Highly cytotoxic trithiolato-bridged dinuclear Rh(III) and Ir(III) complexes

Article abstract of DOI:10.1016/j.jorganchem.2014.05.021

Water soluble trithiolato-bridged cationic complexes of the type [(η⁵-C₅Me₅)₂M ₂(μ-SC₆H₄-p-X)₃]⁺ (M = Rh, X = H, 1; CH₃, 3; OCH₃, 5; P

Full text of DOI:10.1016/j.jorganchem.2014.05.021

Accepted Manuscript
Highly cytotoxic trithiolato-bridged dinuclear Rh(III) and Ir(III) complexes
Gajendra Gupta , Benjamin S. Murray , Paul J. Dyson , Bruno Therrien
PII:
S0022-328X(14)00258-7
10.1016/j.jorganchem.2014.05.021
JOM 18593
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 16 April 2014
Revised Date: 5 May 2014
Accepted Date: 7 May 2014
Please cite this article as: G. Gupta, B.S. Murray, P.J. Dyson, B. Therrien, Highly cytotoxic trithiolato-
bridged dinuclear Rh(III) and Ir(III) complexes, Journal of Organometallic Chemistry (2014), doi:
10.1016/j.jorganchem.2014.05.021.
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ACCEPTED MANUSCRIPT
Highly cytotoxic trithiolato-bridged dinuclear Rh(III) and Ir(III) complexes
Gajendra Guptaa, Benjamin S. Murrayb, Paul J. Dysonb, Bruno Therriena,*
a Institute of Chemistry, University of Neuchatel, Avenue de Bellevaux 51, CH-2000
Neuchatel, Switzerland
b Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne
(EPFL), CH-1015 Lausanne, Switzerland
ABSTRACT
Water soluble trithiolato-bridged cationic complexes of the type [(η5-C5Me5)2M2(ꢀ-SC6H4-p-
X)3]+ (M = Rh, X = H, 1; CH3, 3; OCH3, 5; Pri, 7; But, 9; M = Ir, X = H, 2; CH3, 4; OCH3, 6;
Pri, 8; But, 10) were synthesized and isolated as their chloride salts by reacting
pentamethylcyclopentadienyl rhodium and iridium dimers [(η5-C5Me5)2M2(ꢀ-Cl)2Cl2] in
ethanol with the corresponding thiophenol. All complexes were isolated in good yields and
were fully characterized including single-crystal X-ray structure analysis on representative
complexes. The complexes were found to have IC50 values in the nanomolar range in human
ovarian A2780 cancer cells, but did not display selectivity with respect to noncancerous
human HEK293 embryonic kidney cells.
Keywords: Half-sandwich complexes; Dinuclear complexes; Thiolato-bridging ligands;
Lipophilicity; Anticancer activity.
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GRAPHICAL ABSTRACT
Water-soluble trithiolato-bridged pentamethylcyclopentadienyl Rh(III) and Ir(III) complexes
have been synthesized and characterized. The cytotoxicity of all complexes has been
established using cancerous and noncancerous cell lines. The cationic complexes are highly
cytotoxic, with IC50 values in the nanomolar range.
HIGHLIGHTS
ꢁ Synthesis of dinuclear half-sandwich complexes bridged by thiolato ligands.
ꢁ The single-crystal X-ray structure analysis of three derivatives is presented.
ꢁ The antiproliferative activity of all complexes has been evaluated in vitro.
ꢁ Highly cytotoxic complexes on cancerous and noncancerous cells.
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1. Introduction
The medicinal properties of organometallic complexes is an area of growing interest and
virtually all key types of ligands encountered in organometallic chemistry have been
considered [1]. Of these, arene ruthenium complexes have received considerable attention [2],
including dinuclear [3] and polynuclear [4] systems, while the half-sandwich rhodium and
iridium analogues have been studied to a lesser extent [5].
Dinuclear complexes bridged by thiolato ligands are an important class of compounds.
Such a structural motif is found at the active site of hydrogenases [6], which has inspired the
development of synthetic catalysts based on this fragment [7]. Among thiolato-bridged
dinuclear complexes those containing half-sandwich units have been known for many years
[8]. However, only recently they were found to exhibit in vitro antiproliferative activity
against various cancer cell lines in the nanomolar range [9].
