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Selenoquinones stabilized by ruthenium(II) arene complexes: synthesis, structure, and cytotoxicity.
DOI: 10.1002/chem.201304991
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& Ruthenium Selenoquinone Complexes
Selenoquinones Stabilized by Ruthenium(II) Arene Complexes:
Synthesis, Structure, and Cytotoxicity
Julien Dubarle-Offner,[a, b] Catherine M. Clavel,[c] Geoffrey Gontard ,[a, b] Paul J. Dyson,[c] and
Hani Amouri *[a, b]
Abstract: A new series of monoselenoquinone and diselenoquinone p complexes, [(h6-p-cymene)Ru(h4-C6R4SeE)] (R = H,
E = Se (6); R = CH3, E = Se (7); R = H, E = O (8)), as well as selenolate p complexes [(h6-p-cymene)Ru(h5-C6H3R2Se)][SbF6]
(R = H (9); R = CH3 (10)), stabilized by arene ruthenium moieties were prepared in good yields through nucleophilic
substitution reactions from dichlorinated-arene and hydroxymonochlorinated-arene
ruthenium
complexes
[(h6-pcymene)Ru(C6R4XCl)][SbF6]2 (R = H, X = Cl (1); R = CH3, X = Cl
(2); R = H, X = OH (3)) as well as the monochlorinated p com-
plexes [(h6-p-cymene)Ru(h5-C6H3R2Cl)][SbF6]2 (R = H (4); R =
CH3 (5)). The X-ray crystallographic structures of two of the
compounds, [(h6-p-cymene)Ru(h4-C6Me4Se2)] (7) and [(h6-pcymene)Ru(h4-C6H4SeO)] (8), were determined. The structures
confirm the identity of the target compounds and ascertain
the coordination mode of these unprecedented ruthenium
p complexes of selenoquinones. Furthermore, these new
compounds display relevant cytotoxic properties towards
human ovarian cancer cells.
Introduction
Unlike quinones, which are a prominent class of compounds
that play an important role in chemistry and biology, the related selenium quinones “C6H4Se2” are unstable and consequently
do not exist in nature, and hence their chemical and biological
properties remain unknown.[1] In fact, the replacement of the
oxygen atoms in quinone by the heavier chalcogen atoms,
sulfur or selenium, leads to highly reactive intermediates that
cannot be isolated in pure form due to the instability of the
unnatural functional groups C=E (E = S, Se).[2] Thus, examples
of isolated thioquinones are scarce and the parent compound
has been generated and characterized spectroscopically only
at low temperature (10 K) in an argon matrix.[3] These procedures illustrate the difficulty in isolating and stabilizing thioquinones. As for the hypothetical selenoquinone molecule
(Figure 1), it is even less stable. Our group has demonstrated
that group 9 transition metal complexes and in particular the
[a] Dr. J. Dubarle-Offner, G. Gontard , Dr. H. Amouri
Sorbonne Universits, UPMC Univ Paris 06, Universit Pierre et Marie Curie
Institut Parisien de Chimie Molculaire (IPCM) UMR 8232
4 place Jussieu, 75252 Paris cedex 05, France
Fax: (+ 33) 1-44-27-38-41
E-mail: hani.amouri@upmc.fr
[b] Dr. J. Dubarle-Offner, G. Gontard , Dr. H. Amouri
CNRS, Centre National de la Recherche Scientifique
Institut Parisien de Chimie Molculaire (IPCM) UMR 8232
4 place Jussieu, 75252 Paris cedex 05, France
Fax: (+ 33) 1-44-27-38-41
[c] C. M. Clavel, Prof. P. J. Dyson
Institut des Sciences et Ingnierie Chimiques
Ecole Polytechnique Fderale de Lausanne (EPFL)
1015 Lausanne (Switzerland)
Chem. Eur. J. 2014, 20, 5795 – 5801
Figure 1. Schematic drawing of the parent diselenoquinone molecule (reactive intermediate), the only known iridium-stabilized diselenoquinone (our
previous work, Ref. [6]), and the ruthenium-stabilized diselenoquinone (current work).
