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Synthesis, characterization and chemosensitivity studies of half-sandwich ruthenium, rhodium and iridium complexes containing к and к aroylthiourea ligands
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Synthesis, characterization and chemosensitivity studies of half-sandwich
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ruthenium, rhodium and iridium complexes containing к1(S) and к2(N,S) aroylthiourea
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ligands
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Agreeda Lapasama, Omar Hussainb, Roger M Phillipsb, Werner Kaminskyc,
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Mohan Rao Kolliparaa*
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a
Centre for Advanced Studies in Chemistry, North-Eastern Hill University, Shillong 793022,
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India. E-mail: mohanrao59@gmail.com; kmrao@nehu.ac.in
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b
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HD1 3DH, UK
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c
Department of Pharmacy, School of Applied Sciences, University of Huddersfield, Huddersfield
Department of Chemistry, University of Washington, Seattle, WA 98195, USA
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Graphical Abstract
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Abstract
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The reaction of [(p-cymene)RuCl2]2 and [Cp*MCl2]2 (M = Rh/Ir) metal precursors with
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aroylthiourea ligands (L1-L3) yielded a series of neutral mono-dentate complexes 1-9. The
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neutral mono-dentate coordination of aroylthiourea with metals via S atom was confirmed by
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single crystal X-ray diffraction study. Further reaction of mono-dentate complexes 1-9 with
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excess NaN3 in polar solvent resulted in the formation of highly strained four member ring к2(N,S)
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azido complexes 10-18. Further these complexes were treated with activated alkynes to isolate
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triazole complexes, but unfortunately the reaction was unsuccessful. All these complexes were
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fully characterized by various spectroscopic techniques. The molecular structures of the
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representative complexes have been determined by single crystal X-ray diffraction studies. The
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molecular structures of the complexes revealed typical piano stool geometry around the metal
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center. The chemosensitivity activities of the complexes 1-9 evaluated against the cancer cell line
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HCT-116 (human colorectal carcinoma) and ARPE-19 (human retinal epithelial cells) cell line.
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Of these, complex 3 was the most potent and whilst its potency was less than cisplatin, its
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selectivity for cancer as opposed to non-cancer cell lines in vitro was comparable to cisplatin.
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Keywords: Ruthenium, rhodium, iridium, thiourea, chemosensitivity.
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Introduction
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The discovery of the anticancer activity of cisplatin by Rosenberg led to the development
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of numerous metal-based compounds as potential drugs in the war on cancer. Platinum based
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drugs namely cisplatin, carboplatin and oxaliplatin are among the most effective anticancer
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drugs, which have been widely used [1-2]. However, some drawback such as neurotoxicity,
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nephrotoxicity, intrinsic resistance of some tumors and dose-limiting side effects has limited the
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use of the platinum diammine compounds, cisplatin and carboplatin [3]. In order to overcome
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these obstacles and develop safer and more effective remedial agents, intensive efforts have been
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devoted toward the design and pharmacological evaluation of other metal-based drugs [4-5]. In
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the search for anticancer agents containing metals other than platinum, ruthenium compounds
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turned out to be the most promising ones, largely because the ligand exchange kinetics of metal
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complexes in aqueous solution, (which seem to be crucial for the anticancer activity) is favored
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[6-7]. Ruthenium has therefore been considered to be an attractive alternative to platinum
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particularly as many ruthenium compounds are not very toxic and some ruthenium compounds
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have been shown to be quite selective for cancer cells [8-9]. Following the first in vitro study of
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arene ruthenium compounds as anticancer agents by Tocher et al., in 1992, the field of antitumor
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and anti-metastatic arene ruthenium complexes has received considerable attention and several
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anticancer ruthenium complexes, NAMI-A and KP1019 exerted potent activities against
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numerous tumor cells [10, 11]. Furthermore, (p-cymene)Ru complexes like [RuCl2(p-
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cymene)(pta)] (RAPTA-C), show attracted considerable attention due to their promising anti-
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metastatic activity in vivo activities on the inhibition of metastasis growth, together with a high
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selectivity and low general toxicity [12]. In addition Cp*rhodium and Cp*iridium complexes
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have also attracted considerable current interest due to their potential anticancer activity [13-17].
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Some of the d6 metal complexes of ruthenium (II) [18, 19], rhodium (III) [17] and iridium (III)
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[20, 21] have also been found to inhibit the tumors by their selective interactions with cellular
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biomolecules.
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Aroylthiourea ligands have been noted for their versatility because they are able to
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coordinate to a wide range of metal ions as neutral, monobasic or dibasic ligands [22]. N, N-
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Disubstituted thiourea being versatile precursors has been subjected to a various structural
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modifications in order to prepare a variety of their derivatives with different biological aspects.
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Some of N, N-disubstituted thiourea themselves are remarkable owing to their pharmacological
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and biological importance [23]. In vitro studies have revealed that various classes of thiourea are
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useful as potential antiviral, antibacterial, antifungal, antitubercular, anti-inflammatory,
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herbicidal, insecticidal and anticancer agent [24-31]. Thiourea may react with other reagents
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having different functionalities to yield active compounds of biological significance. The
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biological importance of both aroylthiourea and the ruthenium-arene unit has prompted us to
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explore the biological applications of ruthenium-arene complexes containing aroylthiourea
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ligand. Herein we describe the synthesis of [(arene)MCl2] core complexes containing S donor
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aroylthiourea ligand and evaluate their cytotoxic properties and non-cancer cells in vitro.
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In recent years, we have reported many organometallic complexes including half-
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sandwich platinum group metal complexes containing thiourea ligands [32-34]. Recently we
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have also reported the synthesis of strained complexes of arene d6 metals containing
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benzoylthiourea ligand [35].
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synthesis of neutral mono-dentate half-sandwich arene ruthenium, rhodium and iridium
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complexes containing aroylthiourea derivatives and their reactivity with azide. Ligands used in
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this study are shown in (Chart 1).
In continuation of our previous work, herein we report the
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Chart 1. Ligands used in present study.
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2. Experimental Section
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2.1.
Physical methods and materials
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The reagents used were of commercial quality and used without further purification.
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Benzoyl chloride, ammonium thiocyanate, aniline and 4-chloroaniline were purchased from
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Sigma-Aldrich. 4-Nitroaniline was obtained from Alfa Aesar. The syntheses of all the complexes
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were performed without using any inert atmosphere. All solvents used for syntheses were dried
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and distilled prior to use according to standard procedures. Starting compounds [(p-
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cymene)RuCl2]2 were prepared according to reported method [36], and [Cp*MCl2]2 (M = Rh/Ir)
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complexes were synthesized by using an
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microwave vials equipped with magnetic stirring bars which is described in experimental
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section. Infrared (IR) spectra (400-4000 cm-1) were recorded on a Perkin-Elmer 983
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spectrophotometer with compounds being dispersed as KBr discs. 1H NMR spectra were
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recorded on a Bruker Avance II 400 MHz instrument using CDCl3 as solvent chemical shifts
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were referenced to TMS. Mass spectra were obtained from Waters ZQ 4000 mass spectrometer
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by ESI method using acetonitrile as solvent. Absorption spectra were recorded on a Perkin-Elmer
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Lambda 25 UV/Vis spectrophotometer in the range of 200-600 nm at room temperature in
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acetonitrile. Elemental analyses of the complexes were performed on a Perkin-Elmer 2400 CHN
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analyzer.
