the basis of the struc-
tural analysis of 8[ClO4]2, which showed a rather long
Ru-N (acetronitrile) bond which is trans to the imine N
atom of the bridging ligand.
Experimental Section
General Considerations. 2,5-Dihydroxybenzoquinone, 2-(tri-
fluoromethyl)aniline, 2-(methylthio)aniline, and PPh3 were pur-
chased from Sigma-Aldrich and Ru2(Cym)2Cl4 from ABCR.
For the metal complexes, all manipulations were carried out
under an argon atmosphere. The solvents used for metal com-
plex syntheses were dried and distilled under argon and degassed
by common techniques prior to use.
Instrumentation. The 1H, 13C{1H}, and 31P{1H} NMR spec-
tra were recorded on a Bruker AC 250 spectrometer. Electronic
absorption spectra were recorded on J&M TIDAS and Shimadzu
UV 3101 PC spectrophotometers. EPR spectra in the X-band
were recorded with a Bruker System EMX. EPR simulations
were carried out by the Simfonia program of Bruker. Cyclic
voltammetry was carried out in 0.1 M Bu4NPF6 solutions using
a three-electrode configuration (glassy-carbon working electrode,
Pt counter electrode, Ag wire as pseudoreference) and a PAR 273
potentiostat and function generator. The ferrocene/ferrocenium
(Fc/Fcþ) couple served as an internal reference. Elemental ana-
lyses were performed by the Perkin-Elmer Analyzer 240. Mass
spectrometry experiments were carried out using a Bruker Dal-
tronics Mictrotof-Q mass spectrometer
Conclusion
We have reported here on a straightforward one-pot and
green synthesis of symmetrically and rare asymmetrically
substituted biologically relevant p-quinone ligands. Some of
the ligands also contain an additional SMe donor group
which could act as a potentially hemilabile donor. Structural
characterization of the ligands shows a delocalization of
the double bonds in these molecules and the importance
of charge separated W-like merocyanine groups for their
complete understanding. Complexes of the form [{Cl(η6-
Cym)Ru}2(μ-BL-2H)] (BL-2H = bridging quinine ligand)
were synthesized with the doubly deprotonated forms of all
the ligands. Structural characterization of some of these
complexes has shown the η6-coordination mode of the arene
ligand and localization of the double bonds within the
p-quinone bridge. Reactions of these complexes with AgClO4
lead to the unprecedented substituent induced release of
p-Cym from these complexes only in cases where an addi-
tional SMe group is present in the bridging ligand. Structural
characterization of the thus formed complex [{(CH3CN)3Ru}2-
(μ-L-2H4)][ClO4]2 shows that the bridging ligand binds in a
bis-pincer-like meridional bis-tridentate fashion. The in-
crease in the Lewis acidity at the metal center on chloride
abstraction is made responsible for the coordination of the
SMe group, and the inability of the rigid bridging ligand to
take up a facial coordination as demanded by a piano-stool
configuration is suggested to induce p-Cym release. Such
stepwise reactivity of this complex shows the possible use of
the SMe groups in hemilabile behavior. Electrochemical
investigations on 82þ show the presence of two one-electron
oxidation processes at relatively low potentials as well as a
reduction process. EPR spectroscopy confirms the first
oxidation process as metal centered and the reduction
process as ligand centered. The presence of the labile solvent
molecules in 8[ClO4]2 makes this a good starting material for
Syntheses. 2-[2-(Trifluoromethyl)-anilino]-5-hydroxy-1,4-ben-
zoquinone (L1). 2,5-Dihydroxybenzoquinone (300 mg, 2.15 mmol)
was dissolved in acetic acid (40 mL), and 2-(trifluoromethyl)-
aniline (345 mg, 2.15 mmol) was added dropwise. This was
accompanied by a sudden color change from yellow to red. The
solution was refluxed for 4 h and allowed to cool down to room
temperature. After the addition of water (200 mL), a red solid
precipitated and could be collected by filtration. The crude
product was cleaned by column chromatography using silica
and CH2Cl2/MeOH (10/1) as the eluent. After evaporation of
the solvent, the product was obtained as a red solid (407 mg, 67%).