Trithiolato-bridged dinuclear arene ruthenium complexes have yielded IC50 values as low
as 30 nM against human ovarian cancer cells with the most active compound being the tert-
butyl thiolato-bridged p-cymene ruthenium derivative [(η6-p-MeC6H4Pri)2Ru2(ꢀ-SC6H4-p-
But)3]+ [10]. These ruthenium derivatives also catalyze the oxidation of glutathione, which in
cells could lead to an increase of reactive oxygen species (ROS) since glutathione is a natural
ROS scavenger [11]. Other mechanisms/targets for the potent cytotoxicity of these complexes
cannot be excluded.
Recently, we showed that the thiolato-bridged pentamethylcyclopentadienyl (C5Me5)
rhodium and iridium analogues exhibit similar cytotoxicity to the arene ruthenium compounds
with IC50 values also in the submicromolar range [12]. In contrast to the dinuclear arene
ruthenium complexes, the rhodium and iridium thiolato-bridged species do not catalyze the
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oxidation of glutathione, indicating another mode of action [12a]. In an extension of these
nascent studies, herein, we describe a series of new trithiolato-bridged Rh(III) and Ir(III) half-
sandwich complexes and their cytotoxicity on ovarian cancer (A2780) cancer cells and
noncancerous human embryonic kidney (HEK293) cells.
2. Results and discussion
Reaction of the dinuclear dichloro-bridged complexes [(η5-C5Me5)2M2(ꢀ-Cl)2Cl2] (M = Rh
and Ir) with three equivalents of para-substituted thiols in ethanol under reflux led to the
formation of the cationic trithiolato-bridged complexes of the general formula [(η5-
C5Me5)2M2(ꢀ-SC6H4-p-X)3]+ (M = Rh; R = H, 1; R = Me, 3; R = OMe; 5, R = Pri, 7; R = But,
9; M = Ir; R = H, 2; R = Me, 4; R = OMe; 6, R = Pri, 8; R = But, 10). All complexes were
isolated in good yield as the chloride salt (Scheme 1). The salts [1]Cl and [3]PF6 have been
previously reported [13].
Scheme 1. Synthesis of the trithiolato-bridged complexes [1]Cl−[10]Cl.
These compounds are not hygroscopic and are stable in air and in solution. They are
sparingly soluble in polar solvents including dichloromethane, chloroform, acetone, and
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acetonitrile and insoluble in non-polar solvents. In addition, [1]Cl−[10]Cl are moderately
soluble in water. All complexes were isolated in good yields and fully characterized by
1
13
elemental analysis, H, C NMR and UV-visible spectroscopy, and electro-spray ionization
mass spectrometry (see experimental section). The analytical data of the compounds are
consistent with the expected structures. The resonances of the thiolato ligands are observed at
1
lower frequencies than those of the uncoordinated thiols in the H NMR spectra of the
complexes. Electrospray ionization mass spectra for [1]Cl−[10]Cl display the expected
molecular ion peak corresponding to the intact cation. In the electronic absorption spectra of
dichloromethane solutions of the complexes, intense transitions in the visible region are
observed and assigned to MLCT (metal-ligand charge transfer) bands, while intra-ligand
transitions are observed at longer wavelengths.
1
The stability of the cations [1]+−[10]+ was studied by H NMR spectroscopy in
D2O/DMSO-d6 (90%/10%, v/v) solutions: Solvents used to prepare the stock solutions of the
compounds for biological tests. Over a period of 24 h, no changes were observed in the
spectra, suggesting that the complexes are suitable for antiproliferative activity studies.
Molecular structures
Crystals suitable for single-crystal X-ray structure analysis were obtained for [3]Cl, [4]Cl
and [5]Cl. The molecular structure of the cations [3]+, [4]+ and [5]+ are shown in Figures 1-3,
respectively. The molecular structures of the cations comprise a closed trigonal bipyramid
M2S3 framework, with each metal being coordinated to an η5-C5Me5 ligand and three sulfur
atoms. The M-S bond distances [ranging from 2.3846(7) to 2.4215(5) Å] and M-S-M angles
[ranging from 76.11(3) to 80.16(2)°] are similar to those found in analogous trithiolato-
bridged half-sandwich complexes [8]. The RhꢁꢁꢁRh distance is 3.2250(3) Å in [3]+ and
3.2374(3) Å in [5]+, and in [4]+ the IrꢁꢁꢁIr distance is 3.3172(2) Å. Overall, all geometrical
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parameters are consistent with those found in similar trithiolato-bridged half-sandwich
complexes [8].