Anton Paar monowave 50 synthesizer in 10 mL
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2.2. Single-crystal X-ray structures analyses
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The crystal of complexes 2, 3, 4, 5, 6, 7, 8, 10, 16 and 17 were obtained by slow diffusion
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of hexane over dichloromethane solution of the corresponding complexes. Single crystal X-ray
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diffraction measurement was carried out on an Oxford Diffraction Xcalibur Eos Gemini
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diffractometer at 293 K using graphite monochromated Mo-Kα radiation (λ = 0.71073 Å). The
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strategy for the data collection was evaluated using the CrysAlisPro CCD software. Crystal data
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were collected by standard ‘‘phi–omega scan’’ techniques and were scaled and reduced using
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CrysAlisPro RED software. The structures were solved by direct methods using SHELXS-97
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and refined by full-matrix least squares with SHELXL-97 refining on F2 [37]. The positions of
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all the atoms were obtained by direct methods. Metal atoms in the complex were located from
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the E-maps and non-hydrogen atoms were refined anisotropically. The hydrogen atoms bound to
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the carbon were placed in geometrically constrained positions and refined with isotropic
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temperature factors, generally 1.2Ueq of their parent atoms. Crystallographic and structure
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refinement parameters for the complexes are summarized in Table S1 and Table S2, and selected
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bond lengths and bond angles are presented in Table 1 and Table 2. Figures (1-7) were drawn
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with ORTEP3 [38].
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2.3. Cell line testing
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The human colorectal carcinoma cell line HCT116 p53 +/+ cells and the non-cancer
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human retinal epithelial cell line ARPE-19 were obtained from the American Type Culture
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Collection. Antiproliferative activity of the compounds was evaluated using the standard MTT
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(3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) cellular viability assay as
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described elsewhere [39]. Briefly, cells were seeded into 96 well plates at 1.5 x 10 3 cells per well
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and incubated for 24 hours at 37 °C in an atmosphere of 5% CO 2 prior to drug exposure. Stock
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solution was freshly prepared by dissolving each of the compounds in dimethylsulphoxide
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(DMSO) at a concentration of 100 mM, which was subsequently diluted with medium to obtain
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drug solutions ranging from 0.5 to 100 μM. The final DMSO concentration was 0.1% (v/v),
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which is nontoxic to cells. Cisplatin was dissolved in phosphate buffered saline at a stock
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concentration of 25 mM. The cells were exposed to a range of drug concentrations for 96 hours
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and cell survival was determined using the MTT assay. Following drug exposure 20 µL of MTT
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(0.5 mg/ml) in phosphate buffered saline was added to each well and it was further incubated at
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37°C for 4 hours in an atmosphere containing 5% CO2. The solution was then removed and the
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formed formazan crystals was dissolved in 150 µM DMSO. The absorbance of the resulting
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solution was recorded at 550nm using an ELISA spectrophotometer. The percentage of cell
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survival was calculated by dividing the true absorbance of treated cell by the true absorbance for
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controls (exposed to 0.1% DMSO). The IC50 values were determined from plots of percentage
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survival against drug concentration. Each experiment was performed in triplicate and a mean
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value obtained and stated as IC50 (µM) ± SD. To compare the response of non-cancer cells to
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cancer cells, the selectivity index (SI) was also calculated which is defined as the IC50 for ARPE-
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19 cells divided by the IC50 for HCT-116 cells. Values ˃1 indicate that complexes have selective
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activity against cancer compared to non-cancer cells in vitro.
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2.4. General procedure for synthesis of ligands (L1-L3)
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Freshly prepared benzoyl isothiocyanate was mixed in a 1:1 molar ratio with the desired
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substituted aniline in dry acetone and the mixture was reflux at 50 0C for about 5 h. On cooling,
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the reaction mixture was slowly poured into acidified (pH 4–5) chilled water and stirred well
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with a glass rod. The solid, which formed, was separated by filtration and the precipitates were
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washed with distilled water and dried at room temperature (Scheme 1).
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Scheme 1. Synthesis of thiourea ligands (L1-L3)
2.5. General preparation of [Cp*MCl2]2 (M = Rh/Ir)
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RhCl3 .3H2O (0.50 g) or IrCl3 .3H2O (0.50 g) was dissolved in MeOH (3 ml) in a mono-
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wave vial, and 0.5 ml of 1,2,3,4,5-pentamethylcyclopentadiene was added. The vial was placed
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in the mono-wave instrument the pressure was set at 20 bar and heated to 110 °C with stirring for
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45 minutes. After cooling to room temperature, the vial was opened. After short vigorous
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shaking, the precipitate was allowed to settle down, and the solvent was decanted. The
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microcrystalline product was isolated, washed with diethyl ether (3×5 ml), and dried under
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vacuum. Yield: (88%)
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2.6. General procedure for synthesis of neutral complexes (1-9)
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A mixture of starting metal precursor (0.1 mmol) and ligands (0.2 mmol) were dissolved
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in dry methanol (10 ml) and stirred at room temperature for 6 hours (Scheme-2). A yellow
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colored compound precipitated out from the reaction mixture. The precipitate was filtered,
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washed with cold methanol (5 ml) and diethyl ether (2 x 5 ml) and dried in vacuum.
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Scheme 2. Schematic representation for the synthesis of complexes (1-9)
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2.6.1. [(p-cymene)Ru(к1(S)-L1)Cl2] (1)
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Yield: (68%); IR (KBr, cm-1): 3068-3440 ν(N-H), 1665 ν(C=O), 1213 ν(C=S); 1H NMR (400 MHz,
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CDCl3, ppm): 12.91 (s, 1H, NH), 11.29 (s,1H, NH), 8.22 (d, 2H, J = 8 Hz), 7.82 (d, 1H, J = 8
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Hz), 7.49 (t, 1H, J = 8 Hz), 7.38-7.45 (m,5H), 7.32 (t, 1H, J = 8 Hz), 5.33 (d, 2H, J = 8 Hz), 5.18
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(d, 2H, J = 8 Hz) 2.82-2.93 (sept, 1H), 2.17 (s, 3H), 1.23 (d, 6H, J = 8 Hz); ESI-MS (m/z):
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490.96 [M-2Cl]+; UV-Vis { Acetonitrile, λmax nm (ε/10-4 M-1 cm-1)}: 255 (0.95), 364(0.12). Anal.
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Calc. for C24H26Cl2N2ORuS (562.52): C, 51.24; H, 4.66; N, 4.98. Found: C, 51.30; H, 4.63; N,
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4.76.
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2.6.2. [Cp*Rh(к1(S)-L1)Cl2](2)
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Yield: (72%); IR (KBr, cm-1): 3052-3447 ν(N-H), 1667 ν(C=O), 1210 ν(C=S); 1H NMR (400 MHz,
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CDCl3, ppm): 13.06 (s, 1H, NH), 11.40 (s, 1H, NH), 8.27 (d, 2H, J = 8 Hz), 7.48-7.52 (m, 3H),
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7.43 (d, 2H, J = 12 Hz), 7.41 (d, 1H, J = 4 Hz), 7.38 (d, 2H, J = 12 Hz), 7.29 (t, 1H, J = 12 Hz),
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1.56 (s, 15H). ESI-MS (m/z): 493.02 [M-2Cl]+; UV-Vis {Acetonitrile, λmax nm (ε/10-4 M-1 cm-
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C, 51.01; H, 4.75; N, 5.15.
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2.6.3. [Cp*Ir(к1(S)-L1)Cl2](3)
)}: 263 (0.45). Anal. Calc. for C24H27Cl2N2ORhS (565.36): C, 50.99; H, 4.81; N, 4.95. Found:
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Yield: (56%); IR (KBr, cm-1): 3054-3436 ν(N-H), 1668 ν(C=O), 1211 ν(C=S); 1H NMR (400 MHz,
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CDCl3, ppm): 13.06 (s, 1H, NH),11.84 (s, 1H, NH), 8.41 (d, 2H, J = 8 Hz), 7.60 (t, 1H, J = 8
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Hz), 7.51-7.56 (m, 4H), 7.45 (t, 2H, J = 8 Hz), 7.37 (t, 1H, J = 8Hz), 1.65 (s, 15H); ESI-MS
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(m/z): 581.01 [M-2Cl]+; UV-Vis {Acetonitrile, λmax nm (ε/10-4 M-1 cm-1)}: 257(0.30), 350
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(0.067). Anal. Calc. for C24H27Cl2 IrN2OS (654.67): C, 44.03; H, 4.16; N, 4.28. Found: C, 44.01;
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H, 4.29; N, 4.05.