Anal. Calcd for C13H8F3NO3: C, 54.19; H, 3.24; N, 4.95. Found:
C, 54.42; H, 3.28; N, 4.64. 1H NMR (250 MHz, CDCl3): δ 5.84 (s,
1H, quinone-H), 6.03 (s, 1H, quinone-H), 7.39(t, 3JH-H =8.0 Hz,
3
1H, aryl-H), 7.46 (d, JH-H = 8.0 Hz, 1H, aryl-H), 7.62 (t,
3
3JH-H = 8.0 Hz, 1H, aryl-H), 7.74 (d, JH-H = 8.0 Hz, 1H,
aryl-H), 7.92 (s, 1H, NH). 13C{1H} NMR (62.9 MHz, CDCl3): δ
95.9 (OdC-C-C-NHR), 103.1 (OH-C-C-C-CdO), 123.2
1
2
(q, JC-F = 273 Hz, CF3), 125.1 (q, JC-F = 30 Hz, CF3-C),

1158 Inorganic Chemistry, Vol. 50, No. 3, 2011
Schweinfurth et al.
126.0 (aryl-C), 126.9 (aryl-C), 127.4 (q, 3JC-F = 5 Hz, CF3-C-
CH), 133.0 (aryl-C), 134.7 (q, 3JC-F = 2 Hz, CF3-C-C-NHR),
147.0 (NHR-C-CdO), 157.9 (OH-C-CdO), 180.4
(OdC-C-NHR), 182.2 (OdC-C-OH). 19F{1H} NMR (235
MHz, CDCl3): δ -61.5.