Figure 1. Molecular structure of [3]+ with ellipsoids at the 50% probability level; H atoms,
Cl- and CHCl3 molecules omitted for clarity.
Figure 2. Molecular structure of [4]+ with ellipsoids at the 50% probability level; H atoms,
Cl- and CH2Cl2 molecule omitted for clarity.
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Figure 3. Molecular structure of [5]+ with ellipsoids at the 50% probability level; H atoms,
Cl- and HCl molecule omitted for clarity.
HCl is present in the crystal packing of [(η5-C5Me5)2Rh2(ꢀ-SC6H4-p-OMe)3]Cl ([5]Cl),
which is also apparent from the elemental analysis of this salt (the HCl is generated during the
synthesis, see Scheme 1). However, we were unable to distinguish between the HCl and the
Cl- in the crystal, the hydrogen being fixed arbitrary on one position. A HCl molecule was
previously observed in the crystal packing of the analogous complex [(η5-C5Me5)2Ir2(ꢀ-
SCH2CH2C6H5)3]Cl ꢁ HCl [12a].
Antiproliferative activity
The antiproliferative activity of [1]Cl−[10]Cl was evaluated against human A2780 ovarian
cancer cells and on human HEK293 embryonic kidney cells, as a model for healthy cells. The
IC50 values (IC50 is the drug concentration necessary for 50% inhibition of cell viability) after
72 h of cell exposure are listed in Table 1, together with their resistance factors (RF). For
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comparison, the IC50 values of the corresponding trithiolato-bridged dinuclear p-cymene
ruthenium complexes (Ru-analogues) are also listed in Table 1.
Table 1. IC50 values of compounds [1]Cl–[10]Cl toward human cancer cells A2780 and
healthy cells HEK293 after 72 h exposure (RF = resistance factor).
compound
A2780
(ꢀM)
HEK293
(ꢀM)
RF
cisplatin
0.86±0.06
0.07±0.01
0.07±0.01
0.24±0.01
0.05±0.01
0.04±0.01
0.13±0.01
0.04±0.01
0.06±0.01
0.18±0.03
0.04±0.01
0.05±0.01
0.08±0.01
0.06±0.01
0.03±0.01
0.03±0.01
4.41±0.37
0.03±0.01
0.03±0.01
0.80±0.03
0.03±0.01
0.03±0.01
NA
0.04±0.01
0.03±0.01
0.29±0.02
0.06±0.01
0.08±0.01
0.16±0.02
0.16±0.02
0.07±0.01
0.03±0.01
5.1
0.4
0.4
3.3
0.6
0.8
[(η5-C5Me5)2Rh2(ꢀ-SC6H5)3]Cl ([1]Cl)
[(η5-C5Me5)2Ir2(ꢀ-SC6H5)3]Cl ([2]Cl)
(p-cymene)Ru-analogue
[(η5-C5Me5)2Rh2(ꢀ-SC6H4-p-Me)3]Cl ([3]Cl)
[(η5-C5Me5)2Ir2(ꢀ-SC6H4-p-Me)3]Cl ([4]Cl)
(p-cymene)Ru-analogue
[(η5-C5Me5)2Rh2(ꢀ-SC6H4-p-OMe)3]Cl ([5]Cl)
[(η5-C5Me5)2Ir2(ꢀ-SC6H4-p-OMe)3]Cl ([6]Cl)
(p-cymene)Ru-analogue
[(η5-C5Me5)2Rh2(ꢀ-SC6H4-p-Pri)3]Cl ([7]Cl)
[(η5-C5Me5)2Ir2(ꢀ-SC6H4-p-Pri)3]Cl ([8]Cl)
(p-cymene)Ru-analogue
[(η5-C5Me5)2Rh2(ꢀ-SC6H4-p-But)3]Cl ([9]Cl)
[(η5-C5Me5)2Ir2(ꢀ-SC6H4-p-But)3]Cl ([10]Cl)
(p-cymene)Ru-analogue
1.0
0.5
1.6
1.5
1.6
2.0
2.7
2.3
1.0
All compounds exhibit high cytotoxicity towards both the A2780 and HEK293 cell lines
(IC50 values of 30-160 nM), with IC50 values ca. 10 – 30 fold lower than cisplatin. Within this
series there is little difference in the cytotoxicity values for analogous Rh and Ir complexes,
an exception being compounds [9]Cl and [10]Cl, where the rhodium complex is less cytotoxic
than the iridium analogue in both cell lines. Complexes bearing unsubstituted or p-Me-
substituted thiophenol bridges, i.e. [1]Cl−[4]Cl, lower IC50 values are observed in the
HEK293 cell line than the cancerous A2780 cell line. With the more bulky and lipophilic, Pri
and But-substituted thiophenol this cytotoxicity profile is reversed, with the compounds
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[7]Cl−[10]Cl being more active toward the A2780 cell line than the HEK293 cell line. This
selectivity was most pronounced for [9]Cl with a RF of 2.7, however, this selectivity profile is
still lower than that of cisplatin (5.1). The related ruthenium structures are all less cytotoxic
than their iridium or rhodium analogues with the exception of the compound containing But-
substituted thiophenol bridges, which is as cytotoxic as [(η5-C5Me5)2Ir2(ꢀ-SC6H4-p-But)3]Cl
([10]Cl) in the A2780 cell line and more cytotoxic than [10]Cl in the HEK293 cell line.
