2.1 Synthesis of ligands

Ligands L1 and L2 were obtained in 76% and 73% yield respectively, by reacting dimesylates 1 [8] and 2 [11] with excess sodium imidazolide in DMF (DMF = N,N-dimethylformamide). Note that undeprotonated imidazole only led to partial substitution of the mesylate groups, even when operating with a large excess of nucleophilic reagent. The ESI-MS spectrum of each ligand showed a major peak corresponding to the [M + H]⁺ ion (see experimental section). Both the ¹³C and ¹H NMR spectra of L1 are consistent with the C₂ symmetry of the ligand. Thus for example, its ¹H NMR spectrum displays a single ABX spectrum for the carbon atoms of the two imidazole rings. In contrast, that of L2 displays two distinct ABX patterns reflecting the absence of symmetry of this β-CD-based molecule (Fig. 1 and Scheme 1).

A single crystal X-ray diffraction study carried out on L1 (Table 1) allowed us to locate the imidazole rings with respect to the cavity in the solid state (Fig. 2). The H-4 and H-5 atoms of both imidazoles are pointing towards the CD axis, thus blocking the entrance of the cavity. The interplanar angle between the imidazole rings is 64°; the H-5…H’-5 and H-4…H’-4 separations being 2.49 Å and 2.89 Å, respectively. The N-3 atoms, which are susceptible to coordinate metal centres, have both their lone pair oriented towards the cavity exterior. Despite the large separation between these two nitrogen atoms (N-3…N’-3 6.19 Å) in the solid state, it may be anticipated that rotation of the imidazole moieties by 180° about the corresponding C-6–N axes will make them suitable for chelation. Noteworthy, the CD scaffold has an almost perfect circular shape with all the glucose units adopting the standard ⁴C₁ conformation. Such a conformation is likely to occur also in solution because of the very narrow range of chemical shifts in which the anomeric protons resonate (Δδ = 0.08 ppm). Finally, a pentane molecule is hosted inside the CD cavity, which augurs well for the ability of the cone-shaped hollow molecule to form inclusion complexes in solution.

2.2 Synthesis of chelate complexes

Despite the presence of freely rotating imidazole arms, both ligands turned out to behave as chelators towards platinum(II) ions. Indeed, reaction of L1 and L2 with K₂[PtCl₄] in water led to the formation of chelate complexes 3 and 4 in 23% and 51% yield, respectively, after column chromatography. Interestingly, the use of water as solvent seems to be critical since much lower yields of 3 and 4 were obtained when the ligands were reacted with [PtCl₂(PhCN)₂] in organic solvents, the reaction leading then to significant amounts of oligomeric material. Formation of chelate complexes was inferred from the mass spectra, which revealed major peaks at m/z = 1584.5 for 3 and m/z = 1789.7 for 4 corresponding to [M + Na]⁺ ions. Consistent with a coordinated platinum atom, the H-4 and H-5 imidazole protons of complex 3 no longer resonate at the same frequency (δ = 7.29 and 7.07) as in the free ligand (δ = 7.00 for both protons in L1). The same observation holds for complex 4, as its H-4 and H-5 imidazole protons underwent an even stronger differentiation (up to Δδ = 0.53 ppm vs. 0.11 ppm in the free ligand). For both complexes, the anomeric signals appear in a narrow chemical shift range (Δδ = 0.08 ppm and Δδ = 0.19 ppm, respectively) close to that observed in the free ligands, which means that the CD scaffolds did not undergo major distortions upon complexation. The coordination geometry about the Pt(II) ion was assigned using IR spectroscopy. The observation of two narrow peaks at 336 and 330 cm⁻¹ for complex 3, and at 338 and 330 cm⁻¹ for complex 4 is in accord with a cis-arrangement of the chlorido ligands. Noteworthy, the PtCl₂ unit is most likely located outside the cavity since no downfield shift was detected for inner cavity protons upon complexation [6]. The water-soluble complexes 3 and 4 can be regarded as analogues of cis-platinum or similar complexes displaying antitumoral activity [12]. The possibility of having biologically-active metallocyclodextrins capable of hosting coformulating drugs in water [13] prompted us to synthesise an analogue of the promising cytotoxic KP 418 ruthenium complex [14]. Thus, treatment of ligands L1 and L2 with Na[trans-RuCl₄(DMSO)₂] [15] in an acetone/DMSO mixture afforded modest yields of complexes 5 (5%) and 6 (12%) respectively, together with oligomeric materials that were not recovered. Again, water-soluble complexes were obtained. As for the platinum chelate complexes, the best yield was observed with ligand L2, probably because the larger β-CD is better suited for accommodating the sterically demanding metal fragment. The chelation of a [RuCl₃(DMSO)] unit by both ligands was inferred from mass spectrometry. The ESI-MS spectra of 5 and 6 showed major peaks corresponding to [M + Na]⁺ ions, respectively at m/z = 1606.4 and m/z = 1810.6. In keeping with trans disposed imidazolyl groups, the ¹H NMR spectrum of paramagnetic 5 is typically that of a C₂-symmetric molecule. In the ¹H NMR spectrum of 6, the imidazole signals closely resemble those of their counterparts in 5, so that a trans N–Ru–N arrangement can reasonably be assigned also to this complex. The IR spectra of both complexes display strong bands that are indicative of a S-coordinated DMSO ligand (1086 and 426 cm⁻¹ for complex 5, and 1086 and 428 cm⁻¹ for complex 6) (Scheme 2) [15].