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2.6.4. [(p-cymene)Ru(к1(S)-L2)Cl2](4)
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Yield: (73%); IR (KBr, cm-1): 3171-3350 ν(N-H), 1657 ν(C=O), 1206 ν(C=S); 1H NMR (400 MHz,
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CDCl3, ppm): 12.96 (s, 1H, NH), 11.36 (s, 1H, NH), 8.27 (d, 2H, J = 4 Hz ), 7.57 (t, 1H, J = 8
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Hz), 7.50-7.44 (m, 6H), 5.41 (d, 2H, J = 8 Hz), 5.26 (d, 2H, J = 8 Hz), 2.91-2.98 (sept, 1H), 2.24
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(s, 3H), 1.30 (d, 6H, J = 8 Hz); ESI-MS (m/z): [M-2Cl]+; UV-Vis {Acetonitrile, λmax nm (ε/10-4
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M-1 cm-1)}: 260 (0.73), 357 (0.10). Anal. Calc. for C24H25Cl3N2ORuS (596.96): C, 48.29; H,
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4.22; N, 4.69. Found: C, 48.33; H, 4.22; N, 4.77,
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2.6.5. [Cp*Rh(к1(S)-L2)Cl2] (5)
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Yield: (81%); IR (KBr, cm-1): 3128-3434 ν(N-H), 1665 ν(C=O), 1211 ν(C=S); 1H NMR (400 MHz,
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CDCl3, ppm): 13.10 (s, 1H, NH), 11.50 (s, 1H, NH), 8.34 (d, 2H, J = 8 Hz), 7.58 (t, 1H, J = 8
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Hz), 7.49-7.53 (m, 4H, J = 8 Hz), 7.43 (d, 2H, J = 8 Hz), 1.75 (s, 15H); ESI-MS (m/z): 527.19
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[M-2Cl]+; UV-Vis {Acetonitrile, λmax nm (ε/10-4 M-1 cm-1)}: 264 (0.38). Anal. Calc. for
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C24H26Cl3N2ORhS (599.81): C, 48.06; H, 4.37; N, 4.67. Found: C, 47.85; H, 4.42; N, 4.45.
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2.6.6. [Cp*Ir(к1(S)-L2)Cl2] (6)
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Yield: (73%); IR (KBr, cm-1): 3056-3430 ν(N-H), 1669 ν(C=O), 1204 ν(C=S); 1H NMR (400 MHz,
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CDCl3, ppm): 13.06 (s, 1H, NH), 11.88 (s,1H, NH), 8.40 (d, 2H, J = 8 Hz), 7.60 (t, 1H, J = 8
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Hz), 7.47-7.55 (m, J = 8 Hz, 4H), 7.44 (dd, 2H, J = 8 Hz), 1.61 (s, 15H); (m/z) ESI-MS:
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617.22 [M-2Cl]+; UV-Vis {Acetonitrile, λmax nm (ε/10-4 M-1 cm-1)}: 271(0.83), 355 (0.078).
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Anal. Calc. for C24H26Cl3IrN2OS (689.12): C, 41.83; H, 3.80; N, 4.07. Found: C, 41.84; H, 3.82;
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N, 4.15.
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2.6.7. [(p-cymene)Ru(к1(S)-L3)Cl2] (7)
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Yield: (84%); IR (KBr, cm-1): 3164-3467 ν(N-H), 1659 ν(C=O), 1209 ν(C=S); 1H NMR (400 MHz,
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CDCl3, ppm): 13.41 (s, 1H, NH), 11.49 (s, 1H, NH), 8.35 (d, 2H, J = 8 Hz), 8.27 (d, 2H, J = 8
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Hz), 7.77 (d, 2H, J = 8 Hz), 7.58 (t, 1H, J = 4 Hz), 7.50 (t, 2H, J = 8 Hz), 5.45 (d, 2H, J = 8 Hz),
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5.30 (d, 2H, J = 8 Hz), 2.91-3.02 (sept, 1H), 2.27 (s, 3H), 1.31 (d, 6H); ESI-MS (m/z): 535.13
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[M-2Cl]+; UV-Vis {Acetonitrile, λmax nm (ε/10-4 M-1 cm-1)}: 281 (0.40), 347 (0.22). Anal. Calc.
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for C24H25Cl2N3O3RuS (607.51): C, 47.45; H, 4.15; N, 6.92. Found: C, 47.43; H, 4.16; N, 6.74.
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2.6.8. [Cp*Rh(к1(S)-L3)Cl2] (8)
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Yield: (75%); IR (KBr, cm-1): 3238-3435 ν(N-H), 1671 ν(C=O), 1206 ν(C=S); 1H NMR (400 MHz,
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CDCl3, ppm): 13.48 (s, 1H, NH), 11.55 (s,1H, NH), 8.27 (d, 4H, J = 8 Hz), 7.75 (d, 2H, J = 8
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Hz), 7.53 (t, 1H, J = 8 Hz), 7.41 (t, 2H, J = 8 Hz), 1.59 (s, 15H); ESI-MS (m/z): 538.08[M-2Cl]+;
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UV-Vis {Acetonitrile, λmax nm (ε/10-4 M-1 cm-1)}: 259 (1.71). Anal. Calc. for C24H26Cl2N3O3RhS
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(610.36): C, 47.23; H, 4.29; N, 6.88. Found: C, 47.25; H, 4.30; N, 6.74.
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2.6.9. [Cp*Ir(к1(S)-L3)Cl2] (9)
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Yield: (79%) ;IR (KBr, cm-1): 3241-3447 ν(N-H), 1671 ν(C=O), 1210 ν(C=S); 1H NMR (400 MHz,
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CDCl3, ppm) : 13.53 (s, 1H, NH), 12.03 (s, 1H, NH), 8.42 (d, 2H, J = 4 Hz), 8.34 (d, 2H, J = 8
224
Hz), 7.80 (d, 2H, J = 4 Hz), 7.63 (t, 1H, J = 8 Hz), 7.55 (t, 2H, J = 8 Hz), 1.64 (s, 15H); ESI-MS
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(m/z): 626.14 [M-2Cl]+; UV-Vis {Acetonitrile, λmax nm (ε/10-4 M-1 cm-1)}: 275 (1.11), 345
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(0.22). Anal. Calc. for C24H26Cl2IrN3O3S (699.67): C, 41.20; H, 3.75; N, 6.01. Found: C, 41.19;
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H, 3.78; N, 6.17.
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2.7. General procedure for synthesis of azido complexes (10-18)
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For the synthesis of azido complexes 10-18 these two reaction routes are possible-:
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Route a: A suspension of the corresponding starting complexes 1–9 and NaN3 in 1:5 molar ratios
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was suspended in dry methanol (10 ml) and stirred at room temperature for 8h (Scheme 3). The
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solvent was removed to dryness using rotary evaporator. The residue was extracted with
233
dichloromethane, filtered and precipitated with hexane. This accounts for the higher yield of
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complexes by this route as compared to that obtained by the other route (route b).
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Route b: In addition, the terminal azido complexes 10, 13, 16 have also been prepared by
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treatment of azido dimer [(p-cymene)Ru(-N3)Cl]2 with Ligands L1-L3 in dry methanol. The
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resulting mixture was stirred for 8h at room temperature. After completion of the reaction, the
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solvent was removed to dryness using rotary evaporator the expected complex was extracted
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with dichloromethane, filtered, precipitated with hexane and dried in vacuum.