Cp*Ir moiety (Cp* = pentamethylcyclopentadienyl) have profound stabilizing properties towards reactive intermediates.[4]
Indeed, ortho-quinone methides as well as ortho- and para-dithiobenzoquinones were isolated as p complexes of Cp*Ir and
their molecular structures were determined.[5] More recently,
the first molecular structure of a diselenoquinone p complex
stabilized by Cp*Ir was confirmed by a single-crystal X-ray diffraction study.[6] Furthermore, this organometallic p complex
exhibits interesting anticancer activity towards human A2780
ovarian cancer cells with a cytotoxicity (IC50 = 5 mm) comparable to that of the benchmark metallodrug cisplatin (IC50 =
3 mm).[6] Indeed, metallocenes and organometallic p complexes
are currently being extensively studied as putative anticancer
agents as potential substitutes for the well-known clinically applied platinum-based drugs.[7]
Pursuing our research in the area of metal-stabilized reactive
intermediates, we investigated other organometallic moieties
that might stabilize the diselenoquinone reactive species. In
this context, the (p-cymene)Ru moiety appeared to be of interest. In addition to forming stable p complexes, this metal fragment is frequently encountered in the development of metal
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complexes with pharmacologically relevant properties.[8] In this
context, the most widely studied compounds are the halfsandwich complexes with either one or two chloride (leaving
group) ligands. Various techniques have been used to show
that these types of complexes can bind to biomolecular targets, and crystal structures confirming the loss of the chloride
ligands on binding to cancer-relevant targets have been reported.[9] Full-sandwich complexes comprising an arene ring
and a cyclopentadienyl or Cp* ring have also been evaluated,
and the complexes with the more lipophilic Cp* group display
cytotoxicites equivalent to cisplatin.[10]
Herein, we describe the synthesis and characterization of
a novel family of mono- and diselenoquinone complexes. The
X-ray molecular structures of two compounds of the above
series are also presented. Furthermore, the cytotoxicity of the
new complexes were investigated and compared to that of
the iridium compound.
Results and Discussion
Synthesis and characterization of chlorinated-arene
ruthenium p complexes 1–5
The coordination and activation of electron-poor halogenated
arenes by reaction with [Cp*Ru(CH3CN)3][OTf] (Tf = trifluoromethanesulfonyl) have been widely studied;[11] however, the related complexes with the (p-cymene)Ru moiety are less well investigated.[12] Hence, the synthesis of the novel organometallic
mono- and dichlorinated-arene and hydroxymonochlorinatedarene p complexes [(p-cymene)Ru(arene-(X)(Cl))][SbF6]2 (1–5)
(X = OH, Cl) was realized according to the following procedure.
A solvated [(h6-p-cymene)Ru(solvent)3][SbF6]2 compound was
generated in situ from the dimeric compound [(h6-p-cymene)RuCl2]2 and silver salt AgSbF6 in acetone, the filtered solution
was poured into an excess of the desired halogenated arene
ligand, and the mixture was stirred. The solvent was then
evaporated to dryness, trifluoroacetic acid was added, and the
mixture was heated to 90 8C for 2 h. Complexes 1 to 5 were
isolated as white air-stable powders in good yields (75 to 90 %;
Scheme 1).
All of the dicationic sandwich complexes were fully characterized by NMR spectroscopy and elemental analysis (see the
Experimental Section). 1H and 13C NMR spectra, recorded in
Scheme 1. Synthesis of (p-cymene)ruthenium halogenated-arene complexes
1–5.
Chem. Eur. J. 2014, 20, 5795 – 5801
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CD3NO2, showed the coordination of the halogenated arene
ring to the (p-cymene)Ru moiety. For instance, complex 1 exhibits a singlet at d = 7.39 ppm, attributed to the halogenated
aromatic protons slightly downfield relative to the free aromatic ligand, and a doublet of doublets due to the (p-cymene)Ru
unit at d = 7.10 ppm, which is downfield relative to the starting
material ruthenium dimer [(p-cymene)2Ru(m-Cl)2Cl2]. Furthermore, three signals for the alkyl protons of the (p-cymene)Ru
moiety are displayed at d = 2.97, 2.49, and 1.42 ppm, respectively, which are also downfield relative to the starting material.
Full spectroscopic data of complexes 1–5 are given in the Experimental Section.
Synthesis and characterization of mono- and diselenoquinone ruthenium p complexes 6–8 and the selenolate
ruthenium complexes 9 and 10
Organometallic sandwich and half-sandwich complexes are
well known to drastically modify the electrophilicity and hence
the reactivity of the aromatic unit coordinated to the metal
center.[5, 11] The arene rings are mostly susceptible to nucleophilic additions and halogen-substitution reactions as illustrated in our complexes (see below). The preparation of the novel
family of selenoquinone p compounds followed the path already described by us for the synthesis of the para-diselenobenzoquinone–iridium complex.[6] Thus, the white dihalogenated RuII complexes 1 and 2 were reacted in acetonitrile with
Na2Se through a double nucleophilic substitution reaction to
afford the neutral ruthenium diselenobenzoquinone p complexes 6 and 7 as deep-red powders in almost quantitative
yields (Scheme 2).
Scheme 2. Preparation of diselenoquinone p complexes [(p-cymene)Ru(C6H4Se2)] (6) and [(p-cymene)Ru(C6Me4Se2)] (7).
Complexes 6 and 7 were fully characterized by spectroscopic
methods and elemental analysis. For instance, the 1H NMR
spectrum of [(p-cymene)Ru(C6H4Se2)] (6) recorded in CD2Cl2
showed an upfield shift of the four protons of the p-bonded
selenoquinone “h-C6H4Se2” unit relative to that of starting complex [(p-cymene)Ru(C6H4Cl2)][SbF6]2 (1), which appeared as a singlet at d = 6.40 ppm. In a similar fashion the four aromatic protons of the (p-cymene)Ru unit appeared as a doublet of doublets centered at d = 6.30 ppm upfield relative to that of 1.