4.1 General procedures

All manipulations were performed in Schlenk-type flasks under dry nitrogen. Solvents were dried by conventional methods and distilled immediately prior to use. Deuterated solvents were passed down a 5 cm-thick alumina column and stored under nitrogen over molecular sieves (4 Å). FAR-IR and IR spectra were recorded, respectively, on Nicolet 6700 and Bruker Alpha spectrophotometers. All NMR spectra were recorded on a FT Bruker AVANCE 300 instrument. ¹H NMR spectral data were referenced to residual protiated solvents (δ = 7.26 for CDCl₃), ¹³C{¹H} chemical shifts are reported relative to deuterated solvents (δ = 77.00 for CDCl₃). Mass spectra were recorded on a Bruker MicroTOF spectrometer (ESI) using CH₂Cl₂, MeCN or MeOH as solvent. Elemental analyses were performed by the Service de Microanalyse, Institut de Chimie UMR 7177 CNRS-UDS, Strasbourg. Melting points were determined with a Büchi 535 capillary melting-point apparatus. All commercial reagents were used as supplied. Dimesylates 1 [8] and 2, [11] and Na[trans-RuCl₄(DMSO)₂] [15] were prepared according to literature procedures. The numbering of the atoms within a glucose unit is as shown in Fig. 3.

4.2 Synthesis of 6^A6^D-dideoxy-6^A,6^D-bis(1-imidazolyl)-2^A,2^B,2^C,2^D,2^E,2^F,3^A,3^B,3^C,3^D,3^E,3^F,6^B,6^C,6^E,6^F-hexadeca-O-methyl-α-cyclodextrin (L1)

