Cycloruthenated Imines: A Step into the Nanomolar Region

Arsenii A. Vasil’ev; Ivan I. Troshin; Pavel G. Shangin; Ksenia M. Voroshilkina; Ilya A. Shutkov; Alexey A. Nazarov; Aleksei V. Medved'ko

doi:10.20944/preprints202512.0562.v1

Submitted:

30 November 2025

Posted:

09 December 2025

You are already at the latest version

Abstract

A new series of promising and easily accessible antiproliferative agents based on cy-cloruthenated imines of benzene and thiophene carbaldehydes has been developed and fully characterized using UV-Vis spectroscopy, X-ray diffraction, NMR, HRMS, and cyclic voltammetry. The biological activity of these compounds was tested against A2780, cis-platin-resistant A2780, and HEK293 cell lines, and they exhibited nanomolar IC50 values. They also showed a selectivity index of up to 2.5, indicating their potential as promising antiproliferative compounds.

Keywords:

cycloruthenated complexes

;

imines

;

benzene

;

thiophene

;

cytotoxicity

Subject:

Chemistry and Materials Science - Organic Chemistry

1. Introduction

Despite global efforts to treat cancer, global mortality rates and newly diagnosed cancers continue to rise steadily. Malignant tumors remain a key factor limiting life expectancy. Chemotherapy is a traditional and widely used method of cancer treatment. Some of the most popular anticancer drugs are platinum compounds: cisplatin, carboplatin, and others. They have proven their effectiveness; however, despite their advantages, they can cause serious side effects, including hepatotoxicity, neurotoxicity, ototoxicity, and others [1,2]. Therefore, the scientific community is faced with the task of creating analogues of platinum compounds devoid of the above-mentioned drawbacks. Other transition metals, such as copper, iridium, osmium, gold, and ruthenium compounds, are being actively studied as anticancer agents [3,4]. Ruthenium is the most promising in this series, since it has broad coordination capabilities, unique mechanisms of anticancer activity in living cells, and its compounds are more accessible for commercial use than iridium or platinum precursors. Several families of anticancer drugs have already been developed based on ruthenium, including wide-layered complexes such as the NAMI type [5] and the RAPTA-type [6]. Photosensitizers based on ruthenium complexes can also be used for photodynamic cancer therapy [7,8]. A large number of ruthenium cyclometallic compounds containing a metal-carbon bond have been described in the literature. They are often used as dyes for DSSCs[9], as well as catalysts for oxidation [10] and cross-coupling [11]. At the same time, the literature also contains examples of the use of cycloruthenated complexes as anticancer drugs [12,13,14,15,16,17,18,19,20,21] Several years ago, we published a paper in which we synthesized ruthenium cyclometallic compounds containing a thiophene moiety [22]. A study of their anticancer properties showed that they are an order of magnitude more cytotoxic than the model drug cisplatin [23]. The role of substituents in the thiophene ring was studied, and it was shown that halogen substituents have virtually no effect on the IC₅₀ values. However, the effect of substituents in the aniline fragment on cytotoxicity remains unexplored. Furthermore, it was necessary to study the effect of replacing the aldehyde moiety with the benzene moiety.

2. Results and Discussion

2.1. Synthesis

All intermediate compounds and target complexes were obtained using methods similar to those described previously [23] (Scheme 1). Cycloruthenated complexes 3a-o were synthesized with moderate to good yields by a two-step procedure by cyclometallation of imines and chelation of the resulting acetonitrile complexes 2a-o. The remaining coordination sites were occupied by 2,2′-bipyridines to stabilize ruthenium in the (II) oxidation state, while aromatic ligands increase lipophilicity, facilitating transport across biological membranes. It is believed that ruthenium anticancer agents can bind to nuclear DNA via intercalation interactions; therefore, the presence of aromatic ligands enables stacking interactions between the ruthenium ring and nitrogenous base pairs.

2.2. Crystallography

From a crystallographic point of view, the obtained complexes have a similar structure (Table S1, Figures S30-S51). Thus, the lengths of the Ru-C bonds are in the range of 2.008-2.032 Å, Ru-N(aniline) - 2.062–2.123 Å, Ru-N, located opposite the Ru-C bond - 2.132–2.172 Å (Table 1). The plane of the aniline ring is inclined relative to the plane of the five-membered ring with the ruthenium atom with the dihedral angle 40.65–65.66 °. The sign of this angle is not characteristic, either for acetonitrile, or for bipyridine complexes. It is worth noting that the formation of the bipyridine complex decreases the modulus of the dihedral angle by an average of 10 ° (cf. 2a and 3a, 2b and 3b, 2e and 3e, 2f and 3f). In bipyridine complexes, one fragment is more distorted than the other. The dihedral angle between the two pyridine rings ranges from 1.85° to 10.77°. The dihedral angle of the second fragment is approximately 1°.

2.3. UV-vis Examination

UV spectra were recorded for complexes 3a–3o in acetonitrile (Figure 1) to determine their optical properties. All absorption spectra in acetonitrile exhibit two intensity bands: 250–300 nm (corresponding to the absorption bands of aromatic systems) and 450–600 nm (arising after metal coordination with 2,2′-bipyridine). This can be visually observed: during the reaction, acetonitriles are replaced by bipyridines, and the compounds change from orange to dark purple.

Stability of 3a-o was also assessed in 0.5% DMSO solution in aqueous phosphate buffer (pH 7.4, 37 °C, 100 μM NaCl, 77.4 μM Na2HPO4, 22.6 μM NaH2PO4) or saline by comparing the UV spectrum of solutions of complexes 3a-o, recorded immediately after solution preparation, and the UV spectrum of the same solution after 18 h of incubation at room temperature (Figures S52-S53). The spectra were compatible for all the complexes, indicating that they were sufficiently stable. A slight change in the intensity of signals is due to the slow degradation of ruthenium complexes with the formation of aqua- and oxo-complexes, as well as partial precipitation, which is typical for ruthenium compounds [24].

2.4. Electrochemistry

The introduction of electron-withdrawing substituents increases the E^1/2_ox1 value of the Ru²⁺/Ru³⁺ transition by an average of 40-60 mV (Table 2). The electron-donating methoxy group (3f and 3l) weakly reduces this potential. When comparing the nitro group in the thiophene ring [23] with the nitro group in the aniline ring, the latter shifts the oxidation potential less strongly (257 mV vs 215 mV). Overall, the oxidation potentials for the phenyl and thiophene derivatives are close to each other, except for the ethoxycarbonyl derivatives 3g and 3m, for which the potential differs by almost a factor of two.

2.5. Biological Study

The in vitro antiproliferative activity of the synthesized Ru-organometallic compounds and several starting ligands was evaluated against three human cell lines using the MTT assay. We selected a small panel of cell lines that provided insights into the efficacy and potential therapeutic utility of the compounds. The panel includes the A2780 human ovarian carcinoma cell line, which is sensitive to cisplatin, its cisplatin-resistant counterpart, A2780cis, also a non-malignant human embryonic kidney cell line, HEK293. The use of A2780 and A2780cis paired cell lines allowed us to directly assess the ability of the compounds to overcome resistance mechanisms. The inclusion of the HEK293 cell line can give us preliminary indication of selectivity against non-cancerous cells. Cisplatin, a clinically used drug, was used as a positive control in all experiments. All studies were performed in triplicate and repeated in three independent experiments. The results, expressed as the half-maximal inhibitory concentration after 72 h incubation (IC₅₀), are summarized in Table 3.