3JH-H = 6.9 Hz, 3H, CH(CH3)2), 1.27 (d, 3JH-H = 6.9 Hz, 3H,
CH(CH3)2), 1.89 (s, 3H, CH3), 2.20 (s, 3H, CH3), 2.46 (sept,
3JH-H = 7.9 Hz, 1H, CH(CH3)2), 2.86 (sept, 3JH-H = 6.9 Hz,
1H, CH(CH3)2), 4.92 (s, 1H, quinone-H), 4.96 (d, 3JH-H = 5.9
Hz, 1H, arene-H), 5.25 (d, 3JH-H = 5.6 Hz, 1H, arene-H), 5.27
(d, 3JH-H = 5.6 Hz, 2H, arene-H), 5.40 (d, 3JH-H = 6.0 Hz, 2H,
2,5-Di-[2-(trifluoromethyl)-anilino]-1,4-benzoquinone (L2). The
compound was prepared following the procedure for L1 by using
2,5-dihydroxybenzoquinone (300 mg, 2.15 mmol) and two equiva-
lentsof 2-(trifluoromethyl)aniline (690 mg, 4.30 mmol). The crude
product was cleaned by column chromatography using silica and
CH2Cl2 as the eluent. After evaporation of the solvent, the
product was obtained as a red solid (682 mg, 73%). X-ray-quality
crystals could be grown by the slow diffusion of hexane into a
dichloromethane solution. Anal. Calcd for C20H12F6N2O2: C,
3
arene-H), 5.48 (d, JH-H = 4.6 Hz, 1H, arene-H), 5.50 (d,
3JH-H = 4.6 Hz, 1H, arene-H), 5.85 (s, 1H, quinone-H), 7.39 (t,
3
3JH-H = 7.9 Hz, 1H, aryl-H), 7.57 (t, JH-H = 6.9 Hz, 1H,
=
aryl-H), 7.67 (d, 3JH-H = 8.7 Hz, 1H, aryl-H), 7.71 (d, 3JH-H
8.3 Hz, 1H, aryl-H).
[{Cl(η6-Cym)Ru}2(μ-L-2H2)] (2). The compound was prepared
following the procedure for 1 by using Ru2(Cym)2Cl4 (80 mg,
0.13 mmol) and ligand L2 (55.4 mg, 0.13 mmol). The desired
product was obtained as a purple solid (114 mg, 91%). Crystals for
X-ray diffraction could be obtained from the slow evaporation of
a CH2Cl2 solution. Anal. Calcd for C40H38Cl2F6N2O2Ru2: C,
49.75; H, 3.97; N, 2.90. Found: C, 49.64; H, 3.86; N, 2.82. MS (ESI)
Calcd for C40H38ClF6N2O2Ru2 ([M - Cl-]þ) and C40H38F6-
N2O2Ru2 ([M - 2 Cl-]2þ): m/z 931.06 and 447.44. Found:
931.06 and 447.56. 1H NMR (250 MHz, CD2Cl2): δ 1.09 (d,
1
56.35; H, 2.84; N, 6.57. Found: C, 56.08; H, 2.83; N, 6.48. H
NMR (250 MHz, CDCl3): δ 5.87 (s, 2H, quinone-H), 7.36 (t,
3JH-H = 8 Hz, 2H, aryl-H), 7.50 (d, 3JH-H = 8.0 Hz, 2H, aryl-H),
7.62 (t, 3JH-H = 8.0 Hz, 2H, aryl-H), 7.73 (d, 3JH-H = 8 Hz, 2H,
aryl-H), 8.02 (s, 2H, NH). 13C{1H} NMR (62.9 MHz, CDCl3): δ
96.9 (OdC-C-C-NHR), 123.4 (q, 1JC-F = 273 Hz, CF3), 124.9
(q, 2JC-F = 30 Hz, CF3-C-CH)), 125.9 (aryl-C), 126.4 (aryl-C),
3
3
3JH-H = 7 Hz, 6H, CH(CH3)2), 1.16 (d, JH-H = 7 Hz, 6H,
127.4 (q, JC-F = 5 Hz, CF3-C-CH-CH)), 133.0 (aryl-C),
135.3 (q, 3JC-F = 2 Hz, CF3-C-C-NHR), 146.8 (NHR-C-
CdO), 180.3 (OdC-C-NHR). 19F{1H} NMR (235 MHz,
CDCl3): δ -61.5.
CH(CH3)2), 1.86 (s, 6H, CH3), 2.31 (sept, 3JH-H = 7.0 Hz, 1H,
CH(CH3)2), 2.40 (sept, 3JH-H = 7.0 Hz, 1H, CH(CH3)2), 4.89 (d,
3JH-H = 6.5 Hz, 2H, arene-H), 4.95 (s, 2H, quinone-H), 5.19 (d,
3
3JH-H = 6.0 Hz, 2H, arene-H), 5.31 (d, JH-H = 6.1 Hz, 4H,
2-[2-(Methylthio)-anilino]-5-hydroxy-1,4-benzoquinone (L3). The
compound was prepared following the procedure for L1 by using
2,5-dihydroxybenzoquinone (300 mg, 2.15 mmol) and one equiva-
lent of 2-(methylthio)aniline (299 mg, 2.15 mmol). The crude
product was cleaned by column chromatography using silica and
CH2Cl2/MeOH (10/1) as the eluent. After evaporation of the
solvent, the product was obtained as a red solid (332 mg, 51.5%).
Anal. Calcd for C13H11NO3S: C, 59.76; H, 4.24; N, 5.36. Found:
C, 59.28; H, 4.07; N, 5.33. 1H NMR (250 MHz, CDCl3): δ 2.06 (s,
3H, SCH3), 5.27 (s, 1H, quinone-H), 5.97 (s, 1H, quinine-H), 7.24
(m, 2H, aryl-H), 7.37 (m, 2H, aryl-H), 8.33 (s, 1H, NH). 13C{1H}
NMR (62.9 MHz, CDCl3): δ 16.6 (CH3-SR), 95.2 (OdC-
C-C-NHR), 103.3 (OH-C-C-CdO), 123.1 (aryl-C), 126.84
(aryl-C), 127.1 (aryl-C), 129.5 (aryl-C), 133.2 (aryl-C), 135.1
(NHR-C-C-S-CH3), 146.2 (OdC-C-NHR), 158.5 (OH-
C-CdO), 180.1 (OdC-C-NHR), 182.7 (OdC-C-OH).
2,5-Di-[2-(methylthio)-anilino]-1,4-benzoquinone (L4). The com-
pound was prepared following the procedure for L1 by using 2,
5-dihydroxybenzoquinone (300 mg, 2.15 mmol) and two equivalents
of 2-(methylthio)aniline (598 mg, 4.30 mmol). After the reaction, no
further purification was necessary, and the red compound could be
obtained after filtration (720 mg, 87%). Crystals for X-ray diffrac-
tion could be obtained from the slow evaporation of a CHCl3/
MeOH solution. Anal. Calcd for C20H18N2O2S2: C, 62.50; H, 4.74;
arene-H), 7.46 (t, 3JH-H = 7.4 Hz, 2H, aryl-H), 7.63 (t, 3JH-H
7.8 Hz, 2H, aryl-H), 7.74 (m, 4H, aryl-H).
=
[{Cl(η6-Cym)Ru}2(μ-L-2H3)] (3). The compound was pre-
pared following the procedure for 1 by using Ru2(Cym)2Cl4
(80 mg, 0.13 mmol) and ligand L3 (33.9 mg, 0.13 mmol). The
compound was obtained as a reddish-purple solid (96 mg, 92%).