Imidazole (0.327 g, 4.80 mmol) was treated with NaH (0.211 g, 5.28 mmol, 60% dispersion in oil) in dry DMF (10 mL) at room temperature. After 20 min, a solution of 1 (0.650 g, 0.48 mmol) in dry DMF (10 mL) was added to the imidazole/NaH mixture. The reaction mixture was stirred for 14 h at 80°C. MeOH (10 mL) was then added in order to quench excess NaH before removing the solvents in vacuo. NaOH 2 M (30 mL) was added and the aqueous layer was extracted with CH₂Cl₂ (3 × 50 mL). The organic layer was dried over MgSO₄, filtrated and evaporated to dryness. The residue was submitted to column chromatography (SiO₂, CH₂Cl₂/MeOH/NH₄OH (30% w/w NH₃ in water), 93:6:1, v/v) to afford ligand L1 (0.470 g, 76%) as a colourless solid. R_f (SiO₂, CH₂Cl₂/MeOH/NH₄OH, 93:6:1, v/v) = 0.09. mp dec. > 250 °C. ¹H NMR (300.1 MHz, CDCl₃, 25°C): δ (assignment by COSY) = 3.05 (3 H, H-2), 3.15 (3 H, H-2), 3.30–3.99 (26 H, H-3, H-4, H-5, H-6^B,C,E,F), 3.32 (s, 12 H, OMe-6), 3.42 (s, 6 H, OMe-2), 3.44 (s, 6 H, OMe-2), 3.46 (s, 6 H, OMe-2), 3.55 (s, 6 H, OMe-3), 3.60 (s, 12 H, OMe-3), 4.39 (d, 4 H, ³J_H-6,H-5= 3.8 Hz, H-6^A,D), 4.92 (d, 2 H, ³J_H-1,H-2= 3.4 Hz, H-1), 4.97 (d, 2 H, ³J_H-1,H-2= 3.4 Hz, H-1), 5.00 (d, 2 H, ³J_H-1,H-2= 3.1 Hz, H-1), 7.01 (4 H, A and B parts of ABX system, H-4_Im and H-5_Im), 7.59 (2 H, X part of ABX system, H-2_Im) ppm. ¹³C{¹H} NMR (75.5 MHz, CDCl₃, 25°C): δ (assignment by HMQC) = 47.6 [×2] (C-6^A,D), 57.9 [×2], 58.0 [×4], 59.2 [×4], 61.7 [×2], 61.8 [×2], 61.9 [×2] (OMe), 70.6 [×2] (C-6), 71.1 [×2], 71.3 [×2], 71.7 [×2] (C-5), 72.1 [×2] (C-6), 80.9 [×2], 81.0 [×2], 81.2 [×2], 81.9 [×4], 82.1 [×2], 82.2 [×2], 83.4 [×4] (C-2, C-3, C-4), 99.5 [×2], 100.0 [×2], 100.4 [×2] (C-1), 119.7 [×2], 129.1 [×2], 138.5 [×2] (C-imidazole) ppm. MS, m/z (%): 1297.6 (100) [M + H]⁺. Anal. Calcd for C₅₈H₉₆N₄O₂₈: C, 53.69; H, 7.46; N, 4.32. Found C, 53.98; H, 7.55; N, 3.60.

4.3 Synthesis of 6^A,6^D-dideoxy-6^A,6^D-bis(1-imidazolyl)-2^A,2^B,2^C,2^D,2^E,2^F,2^G,3^A,3^B,3^C,3^D,3^E,3^F,3^G,6^B,6^C,6^E,6^F,6^G-nonadeca-O-methyl-β-cyclodextrin (L2)