Based on the initial analysis of the data, we can conclude that the IC₅₀ values for all Ru compounds fall within the medium to high nanomolar range, suggesting a high level of cytotoxicity against both malignant and non-malignant cells. Moreover, the organometallic compounds appear to be several times more cytotoxic than cisplatin, approximately 10 times or more, although their selectivity for cancer cells is only moderate. The selectivity index for these compounds does not exceed 2.5, compared to 8.3 for cisplatin.

The presence of a ruthenium atom in a complex determines its biological activity. The data show that ligands such as 1b, 1f, and 1g do not exhibit any cytotoxicity, but the cytotoxicity of N-benzylideneaniline complexes (3b-i) and thiophenylimine compounds (3j-o) against A2780 is virtually identical. On the other hand, thiophenylidenimine ruthenacycles (against A2780cis) are several times more cytotoxic than N-benzylideneaniline complexes. This makes them a promising treatment for cisplatin-resistant tumors.

If we look at the structure of the ligands, we can draw the following conclusions about their activity: the electron-donating OMe group slightly increases cytotoxicity, while the acceptors NO₂ and CF₃ reduce cytotoxicity. At the same time, alkyl substituents (except for tBu) increase the cytotoxicity of both the benzylideneaniline and thiophenylidenimine families of complexes. This can be attributed to their increased lipophilicity.

3. Experimental Section

3.1. General Procedure for Compounds 2a-2o.

Imine 1 (0.40 mmol, 2 eq) dissolved in acetonitrile (15 ml) was added to a three-necked flask equipped with a reflux condenser with [Ru(C₆H₆)Cl₂]₂ (0.20 mmol, 1 eq), potassium hexafluorophosphate (0.80 mmol, 4 eq), potassium acetate (0.60 mmol, 3 eq) and refluxed in an argon atmosphere for 24 hours. The reaction mixture was evaporated, residue was dissolved in DCM (15 ml) and of water (10 ml), organic layer was separated, aqueous layer was washed with DCM (5 ml), organic phases were combined, dried over sodium sulfate and evaporated to dryness. Crude product was purified with column chromatography on silica gel (CHCl₃:CH₃CN 10:1). Crystals suitable for X-ray analysis were grown by diethyl ether vapor diffusion on acetonitrile solution of complexes.

Tetrakis(acetonitrile)[N-((phenyl-κC²)methyliden]aniline-κN]ruthenium(II) hexafluorophosphate (2a).

Orange powder. Yield 60%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.46 (s, 1H), 8.03 (d, J = 7.5 Hz, 1H), 7.64 (dd, J = 7.5, 1.1 Hz, 1H), 7.49–7.42 (m, 2H), 7.39–7.34 (m, 1H), 7.34–7.28 (m, 2H), 7.13 (td, J = 7.4, 1.5 Hz, 1H), 6.96 (td, J = 7.3, 1.2 Hz, 1H), 2.51 (s, 3H), 2.12 (s, 6H), 1.96 (s, 3H).

¹³C NМR (76 MHz, Acetonitrile-d₃): 191.61, 176.62, 152.09, 149.52, 138.15, 129.68, 128.76, 126.63, 124.03, 122.69, 121.81, 120.57, 117.35, 65.30, 14.66, 3.41, 2.93.

HRMS-ESI: calc for [C₁₉H₁₉N₄Ru-CH₃CN]⁺ 405.0647, found 405.0643

Tetrakis(acetonitrile)[N-((phenyl-κC²)methyliden]-4-fluoroaniline-κN]ruthenium(II) hexafluorophosphate (2b).

Orange powder. Yield 73%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.45 (s, 1H), 8.02 (d, J = 7.5 Hz, 1H), 7.63 (d, J = 7.4 Hz, 1H), 7.35–7.28 (m, 2H), 7.22–7.10 (m, 3H), 6.96 (t, J = 7.3 Hz, 1H), 2.51 (s, 3H), 2.12 (s, 6H), 1.96 (s, 3H).

¹³C NМR (151 MHz, Acetonitrile-d₃): 191.83, 176.98, 162.05, 160.44, 149.45, 148.55, 138.21, 129.83, 128.73, 124.55, 121.91, 120.63, 117.40, 115.22, 3.41, 2.94.

HRMS-ESI: calc for [C₁₉H₁₈FN₁₄Ru-CH₃CN]⁺ 423.0534, found 423.0568.

Tetrakis(acetonitrile)[N-((phenyl-κC²)methyliden]-4-methylaniline-κN]ruthenium(II) hexafluorophosphate (2c).

Orange powder. Yield 65%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.43 (s, 1H), 8.01 (d, J = 7.5 Hz, 1H), 7.61 (dd, J = 7.5, 1.1 Hz, 1H), 7.26 (d, J = 8.3 Hz, 2H), 7.19 (d, J = 8.4 Hz, 2H), 7.12 (td, J = 7.4, 1.5 Hz, 1H), 6.96 (td, J = 7.3, 1.1 Hz, 1H), 2.51 (s, 3H), 2.39 (s, 3H), 2.11 (s, 6H), 1.96 (s, 3H).

¹³C NМR (151 MHz, Acetonitrile-d₃): 191.40, 176.19, 149.80, 138.14, 136.59, 129.52, 129.20, 128.53, 123.97, 122.54, 121.76, 120.57, 117.36, 20.11, 3.45, 2.96.

HRMS-ESI: calc for [C₂₀H₂₁N₄Ru-CH₃CN]⁺ 419.0822, found 419.0814.

Tetrakis(acetonitrile)[N-((phenyl-κC²)methyliden]-4-ethylaniline-κN]ruthenium(II) hexafluorophosphate (2d)

Orange powder. Yield 48%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.44 (s, 1H), 8.01 (d, J = 7.5 Hz, 1H), 7.63–7.58 (m, 1H), 7.29 (d, J = 8.2 Hz, 2H), 7.21 (d, J = 8.3 Hz, 2H), 7.12 (t, J = 7.3 Hz, 1H), 6.96 (t, J = 7.3 Hz, 1H), 2.70 (q, J = 7.6 Hz, 2H), 2.51 (s, 3H), 2.12 (s, 6H), 1.96 (s, 3H), 1.26 (t, J = 7.6 Hz, 3H).

¹³C NМR (151 MHz, Acetonitrile-d₃): 191.39, 176.22, 149.97, 149.58, 143.02, 138.14, 129.54, 128.55, 128.08, 123.98, 122.63, 121.77, 120.57, 117.36, 28.10, 15.25, 3.44, 2.97.

HRMS-ESI: calc for [C₂₁H₂₃N₄Ru-CH₃CN]⁺ 433.1210, found 433.1215

Tetrakis(acetonitrile)[N-((phenyl-κC²)methyliden]-4-(tert-butyl)aniline-κN]ruthenium(II) hexafluorophosphate (2e).

Orange powder. Yield 56%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.45 (s, 1H), 8.01 (d, J = 7.4 Hz, 1H), 7.62 (d, J = 7.4 Hz, 1H), 7.48 (d, J = 8.5 Hz, 2H), 7.24 (d, J = 8.4 Hz, 2H), 7.12 (t, J = 7.3 Hz, 1H), 6.96 (t, J = 7.3 Hz, 1H), 2.51 (s, 3H), 2.12 (s, 6H), 1.96 (s, 3H), 1.37 (s, 9H).

¹³C NМR (151 MHz, Acetonitrile-d₃): 191.43, 176.25, 149.73, 138.15, 129.57, 128.57, 125.58, 124.00, 122.31, 121.79, 120.59, 117.38, 34.30, 30.68, 3.43, 2.96.