Calcd for C33H37Cl2NO3SRu2: C, 49.50; H, 4.66; N, 1.75.
Found: C, 49.48; H, 4.60; N, 1.73. MS (ESI) Calcd for
C33H37ClNO3SRu2 ([M - Cl-]þ): m/z 766.02. Found: 766.00.
1H NMR (250 MHz, CDCl3): δ 1.08 (d, 3JH-H = 6.9 Hz, 3H,
CH(CH3)2), 1.16 (d, 3JH-H = 6.9 Hz, 3H, CH(CH3)2), 1.24 (d,
3JH-H = 1.9 Hz, 3H, CH(CH3)2), 1.27 (d, 3JH-H = 2.0 Hz, 3H,
CH(CH3)2), 2.20 (s, 3H, CH3), 2.41 (s, 3H, CH3), 2.53 (s, 3H,
SCH3), 2.85 (sept, 3JH-H = 6.9 Hz, 1H, CH(CH3)2), 3.70 (sept,
3JH-H = 2.6 Hz, 1H, CH(CH3)2), 5.03 (s, 1H, quinone-H), 5.06
(d, 3JH-H = 4.8 Hz, 1H, arene-H), 5.25 (d, 3JH-H = 5.8 Hz, 2H,
3
arene-H), 5.34 (d, JH-H = 5.7 Hz, 1H, arene-H), 5.47 (d,
3
3JH-H =5.2 Hz, 3H, arene-H), 5.58 (d, JH-H =5.4 Hz, 1H,
arene-H), 5.83 (s, 1H, quinone-H), 7.12 (m, 1H, aryl-H), 7.21 (m,
2H, aryl-H), 7.36 (m, 1H, aryl-H).
[{Cl(η6-Cym)Ru}2(μ-L-2H4)] (4). The compound was pre-
pared following the procedure for 1 by using Ru2(Cym)2Cl4
(80 mg, 0.13 mmol) and ligand L4 (49.8 mg, 0.13 mmol). The
compound was obtained as a purple solid (120 mg, 93%). X-ray-
quality crystals could be obtained by the slow diffusion of ether
into a CH3CN/MeOH solution. Anal. Calcd for C40H44Cl2N2-
O2Ru2S2 þ 1/2CH2Cl2: C, 50.44; H, 4.70; N, 2.90. Found: C,
50.33; H, 4.76; N, 3.14. HRMS (ESI) Calcd for C40H44N2O2-
Ru2S2 ([M - 2 Cl-]2þ): m/z 426.0470. Found: 426.0461. 1H
1
N, 7.32. Found: C, 62.44; H, 4.42; N, 7.30. H NMR (250 MHz,
CD2Cl2):δ2.45 (s, 6H, SCH3), 5.95 (s, 2H, quinone-H), 7.27 (m, 4H,
aryl-H), 7.43 (m, 4H, aryl-H), 8.30 (s, 2H, NH). 13C{1H} NMR
(62.9 MHz, CDCl3):δ16.7 (CH3-SR), 96.3 (OdC-C-C-NHR),
123.0 (aryl-C), 126.5 (aryl-C), 126.9 (aryl-C), 129.7 (aryl-C), 132.8
(aryl-C), 135.8 (NHR-C-C-S-CH3), 146.3 (NHR-C-CdO),
180.4 (OdC-C-NHR).