Ligand L2 (0.351 g, 73%) was synthesised as described above from 2 (0.5 g, 0.32 mmol), imidazole (0.22 g, 3.2 mmol) and NaH (0.14 g, 3,5 mmol, 60% dispersion in oil). R_f (SiO₂, CH₂Cl₂/MeOH/NH₄OH (30% w/w NH₃ in water), 93:6:1, v/v) = 0.09. mp dec. > 250°C. ¹H NMR (300.1 MHz, CDCl₃, 25°C): δ (assignment by COSY) = 3.05–3.23 (14 H, H-2, H-4), 3.35 (s, 9 H, OMe-6), 3.37 (s, 3 H, OMe-6), 3.39 (s, 3 H, OMe-6), 3.46 (s, 3 H, OMe-2), 3.47 (s, 3 H, OMe-2), 3.48 (s, 3 H, OMe-2), 3.50 (s, 3 H, OMe-2), 3.51 (s, 3 H, OMe-2), 3.52 (s, 3 H, OMe-2), 3.53 (s, 3 H, OMe-2), 3.60 (s, 3 H, OMe-3), 3.61 (s, 3 H, OMe-3), 3.62 (s, 3 H, OMe-3), 3.63 (s, 3 H, OMe-3), 3.64 (s, 3 H, OMe-3), 3.65 (s, 3 H, OMe-3), 3.66 (s, 3 H, OMe-3), 3.35–4.02 (24 H, H-3, H-5, H-6^B,C,E,F,G), 4.27–4.35 (2 H, H-6^{A or D}), 4.44–4.51 (2 H, H-6^{D or A}), 4.96 (d, 1 H, ³J_H-1,H-2= 3.7 Hz, H-1), 5.00 (d, 1 H, ³J_H-1,H-2= 3.8 Hz, H-1), 5.01 (d, 2 H, ³J_H-1,H-2= 3.31 Hz, H-1), 5.10 (d, 2 H, ³J_H-1,H-2= 4.1 Hz, H-1), 5.11 (d, 1 H, ³J_H-1,H-2= 4.4 Hz, H-1), 6.98 and 7.01 (two pseudo t, 1H [x2], A parts of ABX systems, H-4_Im or H-5_Im), 7.07 and 7.11 (two pseudo t, 1H [x2], B parts of ABX systems, H-5_Im or H-4_Im), 7.59 and 7.62 (two pseudo t, 1 H [x2], X parts of ABX systems, H-2_Im) ppm. ¹³C{¹H} NMR (75.5 MHz, CDCl₃, 25°C): δ (assignment by HMQC) = 47.72 [×2] (C-6^A,D), 58.21, 58.29, 58.38, 58.44, 58.69, 58.92, 58.93, 59.10 [×4], 59.18, 61.02, 61.14, 61.23, 61.42, 61.58 [×3] (OMe), 70.35, 70.53 (C-6), 70.74, 70.86, 70.92, 70.99 [×2], 71.07, 71.20 (C-5), 72.22, 72.30 [×2] (C-6), 80.13, 80.26, 80.32, 80.68, 80.71, 81.11 [×2], 81.49 [×4], 81.68 [×3], 81.87, 81.99, 82.06 [×2], 82.14, 82.68, 83.20 (C-2, C-3, C-4), 98.16, 98.31, 99.26, 99.60 [×3], 99.79 (C-1), 119.91, 120.02, 128.78, 128.84, 138.36, 138.44 (C-imidazole) ppm. MS, m/z (%): 1500.7 (100) [M + Na]⁺. Anal. Calcd for C₆₇H₁₁₂N₄O₃₃: C, 53.59; H, 7.52; N, 3.73. Found C, 53.41; H, 7.71; N 3.52.

4.4 Synthesis of cis-dichlorido[6^A,6^D-dideoxy-6^A,6^D-bis(1-imidazolyl-κN³)-2^A,2^B,2^C,2^D,2^E,2^F,3^A,3^B,3^C,3^D,3^E,3^F,6^B,6^C,6^E,6^F-hexadeca-O-methyl-α-cyclodextrin]platinum(II) (3)