The iridium and rhodium complexes with the para-substituents on the thiophenol bridges
do not significantly contribute to the observed cytotoxicity in the A2780 cell line, illustrated
by the IC50 values remaining relative constant across the series. In the HEK293 cell line the
compounds with the most lipophilic Pri- and But-thiophenol substituents are slightly less
cytotoxicity relative to complexes with H-, Me- and MeO-substituents. In contrast, for the
ruthenium complexes the thiophenol substituents are strongly linked to the overall
cytotoxicity with increasing substituent lipophilicity translating into increased cytotoxicity
against both cell lines. The cytotoxicity of the related ruthenium dinuclear complexes may be
readily modulated by changing the nature of the bridging ligand whereas, in contrast, the
activity of the rhodium and iridium systems is less influenced by the bridging ligand with the
cytotoxicity remaining high regardless of the substituent on the bridging thiophenol ligand.
CONCLUSION
A series of dinuclear pentamethylcyclopentadienyl rhodium and iridium complexes, in
which the two metals are connected via bridging thiolato ligands to afford compounds with a
M2S3 core, are highly cytotoxic, but display limited discrimination between cancerous and
noncancerous cancer cells. The influence of the substituents on the bridging thiolato ligands is
relatively innocuous and therefore precludes a clear path to the systematic development of
more selective derivatives.
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EXPERIMENTAL
Materials and methods
The starting materials [(η5-C5Me5)2Rh2(ꢀ-Cl)2Cl2] and [(η5-C5Me5)2Ir2(ꢀ-Cl)2Cl2] were
prepared according to published methods [14]. All other reagents were commercially
1
available and were used without further purification. H and 13C{1H} NMR spectra were
recorded on Bruker Avance II 400 MHz spectrometers using the residual protonated solvent
as internal standard. Electrospray mass spectra were obtained in positive ion mode with an
LCQ Finnigan mass spectrometer. UV-visible absorption spectra were recorded using an
Uvikon 930 spectrophotometer (10-5 M in CH2Cl2). Microanalysis was carried out by the
Mikroelementaranalytisches Laboratorium, ETH Zürich (Switzerland).
Synthesis of [1]Cl–[10]Cl.
The complex [(η5-C5Me5)2M2(ꢀ-Cl)2Cl2] (M = Rh, 100 mg, 0.16 mmol; M = Ir, 100 mg, 0.13
mmol) was heated to reflux in ethanol (25 mL). Following complete dissolution of the
complex, ca. 1 h, an ethanolic solution (5 mL) of the corresponding thiol (M = Rh, 0.48
mmol; HSC6H4-p-X, X = H, 50 µL (1); X = Me, 61 µL (3); X = OMe, 60 µL (5); X = Pri, 76
µL (7); X = But, 84 µL (9): M = Ir, 0.39 mmol; HSC6H4-p-X, X = H, 39 µL (2); X = Me, 47
µL (4); X = OMe, 47 µL (6); X = Pri, 59 µL (8); X = But, 65 µL (10)) was added dropwise to
the hot solution. The resulting solution was heated to reflux for 3 h, during which the color of
the solution changed to red for the rhodium derivatives and to yellow for the iridium
derivatives. The mixture was cooled to RT and the solvent removed under reduced pressure.