HRMS-ESI: calc for [C₂₃H₂₇N₄Ru-CH₃CN]⁺ 315.6547, found 315.6548.

Tetrakis(acetonitrile)[N-((phenyl-κC²)methyliden]-4-methoxyaniline-κN]ruthenium(II) hexafluorophosphate (2f).

Orange powder. Yield 40%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.42 (s, 1H), 8.01 (d, J = 7.5 Hz, 1H), 7.61 (d, J = 7.4 Hz, 1H), 7.26 (d, J = 8.8 Hz, 2H), 7.11 (t, J = 7.3 Hz, 1H), 7.00–6.92 (m, 3H), 3.84 (s, 3H), 2.51 (s, 3H), 2.11 (s, 6H), 1.96 (s, 3H).

¹³C NМR (151 MHz, Acetonitrile-d₃): 191.19, 175.85, 158.52, 149.61, 145.56, 138.10, 129.41, 128.45, 123.79, 121.74, 120.57, 117.36, 113.75, 55.28, 2.99.

HRMS-ESI: calc for [C₁₉H₁₈N₄ORu]⁺ 419.0812, found 419.0814.

Tetrakis(acetonitrile)[N-((phenyl-κC²)methyliden]-4-ethoxycarbonylaniline-κN]ruthenium(II) hexafluorophosphate (2g).

Orange powder. Yield 50%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.50 (s, 1H), 8.10–8.02 (m, 3H), 7.67 (d, J = 7.3 Hz, 1H), 7.38 (d, J = 8.4 Hz, 2H), 7.14 (t, J = 7.4 Hz, 1H), 6.98 (t, J = 7.3 Hz, 1H), 4.37 (q, J = 7.1 Hz, 2H), 2.52 (s, 3H), 2.12 (s, 6H), 1.96 (s, 3H), 1.38 (t, J = 7.1 Hz, 3H).

¹³C NМR (151 MHz, Acetonitrile-d₃): 192.72, 177.59, 165.84, 155.89, 149.44, 138.28, 130.31, 130.03, 128.98, 124.23, 123.06, 122.02, 120.71, 117.38, 61.00, 13.68, 3.45, 2.96.

HRMS-ESI: calc for [C₂₂H₂₃N₄O₂Ru-CH₃CN]⁺ 477.0853, found 477.0859.

Tetrakis(acetonitrile)[N-((phenyl-κC²)methyliden]-4-nitroaniline-κN]ruthenium(II) hexafluorophosphate (2h).

Orange powder. Yield 45%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.54 (s, 1H), 8.33–8.27 (m, 2H),

8.06 (d, J = 7.5 Hz, 1H), 7.71 (dd, J = 7.5, 1.1 Hz, 1H), 7.51–7.46 (m, 2H), 7.16 (td, J = 7.3, 1.4 Hz, 1H), 6.99 (td, J = 7.4, 1.1 Hz, 1H), 2.52 (s, 3H), 2.13 (s, 6H), 1.96 (s, 3H).¹³C NМR (151 MHz, Acetonitrile-d3): 193.64, 178.56, 157.44, 149.33, 146.21, 138.35, 130. 82, 129.27, 124.44, 123.99, 122.18, 120.82, 117.37, 3.46, 2.99.

HRMS-ESI: calc for [C₁₉H₁₈N₅O₂Ru-CH₃CN]⁺ 435.0765, found 435.0766.

Tetrakis(acetonitrile)[N-((phenyl-κC²)methyliden]-4-(trifluoromethyl)aniline-κN]ruthenium(II) hexafluorophosphate (2i).

Orange powder. Yield 42%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.51 (s, 1H), 8.04 (d, J = 7.5 Hz, 1H), 7.77 (d, J = 8.4 Hz, 2H), 7.68 (d, J = 7.5 Hz, 1H), 7.46 (d, J = 8.3 Hz, 2H), 7.15 (t, J = 7.4 Hz, 1H), 6.98 (t, J = 7.4 Hz, 1H), 2.52 (s, 3H), 2.12 (s, 6H), 1.96 (s, 3H).

¹³C NМR (151 MHz, Acetonitrile-d₃): 192.73, 177.99, 155.22, 149.38, 138.29, 130.39, 129.05, 126.01, 124.27, 123.64, 122.06, 120.74, 117.37, 3.46, 2.99.

HRMS-ESI: calc for [C₂₀H₁₈F₃N₄Ru-CH₃CN]⁺ 473.0528, 473.0524.

Tetrakis(acetonitrile)[N-((thiophene-2-yl-κC²)methyliden]-4-fluoroaniline-κN]ruthenium(II) hexafluorophosphate (2j).

Orange powder. Yield 59%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.38 (s, 1H), 7.82 (d, J = 4.6 Hz, 1H), 7.63 (d, J = 4.1 Hz, 1H), 7.34–7.27 (m, 2H), 7.20–7.13 (m, 2H), 2.51 (s, 3H), 2.12 (s, 6H), 1.96 (s, 3H).

¹³C NMR (76 MHz, Acetonitrile-d₃) δ 202.67, 168.15, 163.47, 160.26, 149.81, 149.78, 138.48, 137.04, 134.08, 125.66, 125.55, 125.23, 123.44, 116.33, 116.04, 31.61, 30.35, 4.32, 3.89, 1.77.

HRMS-ESI: calc for [C₁₉H₁₉BrN₅RuS-CH₃CN]⁺ 470.0387, found 470.0397

Tetrakis(acetonitrile)[N-((thiophene-2-yl-κC²)methyliden]-4-methylaniline-κN]ruthenium(II) hexafluorophosphate (2k).

Orange powder. Yield 48%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.38 (s, 1H), 7.80 (d, J = 4.6 Hz, 1H), 7.62 (d, J = 4.6 Hz, 1H), 7.25–7.16 (m, 4H), 2.51 (s, 3H), 2.38 (s, 3H), 2.12 (s, 6H), 1.96 (s, 3H).

¹³C NMR (75 MHz, Acetonitrile-d₃) δ 201.70, 167.47, 151.03, 138.48, 136.98, 136.91, 133.58, 130.16, 125.11, 123.73, 123.29, 21.05, 4.34, 3.91, 1.77.

HRMS-ESI: calc for [C₁₉H₁₉BrN₅RuS-CH₃CN]⁺ 425.0372, found 425.0362.

Tetrakis(acetonitrile)[N-((thiophene-2-yl-κC²)methyliden]-4-methoxyaniline-κN]ruthenium(II) hexafluorophosphate (2l).

Orange powder. Yield 43%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.39 (s, 1H), 7.82 (d, J = 4.6 Hz, 1H), 7.64 (d, J = 4.6 Hz, 1H), 7.30–7.23 (m, 2H), 7.02–6.96 (m, 2H), 3.86 (s, 3H), 2.54 (s, 3H), 2.14 (s, 6H), 1.99 (s, 3H).

¹³C NMR (76 MHz, Acetonitrile-d₃) δ 201.18, 167.17, 159.05, 146.78, 138.41, 136.93, 133.36, 132.27, 129.73, 125.06, 124.87, 123.27, 114.69, 56.19, 4.34, 3.92.

HRMS-ESI: calc for [C₁₉H₁₉BrN₅RuS-CH₃CN]⁺ 482.0587, found 482.0595.