A solution of L1 (0.150 g, 0.12 mmol) in water (5 mL) was added to a solution of K₂[PtCl₄] (0.50 g, 0.12 mmol) in water (5 mL). After stirring for 14 h, the orange solution turned pale yellow and water (50 mL) was added. The organic layer was extracted with CH₂Cl₂ (3 × 50 mL) before being dried over MgSO₄ and evaporated to dryness. The crude product was purified by column chromatography (SiO₂, CH₂Cl₂/MeOH, 92:8, v/v) and afforded analytically pure 3 (0.040 g, yield 23%) as a beige solid. R_f (SiO₂, CH₂Cl₂/MeOH/NH₄OH, 93:6:1, v/v) = 0.17. mp dec. > 250°C. FAR-IR ν(Pt-Cl) 336 (m) cm⁻¹, ν(Pt-Cl) 330 (s) cm⁻¹. ¹H NMR (300.1 MHz, CDCl₃, 25°C): δ (assignment by COSY) = 3.10–3.21 (12 H, H-2, H-4), 3.47 (s, 6 H, OMe), 3.48 (s, 6 H, OMe), 3.49 (s, 6 H, OMe), 3.51 (s, 6 H, OMe), 3.54 (s, 6 H, OMe), 3.58 (s, 6 H, OMe), 3.61 (s, 6 H, OMe), 3.62 (s, 6 H, OMe), 3.47–4.07 (22 H, H-3, H-5, H-6^B,C,E,F, H-6a^A,D), 4.88 (d, 2 H, ²J_H-6b-H6a= 14.1 Hz, H-6b^A,D), 4.96 (d, 2 H, ³J_H-1,H-2= 3.4 Hz, H-1), 4.99 (d, 2 H, ³J_H-1,H-2= 3.2 Hz, H-1), 5.04 (d, 2 H, ³J_H-1,H-2= 2.9 Hz, H-1), 7.07 (br signal, 2 H, A or B part of ABX system, H-4_Im or H-5_Im), 7.29 (br signal, 2 H, B or A part of ABX system, H-5_Im or H-4_Im), 8.01 (br signal, 2 H, X part of ABX system, H-2_Im) ppm. ¹³C{¹H} NMR (75.7 MHz, CDCl₃, 25°C): δ (assignment by HMQC) = 50.05 [×2] (C-6^A,D), 58.0 [×2], 58.16 [×4], 59.32 [×2], 59.78 [×2], 61.65 [×2], 61.74 [×2], 61.99 [×2] (OMe), 70.41 [×2] (C-6), 71.47 [×2], 72.01 [×2], 72.26 [×2] (C-5), 73.39 [×2] (C-6), 80.53 [×2], 80.83 [×2], 81.14 [×2], 81.26 [×2], 81.68 [×2], 82.01 [×2], 82.26 [×2], 83.81 [×2], 85.04 [×2] (C-2, C-3, C-4), 99.23 [×2], 100.13 [×2], 100.50 [×2] (C-1), 121.82 [×2], 129.9 [×2], 139.06 [×2] (C-imidazole) ppm. MS, m/z (%): 1584.5 (100) [M + Na]⁺. Anal. Calcd for C₅₈H₉₆Cl₂N₄O₂₈Pt: C, 44.56; H, 6.19; N, 3.58. Found C, 45.19; H, 6.42; N, 3.178.

4.5 Synthesis of cis-dichlorido[6^A,6^D-dideoxy-6^A,6^D-bis(1-imidazolyl-κN³)-2^A,2^B,2^C,2^D,2^E,2^F,2^G,3^A,3^B,3^C,3^D,3^E,3^F,3^G,6^B,6^C,6^E,6^F,6^G-nonadeca-O-methyl-β-cyclodextrin]platinum(II) (4)