The resulting oil was washed with diethyl ether and hexane to obtain a powder. The powder
was dissolved in dichloromethane (ca. 5 mL), precipitated with diethyl ether (ca. 100 mL),
filtered and the solid dried under vacuum.
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Compound [(η5-C5Me5)2Rh2(ꢀ-SC6H5)3]Cl ([1]Cl).
Yield: 105 mg (77%). Elemental analysis (%): calcd. for [C38H45Rh2S3]Cl · HCl: C, 52.12; H,
5.29; found C, 51.87; H, 5.69. ESI-MS (MeOH, CH2Cl2): m/z = 804.0 [M-Cl]+. 1H NMR (400
MHz, CDCl3): δ = 7.81 (m, 6H, SC6H5), 7.35 (m, 9H, SC6H5), 1.34 (s, 30H, C5Me5) ppm.
13C{1H} NMR (100 MHz, CDCl3): δ = 8.78, 97.91, 128.83, 128.92, 132.49, 133.24 ppm. UV-
vis (1.0 x 10-5 M, CH2Cl2, 298 K): λmax nm (ε cm-1) = 249 (50500), 286 (52300), 340 (23300),
396 (19400).
[(η5-C5Me5)2Ir2(ꢀ-SC6H5)3]Cl ([2]Cl).
Yield: 100 mg (78%). Elemental analysis (%): calcd. for [C38H45Ir2S3]Cl · HCl: C, 43.29; H,
4.40; found C, 43.31; H, 4.58. ESI-MS (MeOH, CH2Cl2): m/z = 982.2 [M-Cl]+. 1H NMR (400
MHz, CDCl3): δ = 7.77 (m, 6H, SC6H5), 7.37 (m, 9H, SC6H5), 1.38 (s, 30H, C5Me5) ppm.
13C{1H} NMR (100 MHz, CDCl3): δ = 8.50, 91.52, 128.75, 129.35, 130.56, 132.99 ppm. UV-
vis (1.0 x 10-5 M, CH2Cl2, 298 K): λmax nm (ε cm-1) = 243 (78500), 331 (20700).
[(η5-C5Me5)2Rh2(ꢀ-SC6H4-p-Me)3]Cl ([3]Cl).
Yield: 107 mg (75%). Elemental analysis (%): calcd. for [C41H51Rh2S3]Cl · HCl: C, 53.66; H,
5.71; found C, 53.31; H, 5.94. ESI-MS (MeOH, CH2Cl2): m/z = 846.0 [M-Cl]+. 1H NMR (400
3
3
MHz, CDCl3): δ = 7.66 (d, JHH = 8 Hz, 6H, SC6H4CH3), 7.13 (d, JHH = 8 Hz, 6H,
13
SC6H4CH3), 2.36 (s, 9H, SC6H4CH3), 1.32 (s, 30H, C5Me5) ppm. C{1H} NMR (100 MHz,
CDCl3): δ = 8.76, 21.24, 97.66, 128.86, 129.54, 133.14, 138.97 ppm. UV-vis (1.0 x 10-5 M,
CH2Cl2, 298 K): λmax nm (ε cm-1) = 252 (84700), 281 (82000), 310 (63800), 396 (30600).
[(η5-C5Me5)2Ir2(ꢀ-SC6H4-p-Me)3]Cl ([4]Cl).
Yield: 115 mg (86%). Elemental analysis (%): calcd. for [C41H51Ir2S3]Cl: C, 46.46; H, 4.58;
1
found C, 46.28; H, 5.04. ESI-MS (MeOH, CH2Cl2): m/z = 1024.4 [M-Cl]+. H NMR (400
3
3
MHz, CDCl3): δ = 7.60 (d, JHH = 8 Hz, 6H, SC6H4CH3), 7.13 (d, JHH = 8 Hz, 6H,
SC6H4CH3), 2.38 (s, 9H, SC6H4CH3), 1.36 (s, 30H, C5Me5) ppm. 13C{1H} NMR (100 MHz,
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CDCl3): δ = 8.50, 21.18, 91.30, 127.08, 129.41, 132.86, 139.42 ppm. UV-vis (1.0 x 10-5 M,
CH2Cl2, 298 K): λmax nm (ε cm-1) = 244 (63400), 331 (17500).
[(η5-C5Me5)2Rh2(ꢀ-SC6H4-p-OMe)3]Cl ([5]Cl).