Tetrakis(acetonitrile)[N-((thiophene-2-yl-κC²)methyliden]-4-ethoxycarbonylaniline-κN]ruthenium(II) hexafluorophosphate (2m).

Orange powder. Yield 32%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.45 (s, 1H), 8.05 (d, J = 8.5 Hz, 2H), 7.88 (d, J = 4.7 Hz, 1H), 7.66 (d, J = 4.7 Hz, 1H), 7.39 (d, J = 8.4 Hz, 2H), 4.36 (q, J = 7.1 Hz, 2H), 2.52 (s, 3H), 2.12 (s, 6H), 1.96 (s, 3H), 1.38 (t, J = 7.1 Hz, 3H).

¹³C NMR (76 MHz, Acetonitrile-d₃) δ 204.97, 168.66, 166.87, 157.31, 138.94, 137.13, 135.02, 130.96, 129.02, 125.33, 124.17, 123.56, 61.85, 14.63, 4.37, 3.92.

HRMS-ESI: calc for [C₁₉H₁₉BrN₅RuS-CH₃CN]⁺ 524.0694, found 524.0695.

Tetrakis(acetonitrile)[N-((thiophene-2-yl-κC²)methyliden]-4-nitroaniline-κN]ruthenium(II) hexafluorophosphate (2n).

Orange powder. Yield 42%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.50 (s, 1H), 8.27 (d, J = 9.0 Hz, 2H), 7.92 (d, J = 4.7 Hz, 1H), 7.68 (d, J = 4.7 Hz, 1H), 7.49 (d, J = 9.0 Hz, 2H), 2.52 (s, 3H), 2.12 (s, 6H), 1.96 (s, 3H).

¹³C NMR (76 MHz, Acetonitrile-d₃) δ 207.50, 169.44, 159.04, 146.53, 139.30, 137.28, 136.07, 125.48, 125.39, 124.97, 123.77, 31.59, 30.34, 4.37, 3.94, 1.77.

HRMS-ESI: calc for [C₁₉H₁₉BrN₅RuS-CH₃CN]⁺ 497.0332, found 497.0344.

Tetrakis(acetonitrile)[N-((thiophene-2-yl-κC²)methyliden]-4-(trifluoromethyl)aniline-κN]ruthenium(II) hexafluorophosphate (2o).

Orange powder. Yield 46%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.46 (s, 1H), 7.88 (d, J = 4.6 Hz, 1H), 7.74 (d, J = 8.3 Hz, 2H), 7.66 (d, J = 4.6 Hz, 1H), 7.46 (d, J = 8.2 Hz, 2H), 2.52 (s, 3H), 2.12 (s, 6H), 1.96 (s, 3H).

¹³C NMR (76 MHz, Acetonitrile-d₃) δ 205.10, 169.01, 156.59, 138.89, 137.13, 135.13, 128.29, 127.86, 126.88 (q, J = 3.8 Hz), 125.36, 124.75, 123.60, 4.38, 3.94.

HRMS-ESI: calc for [C₁₉H₁₉BrN₅RuS-CH₃CN]⁺ 520.0356, found 520.0367.

3.1. General Procedure for Compounds 3a-3o.

Complex 2 (0.30 mmol, 1 eq) and 2,2’-bipyridine (0.60 mmol, 2 eq) were introduced into a flask equipped with a reflux condenser, ethanol (18 ml) was added, and the mixture was refluxed in an argon atmosphere for 4 hours. The reaction mixture was evaporated and purified with column chromatography on silica gel (CHCl₃:CH₃CN 10:1). The product was dissolved in minimal volume of CH₃CN and added dropwise to large excess of diethyl ether under vigorous stirring. The precipitate was filtered, washed with diethyl ether and dried in vacuo for 3 h. Crystals suitable for X-ray analysis were grown by diethyl ether vapor diffusion on acetonitrile solution of complexes.

Bis(2,2՛-bipiridine)[N-((phenyl-κC²)methyliden]aniline-κN]ruthenium(II) hexafluorophosphate (3a).

Dark purple powder. Yield 75%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.73 (s, 1H), 8.63 (d, J = 5.7 Hz, 1H), 8.33 (d, J = 8.2 Hz, 2H), 8.13 (d, J = 8.2 Hz, 1H), 8.00 (dd, J = 12.8, 6.9 Hz, 2H), 7.84 (p, J = 7.7 Hz, 3H), 7.78–7.64 (m, 4H), 7.40 (t, J = 6.6 Hz, 1H), 7.31 (t, J = 6.6 Hz, 1H), 7.19 (t, J = 6.5 Hz, 2H), 7.02–6.81 (m, 5H), 6.53 (dd, J = 12.5, 7.3 Hz, 3H).

¹³C NМR (151 MHz, Acetonitrile-d₃): 201.76, 176.18, 158.78, 158.01, 157.64, 155.56, 155.43, 153.29, 151.82, 151.24, 150.07, 149.36, 136.77, 136.36, 136.09, 135.10, 134.81, 131.82, 130.09, 129.47, 127.43, 127.39, 127.35, 127.16, 127.05, 124.02, 123.67, 123.21, 122.64, 121.63.

CHN calc. for С₃₃H₂₆N₅RuPF₆*0.2C₄H₁₀O: C: 53.29; H: 3.53; N: 9.31. Obs. C: 53.29; H: 3.52; N: 9.39.

Bis(2,2՛-bipiridine)[N-((phenyl-κC²)methyliden]-4-fluoroaniline-κN]ruthenium(II) hexafluorophosphate (3b).

Dark purple powder. Yield 77%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.72 (s, 1H), 8.59 (d, J = 5.7 Hz, 1H), 8.34 (d, J = 8.1 Hz, 2H), 8.15 (d, J = 8.1 Hz, 1H), 8.05 (d, J = 8.2 Hz, 1H), 7.96 (d, J = 5.6 Hz, 1H), 7.84 (p, J = 7.2 Hz, 3H), 7.78–7.70 (m, 3H), 7.66 (d, J = 5.3 Hz, 1H), 7.39 (t, J = 6.6 Hz, 1H), 7.31 (t, J = 6.7 Hz, 1H), 7.20 (q, J = 6.2 Hz, 2H), 6.87 (p, J = 7.4 Hz, 2H), 6.66 (t, J = 8.7 Hz, 2H), 6.58–6.47 (m, 3H).

¹³C NМR (151 MHz, Acetonitrile-d₃): 200.85, 175.57, 161.43, 159.82, 157.77, 157.04, 156.67, 154.49, 152.32, 150.34, 149.15, 148.33, 147.22, 135.94, 135.21, 134.22, 133.92, 130.96, 129.22, 126.58, 123.49, 122.37, 120.73, 117.38, 115.10.

CHN calc. for C₃₃H₂₅N₅RuPF₇: C: 52.39; H: 3.33; N: 9.26. Obs. C: 52.23; H: 3.21; N: 9.09.

Bis(2,2՛-bipiridine)[N-((phenyl-κC²)methyliden]-4-methylaniline-κN]ruthenium(II) hexafluorophosphate (3c).

Dark purple powder. Yield 82%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.70 (s, 1H), 8.61 (d, J = 5.7 Hz, 1H), 8.33 (d, J = 8.2 Hz, 2H), 8.14 (d, J = 8.1 Hz, 1H), 8.04 (d, J = 8.1 Hz, 1H), 7.96 (d, J = 5.6 Hz, 1H), 7.88–7.78 (m, 3H), 7.76–7.68 (m, 3H), 7.66 (d, J = 5.3 Hz, 1H), 7.39 (t, J = 6.7 Hz, 1H), 7.30 (t, J = 6.7 Hz, 1H), 7.22–7.16 (m, 2H), 6.91–6.80 (m, 2H), 6.73 (d, J = 8.0 Hz, 2H), 6.52 (d, J = 7.1 Hz, 1H), 6.41 (d, J = 8.0 Hz, 2H), 2.12 (s, 3H).