Moreover, the three alkyl signals of the (p-cymene)Ru unit appeared at d = 2.65, 2.13, and 1.36 ppm, respectively, and were
also upfield relative to the dihalogenated p complex 1. Full
characterization details of both complexes are given in the Experimental Section. Furthermore, after many attempts, crystals
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of 7 were grown from CH2Cl2/Et2O and the structure was determined by X-ray diffraction, which confirmed the formation of
the target complex (see below).
To probe the effect of the selenium center on the anticancer
activity of this kind of complex, we attempted the synthesis of
a mixed selenoquinone p complex [(p-cymene)Ru(C6H4SeO)] (8)
starting from the complex 3 carrying a p-bonded para-chlorophenol. We anticipated that chloride substitution by a selenide
anion and subsequent phenol deprotonation should give the
target mixed selenoquinone p complex [(p-cymene)Ru(C6H4SeO)] (8).
Thus, in a similar way to that described for 1 and 2, complex 3 reacted with NaSe2 through nucleophilic substitution of
one chloride ligand with the simultaneous deprotonation of
the phenol leading to the desired monoselenoquinone complex [(p-cymene)Ru(C6H4SeO)] (8) in 97 % yield (Scheme 3). As
Molecular structures of diselenobenzoquinone
[(p-cymene)Ru(C6Me4Se2)] (7) and monoselenoquinone
[(p-cymene)Ru(C6H4SeO)] (8)
Single crystals suitable for X-ray diffraction analysis of complexes 7 and 8 were obtained at room temperature by vapor
diffusion of diethyl ether into a dichloromethane solution.
Crystal data are given in Table 1, the molecular structures of 7
and 8 are depicted in Figure 2, and key bond parameters are
listed in Table 2. The crystal structure of 7 contains partial disorder for the p-bonded diselenoquinone unit. This disorder
was successfully modeled by using two orientations with
a ratio of 60:40, in which the positions of all six carbon atoms
of the ring remain unchanged. Four of these atoms (C1, C3,
C4, and C6) are bound alternatively to a methyl group or to selenium and their positions are averaged. However, the structure clearly indicates that the (p-cymene)Ru moiety is coordi-
Table 1. Crystallographic data for [(h6-p-cymene)Ru(h4-C6Me4Se2)] (7) and
[(h6-p-cymene)Ru(h4-C6H4SeO)] (8).
Scheme 3. Preparation of monoselenoquinone mixed complex [(pcymene)Ru(C6H4SeO)] (8).
expected, the 1H NMR spectrum of 8 recorded in CD2Cl2
showed a general upfield shift relative to 3. For instance, the
four protons of the monoselenoquinone unit “h-C6H4SeO”
appear as two doublets at d = 5.66 and 5.01 ppm, and the aromatic protons of the (p-cymene)Ru unit give rise to a pair of
doublets at d = 6.08 and 5.94 ppm. As described previously,
the three signals attributed to the alkyl protons of the (p-cymene)Ru unit are all upfield relative to the starting material 3.
Furthermore, crystals of 8 were grown from a solution of
CH2Cl2/Et2O and the structure was determined by X-ray diffraction to confirm the formation of this unique complex displaying both quinone and selenoquinone functions (see below).
The preparation of the cationic ruthenium selenolate p complexes 9 and 10 was also carried out to probe the charge
effect of these compounds on their antitumor activities relative
to the neutral complexes. The halogen precursors 4 and 5
were then treated with Na2Se in acetonitrile in a similar way to
that described for 1–3 and provided, following purification, the
ruthenium selenolate arene salts [(p-cymene)Ru(h5-C6H5Se)][SbF6] (9) and [(p-cymene)Ru(h5-C6H3Me2Se)][SbF6] (10) as red
microcrystalline powders (Scheme 4).
Compound
7
8
chemical formula
formula weight
crystal system
space group
a []
b []
c []
a [8]
b [8]
g [8]
V [3]
Z
1calcd [Mg m 3]
T [K]
l []
m [mm 1]
F(000)
crystal size [mm3]
q range for data
collection [8]
index ranges
C20H26RuSe2
525.40
trigonal
R3̄
34.1673(9)
34.1673(9)
11.2302(3)
90
90
120
8637.9(5)
18
1.818
200(1)
1.54178
10.902
4644
0.2 0.05 0.05
2.55 to 66.42
C16H18ORuSe
406.33
monoclinic
P21/c
7.3345(2)
9.5268(3)
20.9231(6)
90
97.0860(10)
90
1450.82(7)
4
1.860
200(1)
1.54178
11.512
800
0.25 0.15 0.15
4.26 to 66.48
39 h 40
40 k 36
10 l 8
8594
3201 [R(int) = 0.0349]
8h8
11 k 9
24 l 24
10 389
2521 [R(int) = 0.0227]
95.7 % to q = 65.918
semiempirical from
equivalents
0.5186 and 0.7527
98.1 % to q = 66.488
semiempirical from
equivalents
0.3182 and 0.1570
full-matrix leastsquares on F2
3201/1/253
full-matrix leastsquares on F2
2521/0/176
1.030
R1 = 0.0324,
wR2 = 0.0753
R1 = 0.0443,
wR2 = 0.0806
0.621 and 0.327
1.142
R1 = 0.0216,
wR2 = 0.0602
R1 = 0.0219,
wR2 = 0.0604
0.514 and 0.402
reflections collected
independent
reflections
completeness
absorption correction
max. and min.