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241
Scheme 3. Schematic representation for the synthesis of complexes (10-18)
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2.7.1. [(p-cymene)Ru(к2(N,S)-L1)N3] (10)
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Yield: (68%); IR (KBr, cm-1): 3433 ν(N-H), 2030 ν(N3), 1617 ν(C=O), 1192 ν(C=S); 1H NMR (400
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MHz, CDCl3, ppm): 12.54 (s, 1H), 8.04 (d, 2H, J = 8 Hz), 7.51-7.58 (m, 5H), 7.40 (t, 2H, J = 8
245
Hz), 7.28 (d, 1H, J = 8 Hz), 5.24 (d, 1H, J = 4 Hz), 4.67 (d, 1H, J = 4 Hz), 4.62 (d, 1H, J = 4 Hz),
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4.46 (d, 1H, J = 8 Hz), 2.60-2.70 (sept, 1H), 2.09 (s, 3H), 1.20 (d, 6H, J = 8 Hz). 13C NMR (100
247
MHz,CDCl3, ppm): 186.06, 178.67, 137.58, 135.40, 131.14, 129.20, 128.07, 123.82, 100.86,
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100.28, 83.90, 83.11, 80.40, 78.57, 31.27, 23.26, 21.76, 18.02; UV-Vis {Acetonitrile, λmax nm
249
(ε/10-4 M-1 cm-1)}: 284 (0.75), 422 (0.18).
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2.7.2. [Cp*Rh(к2(N,S)-L1)N3] (11)
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Yield: (68%); IR (KBr, cm-1): 3436 ν(N-H), 2034 ν(N3),1627 ν(C=O), 1191ν(C=S); 1H NMR (400 MHz,
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CDCl3, ppm): 12.74 (s, 1H), 8.21 (d, 2H, J = 8 Hz), 7.55 (t, 3H, J = 8 Hz), 7.47-7.52 (m, 3H),
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7.40 (t, 3H, J = 8 Hz), 1.41 (s, 15H); ESI-MS (m/z): 493.16 [M-N3]+. UV-Vis {Acetonitrile, λmax
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nm (ε/10-4 M-1 cm-1)}: 293 (0.85), 422 (0.18). Anal. Calc. for C24H26N5ORhS (535.97): C, 53.83;
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H, 4.89; N, 13.08. Found: C, 53.87; H, 4.82; N, 13.11.
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2.7.3. [Cp*Ir(к2(N,S)-L1)N3] (12)
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Yield: (56%); IR (KBr, cm-1): 3420ν(N-H), 2036 ν(N3), 1618 ν(C=O), 1198 ν(C=S); 1H NMR (400
258
MHz, CDCl3, ppm): 12.75 (s, 1H), 8.22 (d, 1H, J = 8 Hz), 8.10 (d, 1H, J = 8 Hz), 7.57 (d, 1H, J =
259
8 Hz), 7.48 (t, 3H, J = 4 Hz), 7.40 (d, 2H, J = 4 Hz), 7.33 (d, 1H, J = 4 Hz), 1.65 (s, 15H).13C
260
NMR (100 MHz,CDCl3, ppm): 173.44, 167.77, 145.68, 139.88, 130.33, 129.59, 127.42, 125.25,
261
126.25, 89.45, 9.02; ESI-MS (m/z): 582.80 [M-N3]+. UV-Vis {Acetonitrile, λmax nm (ε/10-4 M-1
262
cm-1)}: 204 (0.832), 361 (0.41).
263
2.7.4. [(p-cymene)Ru(к2(N,S)-L2)N3] (13)
264
Yield: (71%); IR (KBr, cm-1): 3433 ν(N-H), 2030 ν(N3), 1611 ν(C=O), 1193 ν(C=S); 1H NMR (400
265
MHz, CDCl3, ppm): 12.50 (s, 1H), 8.02 (d, 2H, J = 4 Hz), 7.51-7.58 (m, 3H), 7.46 (d, 2H, J = 8
266
Hz), 7.35 (d, 2H, J = 12 Hz), 5.25 (d, 1H, J = 8 Hz), 4.67 (d, 1H, J = 4 Hz), 4.62 (d, 1H, J = 4
14
267
Hz), 4.46 (d, 1H, J = 4 Hz), 2.59-2.69 (sept, 1H), 2.08 (s,3H), 1.19 (d, 6H); 13C NMR (100
268
MHz,CDCl3, ppm): 189.13, 178.67, 131.97, 129.33, 129.02, 128.79, 128.08, 127.18, 125.17,
269
121.57, 99.67, 97.27, 83.82, 81.96, 80.10, 31.28, 30.18, 22.31, 17.52; UV-Vis {Acetonitrile, λmax
270
nm (ε/10-4 M-1 cm-1)}: 277 (0.92), 443 (0.16).
271
2.7.5. [Cp*Rh(к2(N,S)-L2)N3] (14)
272
Yield: (65%); IR (KBr, cm-1): 3423 ν(N-H), 2037 ν(N3), 1621 ν(C=O), 1190 ν(C=S); 1H NMR (400
273
MHz, CDCl3, ppm): 12.72 (s,1H), 8.20 (d, 2H, J = 8 Hz), 7.49-7.52 (m, 5H), 7.35 (d, 2H, J = 12
274
Hz), 1.41 (s, 15H); 13C NMR (100 MHz,CDCl3, ppm): 186.76, 176.69, 134.59, 134.35, 131.92,
275
131.66, 129.28, 128.94, 127.61, 127.18, 93.15, 8.72; UV-Vis {Acetonitrile, λmax nm (ε/10-4 M-1
276
cm-1)}: 265 (0.90), 430 (0.17). Anal. Calc. for C24H25ClN5ORhS (569.91): C, 50.58; H, 4.42; N,
277
12.29. Found: C, 50.65; H, 4.45; N, 12.18.
278
2.7.6. [Cp*Ir(к2(N,S)-L3)N3] (15)
279
Yield: (54%); IR (KBr, cm-1): 3402 ν(N-H), 2037 ν(N3), 1619 ν(C=O ), 1194ν(C=S); 1H NMR (400
280
MHz, CDCl3, ppm): 8.04 (d, 2H, J = 8 Hz), 7.47 (d, 2H, J = 8 Hz), 7.37 (t, 3H, J = 8 Hz), 6.59 (d,
281
2H, J = 12 Hz), 1.68 (s, 15H); ESI-MS (m/z): 612.96 [M-N3]+.UV-Vis {Acetonitrile, λmax nm
282
(ε/10-4 M-1 cm-1)}: 257 (0.59), 361(0.22).
283
2.7.7. [(p-cymene)Ru(к2(N,S)-L3)N3] (16)
284
Yield: (69%); IR (KBr, cm-1): 3432 ν(N-H), 2035 ν(N3), 1627 ν(C=O), 1189 ν(C=S); 1H NMR (400
285
MHz, CDCl3, ppm):12.98 (s, 1H), 8.26 (d, 2H, J = 8 Hz), 8.03 (d, 2H, J = 8 Hz), 7.76 (d, 2H, J =
286
8 Hz), 7.53- 7.62 (m, 3H), 5.30 (d, 1H, J = 8 Hz), 4.72 (d, 1H, J = 8 Hz), 4.66 (d, 1H, J = 8 Hz),
287
4.50 (d, 1H, J = 4 Hz), 2.61-2.71 (sept, 1H), 2.10 (s, 3H), 1.21 (d, 6H, J = 8 Hz); ESI-MS (m/z):
288
536.08 [M-N3]+. UV-Vis {Acetonitrile, λmax nm (ε/10-4 M-1 cm-1)}: 278(1.16), 339 (0.68). Anal.
15
289
Calc. for C24H24N6O3RuS (577.62): C, 49.90; H, 4.19; N, 14.55. Found: C, 49.89; H, 4.23; N,
290
14.68.