¹³C NМR (76 MHz, Acetonitrile-d3): 200.41, 174.77, 157.82, 157.03, 156.67, 154.60, 154.43, 152.31, 150.23, 149.08, 148.62, 148.44, 136.06, 135.78, 135.38, 135.05, 134.08, 133.79, 130.62, 128.91, 126.40, 126.17, 123.02, 122.70, 122.29, 121.47, 120.68, 117.36, 19.80.

CHN calc. for C₃₄H₂₈N₅RuPF₆: C: 54.26; H: 3.75; N: 9.30. Obs. C: 54.07; H: 3.70; N: 9.34.

Bis(2,2՛-bipiridine)[N-((phenyl-κC²)methyliden]-4-ethylaniline-κN]ruthenium(II) hexafluorophosphate (3d).

Dark purple powder. Yield 85%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.71 (s, 1H), 8.62 (d, J = 5.5 Hz, 1H), 8.33 (d, J = 8.3 Hz, 2H), 8.12 (d, J = 8.1 Hz, 1H), 8.02–7.95 (m, 2H), 7.89–7.78 (m, 3H), 7.76–7.63 (m, 4H), 7.39 (ddd, J = 7.3, 5.7, 1.4 Hz, 1H), 7.30 (ddd, J = 7.3, 5.7, 1.4 Hz, 1H), 7.19 (ddd, J = 7.5, 6.0, 1.1 Hz, 2H), 6.89 (td, J = 7.3, 1.5 Hz, 1H), 6.83 (td, J = 7.2, 1.7 Hz, 1H), 6.76–6.71 (m, 2H), 6.56–6.51 (m, 1H), 6.41–6.36 (m, 2H), 2.42 (q, J = 7.6 Hz, 2H), 1.05 (t, J = 7.6 Hz, 3H).

¹³C NМR (76 MHz, Acetonitrile-d₃): 200.43, 174.66, 157.85, 157.04, 156.66, 154.40, 152.33, 150.29, 149.07, 148.48, 142.53, 135.77, 135.33, 135.05, 134.04, 133.76, 130.61, 129.01, 127.76, 126.40, 126.15, 123.03, 122.63, 122.22, 121.52, 120.64, 117.35, 27.80, 15.28.

CHN calc. for C₃₅H₃₀N₅RuPF₆: C: 54.66; H: 3.94; N: 9.31. Obs. C: 54.87; H: 3.93; N :9.13.

Bis(2,2՛-bipiridine)[N-((phenyl-κC²)methyliden]-4-(tert-butyl)aniline-κN]ruthenium(II) hexafluorophosphate (3e).

Dark purple powder. Yield 78%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.71 (s, 1H), 8.64 (d, J = 5.8 Hz, 1H), 8.34 (d, J = 8.1 Hz, 2H), 8.09 (d, J = 8.1 Hz, 1H), 7.98 (d, J = 5.7 Hz, 1H), 7.94 (d, J = 8.1 Hz, 1H), 7.89–7.77 (m, 4H), 7.73 (d, J = 7.3 Hz, 1H), 7.67 (t, J = 7.8 Hz, 1H), 7.62 (d, J = 5.3 Hz, 1H), 7.39 (t, J = 6.6 Hz, 1H), 7.30 (t, J = 6.6 Hz, 1H), 7.19 (q, J = 6.0 Hz, 2H), 6.92–6.81 (m, 4H), 6.55 (d, J = 7.2 Hz, 1H), 6.33 (d, J = 8.0 Hz, 2H), 1.15 (s, 9H).

¹³C NМR (76 MHz, Acetonitrile-d₃): 205.61, 179.79, 163.22, 162.35, 161.97, 159.96, 159.68, 157.66, 155.67, 154.44, 154.39, 153.81, 153.10, 141.05, 140.62, 140.38, 139.31, 139.03, 135.87, 134.34, 131.42, 130.49, 128.36, 127.86, 127.48, 126.43, 125.94, 122.66, 39.21, 35.77.

CHN calc. for C₃₇H₃₄N₅PF₆Ru: C: 55.92; H: 3.84; N: 8.73. Obs. C: 55.90; H: 4.24; N :9.10.

Bis(2,2՛-bipiridine)[N-((phenyl-κC²)methyliden]-4-methoxyaniline-κN]ruthenium(II) hexafluorophosphate (3f).

Dark purple powder. Yield 84%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.69 (s, 1H), 8.60 (d, J = 5.0 Hz, 1H), 8.33 (d, J = 8.2 Hz, 2H), 8.14 (d, J = 8.1 Hz, 1H), 8.05 (d, J = 8.2 Hz, 1H), 7.98–7.94 (m, 1H), 7.88–7.78 (m, 3H), 7.76–7.70 (m, 3H), 7.68–7.65 (m, 1H), 7.39 (ddd, J = 7.3, 5.7, 1.4 Hz, 1H), 7.30 (ddd, J = 7.4, 5.7, 1.4 Hz, 1H), 7.23–7.16 (m, 2H), 6.88 (td, J = 7.2, 1.5 Hz, 1H), 6.82 (td, J = 7.2, 1.7 Hz, 1H), 6.55–6.50 (m, 1H), 6.45 (s, 4H), 3.62 (s, 3H).

¹³C NМR (151 MHz, Acetonitrile-d₃): 200.28, 174.42, 157.92, 157.83, 157.07, 156.71, 154.68, 154.42, 152.33, 150.31, 149.09, 148.46, 144.23, 135.82, 135.32, 135.04, 134.08, 133.78, 130.53, 128.94, 126.45, 126.19, 123.06, 122.71, 120.66, 117.37, 113.52, 55.12.

CHN calc. for C₃₄H₂₈N₅ORuPF₆: C: 53.13; H: 3.67; N: 9.11. Obs. C: 52.87; H: 3.76; N: 9.17.

Bis(2,2՛-bipiridine)[N-((phenyl-κC²)methyliden]-4-ethoxycarbonylaniline-κN]ruthenium(II) hexafluorophosphate (3g).

Dark purple powder. Yield 75%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.78 (s, 1H), 8.60 (dd, J = 5.7, 0.7 Hz, 1H), 8.34 (dq, J = 8.2, 1.2 Hz, 2H), 8.14 (d, J = 8.0 Hz, 1H), 8.02 (d, J = 8.2 Hz, 1H), 7.97–7.94 (m, 1H), 7.90–7.78 (m, 4H), 7.73–7.65 (m, 3H), 7.57–7.52 (m, 2H), 7.40 (ddd, J = 7.3, 5.7, 1.4 Hz, 1H), 7.32 (ddd, J = 7.3, 5.7, 1.4 Hz, 1H), 7.24–7.17 (m, 2H), 6.91 (td, J = 7.3, 1.5 Hz, 1H), 6.86 (td, J = 7.3, 1.7 Hz, 1H), 6.63–6.56 (m, 3H), 4.25 (q, J = 7.1 Hz, 2H), 1.30 (t, J = 7.1 Hz, 3H).