transmission
refinement method
data/restraints/
parameters
goodness-of-fit on F2
final R indices [I > 2s(I)]
R indices (all data)
Scheme 4. Preparation of cationic selenolate p complexes [(p-cymene)Ru(h5C6H5Se)][SbF6] (9) and [(p-cymene)Ru(h5-C6H3Me2Se)][SbF6] (10).
Chem. Eur. J. 2014, 20, 5795 – 5801
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Figure 2. Molecular structures of [(h6-p-cymene)Ru(h4-C6Me4Se2)] (7; left) and
[(h6-p-cymene)Ru(h4-C6H4SeO)] (8; right) with atom numbering systems. Hydrogen atoms are omitted for clarity.
Table 2. Selected bond lengths and angles for [(h6-p-cymene)Ru(h4C6Me4Se2)] (7) and [(h6-p-cymene)Ru(h4-C6H4SeO)] (8).
Lengths []/Angles [8]
7
8
Ru C2
Ru C5
Ru C3
Ru C6
Ru C1
Ru C4
C4 O1
C1 Se1A
C4 Se2A
C1 Se1
2.217(4)
2.219(4)
2.275(4)
2.260(4)
2.283(4)
2.270(4)
–
1.838(4), 1.919(4)
1.957(4), 1.890(4)
–
2.188(2)
2.203(2)
2.215(2)
2.195(2)
2.295(2)
2.496(2)
1.237(3)
–
–
1.873(3)
C2-C1-C6
C3-C4-C5
C8-C7-C12
C9-C10-C11
C15-C14-C16
118.7(4)
118.9(4)
117.1(5)
116.7(5)
110.9(5)
114.8(2)
110.6(2)
117.5(2)
117.3(2)
110.2(3)
Anticancer activity of complexes 6–10 towards human
ovarian cancer cells
The cytotoxicity of the compounds was evaluated against
human ovarian cancer cells, cisplatin-sensitive A2780 cells and
A2780R cells with acquired resistance to cisplatin, by using the
MTT assay (see the Experimental Section). IC50 values of complexes 6–10, that is, the drug concentration killing 50 % of the
cells, are listed in Table 3.
Table 3. IC50 values of complexes 6–10 against A2780 and A2780R
human ovarian cancer cells at 72 h.
nated to only four diene carbon atoms of the p-diselenoquinone unit. The average Ru C=(Se/C) distance of 2.272(4) is
significantly longer than the Ru C=C distances, average
2.218(4) (C2, C5), yet shorter than the Ir C=Se distance, average 2.359 , for the only known compound [Cp*Ir(C6H4Se2)] reported previously by us.[6] Moreover, the C Se bond lengths
for 7 average 1.901(4) , which is slightly longer than that reported for the iridium selenoquinone complex, that is, 1.870 .
The structure also shows that the h4-selenoquinone ligand
adopts a boatlike conformation, although the angles between
the selenoquinonoid carbon atoms and the diene plane could
not be determined precisely for 7 due to the partial disorder.
The molecular structure of 8 confirmed the formation of the
target complex and shows that the (p-cymene)Ru moiety is
indeed coordinated to only four diene carbon atoms. The Ru
C=C bond lengths average 2.200(2) and are shorter than the
Ru C=Se distance, 2.295(2) , and that of Ru C=O, 2.496(2) .
Remarkably, the boatlike conformation displayed by the monoselenoquinonoid unit is nonsymmetric with hinge angles of
q = 6.4(3)8 for C Se and q = 19.7(2)8 for C O, consistent with
the electronic nature of each of the chalcogen atoms attached
to the ring. The C Se distance determined for 8 is 1.873(3) ,
which is indicative of partial double-bond character and comparable (C=Se, 1.870 ) to that found for the related iridium selenoquinone compound [Cp*Ir(C6H4Se2)].[6] These bond lengths
Chem. Eur. J. 2014, 20, 5795 – 5801
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are shorter than that reported for diselenocin with a C Se
single bond of 1.924(8) [13] and are closer in value to the C=Se
double bond of 1.857(9) reported for 2-selenoxoperhydro1,3-selenazin-4-one.[14] The C=Se bond in 8 is slightly longer
than that reported for seleno-acrylamide with a C=Se doublebond length of 1.837(4) ,[15] selenobenzyl amide of length
1.830(2) ,[16] and 4,4’-dimethoxy-selenobenzophenone with
a C=Se bond length of 1.79 .[17] However, the reported bond
length for a selenoaldehyde–tungsten complex is 1.854 ,[18]
which is comparable to that found in 8. Consequently, the free
C=Se bond is expected to be shorter than that present in
a metal complex.