291
2.7.8. [Cp*Rh(к2(N,S)-L3)N3] (17)
292
Yield: (58%); IR (KBr, cm-1): 3428 ν(N-H), 2034 ν(N3), 1614 ν(C=O), 1193 ν(C=S); 1H NMR (400
293
MHz, CDCl3, ppm): 13.13 (s, 1H), 8.20 (d, 2H, J = 8 Hz), 8.13 (d, 2H, J = 8 Hz), 7.73 (d, 2H, J
294
= 8 Hz), 7.49 (t, 1H, J = 8 Hz), 7.43 (t, 1H, J = 8 Hz), 1.36 (s, 15H); ESI-MS (m/z): 537.08 [M-
295
N3]+. UV-Vis {Acetonitrile, λmax nm (ε/10-4 M-1 cm-1)}: 269 (0.96), 338 (0.68), 432 (0.16).
296
2.7.9. [Cp*Rh(к2(N,S)-L3)N3] (18)
297
Yield: (62%); IR (KBr, cm-1): 3432 ν(N-H), 2030 ν(N3), 1627 ν(C=O), 1202ν(C=S); 1H NMR (400
298
MHz, CDCl3, ppm): 8.39 (d, 1H, J = 8 Hz), 7.96 (d, 1H, J = 8 Hz), 7.83 (d, 1H, J = 8 Hz), 7.71
299
(d, 2H, J = 8 Hz), 7.50 (d, 2H, J = 8 Hz), 7.37 (t, 2H, J = 8 Hz), 1.74 (s, 15H); ESI-MS (m/z):
300
628.14 [M-N3]+. UV-Vis {Acetonitrile, λmax nm (ε/10-4 M-1 cm-1)}: 281 (0.44), 344 (0.30).
301
3.
Results and discussion
302
3.1.
Synthesis of complexes
303
The metal complexes 1-9 were synthesized by the reaction of Ru, Rh and Ir metal
304
precursors with the thiourea ligands L1-L3 in methanol and are represented in (Scheme 2). All
305
these metal complexes were obtained in good yield and are yellow or red in color. They are
306
stable in air as well as in solid state, and are non-hygroscopic. These complexes were isolated as
307
neutral complexes with mono-dentate к1(S) coordination. Azido compounds were synthesized by
308
the substitution of the chloride ligand by azide group following two routes. Treatment of half-
309
sandwich mononuclear complexes 1-9 with five fold of NaN3 in methanol (Scheme 3) resulted in
310
the substitution of the chloride ligand and the formation of highly strained four membered
311
chelated к2(N,S) azido complexes 10-18 (Scheme 3 route a). Similarly, these terminal azido
16
312
complexes 10, 13, and 16 can be prepared from the binuclear p-cymene ruthenium azido
313
complexes [(p-cymene)Ru(-N3)Cl]2 by reacting with ligand L1-L3 in methanol (route b).
314
However, ‘route a’ is more preferable than ‘route b’ as it gives higher percentage yield of the
315
expected complex, hence we reported the yield obtained through this route in the experimental
316
section. Our effort to make triazole complexes by reaction of terminal azido complexes with
317
excess of dimethylacetylenedicarboxylate (MeO2CC2CO2Me) or diethylacetylenedicarboxylate
318
(EtO2CC2CO2Et) in dichloromethane was unsuccessful. Further we have carried out the
319
antibacterial studies for ligands and complexes against four pathogenic bacteria viz., S. aureus, E.
320
coli, B. thuringiensis and P. aeruginosa but none of the compounds showed any activity. All the
321
synthesized complexes are soluble in common organic solvents such as dichloromethane,
322
acetonitrile and acetone but insoluble in diethyl ether and hexane. All the synthesized ligands
323
and complexes were fully characterized by various spectroscopic techniques.
324
3.2.
Spectroscopic characterization of Complexes
325
The IR spectra of free aroyl thiourea ligands showed characteristic stretching frequencies
326
at 3076-3312 cm−1 corresponding to ν(N−H) which also present in the same region in all the
327
complexes indicating that deprotonation does not occur. A strong band observed in the region
328
1657–1661 cm−1 in the FT-IR spectra of the ligands was assigned to the ν(C=O), the stretching
329
vibration ν(C=O) bands remain unaltered upon complexation indicating non participation of
330
carbonyl oxygen in coordination. The characteristic band for ν(C=S) appeared at 1232–1241 cm−1
331
in the spectra of L1-L3 was shifted to lower frequency (1189–1213 cm−1) on complexation
332
indicating involvement of sulfur in coordination to the metal center.
333
The IR spectra of the azido complexes 10-18 showed sharp absorption band at
334
frequencies 2030-2037 cm-1 corresponding to terminal ʋN3. When synthesis via route b the IR
17
335
spectra of these complexes also show absence of the bridging azido band at 2065 cm-1 and the
336
appearance of new bands for terminal azido group in the above mentioned range. This leads us to
337
infer the formation of terminal azido complexes.
338
The 1H NMR spectra of the complexes 1-9 (Figure S1-S8) show a downfield shift in
339
protons of ligand after forming complexes, which is due to the deshielding effect exerted by
340
metal on the ligands. The 1H NMR of the complexes 1-9 show two singlet around 13.53-12.96
341
and 11.88-11.29 which is attributed to the N-H proton signals of thiocarbonyl and carbonyl
342
attached N-H respectively. The appearance of two N-H signals in all the complexes indicates that
343
the N-H group is not involved in bonding. Resonances due to the aromatic ligands protons were
344
all in the expected range of 8.29-7.21 ppm, which indicates the coordination of the thiourea
345
ligand to the metal center. In addition to the signals for the ligand protons, a sharp singlet was
346
observed for all the rhodium and iridium complexes between 1.58-1.63 ppm corresponding to the
347
methyl protons of the Cp* ring. The 1H NMR spectra of complexes 1, 4 and 7 displays a doublet
348
for methyl protons of isopropyl group at 1.23 ppm, 1.30 ppm and 1.31 ppm respectively, a
349
singlet at 2.17 ppm, 2.24 ppm and 2.27 ppm for methyl group, a septet at 2.86 ppm, 2.94 ppm
350
and 2.96 ppm for one proton of isopropyl group of p-cymene moiety. Two doublets were
351
observed in the range 5.18 ppm- 5.45 ppm corresponds to the aromatic protons of p-cymene.
352
The 1H NMR spectra of all the azido complexes 10-18 (Figure S9-S16) show the
353
disappearance of one N–H proton, which strongly supports the deprotonation of one amido
354
hydrogen and this has also been confirmed from molecular structures. The deprotonation of
355
amido hydrogen (NH) resulted in the generation of negative charge on amido nitrogen atom,
356
which leads to the formation of neutral complexes 10-18. The azido complexes show a singlet
357
around 12.50-13.13, which is attributed to one N-H proton signals. The appearance of one N-H
18
358
signal in all the complexes indicates that only one N-H group involved in bonding. Resonances
359
due to the aromatic ligands protons were all in the same range of 8.40-7.27 ppm. The rhodium
360
and iridium complexes displayed only one singlet for the methyl protons of the Cp* group
361
around 1.52-1.75 ppm. The binding of the azide ligand to the ruthenium atom in mononuclear
362
ruthenium complexes leads to the splitting of the p-cymene ring protons upon coordination of the
363
ligand to the p-cymene moiety. The signals associated with the p-cymene ring protons consisted
364
of four doublets around 5.29-4.50 ppm. This unexpected pattern of signals for the p-cymene
365
ligand is consisted with the metal center being chiral upon coordination of the azide ligand and
366
these results correlates well with similar reported complexes [35]. In addition the methine and
367
methyl protons of the p-cymene group exhibited septet around 2.65 ppm and singlet around 2.09
368
ppm.