¹³C NМR (76 MHz, Acetonitrile-d₃): 201.83, 176.20, 165.42, 157.69, 157.00, 156.65, 154.68, 154.52, 152.36, 150.30, 149.12, 148.29, 135.94, 135.50, 135.29, 134.32, 134.01, 131.44, 129.69, 129.41, 128.07, 126.62, 126.25, 123.10, 122.82, 122.38, 122.02, 120.77, 117.35, 60.92, 13.54.

CHN calc. for C₃₆H₃₀N₅O₂RuPF₆*0.16CHCl₃: C: 52.13; H:3.88; N: 8.71. Obs. C: 52.40; H:3.84; N: 8.73.

Bis(2,2՛-bipiridine)[N-((phenyl-κC²)methyliden]-4-nitroaniline-κN]ruthenium(II) hexafluorophosphate (3h).

Dark purple powder. Yield 79%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.85–8.78 (m, 1H), 8.60–8.53 (m, 1H), 8.38–8.31 (m, 2H), 8.15–8.09 (m, 1H), 8.04–7.98 (m, 1H), 7.93 (t, J = 5.6 Hz, 1H), 7.90–7.79 (m, 4H), 7.77–7.64 (m, 5H), 7.43–7.36 (m, 1H), 7.33 (t, J = 6.6 Hz, 1H), 7.27–7.17 (m, 2H), 6.96–6.83 (m, 2H), 6.72–6.64 (m, 2H), 6.63–6.57 (m, 1H).

¹³C NМR (151 MHz, Acetonitrile-d₃): 202.80, 177.17, 157.64, 157.02, 156.67, 156.18, 154.60, 154.42, 152.42, 150.40, 149.12, 148.25, 145.46, 136.15, 135.60, 135.46, 134.51, 134.19, 131.98, 129.73, 126.87, 126.72, 126.50, 126.31, 124.05, 123.20, 123.16, 122.95, 122.60, 120.87, 117.35.

CHN calc. for C₃₃H₂₅N₆O₂PF₆Ru*0.44CHCl₃*0.34C₄H₁₀O: C: 48.51; H: 3.38; N: 9.75. Obs. C: 48.51; H: 3.21; N :9.75.

Bis(2,2՛-bipiridine)[N-((phenyl-κC²)methyliden]-4-(trifluoromethyl)aniline-κN]ruthenium(II) hexafluorophosphate (3i).

Dark purple powder. Yield 82%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.78 (s, 1H), 8.59 (d, J = 5.7 Hz, 1H), 8.34 (d, J = 8.1 Hz, 2H), 8.13 (d, J = 8.1 Hz, 1H), 8.02–7.95 (m, 2H), 7.91–7.78 (m, 4H), 7.74–7.63 (m, 3H), 7.40 (t, J = 6.7 Hz, 1H), 7.33 (t, J = 6.7 Hz, 1H), 7.25–7.17 (m, 4H), 6.89 (q, J = 6.6 Hz, 2H), 6.64 (d, J = 8.0 Hz, 2H), 6.59 (d, J = 6.9 Hz, 1H).

¹³C NМR (76 MHz, Acetonitrile-d₃): 201.70, 176.46, 157.69, 157.00, 156.63, 154.57, 152.34, 150.34, 149.16, 148.27, 135.92, 135.52, 135.34, 135.27, 134.34, 134.04, 131.46, 129.48, 126.64, 126.42, 126.24, 125.65, 123.11, 122.82, 122.53, 122.33, 120.80, 117.34.

CHN calc. for C₃₄H₂₅N₅RuPF₉*0.16CH₃CN: C: 50.47; H: 3.15; N: 8.85. Obs. C: 50.47; H: 3.15; N: 8.84.

Bis(2,2՛-bipiridine)[N-((thiophene-2-yl-κC²)methyliden]-4-fluoroaniline-κN]ruthenium(II) hexafluorophosphate (3j).

Dark purple powder. Yield 82%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.64 (s, 1H), 8.51 (d, J = 4.9 Hz, 1H), 8.32 (d, J = 8.1 Hz, 2H), 8.14 (d, J = 8.0 Hz, 1H), 8.07 (d, J = 8.2 Hz, 1H), 7.91–7.71 (m, 6H), 7.68 (d, J = 4.7 Hz, 1H), 7.61 (d, J = 4.7 Hz, 1H), 7.41 (ddd, 1H), 7.31 (ddd, 1H), 7.26–7.16 (m, 2H), 6.68–6.58 (m, 2H), 6.51–6.43 (m, 3H).

¹³C NMR (76 MHz, Acetonitrile-d₃) δ 212.13, 166.43, 162.82, 159.60, 158.52, 158.39, 157.85, 155.74, 155.42, 153.95, 151.77, 150.03, 148.60, 148.56, 138.59, 136.93, 136.22, 135.82, 135.46, 135.18, 134.74, 127.58, 127.50, 127.31, 127.16, 124.61, 124.50, 124.03, 123.85, 123.69, 123.38, 116.06, 115.76.

CHN calc. for C₃₁H₂₃F₇N₅OPRuS: C: 48.82; H: 3.04; N: 9.18 Obs. C: 48.83; H: 3.04; N: 9.18.

Bis(2,2՛-bipiridine)[N-((thiophene-2-yl-κC²)methyliden]-4-methylaniline-κN]ruthenium(II) hexafluorophosphate (3k).

Dark purple powder. Yield 80%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.63 (s, 1H), 8.53 (d, J = 5.7 Hz, 1H), 8.31 (d, J = 8.1 Hz, 2H), 8.14 (d, J = 8.0 Hz, 1H), 8.06 (d, J = 8.1 Hz, 1H), 7.90–7.69 (m, 6H), 7.67–7.63 (m, 1H), 7.61 (d, J = 5.4 Hz, 1H), 7.44–7.36 (m, 1H), 7.33–7.26 (m, 1H), 7.19 (q, 2H), 6.71 (d, J = 8.1 Hz, 2H), 6.45 (d, J = 4.6 Hz, 1H), 6.39 (d, J = 8.3 Hz, 2H), 2.11 (s, 3H).

¹³C NMR (76 MHz, Acetonitrile-d₃) δ 211.31, 165.81, 158.60, 158.40, 157.88, 155.77, 155.43, 153.94, 151.67, 149.99, 138.53, 136.81, 136.32, 136.08, 135.36, 135.33, 135.08, 134.70, 129.90, 127.44, 127.37, 127.28, 127.16, 123.99, 123.80, 123.65, 123.34, 122.66, 20.75.

CHN calc. for C₃₂H₂₆F₆N₅PRuS: C: 50.66; H: 3.45; N: 9.23 Obs. C: 50.48; H: 3.48; N: 9.20.

Bis(2,2՛-bipiridine)[N-((thiophene-2-yl-κC²)methyliden]-4-methoxyaniline-κN]ruthenium(II) hexafluorophosphate (3l).

Dark purple powder. Yield 77%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.61 (s, 1H), 8.53 (d, J = 4.9 Hz, 1H), 8.31 (d, J = 8.1 Hz, 2H), 8.14 (d, J = 8.1 Hz, 1H), 8.06 (d, J = 8.2 Hz, 1H), 7.90–7.70 (m, 6H), 7.64 (d, J = 4.6 Hz, 1H), 7.61 (d, J = 4.6 Hz, 1H), 7.40 (ddd, J = 7.3, 5.7, 1.4 Hz, 1H), 7.30 (ddd, J = 7.3, 5.7, 1.4 Hz, 1H), 7.25–7.15 (m, 2H), 6.45 (d, J = 4.6 Hz, 1H), 6.42 (br.s, 3H), 3.61 (s, 3H).