Yield: 125 mg (83%). Elemental analysis (%): calcd. for [C41H51O3Rh2S3]Cl · HCl: C, 50.99;
1
H, 5.43; found C, 50.83; H, 5.52. ESI-MS (MeOH, CH2Cl2): m/z = 894.0 [M-Cl]+. H NMR
3
3
(400 MHz, CDCl3): δ = 7.72 (d, JHH = 8 Hz, 6H, SC6H4OCH3), 6.88 (d, JHH = 8 Hz, 6H,
SC6H4OCH3), 3.87 (s, 9H, OCH3), 1.34 (s, 30H, C5Me5) ppm. 13C{1H} NMR (100 MHz,
CDCl3): δ = 8.83, 55.55, 97.63, 114.39, 122.75, 134.47, 160.38 ppm. UV-vis (1.0 x 10-5 M,
CH2Cl2, 298 K): λmax nm (ε cm-1) = 251 (64600), 281 (65200), 333 (45100), 400 (24400).
[(η5-C5Me5)2Ir2(ꢀ-SC6H4-p-OMe)3]Cl ([6]Cl).
Yield: 90 mg (65%). Elemental analysis (%): calcd. for [C41H51Ir2O3S3]Cl · 2 HCl: C, 41.70;
H, 4.52; found C, 41.72; H, 4.44. ESI-MS (MeOH, CH2Cl2): m/z = 1072.3 [M-Cl]+. 1H NMR
3
3
(400 MHz, CDCl3): δ = 7.69 (d, JHH = 8 Hz, 6H, SC6H4OCH3), 6.88 (d, JHH = 8 Hz, 6H,
SC6H4OCH3), 3.86 (s, 9H, OCH3), 1.38 (s, 30H, C5Me5) ppm. 13C{1H} NMR (100 MHz,
CDCl3): δ = 8.60, 55.61, 91.32, 114.22, 121.11, 134.21, 160.53 ppm. UV-vis (1.0 x 10-5 M,
CH2Cl2, 298 K): λmax nm (ε cm-1) = 249 (73200), 280 (52100), 329 (24800), 361 (17500).
[(η5-C5Me5)2Rh2(ꢀ-SC6H4-p-Pri)3]Cl ([7]Cl).
Yield: 90 mg (58%). Elemental analysis (%): calcd. for [C47H63Rh2S3]Cl · HCl: C, 56.34; H,
6.44; found C, 56.66; H, 6.37. ESI-MS (MeOH, CH2Cl2): m/z = 930.1 [M-Cl]+. 1H NMR (400
3
3
MHz, CDCl3): δ = 7.68 (d, JHH = 8 Hz, 6H, SC6H4CH(CH3)2), 7.18 (d, JHH = 8 Hz, 6H,
SC6H4CH(CH3)2), 2.92 (sept, 3H, SC6H4CH(CH3)2), 1.31 (s, 30H, C5Me5), 1.27 (s, 18H,
SC6H4CH(CH3)2) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ = 8.69, 23.87, 33.77, 97.71,
126.83, 129.22, 133.15, 150.04 ppm. UV-vis (1.0 x 10-5 M, CH2Cl2, 298 K): λmax nm (ε cm-1)
= 251 (55400), 281 (51000), 310 (40000), 398 (18700).
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[(η5-C5Me5)2Ir2(ꢀ-SC6H4-p-Pri)3]Cl ([8]Cl).
Yield: 91 mg (63%). Elemental analysis (%): calcd. for [C47H63Ir2S3]Cl · HCl: C, 47.82; H,
1
5.46; found C, 47.80; H 5.34. ESI-MS (MeOH, CH2Cl2): m/z = 1108.4 [M-Cl]+. H NMR
(400 MHz, CDCl3): δ = 7.64 (d, 3JHH = 8 Hz, 6H, SC6H4CH(CH3)2), 7.19 (d, 3JHH = 8 Hz, 6H,
SC6H4CH(CH3)2), 2.93 (sept, 3H, SC6H4CH(CH3)2), 1.36 (s, 30H, C5Me5), 1.27 (s, 18H,
SC6H4CH(CH3)2) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ = 8.45, 23.91, 33.72, 91.34,
126.71, 127.43, 132.87, 150.46 ppm. UV-vis (1.0 x 10-5 M, CH2Cl2, 298 K): λmax nm (ε cm-1)
= 245 (78500), 333 (20800).