369
The 13C NMR spectra of the complexes further justify the coordination of the ligands and
370
formation of complexes. The 13C NMR spectra of the representative complexes are provided in
371
the supplementary information (Figures S29-S31). The 13C NMR spectra of the complexes
372
displayed signals associated with the ligand carbons, p-cymene ligand carbons, methyl carbon of
373
Cp* and ring carbon of Cp*. The carbon resonance of the thiocarbonyl (C=S) group appeared in
374
the lower frequency region around 173.44 to 186.76 ppm and the carbonyl (C=O) group
375
appeared in the range of 178.67 to 167.77 ppm. The aromatic carbons signals for the ligands
376
were observed in the range of 121.57 to 145.68 ppm. The methyl, methine and isopropyl carbon
377
resonances of the p-cymene ligand were observed in the region around 17.52 to 31.28 ppm. The
378
signals associated with the ring carbons of the Cp* ligand was observed in the region 89.45 to
379
93.15 ppm in contrast the methyl carbon resonances was observed as a sharp peak at 8.72 and
19
380
9.02 ppm. Overall results from the NMR spectral studies strongly support the formation of the
381
metal complexes.
382
The mass spectra of the complexes are presented in the supplementary information Figure
383
S17-S28. Complexes display their predominant molecular ion peaks at m/z: 490.96, 493.02,
384
581.01, 524.23, 527.19, 617.22, 535.13, 538.08 and 659.12 respectively which correspond to [M-
385
2Cl]+ ion peak. Complexes 11, 12, 15, 16, 17, and 18 display their predominant peaks at m/z:
386
493.16, 582.80, 616.96, 536.08, 537.08, and 628.14 respectively which correspond to [M-N3]+.
387
The appearance of these peaks in its mass spectra clearly indicates the formation of thiourea
388
metal complexes. The peaks corresponding to the loss of the thiourea ligands as well as the arene
389
ring are not observed which indicates the strong metal to ligand and metal to arene bond. The
390
mass spectral values strongly justify the composition and formation of these complexes.
391
The electronic spectra of the complexes were recorded in acetonitrile at 10-4 M
392
concentration at room temperature. The electronic spectra of complexes display two absorption
393
band in the higher energy region around 230-340 nm (figure S32-33). The band in the range of
394
230-280 nm can be assigned as π-π* and n-π * transition. The band in the lower energy region
395
around 345-405 nm can be assigned as metal (dπ) to π* ligand charge transfer (MLCT).
396
3.3. Description of the molecular structures of complexes
397
The molecular structure of the complexes along with the crystallographic numbering
398
schemes is depicted in the Figures 1-7. Because of low theta value the crystal structures of
399
complexes 6 and 17 are presented here to only confirm the structure and composition of
400
molecule. The summary of the crystal data, data collection and structure refinement parameters
401
are summarized in Table S1 and Table S2. Selected bond lengths, bond angles and metal atom
402
involving ring centroid values are listed in Table 1 and Table 2. The crystals of the complexes 2,
20
403
3, 4, 5, 6, 7, 8, 10, 16 and 17 suitable for X-ray diffraction study were obtained by slow diffusion
404
of hexane to the concentrated dichloromethane solutions of the compound. By carrying out the
405
single crystal analyses we were able to confirm the variety of bonding modes associated with the
406
ligand. The complexes adopted a piano-stool geometry, where p-cymene and Cp* moiety served
407
as the top of the stool and the three leg sites were occupied by sulfur from ligands and two
408
terminal chlorides. The metal atom in these complexes is situated in a pseudo-octahedral
409
arrangement with the ligand coordinating through the sulfur atom. In complexes 1-9 the thiourea
410
ligands acted as a neutral mono-dentate ligand coordinating metal via S atom.
411
Complexes 2, 3, 5 and 8 crystallized in monoclinic with space group P21/c. Complex 4
412
crystallized in monoclinic system with space group C2/c, whereas Complex 7 crystallized in
413
triclinic system with space group P ͞1. The distance between the metal M to centroid of the p-
414
cymene/Cp* ring are {1.787 (2), 1.778 (3), 1.672 (4), 1.689 (5), 1.665 (7), 1.784 (8) Å}. The
415
metal to sulfur bond distances of complexes 2, 3, 4, 5, 7 and 8 were found to be 2.395(1),
416
2.370(2), 2.418(1), 2.366(1), 2.4004(7) and 2.3857 (8) respectively, whereas the M-Cl1 bond
417
distances of complexes 2, 3, 4, 5, 7 and 8 were found to be 2.413(1), 2.423(1), 2.426(1),
418
2.440(1), 2.4338(5) and 2.4253(9) and the M-Cl2 bond distances were found to be 2.427(1),
419
2.410 (2), 2.406 (1), 2.425 (1), 2.4319 (7) and 2.411 (1) respectively which are comparable with
420
earlier reported complexes [34]. The C-S bond length in these complexes lie in the range 1.688-
421
1.703 Å which are in good agreement with other related compounds for a C=S double bond [40].
422
The bond angle values S-M-Cl and Cl-M-Cl are found to be in the range 87.67-94.09º thus
423
suggesting the pseudo octahedral arrangement around the metal center.
424
Further reaction of the mono-dentate thiourea p-cymene ruthenium, Cp* rhodium and
425
Cp* iridium complexes with excess of sodium azide resulted in deprotonation of the amido
21
426
hydrogen which changed the bonding behavior of the thiourea ligand towards both p-cymene
427
ruthenium and Cp* rhodium complexes as confirmed from the molecular structures. X-ray
428
studies of these complexes revealed that upon coordination of azide group to the metal it cause
429
deprotonation of amido N-H and the bonding of the thiourea derivatives were altered. All the
430
thiourea derivatives revealed interesting coordination towards metal upon coordination of the
431
azide group. The p-cymene ruthenium azido complexes 10 and 16 crystallized in monoclinic
432
system with space group P 21/c and P21/n respectively. Whereas the Cp*rhodium azido complex
433
17 crystallized in monoclinic system with space group P21/n. The deprotonation of the amido
434
hydrogen (NH) forced the thiourea ligand to coordinate metal in an anionic bidentate chelating
435
fashion via S and N thus forming a highly strained four membered chelated ring and the
436
oxidation state of metal is balanced by the amido group nitrogen and azide nitrogen. The distance
437
between the metal M to centroid of the p-cymene/Cp* ring in complexes 10, 16 and 17 are 1.675,
438
1.678 and 1.784 Å [41]. The metal to sulfur bond distance of complex 16 is 2.406(1) was found
439
to be slightly longer than complex 17 2.398(2) Å whereas the metal to azide bond distance are
440
2.107(4) and 2.125(5) Å respectively. The C=S bond length in complex 17 is 1.723(4) Å was
441
slightly longer than that in complex 16 1.711(4) Å. The bond angle values N-M-N and N-M-S
442
for complexes 10, 16 and 17 are given in Table 2. The bite angle of complexes 10, 16 and 17 are
443
67.27º, 65.86o and 67º respectively which is the strain angle giving a pseudo-octahedral
444
arrangement of piano stool half sandwich complex.
445
Furthermore, the crystal structure of complex 3 display two different types of interaction
446
intramolecular and intermolecular hydrogen bonding; the first interaction is N-H∙∙∙O between the
447
carbonyl oxygen and amido H-atom (1.907 Å), and the N-H∙∙∙Cl between the other amido
448
hydrogen and Cl-atom attached to iridium metal (2.424 Å). The second is C-H∙∙∙π interaction
22
449
between the benzoyl moiety and the H-atom of aniline (3.517 Å) (Figure S34). Similarly the
450
crystal structure of complex 16 exhibits N-H∙∙∙O interaction between the carbonyl oxygen and
451
amido H-atom (1.902Å), the C-H∙∙∙N interaction between the H-atom of p-cymene and azide
452
nitrogen (2.758 Å), and C-H∙∙∙O interaction between the H-atom of p-cymene and O-atom of
453
nitro group (2.415 Å) (Figure S35).
454
455
456
Figure 1. (a) ORTEP diagram of complex 2 and (b) ORTEP diagram of complex 3 with 50%
457
probability thermal ellipsoids. Hydrogen atoms (except on N) are omitted for clarity.