Complex
IC50 in A2780 [mm]
IC50 in A2780R [mm]
6
7
8
9
10
cisplatin[a]
[Cp*Ir(C6H4O2)][a]
[Cp*Ir(C6H4Se2)][a]
25 1
41 3
75 1
19 1
49 3
3
93
5
51 2
61 3
74 2
36 6
240 46
25 2
–
–
[a] Taken from Ref. [6].
The ruthenium selenolate arene salt [(h6-p-cymene)Ru(h5C6H5Se)][SbF6] (9) is the most cytotoxic compound in both cell
lines with an IC50 of 19 mm in A2780 and 36 mm in A2780R
cells, followed closely by the neutral ruthenium diselenobenzoquinone p complex 6 (IC50 = 25 mm in A2780 and 51 mm in
A2780R cells). Previously, we also found the diselenobenzoquinone of iridium to be more cytotoxic than the oxygen-containing analogues (see Table 3), although the cytotoxicity of [Cp*Ir(C6H4Se2)] is closer in value to that of cisplatin in the A2780 cell
line.[6] With methyl substituents on the selenium-bearing arene,
complex 10 exhibits a lower cytotoxicity (IC50 = 49 mm in cisplatin-sensitive cancer cells and IC50 = 240 mm in cisplatin-resistant
cells). The same trend is observed for 6 and 7, with 7 being
less cytotoxic against both cell lines, although to a lesser
extent (IC50 = 41 and 61 mm in A2780 and A2780R, respectively).
Bulkier arenes therefore appear to lower the activity of these
complexes, possibly by reducing their stability in the pharmacological environment so that less of the intact compound
enters the cells. Lastly, compound 8 is the least active com-
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pound against A2780 cells (IC50 = 75 mm) although it maintains
the same level of activity in cisplatin-resistant cells (IC50 =
74 mm). The trends observed here contrast somewhat with previous studies on full-sandwich (arene)Ru complexes combined
with cyclopentadienyl or Cp* rings, in which the more hydrophilic cyclopentadienyl-containing complexes are considerably
less cytotoxic than the more lipophilic complexes containing
the Cp* ring.[10]
Conclusion
We have reported the preparation of a unique family of organometallic ruthenium complexes that stabilize selenolate, diselenobenzoquinone, and monoselenoquinone entities through pbonding interactions to a (p-cymene)RuII moiety. Selenium
compounds have a number of important biological functions,[19] so we assessed the possible cytotoxicity of these
unique compounds on cancer cells. Indeed, it is expected that
the selenoarene ring would slowly dissociate inside the cells
and induce a cytotoxic effect—the presumably solvated (pcymene)Ru byproduct is known to exert negligible cytotoxicity.
The complexes display moderate cytotoxicities although clear
structure–activity correlations could not be gauged. Nevertheless, these compound display interesting properties and in the
future mechanistic studies will be required to delineate their
precise mechanism of action.
Experimental Section
dissolved in a minimum of trifluoroacetic acid (ca. 2–3 mL). The resulting mixture was heated at reflux during 90 min. After cooling,
the filtrate was removed and the precipitate was washed with
small portions of diethyl ether to provide a white air-stable
powder.
Synthesis of [(h6-p-cymene)Ru(h6-1,4-dichlorobenzene)][SbF6]2 (1)
1,4-Dichlorobenzene (white crystalline solid) was used as ligand to
provide complex 1 as a white air-stable powder. Yield: 75 %.
1
H NMR (CD3NO2): d = 7.39 (s, H p-dichlorobenzene, 4 H), 7.12 (d,
3
J = 7.0 Hz, H p-cymene, 2 H), 7.08 (d, 3J = 7.0 Hz, H p-cymene, 2 H),
2.99 (sept, 3J = 6.8 Hz, H iPr, 1 H), 2.49 (s, Me, 3 H), 1.42 ppm (d, 3J =
6.8 Hz, Me iPr, 6 H); 13C NMR (CD3NO2): d = 122.4 (2 C-Cl), 113.9,
112.9 (2 C, p-cymene), 95.2 (2 CH, p-cymene), 93.3 (4 CH, dichlorobenzene), 92.8 (2 CH, p-cymene), 29.2 (1 Me), 19.3 (2 Me), 15.6 ppm
(CH); elemental analysis calcd (%) for C16H18Cl2F12RuSb2
(853.79 g mol 1): C 22.51, H 2.12; found: C 22.42, H 2.07.