3
NMR (400 MHz, CD3CN): δ 1.07 (d, JH-H = 6.9 Hz, 6H,
CH(CH3)2), 1.15 (d, 3JH-H = 6.9 Hz, 6H, CH(CH3)2), 1.82 (s,
6H, CH3), 2.58 (s, 6H, SCH3), 2.91 (sept, 3JH-H = 6.8 Hz, 2H,
CH(CH3)2), 4.78 (s, 2H, quinone-H), 5.01 (d, 3JH-H = 5.8 Hz,
2H, arene-H), 5.39 (d, 3JH-H = 6.0 Hz, 2H, arene-H), 5.52 (d,
[{Cl(η6-Cym)Ru}2(μ-L-2H1)] (1). Ru2(Cym)2Cl4 (80 mg, 0.13
mmol) and the ligand L1 (36.8 mg, 0.13 mmol) were dissolved in
CH2Cl2 (30 mL) under an argon atmosphere. NEt3 (1.0 mL) was
added, and the solution was stirred overnight at room tempera-
ture. The solution was concentrated, and the product was
precipitated by the addition of hexane. The compound was
filtered, washed with hexane, and dried in vacuo. The compound
was obtained as a reddish-purple solid (92 mg, 86%). Anal.
Calcd for C33H34Cl2F3NO3Ru2: C, 48.18; H, 4.17; N, 1.70.
Found: C, 47.86; H, 4.05; N, 1.66. MS (ESI) Calcd for C33H34-
ClF3NO3Ru2 ([M - Cl-]þ): m/z 788.03. Found: 788.03. 1H
3
3JH-H = 5.9 Hz, 2H, arene-H), 5.55 (d, JH-H = 6.0 Hz, 2H,
arene-H), 7.22 (t, 3JH-H = 6.9 Hz, 2H, aryl-H), 7.30 (d, 3JH-H
=
7.4 Hz, 2H, aryl-H), 7.36 (t, 3JH-H = 7.1 Hz, 2H, aryl-H), 7.44 (d,
3JH-H = 8.1 Hz, 2H, aryl-H).
[{(CH3CN)(η6-Cym)Ru}2(μ-L-2H1)][ClO4]2 (5[ClO4]2). Com-
plex 1 (24.7 mg, 0.03 mmol) and AgClO4 (12.0 mg, 0.06 mmol)
were dissolved in CH3CN (10 mL) under an argon atmosphere and
refluxed for 3 h. After cooling down to room temperature, the
solution was filtered and the filtrate collected. The solvent was
3
NMR (250 MHz, CDCl3): δ 1.09 (d, JH-H = 6.9 Hz, 3H,
CH(CH3)2), 1.16 (d, 3JH-H = 6.9 Hz, 3H, CH(CH3)2), 1.26 (d,

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 1159
evaporated and the product dried in vacuo. The compound was
obtained as a brown solid (20.0 mg, 78%). Anal. Calcd for
C37H40Cl2F3N3O11Ru2: C, 43.03; H, 3.90; N, 4.07. Found: C,
42.79; H, 3.65; N, 3.88. MS (ESI) Calcd for C33H34F3NO3Ru2
was obtained as a green solid (yield: 26.0 mg, 85%). Crystals for
X-ray diffraction could be obtained from a CH3CN/toluene
solution. Anal. Calcd for C32H34Cl2N8O10Ru2S2: C, 37.39; H,
3.33; N, 10.90. Found: C, 37.00; H, 3.51; N, 10.32. HRMS (ESI)
Calcd for C24H22N4O2Ru2S2 ([M - 2 ClO4- - 4 CH3CN]2þ): m/
([M - 2 ClO4 - 2 CH3CN]2þ): m/z 376.53. Found: 376.53. 1H
-
3
1
NMR (250 MHz, CD3CN): δ 1.17 (d, JH-H = 7.0 Hz, 6H,
z 332.9636. Found: 332.9645. H NMR (250 MHz, CD3CN):
CH(CH3)2), 1.28 (d, 3JH-H = 7.0 Hz, 6H, CH(CH3)2), 1.88 (s, 3H,
CH3), 2.09 (s, 3H, CH3CN), 2.15 (s, 3H, CH3CN), 2.21 (s, 3H,
CH3), 2.57 (sept, JH-H = 6.5 Hz, 1H, CH(CH3)2), 2.80 (sept,
δ 2.22 (s, 18H, CH3CN); 2.57 (s, 6H, SCH3), 6.83 (s, 2
H, quinone-H), 7.30 (t, JH-H =7.9 Hz, 2H, aryl-H), 7.47 (t,
3
3
3
3JH-H = 7.3 Hz, 2H, aryl-H), 7.73 (d, JH-H = 7.8 Hz, 2H,
3JH-H = 6.8 Hz, 1H, CH(CH3)2), 4.94 (s, 1H, quinone-H), 5.40 (d,
aryl-H), 8.16 (d, 3JH-H = 7.7 Hz, 2H, aryl-H).