¹³C NMR (76 MHz, Acetonitrile-d₃) δ 210.71, 165.46, 158.59, 158.44, 158.41, 157.88, 155.82, 155.39, 153.93, 151.72, 149.99, 145.56, 138.48, 136.82, 136.06, 135.32, 135.10, 135.04, 134.66, 127.45, 127.37, 127.27, 127.13, 123.99, 123.81, 123.61, 123.32, 114.48, 56.03, 15.64.

CHN calc. for C₃₂H₂₆F₆N₅OPRuS: C: 49.61; H: 3.38; N: 9.04 Obs. C: 49.60; H: 3.39; N: 9.08.

Bis(2,2՛-bipiridine)[N-((thiophene-2-yl-κC²)methyliden]-4-ethoxycarbonylaniline-κN]ruthenium(II) hexafluorophosphate (3m).

Dark purple powder. Yield 77%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.72 (s, 1H), 8.50 (d, J = 4.9 Hz, 1H), 8.33 (d, J = 8.4 Hz, 2H), 8.13 (d, J = 8.1 Hz, 1H), 8.05 (d, J = 8.2 Hz, 1H), 7.92–7.70 (m, 7H), 7.63 (d, J = 4.7 Hz, 1H), 7.55–7.49 (m, 2H), 7.42 (ddd, J = 7.3, 5.7, 1.4 Hz, 1H), 7.32 (ddd, J = 7.3, 5.7, 1.4 Hz, 1H), 7.25 (ddd, J = 7.5, 5.4, 1.2 Hz, 1H), 7.19 (ddd, J = 7.3, 5.7, 1.4 Hz, 1H), 6.63–6.56 (m, 2H), 6.49 (d, J = 4.6 Hz, 1H), 4.24 (q, J = 7.1 Hz, 2H), 1.29 (t, J = 7.1 Hz, 3H).

¹³C NMR (76 MHz, Acetonitrile-d₃) δ 166.89, 166.51, 158.46, 158.41, 157.89, 156.34, 155.61, 155.45, 154.08, 151.80, 150.05, 137.02, 136.80, 136.35, 135.63, 135.37, 134.88, 130.66, 128.29, 127.70, 127.53, 127.36, 127.25, 124.07, 123.90, 123.76, 123.46, 123.19, 61.80, 14.52.

CHN calc. for C₃₄H₂₈F₆N₅O₂PRuS: C: 50.00; H: 3.46; N: 8.57 Obs. C: 50.03; H: 3.48; N: 8.56.

Bis(2,2՛-bipiridine)[N-((thiophene-2-yl-κC²)methyliden]-4-nitroaniline-κN]ruthenium(II) hexafluorophosphate (3n).

Dark purple powder. Yield 65%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.78 (s, 1H), 8.48 (d, J = 5.6 Hz, 1H), 8.34 (d, J = 7.6 Hz, 2H), 8.12 (d, J = 8.0 Hz, 1H), 8.05 (d, J = 8.2 Hz, 1H), 7.95–7.71 (m, 9H), 7.64 (d, J = 5.3 Hz, 1H), 7.43 (t, J = 6.6 Hz, 1H), 7.35–7.26 (m, 2H), 7.20 (t, J = 6.7 Hz, 1H), 6.68 (d, J = 9.0 Hz, 2H), 6.52 (d, J = 4.7 Hz, 1H).

¹³C NMR (76 MHz, Acetonitrile-d₃) δ 217.12, 167.65, 158.41, 158.36, 158.11, 157.88, 155.48, 155.42, 154.14, 151.90, 149.98, 145.73, 139.52, 137.86, 137.24, 136.52, 135.82, 135.56, 135.02, 127.96, 127.64, 127.43, 127.30, 125.02, 124.13, 124.00, 123.95, 123.86, 123.67.

CHN calc. for C₃₁H₂₃F₆N₆O₂PRuS: C: 47.15; H: 2.94; N: 10.64 Obs. C: 46.99; H: 2.96; N: 10.61.

Bis(2,2՛-bipiridine)[N-((thiophene-2-yl-κC²)methyliden]-4-(trifluoromethyl)aniline-κN]ruthenium(II) hexafluorophosphate (3o).

Dark purple powder. Yield 96%.

¹H NMR (300 MHz, Acetonitrile-d₃) δ 8.73 (s, 1H), 8.51 (d, J = 4.9 Hz, 1H), 8.33 (d, J = 7.2 Hz, 2H), 8.13 (d, J = 8.1 Hz, 1H), 8.04 (d, J = 8.2 Hz, 1H), 7.93–7.70 (m, 7H), 7.62 (d, J = 4.8 Hz, 1H), 7.42 (ddd, J = 7.4, 5.7, 1.4 Hz, 1H), 7.32 (ddd, J = 7.3, 5.7, 1.4 Hz, 1H), 7.27–7.17 (m, 4H), 6.63 (d, J = 8.0 Hz, 2H), 6.51 (d, J = 4.7 Hz, 1H).

¹³C NMR (76 MHz, Acetonitrile-d₃) δ 214.53, 167.20, 158.45, 158.41, 157.87, 155.63, 155.49, 155.38, 154.06, 151.82, 150.06, 139.05, 137.01, 136.87, 136.40, 135.65, 135.38, 134.87, 127.73, 127.59, 127.37, 127.23, 126.64, 126.59, 126.54, 126.48, 124.09, 123.92, 123.76, 123.71, 123.41.

CHN calc. for C₃₂H₂₃F₉N₅PRuS: C: 47.30; H: 2.85; N: 8.62 Obs. C: 47.28; H: 2.79; N: 8.63.

4. Conclusions

Two bisheteroleptic ruthenium(II) compounds containing different types of the simplest cyclometallated imines of 2-thiophenecarboxaldehyde and benzaldehyde were synthesized and characterized by NMR, MS, elemental analysis and UV-vis spectroscopy and cyclic voltammetry. The structure of 22 complexes described was proved by means of single crystal X-ray data. Cytotoxic activity was measured on two cancer and one non-cancerous cell line, and the proportion of cell death was measured using the MTT assay. The cytotoxicity of all ruthenium complexes is significantly higher than that of cisplatin, but they have less selectivity.

Supplementary Materials

The following supporting information can be downloaded at: Preprints.org, Experimental details: pp. S2-S4; NMR spectra: pp. S5-S34; Crystallography: pp S35-S52; Stability in PBS: pp S53-S54.

Author Contributions

Conceptualization Vasil’ev A.A., Medved’ko A.V.; investigation, Vasil’ev A.A., Troshin A.I., Shangin P.G., Voroshilkina K.M., Shutkov I.A., Medved’ko A.V.; writing—original draft preparation, Vasil’ev A.A., Troshin A.I.; writing—Nazarov A.A., Medved’ko A.V.; funding acquisition, Medved’ko A.V. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Russian Science Foundation, grant number 24-23-00066.

Institutional Review Board Statement

Not applicable.

Data Availability Statement

Data is contained within the article or supplementary material.

Acknowledgments

Crystal structure determination was performed in the Department of Structural Studies of Zelinsky Institute of Organic Chemistry, Moscow. The authors acknowledge support from the M.V. Lomonosov Moscow State University Program of Development («Feyond-A400» microplate reader (Allsheng, China)) and automated pipetting system «EzMate» (Blue-Ray Biotech , Taiwan).

Conflicts of Interest

The authors declare no conflicts of interest

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Scheme 1. Preparation of ruthenium complexes.