[(η5-C5Me5)2Rh2(ꢀ-SC6H4-p-But)3]Cl ([9]Cl).
Yield: 123 mg (76%). Elemental analysis (%): calcd. for [C50H69Rh2S3]Cl · H2O: C, 58.56; H,
6.98; found C 58.88; H 6.96. ESI-MS (MeOH, CH2Cl2): m/z = 972.0 [M-Cl]+. 1H NMR (400
3
3
MHz, CDCl3): δ = 7.69 (d, JHH = 8 Hz, 6H, SC6H4C(CH3)3), 7.33 (d, JHH = 8 Hz, 6H,
SC6H4C(CH3)3), 1.33 (s, 30H, C5Me5), 1.32 (s, 27H, SC6H4C(CH3)3) ppm. 13C{1H} NMR
(100 MHz, CDCl3): δ = 8.73, 31.31, 34.95, 98.04, 125.98, 129.50, 133.27, 152.60 ppm. UV-
vis (1.0 x 10-5 M, CH2Cl2, 298 K): λmax nm (ε cm-1) = 289 (68400), 389 (18000).
[(η5-C5Me5)2Ir2(ꢀ-SC6H4-p-But)3]Cl ([10]Cl).
Yield: 125 mg (84%). Elemental analysis (%): calcd. for [C50H69Ir2S3]Cl · 3 H2O: C, 48.42;
H, 6.10; found C, 48.53; H 5.65. ESI-MS (MeOH, CH2Cl2): m/z = 1150.3 [M-Cl]+. 1H NMR
3
3
(400 MHz, CDCl3): δ = 7.64 (d, JHH = 8 Hz, 6H, SC6H4C(CH3)3), 7.33 (d, JHH = 8 Hz, 6H,
SC6H4C(CH3)3), 1.35 (s, 30H, C5Me5), 1.32 (s, 27H, SC6H4C(CH3)3) ppm. 13C{1H} NMR
(100 MHz, CDCl3): δ = 8.48, 31.33, 34.93, 91.67, 125.87, 127.71, 132.99, 153.03 ppm. UV-
vis (1.0 x 10-5 M, CH2Cl2, 298 K): λmax nm (ε cm-1) = 241 (64500), 320 (15800).
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Single-Crystal X-Ray Structure Analysis
Orange crystals were grown by slow diffusion of diethylether into a chloroform and
acetone solution for [3]Cl ꢁ 2 CHCl3 and [5]Cl ꢁ HCl, while yellow crystals of [4]Cl ꢁ CH2Cl2
were obtained by vapour deposition of pentane into a dichloromethane solution of [4]Cl. Data
were collected on a Stoe Image Plate Diffraction system equipped with a
φ
circle goniometer,
using Mo-Kα graphite monochromatic radiation (λ = 0.71073 Å) with
φ range 0-200º. The
structures were solved by direct methods using the program SHELXS-97, while the
refinement and all further calculations were carried out using SHELXL-97 [15]. The H-atoms
were included in calculated positions and treated as riding atoms using the SHELXL default
parameters. The non-H atoms were refined anisotropically, using weighted full-matrix least-
square on F2. Crystallographic details for [3]Cl ꢁ 2 CHCl3, [4]Cl ꢁ CH2Cl2 and [5]Cl ꢁ HCl are
summarized in Table 2. Figures 1, 2 and 3 were drawn with Ortep [16].
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Table 2. Crystallographic and structure refinement parameters for [3]Cl ꢁ 2 CHCl3, [4]Cl ꢁ
CH2Cl2 and [5]Cl ꢁ HCl.