Complex 4 (0.070 g, 51%) was synthesized as described above from L2 (0.115 g, 0.077 mmol) and K₂[PtCl₄] (0.032 g, 0.077 mmol). R_f (SiO₂, CH₂Cl₂/MeOH/NH₄OH, 93:6:1, v/v) = 0.14. mp dec. >250°C. FAR-IR ν(Pt-Cl) 338 (m) cm⁻¹, ν(Pt-Cl) 330 (s) cm⁻¹. ¹H NMR (300.1 MHz, CDCl₃, 25°C): δ (assignment by COSY) = 3.12–4.10 (40 H, H-2, H-3, H-4, H-5, H-6^B,C,E,F,G, H-6a^A,D) 3.24 (s, 3 H, OMe), 3.32 (s, 3 H, OMe), 3.40 (s, 3 H, OMe), 3.44 (s, 3 H, OMe), 3.47 (s, 3 H, OMe), 3.50 (s, 3 H, OMe), 3.51 (s, 6 H, OMe), 3.52 (s, 6 H, OMe), 3.54 (s, 3 H, OMe), 3.55 (s, 3 H, OMe), 3.59 (s, 3 H, OMe), 3.60 (s, 3 H, OMe), 3.61 (s, 9 H, OMe), 3.63 (s, 3 H, OMe), 3.67 (s, 3 H, OMe), 4.58 (d, 1 H, ²J_H-6b,H-6a= 12.8 Hz, H-6b^{A or D}), 4.69 (d, 1 H, ²J_H-6b,H-6a= 14.3 Hz, H-6b^{D or A}), 4.95 (d, 1 H, ³J_H-1,H-2= 3.3 Hz, H-1), 5.07–5.10 (5 H, H-1), 5.26 (d, 1 H, ³J_H-1,H-2= 2.4 Hz, H-1), 6.34 and 6.87 (br. signals, 1 H [×2], A parts of ABX systems, H-4_Im or H-5_Im), 7.21 and 7.34 (br. signals, 1 H [×2], B parts of ABX systems, H-5_Im or H-4_Im), 7.93 and 8.47 (br. signals, 1 H [×2], X parts of ABX systems, H-2_Im) ppm. ¹³C{¹H} NMR (75.7 MHz, CDCl₃, 25°C): δ (assignment by HMQC) = 50.47 (C-6^{A or D}), 50.66 (C-6^{D or A}), 58.13, 58.20, 58.50, 58.54, 58.90, 59.16 [×3], 59.27, 59.36 [×3], 60.24, 60.92, 60.97, 61.02, 61.15 [×2], 61.41 (OMe), 69.97 (C-5), 70.21 [×2] (C-6), 71.15, 71.28, 71.33 (C-5), 71.57 (C-6), 71.79, 72.22, 72.48 (C-5), 72.63, 72.82 (C-6), 75.88, 77.25, 78.26, 78.51, 80.12, 80.58, 80.70, 81.06 [×2], 81.36, 81.50 [×3], 81.57, 81.67, 81.85, 82.08, 82.43, 82.80, 82.90 [×2] (C-2, C-3, C-4), 96.32, 97.13, 97.29, 99.17, 99.61, 99.94, 100.10 (C-1), 119.92, 122.41, 127.80, 129.72, 138.38, 139.79 (C-imidazole) ppm. MS, m/z (%): 1789.7 (100) [M + Na]⁺. Anal. Calcd for C₆₇H₁₁₂Cl₂N₄O₃₃Pt: C, 45.53; H, 6.39; N, 3.17. Found C, 44.85; H, 6.39; N, 2.79.

4.6 Synthesis of trans,mer-trichlorido(dimethyl sulfoxide-κS)[6^A,6^D-dideoxy-6^A,6^D-bis(1-imidazoyl-κN³)-2^A,2^B,2^C,2^D,2^E,2^F,3^A,3^B,3^C,3^D,3^E,3^F,6^B,6^C,6^E,6^F-hexadeca-O-methyl-α-cyclodextrin]ruthenium(III) (5)

A solution of L1 (0.150 g, 0.12 mmol) in acetone (6.3 mL) was added to a solution of Na[trans-RuCl₄(DMSO)₂] (0.049 g, 0.12 mmol) in a mixture of acetone (4.1 mL) and DMSO (0.8 mL). After stirring for 14 h at room temperature, the red-orange solution turned yellow-orange. The solution was evaporated to dryness and the crude product was purified by column chromatography (SiO₂, CH₂Cl₂/MeOH, 93:7, v/v), affording analytically pure 5 (0.010 g, 5%). R_f (SiO₂, CH₂Cl₂/MeOH, 90:10, v/v) = 0.33. mp dec. >250°C. IR ν(S = O) 1086 (s) cm⁻¹, ν(Ru-S) 426 (s) cm⁻¹. ¹H NMR (300.1 MHz, CDCl₃, 25°C, paramagnetic): δ = –26.00 (s, 2 H, H-2_Im or H-4_Im or H5_Im),–11.00 (s, 2 H, H-5_Im or H-2_Im or H-4_Im),–5.00 (s, 2 H, H-4_Im or H-5_Im or H-2_Im), 2.80–5.55 (42 H, H-1, H-2, H-3, H-4, H-5, H-6), 2.96 (s, 6 H, OMe), 3.07 (s, 6 H, OMe), 3.12 (s, 6 H, OMe), 3.24 (s, 6 H, OMe), 3.46 (s, 6 H, OMe), 3.55 (s, 6 H, OMe), 3.63 (s, 12 H, OMe) ppm. The DMSO ligand was not detected in the ¹H NMR spectrum. MS, m/z (%): 1606.4 (100) [M + Na]⁺. Anal. Calcd for C₆₁H₁₀₄Cl₃N₄O₂₀RuS: C, 45.88; H, 6.56; N, 3.51. Found C, 46.01; H, 6.72; N, 3.39.