458
23
459
460
Figure 2. (a) ORTEP diagram of complex 4 and (b) ORTEP diagram of complex 5 with 50%
461
probability thermal ellipsoids. Hydrogen atoms (except on N) are omitted for clarity.
462
463
Figure 3. ORTEP diagram of complex 6 with 50% probability thermal ellipsoids. Hydrogen
464
atoms (except on N) are omitted for clarity. Because of low theta value the crystal structure of
465
complex are presented here to only confirm the structure and composition of molecule.
466
24
467
468
Figure 4. (a) ORTEP diagram of complex 7 and (b) ORTEP diagram of complex 8 with 50%
469
probability thermal ellipsoids. Hydrogen atoms (except on N) are omitted for clarity.
470
471
Figure 5. ORTEP diagram of complex 10 with 50% probability thermal ellipsoids. Hydrogen
472
atoms (except on N) are omitted for clarity.
473
25
474
475
Figure 6. ORTEP diagram of complex 16 with 50% probability thermal ellipsoids. Hydrogen
476
atoms (except on N) are omitted for clarity.
477
478
Figure 7. ORTEP diagram of complex 17 with 50% probability thermal ellipsoids. Hydrogen
479
atoms (except on N) are omitted for clarity. Because of low theta value the crystal structure of
480
complex are presented here to only confirm the structure and composition of molecule.
481
26
482
3.5. Chemosensitivity studies
483
The complexes (1-9) were tested for their cytotoxicity against cancer cell line HCT-116
484
(human colon carcinoma) and non-cancer cell line ARPE-19 (human retinal epithelial cells). The
485
response of the cell lines HCT-116 and ARPE-19 (human retinal epithelial cells) to the test
486
complexes 1-9 and cisplatin is presented in tabular form in Table 3. Complexes 5, 6, and 8 were
487
found to be inactive against both the cell line with IC50 values > 100 M. Complexes 1, 2, 7 and
488
9 were found to be less active against HCT-116 cell line. In contrast complexes 3 and 4
489
displayed moderate activity against both cell lines with IC50 value of 35.172 ± 1.175 and 43.751
490
± 2.480 M. Of the complexes evaluated complex 3 was the most potent against both cell lines.
491
The selectivity index (SI) is shown in Table 3, which is defined as the ratio of IC50 values in
492
ARPE-19 cells divided by the IC50 of HCT-116 cells. Complex 3 was also the most selective of
493
the novel complexes evaluated with equitoxic activity observed against both HCT-116 and
494
ARPE-19 cells. Whilst these complexes were not as potent as cisplatin, complex 3 has a
495
selectivity index that is comparable to cisplatin (SI=1.078 and 1.233 respectively) and it is
496
therefore the most promising complex in this series.
497
IC50 = concentration of the drug required to inhibit the growth of 50% of the cancer cells (µM).
498
4. Conclusion
499
In this work, we have successfully synthesized d6 half-sandwich metal complexes bearing
500
thiourea ligands and the reactivity of these complexes towards NaN3. The ligands used in this
501
work exhibited interesting binding modes on reacting with sodium azide. Further reactions of
502
mono-dentate complexes 1-9 with NaN3 resulted in deprotonation of amido hydrogen and
503
change the coordination mode of the thiourea derivative from mono-dentate to bidentate
504
chelating mode. This complexes 10-18 coordinate in a highly strained four membered chelated
27
505
к2(N,S) towards the metal atoms rather than the six membered chelated к2(O,S). As there are two
506
amido groups in the thiourea derivative we expect the coordination of the other amido group as
507
well, but the molecular structure revealed that only the amido adjacent to carbonyl group
508
coordinates to metal which may be due to strong electron withdrawing property of aryl group.
509
Chemosensitivity activity of the complexes carried out against HCT-116 cancer cell line
510
displayed that some of the complexes are cytotoxic. Of these, complex 3 was the most potent and
511
whilst its potency was less than cisplatin, its selectivity for cancer as opposed to non-cancer cell
512
lines in vitro was comparable to cisplatin. Further we have carried out the antibacterial studies
513
performed against four pathogenic bacteria viz., S. aureus, E. coli, B. thuringiensis and P.
514
aeruginosa but none of the compounds showed any activity. The complexes were fully
515
characterized by various spectroscopic studies and their molecular structures were established by
516
single X-ray analysis.
517
Acknowledgements
518
Agreeda Lapasam thanks CSIR- HRDG Delhi, India for providing financial assistance in
519
the form of JRF fellowship. We express our sincere thanks to Dr. Krishna Mohan Poluri, IIT
520
Roorkee for their help to carry out the antibacterial studies. We thank DST-PURSE SCXRD,
521
NEHU-SAIF, Shillong, India for providing Single crystal X-ray analysis and other spectral
522
studies.
523
Supplementary material
524
CCDC 1874292 (2), 1874293 (3), 1874294 (4), 1874295 (5), 1874296 (7), 1874297
525
(8), 1874298 (10), 1874299 (16), contains the supplementary crystallographic data for this paper.
526
These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, by e-
28
527
mailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data
528
Centre, 12, Union Road, Cambridge CB2 1EZ, UK; Fax: +44 1223 336033.
529
References
530
[1]
B. Rosenberg, L. VanCamp, J. E. Trosko, V. H. Mansour, Nature, 222 (1969) 385.
531
[2]
F. Muggia, Gynecol. Oncol., 112 (2009) 275.
532
[3]
B. Rosenberg, Adv. Exp. Med. Biol., 91 (1997) 129.
533
[4]
R. Bieda, I. Ott, M. Dobroschke, A. Prokop, R. Gust, W.S. Sheldrick, J. Biol. Inorg.
534
Chem., 103 (2009) 698.
535
[5]
Z. Liu, P.J. Sadler, Acc. Chem. Res., 47 (2014) 1174.
536
[6]
B.S. Murray, M.V. Babak, C.G. Hartinger, P.J. Dyson, Coord. Chem. Rev., 306 (2016)
537
86.
538
[7]
J. Reedijk, Platinum Met. Rev., 52 (2008) 2.
539
[8]
E. S. Antonarakis, A. Emadi. Cancer Chemother Pharmacol 66 (2010) 1.
540
[9]
G. Süss-Fink, Dalton Trans., (2010) 1673.
541
[10]
F.A. Khan, B. Therrien, G. Süss-Fink, O. Zava, P.J. Dyson, J. Organomet Chem. 730
542
543
(2013) 49-56.
[11]
544
(a) M. Haghdoost, J. Guard, G. Golbaghi, A. Castonguay, Inorg Chem., 57 (2018) 7558.
(b) E. Alessio, Eur. J. Inorg. Chem., (2017) 1549.
545
[12]
S. Thota, D. A. Rodrigues, D. C. Crans, E. J. Barreiro, J. Med. Chem., 61 (2018) 5805.
546
[13]
S. J. Lucas, R. M. Lord, A. M. Basri, S. J. Allison, Roger M. Phillips, A. J. Blackera, P.
547
548
549
C. McGowan, Dalton Trans., (2016) 6812.
[14]
R. K. Gupta, R. Pandey, G. Sharma, R. Prasad, B. Koch, S. Srikrishna, P. Li, Q. Xu, D. S.
Pandey. Inorg. Chem., 52 (2013) 3687.
29
550
[15]
551
552
Parsons, V. Brabec, P.J. Sadler, Inorg. Chem., 46 (2007) 8950.
[16]
553
554
M.A. Scharwitz, I. Ott, Y. Geldmacher, R. Gust, W.S. Sheldrick, J. Organomet. Chem.,
693 (2008) 2299.
[17]
555
556
M. Melchart, A. Habtemariam, O. Novakova, S.A. Moggach, F.P.A. Fabbiani, S.
S.K. Singh, S. Joshi, A.R. Singh, J.K. Saxena, D.S. Pandey, Inorg.Chem., 46 (2007)
10869.