[3]Cl ꢁ 2 CHCl3
C43H53Cl7Rh2S3
1120.00
[4]Cl ꢁ CH2Cl2
C42H53Cl3Ir2S3
1144.77
[5]Cl · HCl
C41H52Cl2O3Rh2S3
965.73
Chemical formula
Formula weight
Crystal system
Space group
Monoclinic
P 21 (no. 4)
Triclinic
Triclinic
P -1 (no. 2)
Yellow block
P -1 (no. 2)
Orange block
Crystal colour and shape Orange block
Crystal size
a (Å)
0.24 x 0.22 x 0.19 0.17 x 0.15 x 0.14 0.26 x 0.23 x 0.21
10.5286(6)
21.6699(12)
10.8306(6)
90
10.5985(5)
10.8746(5)
19.3788(8)
76.066(3)
78.199(3)
82.418(3)
2113.9(2)
2
10.5899(5)
13.4561(6)
15.5188(8)
86.528(4)
71.991(4)
79.192(4)
2065.7(2)
2
b (Å)
c (Å)
α (°)
β (°)
95.918(4)
90
γ (°)
V (Å3)
2457.9(2)
2
Z
T (K)
173(2)
1.513
173(2)
173(2)
Dc (g·cm-3)
ꢀ (mm-1)
Scan range (°)
Unique reflections
1.799
1.553
1.208
6.656
1.117
1.88 < θ < 29.28
13302
1.94 < θ < 29.19
11406
2.05 < θ < 29.21
11164
Observed refls [I>2σ(I)] 12595
Rint 0.0397
9256
0.0551
8435
0.0630
Final R indices [I>2σ(I)]* 0.0225, wR2 0.0517 0.0296, wR2 0.0470 0.0400, wR2 0.0605
R indices (all data)
Goodness-of-fit
0.0249, wR2 0.0528 0.0456, wR2 0.0497 0.0665, wR2 0.0652
1.011
1.038
1.031
Max, Min ꢂρ/e (Å-3)
0.579, - 0.549
0.911, - 1.823
2
0.584, - 0.876
2 2 1/2
* Structures were refined on F0 : wR2 = [Ʃ[w (F0 - Fc2)2] / Ʃw (F0 ) ] , where w-1 = [Ʃ(F0 ) +
2
2
2
(aP)2 + bP] and P = [max(F0 , 0) + 2Fc2]/3
CCDC 989349 [3]Cl ꢁ 2 CHCl3, 989350 [4]Cl ꢁ CH2Cl2 and 989351 [5]Cl ꢁ HCl contain the
supplementary crystallographic data 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.
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Cell Culture and Inhibition of Cell Growth
Human A2780 ovarian carcinoma cells and HEK293 cells were obtained from the
European Collection of Cell Cultures (ECACC) (Salisbury, UK). Cells were cultured in either
RPMI-1640 with GlutaMAX (A2780) or DMEM (Dulbecco’s Modified Eagle Medium) high
glucose with GlutaMAX (HEK 293) medium containing 10% fetal bovine serum (FBS) and
penicillin at 37°C and 5% CO2. Cytotoxicity was determined using the MTT (3-(4,5-
dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide) assay (see below). Cells were seeded
in 96 well plates by the addition of cells as a suspension in their respective media containing
10% FBS (100 ꢀL per well, approximately 4300 cells) and pre-incubated for 24 h.
Fresh stock solutions of the compounds were prepared in DMSO just before injections, then
the stock solution were diluted by addition to the culture medium [RPMI (Roswell Park
Memorial Institute medium) or DMEM for A2780 and HEK 293, respectively]. The stock
solutions were serially diluted to give compound solutions of the desired concentrations.
Complex solutions (100 ꢀL) were then added to plate wells (yielding final compound
solutions in the range 0 to 5 or 0 to 1 ꢀM) and the plates incubated for a further 72 h.
Subsequently, MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide)
solution (20 ꢀL, 5 mg/mL in H2O) was added to each well and the plates incubated for a
further 2 h. The culture medium was then aspirated and the violet formazan precipitate
produced by mitochondrial dehydrogenases of living cells was dissolved by the addition of
DMSO (100 ꢀL) to each well. The absorbance of the resultant solutions at 590 nm, which is
directly proportional to the number of surviving cells, was recorded using a multiwell plate
reader. The percentage of surviving cells was determined by measurement of the absorbance
of wells corresponding to untreated control cells. The reported IC50 values are based on the
mean values from two independent experiments; each concentration level per experiment was
evaluated in triplicate, and those values are reported in Table 1.
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AUTHOR INFORMATION
Corresponding Author
*B.T.: fax, +41-32-7182511; e-mail, bruno.therrien@unine.ch.
ACKNOWLEDGMENTS
Financial support of this work by the Swiss National Science Foundation and a generous loan
of ruthenium chloride hydrate, rhodium chloride hydrate and iridium chloride hydrate by the
Johnson Matthey Research Centre are gratefully acknowledged. G. G. thanks the Swiss
Confederation for a Swiss Government Scholarship.
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