Figure 1. UV-vis spectra of 3a-3o in acetonitrile, concentration 3.4*10^-5 M.

Table 1. Selected bond lengths and angles of ruthenium complexes.

	Aniline-(Ru-N) Dihedral Angle, °	Py-Py Dihedral Angle, °	Ru-N(aniline), Å	Ru-N, Å ^a	Ru-C, Å
2a (H)	+65.66		2.071	2.151	2.026
2b (F)	+58.36		2.065	2.155	2.035
2d (Et)	-52.43		2.069	2.142	2.027
2e (tBu)	-57.51		2.069	2.155	2.025
2f (OMe)	-61.74		2.066	2.152	2.019
2g (CO₂Et)^b	-51.97 +40.65		2.062 2.079	2.158 2.159	2.023 2.017
2h (NO₂)^b	+42.47 +41.62		2.096 2.071	2.157 2.172	2.019 2.008
2i (CF₃)	-51.20		2.063	2.153	2.022
2j (F)	-47.59		2.102	2.139	2.019
2k (Me)	-49.30		2.096	2.136	2.022
2l (OMe) ^b	+52.94 +41.76		2.093 2.114	2.132 2.139	2.018 2.015
2n (NO₂)	-47.17		2.105	2.140	2.020
3a (H)	+45.61	4.22	2.111	2.146	2.031
3b (F)	+49.65	1.85	2.104	2.136	2.030
3c (Me)	+39.77	5.01	2.117	2.152	2.031
3e (tBu)	+48.29	7.07	2.085	2.146	2.029
3f (OMe)	-55.21	3.52	2.063	2.155	2.036
3h (NO₂)	-52.22	3.96	2.091	2.156	2.031
3j (F)	+43.78	8.91	2.123	2.137	2.025
3l (OMe)	+48.94	10.77	2.117	2.148	2.010
3m (CO₂Et)	-58.58	5.47	2.110	2.137	2.018
3o (CF₃)	+55.99	3.79	2.106	2.127	2.019

^a located opposite the Ru-C bond. ^b two independent molecules.

Table 2. The E^1/2 values (mV vs. Fc/Fc⁺) of reduction and oxidation of the studied compounds in 0.1 M Bu₄NPF₆/MeCN were determined as the half-sum of the potentials of the forward and reverse peaks of the CV curves recorded for solutions with a concentration of 2.5 10^-3 M at a potential scan rate of 100 mV s^-1 on a glassy carbon working electrode at 298 K (for irreversible processes marked with an asterisk, the peak potentials are given).

	${E_{p} (E}_{r e d 2}^{1 / 2}), m V$	${E_{p} (E}_{r e d 1}^{1 / 2}), m V$	${E_{p} (E}_{o x 1}^{1 / 2}), m V$	${E_{p} (E}_{o x 2}^{1 / 2}), m V$	Additional peaks
3a (H)	-2277 (-2234)	-2022 (-1981)	139 (95)	1565
3b (F)	-2264 (-2219)	-2010 (-1969)	155 (111)	1607	-2828
3c (Me)	-2015 (-1973)	-2268 (-2226)	144 (99)	1570
3d (Et)	-2278 (-2233)	-2020 (-1981)	136 (92)	1551	-2905
3e (tBu)	-2280 (-2236)	-2026 (-1984)	128 (88)	1556	-2864
3f (OMe)	-2277 (-2235)	-2022 (-1984)	117 (78)	1352
3g^a (CO₂Et)	-2242	-2009 (-1961)	189 (135)	1635	-2551 (C=O reduction)
3h^b (NO₂)	-	-	200 (161)	1679	-1507 (-1467) -NO₂ reduction -1970
3i (CF₃)	-2245 (-2198)	-1996 (-1959)	181 (139)	1611	-2640 (C-F cleavage)
3j (F)	-2245 (-2202)	-1997 (-1956)	145 (102)	1422
3k (Me)	-2253 (-2213)	-2002 (-1962)	117 (77)	1364	-2909
3l (OMe)	-2256 (-2216)	-2003 (-1962)	107 (70)	1183 (1129)	-2874 (shoulder)
3m^c (CO₂Et)	-2226 (-2167)	-1989 (-1931)	78 (127)	1517	-2582 (C=O reduction)
3nd (NO₂)	-	-	215 (165)	1545	-1534 (-1488) (-NO₂ reduction)
3o (CF₃)	-2213 (-2175)	-1976 (-1936)	181 (143)	1460	-2582 (C-F cleavage)

^a C=O reduction is reversible, but too distorted, also affects

E_{r e d 1}^{1 / 2}

peak reversibility. ^b After first reduction of -NO₂ further curve is uninterpretable. ^c C=O reduction is reversible, but too distorted. ^d Very distorted

E_{r e d 2}^{1 / 2}

and

E_{r e d 1}^{1 / 2}

.

Table 3. Antiproliferative activity of ruthenium complexes with thiophene-based imines 2a-e, ligands S4a-e and cisplatin against various human cancer cells R_f showed resistance coefficient (calculated as IC₅₀ on A2780cis divided on IC₅₀ on A2780 cell line). The results are the mean values ± SD of three independent experiments, each of which was done in triplicate. The Selectivity Index is calculated as IC50 on HEK293 divided on IC₅₀ on A2780 cell line.

	IC₅₀ (72 h)/nМ
Compound	А2780	A2780Cis	Rf	HEK293	Selectivity Index, SI
Cisplatin	2640±350	1560±210	5.9	22000±4000	8.3
3b (F)	90 ± 30	250 ± 60	2.8	100 ± 30	1.1
3c (Me)	70 ± 6	120 ± 10	1.7	70 ± 10	1.0
3d (Et)	45 ± 5	150 ± 10	3.3	80 ± 10	1.8
3e (tBu)	70 ± 30	170 ± 30	2.4	68 ± 6	1.0
3f (OMe)	65 ± 4	120 ± 40	1.8	64 ± 7	1.0
3g (CO₂Et)	100 ± 20	230 ± 20	2.3	140 ± 20	1.4
3h (NO₂)	250 ± 30	760 ± 80	3.0	370 ± 80	1.5
3i (CF₃)	80 ± 10	240 ± 20	3.0	107 ± 8	1.3
3j (F)	43±3	91±9	2.1	60 ± 10	1.4
3k (Me)	30±2	10±0.4	0.3	70 ± 30	2.3
3l (OMe)	39±3	39±10	1.0	40 ± 10	1.0
3m (CO₂Et)	57±20	84±12	1.5	140 ± 10	2.5
3n (NO₂)	270±4	960±100	3.6	530 ± 30	2.0
3o (CF₃)	96±3	150±5	6.4	160 ± 30	1.7
1b (F)	> 200000	> 100000	-	21610	-
1f (OMe)	> 200000	> 100000	-	> 200000	-
1g (CO₂Et)	42090	> 100000	-	25430	-

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Cycloruthenated Imines: A Step into the Nanomolar Region

Abstract

Keywords:

Subject:

1. Introduction

2. Results and Discussion

2.1. Synthesis

2.2. Crystallography

2.3. UV-vis Examination

2.4. Electrochemistry

2.5. Biological Study

3. Experimental Section

3.1. General Procedure for Compounds 2a-2o.

3.1. General Procedure for Compounds 3a-3o.

4. Conclusions

Supplementary Materials

Author Contributions

Funding

Institutional Review Board Statement

Data Availability Statement

Acknowledgments

Conflicts of Interest

References

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