3
3JH-H = 6.5 Hz, 1H, arene-H), 5.59 (d, JH-H = 5.0 Hz, 1H,
[{(CH3CN)(PPh3)2Ru}2(μ-L-2H4)][ClO4]2 (9[ClO4]2). Com-
plex 8[ClO4]2 (103 mg, 0.10 mmol) and PPh3 (262 mg, 1.00
mmol) were dissolved in MeOH (15 mL) under an argon atmo-
sphere. The solution was refluxed overnight and the solvent
evaporated. The crude product was purified by multiple column
chromatography using alumina and CH2Cl2/CH3CN (3/2) as
the eluent (three different columns with the same packing
material and the same eluent). The first deep-blue fraction was
collected, and the solvent was evaporated under reduced pres-
sure to afford the pure complex (34.0 mg 18%). Anal. Calcd for
C96H82Cl2N4O10P4Ru2S2: C, 60.28; H, 4.32; N, 2.93. Found: C,
59.94; H, 4.16; N, 3.06. MS (ESI) Calcd for C92H76N2O2-
arene-H), 5.61(d, 3JH-H = 6.0 Hz, 1H, arene-H), 5.69(d, 3JH-H
=
4.1 Hz, 2H, arene-H), 5.74 (d, 3JH-H = 4.1 Hz, 1H, arene-H), 5.85
(d, 3JH-H = 7.2 Hz, 2H, arene-H), 5.87 (s, 1H, quinone-H), 7.18 (t,
3JH-H = 8.4 Hz, 1H, aryl-H), 7.66(t, 3JH-H = 7.8 Hz, 1H, aryl-H),
7.84 (d, 3JH-H = 5.8 Hz, 1H, aryl-H), 7.94(d, 3JH-H = 8.1 Hz, 1H,
aryl-H).
[{(CH3CN)(η6-Cym)Ru}2(μ-L-2H2)][ClO4]2 (6[ClO4]2). By
using complex 2 (29.0 mg, 0.03 mmol) and AgClO4 (12.0 mg,
0.06 mmol) and following the procedure for 5[ClO4]2, the
compound was obtained as a brown-red solid after washing
with n-hexane (3 ꢀ 10 mL) and drying in vacuo (25 mg, 85%).
Anal. Calcd for C44H44Cl2F6N4O10Ru2: C, 44.94; H, 3.77; N,
4.76. Found: C, 44.96; H, 3.72; N, 4.80. HRMS (ESI) Calcd for
P4Ru2S2 ([M - 2 ClO4 - 2 CH3CN]2þ): m/z 816.12. Found:
-
816.13. 1H NMR (250 MHz, CD3CN): δ 2.34 (s, 6H, CH3CN),
3.62 (s, 6H, SCH3), 6.92 (s, 2H, quinone-H), 7.02-7.17 (m, 22H,
aryl-H), 7.20-7.38 (m, 25H, aryl-H), 7.45-7.65 (m, 21H, aryl-
H). 31P NMR (250 MHz, CD3CN): δ 35.45 (d, 2JP-P = 30.7 Hz,
2P), 37.65 (d, 2JP-P = 30.7 Hz, 2P).
C40H38F6N2O2Ru2 ([M - 2 ClO4 - 2 CH3CN]2þ): m/z
-
1
448.0462. Found: 448.0470. H NMR (250 MHz, CD3CN): δ
1.13 (d, 3JH-H = 6.9 Hz, 12H, CH(CH3)2), 1.78 (s, 6H, CH3),
2.15 (s, 6H, CH3CN); 2.30 (sept, JH-H = 5.1 Hz, 1H, CH-
3
3
(CH3)2), 2.55 (sept, JH-H = 6.9 Hz, 1H, CH(CH3)2), 5.01 (s,
X-Ray Crystallography. L2 was crystallized by the slow
diffusion of a dichloromethane solution layered with n-hexane
(1/5). Crystals for L4 were grown by slow evaporation of a
CHCl3/MeOH solution (1/4). Compound 2 was crystallized by
the slow evaporation of a dichloromethane solution. X-ray-
quality crystals of 4 could be obtained by the slow diffusion of
ether into a CH3CN/MeOH (1/1) solution. Crystals of 8[ClO4]2
for X-ray diffraction could be obtained from a CH3CN/toluene
(1/1) solution. Data collection was made using either a four
circle P4 diffractometer (Siemens, Madison (USA)) or a Kappa
CCD diffractometer. The measurements were carried out at
173 K or 100 K by using Mo KR radiation (graphite mono-
chromator). Phase problems were solved using the program
SHELXTL PC 5.03. Despite several attempts, we did not
manage to improve the quality of crystals for 4. The connectivity
however is clearly observed in this case and can be discussed with
confidence. CCDC 788042-788046 contain the CIF files for the
structures reported in the work.