Synthesis of [(h6-p-cymene)Ru(h6-1,4-dichloro-tetramethylbenzene)][SbF6]2 (2)
1,4-Dichloro-tetramethylbenzene (white crystalline solid) was used
as ligand to provide complex 2 as a white air-stable powder. Yield:
80 %. 1H NMR (CD3NO2): d = 6.78 (d, 3J = 6.8 Hz, H p-cymene, 2 H),
6.67 (d, 3J = 6.8 Hz, H p-cymene, 2 H), 2.97 (sept, 3J = 6.8 Hz, H iPr,
1 H), 2.84 (s, 4 Me, 12 H), 2.44 (s, Me, 3 H), 1.40 ppm (d, 3J = 6.8 Hz,
Me iPr, 6 H); 13C NMR (CD3NO2): d = 122.4 (2 C-Cl), 115.8, 113.6 (2 C,
p-cymene), 110.2 (4 C, chloroarene), 97.3 (2 CH, p-cymene), 94.7
(2 CH, p-cymene), 20.7 (1 Me), 29.9 (4 Me), 21.3 (1 Me), 18.6 (2 Me),
16.9 ppm (CH); elemental analysis calcd (%) for C20H26Cl2F12RuSb2
(909.90 g mol 1): C 26.40, H 2.88; found: C 26.45, H 2.89.
General experimental methods
Glassware was oven-dried prior to use. All reactions were carried
out using Schlenk techniques for synthesis of the complexes under
an argon atmosphere. THF and diethyl ether were distilled from
sodium benzophenone. CH2Cl2 was distilled from CaH2. Other reagents were obtained from commercial suppliers and used as received. 1H NMR spectra were recorded at 300 or 400 MHz in CD2Cl2
and CD3NO2. Data are reported as follows: chemical shift in ppm
from tetramethylsilane with the solvent as an internal standard
(CD2Cl2 d = 5.32 ppm, CD3NO2 d = 4.33 ppm), multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet or overlap of
nonequivalent resonances). 13C NMR spectra were recorded at 75
or 100 MHz in CD2Cl2 and CD3NO2. Data are reported as follows:
chemical shift in ppm from tetramethylsilane with the solvent as
an internal standard (CD2Cl2 d = 54.0 ppm, CD3NO2 d = 62.0 ppm).
Infrared spectra were measured using a Tensor 27 (ATR diamond)
Bruker spectrometer. IR data are reported as characteristic bands
(cm 1). The dimer [(h6-p-cymene)RuCl2]2 was synthesized according
to a literature report.[20]
General procedure for the preparation of
[(h6-p-cymene)Ru(h6-chloroarene)][SbF6]2 complexes
A Schlenk flask under argon was charged with AgSbF6 (449 mg,
1.306 mmol) and [(h6-p-cymene)RuCl2]2 (200 mg, 0.326 mmol). Once
dissolved in acetone (10 mL), the reaction mixture was stirred at
room temperature in the dark during 20 min. AgCl precipitate was
removed by filtration and the filtrate was directly poured onto
a large excess of the desired chloroarene (ca. 10 equiv). The acetone was evaporated until dryness. The resulting orange paste was
Chem. Eur. J. 2014, 20, 5795 – 5801
www.chemeurj.org
Synthesis of [(h6-p-cymene)Ru(h6-4-chlorophenol)][SbF6]2 (3)
4-Chlorophenol (white solid) was used as ligand to provide complex 3 as a pale-yellow air-stable powder. Yield: 78 %. 1H NMR
(CD3NO2): d = 7.05 (d, 3J = 6.9 Hz, H p-chlorophenol, 2 H), 6.92 (d,
3
J = 6.3 Hz, H p-cymene, 2 H), 6.85 (d, 3J = 6.3 Hz, H p-cymene, 2 H),
6.66 (d, 3J = 6.9 Hz, H p-chlorophenol, 2 H), 3.86 (s, OH, 1 H), 2.95
(sept, 3J = 6.9 Hz, H iPr, 1 H), 2.42 (s, 1 Me, 3 H), 1.38 ppm (d, 3J =
6.9 Hz, Me iPr, 6 H); 13C NMR (CD3NO2): d = 142.5 (1 C-OH), 122.4
(1 C-Cl), 113.5, 109.8 (2 C p-cymene), 97.1, 95.2 (2 CH p-cymene),
94.7 (2 CH chlorophenol), 94.1, 92.4 (2 CH p-cymene), 83.1, 80.7
(2 CH chlorophenol), 32.9 (1 Me), 22.7 (2 Me), 16.9 ppm (CH); elemental analysis calcd (%) for C16H19ClF12ORuSb2 (835.35 g mol 1): C
23.01, H 2.29; found: C 23.05, H 2.30.