4.7 Synthesis of trans,mer-trichlorido(dimethyl sulfoxide-κS)[6^A,6^D-dideoxy-6^A,6^D-bis(1-imidazolyl-κN³)-2^A,2^B,2^C,2^D,2^E,2^F,2^G,3^A,3^B,3^C,3^D,3^E,3^F,3^G,6^B,6^C,6^E,6^F,6^G-nonadeca-O-methyl-β-cyclodextrin]ruthenium(III) (6)

Complex 6 (0.020 g, 12%) was synthesized as described above from L2 (0,140 g, 0.09 mmol) and Na[trans-RuCl₄(DMSO)₂] (0.039 g, 0.09 mmol). R_f (SiO₂, CH₂Cl₂/MeOH, 90:10, v/v) = 0.41. mp dec. > 250°C. IR ν(S = O) 1086 (s) cm⁻¹, ν(Ru-S) 428 (s) cm⁻¹. ¹H NMR (300.1 MHz, CDCl₃, 25°C, paramagnetic): δ = –26.00 (2 H, H-2_Im or H-4_Im or H-5_Im),–11.00 (2 H, H-5_Im or H-2_Im or H-4_Im),–5.00 (2 H, H-4_Im or H-5_Im or H-2_Im), 2.80–5.55 (49 H, H-1, H-2, H-3, H-4, H-5, H-6), 2.89 (s, 3 H, OMe), 2.96 (s, 3 H, OMe), 2.99 (s, 3 H, OMe), 3.03 (s, 3 H, OMe), 3.14 (s, 3 H, OMe), 3.21 (s, 6 H, OMe), 3.27 (s, 3 H, OMe), 3.47 (s, 3 H, OMe), 3.40 (s, 3 H, OMe), 3.46 (s, 3 H, OMe), 3.51 (s, 3 H, OMe), 3.57 (s, 3 H, OMe), 3.62 (s, 3 H, OMe), 3.70 (s, 3 H, OMe), 3.74 (s, 3 H, OMe), 3.82 (s, 3 H, OMe), 3.87 (s, 12 H, OMe) ppm. The DMSO ligand was not detected. MS, m/z (%): 1810.6 (100) [M + Na]⁺. Anal. Calcd for C₆₉H₁₁₈Cl₃N₄O₃₄RuS: C, 46.37; H, 6.66; N, 3.13. Found C, 46.11; H, 7.08; N, 2.92.

4.8 Crystal structure of L1·0.5 C₅H₁₂

Single crystals of L1 were obtained by slow diffusion of pentane into a dichloromethane solution of the compound. The sample was studied with an Oxford Diffraction Xcalibur Saphir 3 CCD with graphite monochromatised Mo_Kα radiation (for crystal data and structure refinement, see Table 1). The structure was solved with SIR-97 [16], which revealed the non hydrogen atoms of the molecule. After anisotropic refinement, many hydrogen atoms were found with a Fourier Difference. The whole structure was refined with SHELX-97 [17] by the full-matrix least-square techniques (use of F square magnitude; x, y, z, β_ij for N, C and O atoms, x, y, z in riding mode for H atoms). The methoxy carbon atom C18 is subject to large thermal motion. CCDC 727143 contains the supplementary crystallographic data for this report. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.