[18]
557
S. Blanck, J. Maksimoska, J. Baumeister, K. Harms, R. Marmorstein, E. Meggers,
Angew. Chem. Int. Ed., 51 (2012) 5244.
558
[19]
S.P. Mulcahy, E. Meggers, Med. Organomet Chem., Springer, 32 (2010) 141.
559
[20]
S. Mollin, R. Riedel, K. Harms, E. Meggers, J. Inorg. Biochem. 148 (2015) 11.
560
[21]
C. Kunick, I. Ott, Angew. Chem. Int. Ed., 49 (2010) 5226.
561
[22]
N. Gunasekaran, P. Ramesh, M.N.G. Ponnuswamy and R. Karvembu, Dalton Trans.,
562
563
(2011) 12519.
[23]
564
565
R.S. Correa, K.M. de Oliveira, F. G. Delolo, A. Alvarez, R. Mocelo, A.M. Plutin, M.R.
Cominetti, E. E. Castellano, A.A. Batista, J. Inorg Biochem, 150 (2015) 63.
[24]
566
A. Mahajan, S. Yeh, M. Nell, C.E.J. van Rensburg, K. Chibale, Bioorg. Med. Chem.
Lett. 17 (2007) 5683.
567
[25]
W.S.I. Lin, C.N. Lok, K.Yan and C.M. Che, Chem. Commun., 49 (2013) 3297.
568
[26]
R.D. Campo, J.J. Criado, R. Gheorghe, F.J. Gonzalez, M.R. Hermosa, F. Sanz, J.L.
569
Manzano, E. Monte, E.R. Fernandez, J. Inorg. Biochem. 98 (2004) 1307.
570
[27]
Z.H. Li, Y. Zhang, Z.H. Peng, Y.G. Wang, Huaxueshiji 24 (2002) 214.
571
[28]
N. Selvakumaran, N.S.P. Bhuvanesh, A. Endo and R. Karvembu, Polyhedron, 75 (2014)
572
95.
30
573
[29]
N. Selvakumaran, N.S.P. Bhuvanesh and R. Karvembu, Dalton Trans., (2014) 16395.
574
[30]
K. Jeyalakshmi, J. Haribabu, N.S.P. Bhuvanesh, R. Karvembu, Dalton Trans., (2016)
575
12518.
576
[31]
S. Saeed, N. Rashid, P.G. Jones, M. Ali, R. Hussain, Eur. J. Med. Chem., 45 (2010) 1323.
577
[32]
M. Kalidasan, R. Nagarajaprakash, M.R. Kollipara, Trans. Met. Chem., 40 (2015) 531.
578
[33]
M. Kalidasan, R. Nagarajaprakash, S. Forbes, Y. Mozharivskyj, M.R. Kollipara, Z.
579
580
Anorg. Allg. Chem., 641 (2015) 715.
[34]
(a) S. Adhikari, O. Hussain, R.M. Phillips, W. Kaminsky, M.R. Kollipara, Appl.
581
Organomet. Chem., 32 (2018) e4362. (b) S. Adhikari, O. Hussain, R.M. Phillips, W.
582
Kaminsky, M.R. Kollipara, Appl. Organomet. Chem., 32 (2018) e4476.
583
[35]
584
585
(2018) 26.
[36]
586
587
I.L. Mawnai, S Adhikari, W. Kaminsky, M.R. Kollipara, J. Organomet. Chem., 869
(a) M.A. Bennett, T.N. Huang, T.W. Matheson, A.K. Smith, S. Ittel, W. Nickerson,
Inorg. Synth. 21(1982) 74.
[37]
588
(a) G.M. Sheldrick, Acta Crystallogr. Sect.A, 46 (1990) 467.
(b) G.M. Sheldrick, Acta Crystallogr. Sect.A, 64 (2008) 112.
589
[38]
L.J. Farrugia, J. Appl. Crystallogr., 32 (1999) 837.
590
[39]
(a) R.M Phillips, P.B. Hulbert, M.C. Bibby, N.R. Sleigh, J.A. Double. Br J, Cancer. 65
591
(1992) 359.
592
(b) S. Adhikari, D. Sutradhar, S.L. Shepherd, R.M. Phillips, A.K. Chandra, M. R.
593
Kollipara, Polyhedron 117 (2016) 404.
594
595
[40]
K. Jeyalakshmi, J. Haribabu, C. Balachandran, N.S.P. Bhuvanesh, N. Emi, R. Karvembu,
New. J. Chem., 41 (2017) 2672.
31
596
[41]
S. Adhikari, W. Kaminsky, M.R. Kollipara J. Organomet. Chem. 848 (2017) 95.
597
598
Table 1. Selected bond lengths (Å) and bond angles (°) of complexes
Complexes
2
3
4
5
7
8
M(1)-CNT
1.787
1.778
1.672
1.689
1.665
1.784
M(1)-Cl(1)
2.413(1)
2.423(1)
2.426(1)
2.440(1)
2.4338(5)
2.4253(9)
M(1)-Cl(2)
2.427(1)
2.410(2)
2.406(1)
2.425(9)
2.4319(7)
2.411(1)
M(1)-S(1)
2.395(1)
2.370(2)
2.418(1)
2.366(1)
2.4004(7)
2.3857(8)
C=S(1)
1.689(9)
1.694(6)
1.703(5)
1.688(3)
1.695(2)
1.691(3)
Cl(2)- M(1)-Cl(1)
90.52(4)
88.48(5)
88.87(5)
92.75(3)
87.67(2)
90.55(3)
S(1)- M(1)- Cl(1)
94.09(4)
91.47(5)
89.58(5)
92.34(3)
92.22(2)
92.69(3)
S(1) -M(1)-Cl(2)
92.56(4)
93.735
90.57(5)
92.41(3)
91.28(2)
92.73(3)
Bond distances (Å)
Bond Angles (º)
599
600
Table 2. Selected bond lengths (Å) and bond angles (°) of complexes
Complexes
10
16
17
M(1)-CNT
1.675
1.678
1.784
M(1)-N(1)
2.138(2)
2.152(3)
2.161(3)
M(1)-N (azide)
2.127(4)
2.107(4)
2.125(5)
M(1)-S(1)
2.399(1)
2.406(1)
2.398(2)
C=S
1.713(3)
1.711(4)
1.723(4)
C=O
1.220(4)
1.229(5)
1.240(6)
N(1)-M(1)-N (azide)
85.7(1)
87.1(1)
90.7(2)
N(1)-M(1)-S(1)
67.27(7)
65.86(9)
67.0(1)
N(azide)-M(1)-S(1)
87.6(1)
88.8(1)
92.4(1)
Bond distances (Å)
Bond angle (º)
32
601
602
603
Table 3. Response of HCT-116 (human colon cancer) and ARPE-19 to complexes 1-9 and
604
cisplatin. Each IC50 value represents the mean ± standard deviation from three independent
605
experiments. The IC50 selectivity index is defined as the mean IC50 for ARPE-19 cells divided by
606
the mean IC50 for HCT-116 cells with values greater than 1 representing selective cell kill in
607
cancer cells compared to non-cancer cells.
608
IC50 (μM)
Compounds
HCT-116
ARPE-19
Selectivity
Index
Complex 1
52.936 ± 4.815
33.515 ± 1.244
0.633
Complex 2
63.182 ± 1.916
36.604 ± 1.056
0.579
Complex 3
35.172 ± 1.175
37.941 ± 0.964
1.078
Complex 4
43.751 ± 2.480
36.744 ± 0.159
0.838
Complex 5
>100
80.267 ± 1.210
n/a
Complex 6
>100
78.252 ± 1.501
n/a
Complex 7
75.215 ± 4.733
46.913 ± 2.048
0.623
Complex 8
>100
>100
n/a
Complex 9
78.211 ± 8.658
69.301 ± 1.606
0.886
Cisplatin
2.78 ± 1.40
3.43 ± 0.48
1.233
609
33