Synthesis of [(h6-p-cymene)Ru(h6-chlorobenzene)][SbF6]2 (4)
Chlorobenzene (liquid) was used as ligand to provide complex 4 as
a white air-stable powder. Yield: 90 %. 1H NMR (CD3NO2): d = 7.34
(d, 3J = 6.6 Hz, H p-chloroarene, 2 H), 7.15 (d, 3J = 6.3 Hz, H pcymene, 2 H), 7.04 (m, 2 H p-cymene and 2 H p-chloroarene, 4 H),
6.97 (t, 3J = 6.0 Hz, H p-chloroarene, 1 H), 3.08 (sept, 3J = 6.9 Hz, H
iPr, 1 H), 2.56 (s, Me, 3 H), 1.40 ppm (d, 3J = 6.9 Hz, Me iPr, 6 H);
13
C NMR (CD3NO2): d = 125.0 (C-Cl), 116.3, 115.7 (2 C p-cymene),
96.8, 96.2, 95.6, 95.0, 94.4 (4 CH p-cymene, 5 CH chlorobenzene),
+ 32.8 (1 Me), 22.3 (2 Me), 18.9 ppm (CH); 13C NMR (CD3NO2): d =
125.0 (C-Cl), 116.3, 115.7 (2 C p-cymene), 96.8, 96.2, 95.6, 95.0, 94.4
(4 CH p-cymene, 5 CH chlorobenzene), 32.8 (1 Me), 22.3 (2 Me),
18.9 ppm (CH); elemental analysis calcd (%) for C16H19ClF12RuSb2
(819.35 g mol 1): C 23.45, H 2.34; found: C 23.15, H 2.24.
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2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Synthesis of [(h6-p-cymene)Ru(h6-2-chloro-1,3dimethylbenzene)][SbF6]2 (5)
7.2 Hz, H iPr, 1 H), 2.28 (s, Me, 3 H), 1.36 ppm (d, 3J = 7.2 Hz, Me iPr,
6 H); elemental analysis calcd (%) for C16H19F6RuSbSe
(627.10 g mol 1): C 30.64, H 3.05; found: C 30.59, H 3.06.
1,4-Dichlorobenzene (white crystalline solid) was used as ligand to
provide complex 5 as a white air-stable powder. Yield: 85 %.
1
H NMR (CD3NO2): d = 7.07 (d, 3J = 6.0 Hz, H p-chloroarene, 2 H),
6.93 (d, 3J = 6.8 Hz, H p-cymene, 2 H), 6.82 (d, 3J = 6.0 Hz, H p-chloroarene, 1 H), 6.80 (d, 3J = 6.8 Hz, H p-cymene, 2 H), 3.05 (sept, 3J =
7.2 Hz, H iPr, 1 H), 2.74 (s, 2 Me, 6 H), 2.52 (s, Me, 3 H), 1.39 ppm (d,
3
J = 7.2 Hz, Me iPr, 6 H); 13C NMR (CD3NO2): d = 123.1 (C-Cl), 116.7,
114.2 (2 C, p-cymene), 113.3 (2 C-Me, chloroarene), 96.4, 94.5, 93.4
(7 CH), 32.3 (2 Me, chloroarene), 21.9 (1 Me, p-cymene), 19.2 (2 Me,
p-cymene), 17.7 ppm (CH, p-cymene); elemental analysis calcd (%)
for C18H23ClF12RuSb2 (847.40 g mol 1): C 25.51, H 2.74; found: C
25.58, H 2.78.
General procedure for the preparation of selenium-derived
complexes
Treatment at room temperature of the appropriate dicationic
ruthenium sandwich complex (0.2 mmol) with an excess of Na2Se
(ca. 10 equiv) in CH3CN (15 mL) provided the desired selenium-derived complex after filtration through celite with dichloromethane.
Synthesis of [(h6-p-cymene)Ru(h4-1,4-diselenobenzoquinone)] (6)
Treatment of complex 1 provided the red neutral complex 6. Yield:
99 %. 1H NMR (CD2Cl2): d = 6.40 (s, H p-quinone, 2 H), 6.39 (s, H pquinone, 2 H), 6,36 (d, 3J = 6.8 Hz, H p-cymene, 2 H), 6.25 (d, 3J =
6.8 Hz, H p-cymene, 2 H), 2.65 (sept, 3J = 6.8 Hz, H iPr, 1 H), 2.14 (s,
Me, 3 H), 1.37 ppm (d, 3J = 6.8 Hz, Me iPr, 6 H); elemental analysis
calcd (%) for C16H18RuSe2 (469.30 g mol 1): C 40.95, H 3.87; found: C
40.91, H 3.91.
Synthesis of [(h6-p-cymene)Ru(h4-1,4-diseleno-tetramethylbenzoquinone)] (7)
Treatment of complex 2 provided the red neutral complex 7. Yield:
98 %. 1H NMR (CD2Cl2): d = 5.33 (d, 3J = 6.4 Hz, H p-cymene, 2 H),
5.07 (d, 3J = 6.4 Hz, H p-cymene, 2 H), 2.70 (sept, 3J = 7.2 Hz, H iPr,
1 H), 2.64 (s, 4 Me, 12 H), 2.05 (s, Me, 3 H), 1.27 ppm (d, 3J = 7.2 Hz,
Me iPr, 6 H); 13C NMR (CD2Cl2): d = 140.9 (C=Se), 111.9, 106.1, 101.5
(3 C Ar), 92.0, 89.2 (4 CH Ar), 26.1 (Me), 25.0 (4 Me), 21.7 (2 Me),
12.8 ppm (CH); elemental analysis calcd (%) for C20H26RuSe2·H2O
(543.43 g mol 1): C 44.20, H 5.19; found: C 44.28, H 4.93.