2H, quinone-H), 5.08 (d, 3JH-H = 6.0 Hz, 1H, arene-H), 5.31 (d,
3JH-H = 6.5 Hz, 1H, arene-H), 5.56 (d, 3JH-H = 7.0 Hz, 4H,
arene-H), 5.61(d, 3JH-H =5.6Hz, 2H, arene-H), 7.44(t, 3JH-H
=
8.2 Hz, 1H, aryl-H), 7.65 (t, 3JH-H = 7.8 Hz, 2H, aryl-H), 7.80 (t,
3JH-H = 6.7 Hz, 1H, aryl-H), 7.87 (d, 3JH-H = 6.6 Hz, 2H, aryl-
H), 7.93 (d, 3JH-H = 7.4 Hz, 2H, aryl-H).
[(CH3CN)(η6-Cym)Ru(μ-L-2H3)Ru(CH3CN)3][ClO4]2
(7[ClO4]2). By using complex 3 (24.0 mg, 0.03 mmol) and
AgClO4 (12.0 mg, 0.06 mmol) and following the procedure for
5[ClO4]2, the compound was obtained as a bluish green solid
after washing with n-hexane (3 ꢀ 10 mL) and drying in vacuo
(18.9 mg, 83%). Anal. Calcd for C31H35Cl2N5O11Ru2S: C,
38.84; H, 3.68; N, 7.30. Found: C, 38.47; H, 3.65; N, 7.05.
-
HRMS (ESI) Calcd for C25H26N2O3Ru2S ([M - 2 ClO4 - 3
CH3CN]2þ, C23H25NO4Ru2S [M - 2 ClO4 - 4 CH3CN þ
-
H2O]2þ, and C23H23NO3Ru2S [M - 2 ClO4- - 4 CH3CN]2þ):
m/z 318.9876, 307.4796, and 298.4743. Found: 318.9881,
307.4812, and 298.4736. 1H NMR (250 MHz, CD3CN): δ 1.34
(d, 3JH-H = 6.9 Hz, 6H, CH(CH3)2), 2.14 (s, 9H, CH3CN), 2.27
(s, 3H, CH3CN), 2.57 (s, 3H, CH3), 2.58 (s, 3H, SCH3), 3.15
Acknowledgment. B.S. is indebted to the Stiftung Baden-
€
Wurttemberg for financial support of this project through the
3
3
(sept, JH-H = 5.5 Hz, 1H, CH(CH3)2), 5.62 (d, JH-H = 6.3
Hz, 2H, arene-H), 5.89 (d, 3JH-H = 6.4 Hz, 2H, arene-H), 5.95
(s, 1H, quinone-H), 6.66 (s, 1H, quinone-H), 7.48 (m, 2H, aryl-H),
7.72 (dd, 3JH-H = 10.2 Hz, 4JH-H = 1.6 Hz, 1H, aryl-H), 8.03
(dd, 3JH-H = 8.2 Hz, 4JH-H = 1.0 Hz, 1H, aryl-H).
[{(CH3CN)3Ru}2(μ-L-2H4)][ClO4]2 (8[ClO4]2). By using com-
plex 4 (27.7 mg, 0.03 mmol) and AgClO4 (12.0 mg, 0.06 mmol)
and following the procedure for 5[ClO4]2, the desired compound
Eliteprogram for Postdocs. Deutsche Forschungsgemeinschaft
(DFG, SFB 706) is also kindly acknowledged for financial
support. We are thankful to Dr. S. Strobel, Dr. I. Hartenbach,
and Dr. F. Lissner for crystallographic measurements.
Supporting Information Available: Crystallographic informa-
tion files for 2, 4, 8[ClO4]2, L2, and L4. This material is available
free of charge via the Internet at http://pubs.acs.org.