Synthesis of [(h6-p-cymene)Ru(h4-1-oxo-4-selenobenzoquinone)] (8)
Treatment of complex 3 provided the red neutral complex 8. Yield:
95 %. 1H NMR (CD2Cl2): d = 6.08 (d, 3J = 7.2 Hz, H p-quinone, 2 H),
5.95 (d, 3J = 6.3 Hz, H p-cymene, 2 H), 5.66 (d, 3J = 6.3 Hz, H pcymene, 2 H), 5.01 (d, 3J = 7.2 Hz, H p-quinone, 2 H), 2.85 (sept, 3J =
7.2 Hz, H iPr, 1 H), 2.20 (s, Me, 3 H), 1.33 ppm (d, 3J = 7.2 Hz, Me iPr,
6 H); elemental analysis calcd (%) for C16H18ORuSe (406.34 g mol 1):
C 47.29, H 4.46; found: C 47.35, H 4.49.
Synthesis of [(h6-p-cymene)Ru(h5-1,3-dimethyl-phenseleno)][SbF6] (10)
Treatment of complex 5 provided the orange monocationic complex 10. Yield: 90 %. 1H NMR (CD2Cl2): d = 6.57 (d, 3J = 7.2 Hz, H pphenseleno, 2 H), 6.37 (m, H p-phenseleno and H p-cymene, 3 H),
6.30 (m, H p-phenseleno and H p-cymene, 4 H), 2.91 (sept, 3J =
7.2 Hz, H iPr, 1 H), 2.28 (s, Me, 3 H), 1.36 ppm (d, 3J = 7.2 Hz, Me iPr,
6 H); 13C NMR (CD2Cl2): d = 157.6 (C=Se), 117.3, 111.3, 106.5 (4 C),
94.6, 90.0, 89.2, 85.1 (7 CH), 31.7 (1 Me, p-cymene), 26.0, 23.2 (4 Me),
17.7 ppm (CH, p-cymene); elemental analysis calcd (%) for
C16H19F6RuSbSe (627.10 g mol 1): C 30.64, H 3.05; found: C 30.66, H
3.01.
X-ray crystal structure determination of [(h6-p-cymene)Ru(h4-1,4-diseleno-tetramethylbenzoquinone)] (7) and
[(h6-p-cymene)Ru(h4-1-oxo-4-selenobenzoquinone)] (8)
Data were collected on a Bruker Kappa-APEXII instrument. Unit-cell
parameter determination, data collection strategy, and integration
were carried out with the Bruker APEX2 suite of programs. Multiscan absorption correction was applied[21] and the structures were
solved using SIR92[22] and refined anisotropically by full-matrix
least-squares methods using SHELXL-2013.[23] CCDC-964943 (7) and
964944 (8) contain the supplementary crystallographic data (excluding structure factors) for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Cell culture and inhibition of cell growth
Human A2780 and A2780cisR ovarian cancer cells were obtained
from the European Collection of Cell Cultures (Salisbury, UK). Cells
were grown routinely in RPMI-1640 medium supplemented with
10 % fetal calf serum (FCS) and antibiotics at 37 8C and 5 % CO2. Cytotoxicity was determined using the MTT assay (MTT = 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide). Cells
were seeded in 96-well plates as monolayers with cell solution
(100 mL, approximately 20 000 cells) per well and preincubated for
24 h in medium supplemented with 10 % FCS. Compounds were
prepared as a DMSO solution, then dissolved in the culture
medium and serially diluted to the appropriate concentration to
give a final DMSO concentration of 0.5 %. Drug solution (100 mL)
was added to each well and the plates were incubated for another
72 h. Subsequently, MTT solution (5 mg mL 1) was added to the
cells and the plates were incubated for a further 2 h. The culture
medium was aspirated, and the purple formazan crystals formed
by the mitochondrial dehydrogenase activity of vital cells were dissolved in DMSO. The optical density, directly proportional to the
number of surviving cells, was quantified at 540 nm using a multiwell plate reader and the fraction of surviving cells was calculated
from the absorbance of untreated control cells. Evaluation was
based on means from two independent experiments, each comprising three microcultures per concentration level.
Synthesis of [(h6-p-cymene)Ru(h5-phenseleno)][SbF6] (9)
Treatment of complex 4 provided the orange monocationic complex 9. Yield: 90 %. 1H NMR (CD2Cl2): d = 6.57 (d, 3J = 7.2 Hz, H pphenseleno, 2 H), 6.37 (m, H p-phenseleno and H p-cymene, 3 H),
6.30 (m, H p-phenseleno and H p-cymene, 4 H), 2.91 (sept, 3J =
Chem. Eur. J. 2014, 20, 5795 – 5801
www.chemeurj.org
Acknowledgements
We thank the CNRS, UPMC Univ Paris 06, and SNSF for financial
support.
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2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper
Keywords: cytotoxicity · pi interactions
sandwich complexes · selenoquinones
·
ruthenium
·
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Received: December 20, 2013
Published online on March 26, 2014
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2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim