Bis(2,2′-bipyridine){ethyl 4′-[N-(4-carbamoylphen­yl)carbamo­yl]-2,2′-bi­pyridine-4-carboxyl­ate}ruthenium(II) bis­[hexa­fluorido­phosphate(V)]

Masanari Hirahara; Shigeyuki Masaoka; Ken Sakai

doi:10.1107/S1600536809002360

. 2009 Jan 28;65(Pt 2):m228–m229. doi: 10.1107/S1600536809002360

Bis(2,2′-bipyridine){ethyl 4′-[N-(4-carbamoylphenyl)carbamoyl]-2,2′-bipyridine-4-carboxylate}ruthenium(II) bis[hexafluoridophosphate(V)]

Masanari Hirahara ^a, Shigeyuki Masaoka ^a, Ken Sakai ^a,^*

PMCID: PMC2968400 PMID: 21581819

Abstract

In the title compound, [Ru(C₁₀H₈N₂)₂(C₂₁H₁₈N₄O₄)](PF₆)₂, the Ru^II complex cation reveals a slightly distorted octahedral coordination. The coordination bonds of the 4,4′-substituted bipyridyl donors [Ru—N = 2.038 (3) and 2.051 (3) Å] are shorter than those of the 2,2′-bipyridyl donors [Ru—N1 = 2.065 (3)–2.077 (3) Å], due to the electron-withdrawing effects of the substituents at the 4,4′-positions. The angles between the pyridyl planes of the three bipyridyl ligands are 1.5 (2), 6.3 (3) and 8.7 (2)°, respectively. The cations are connected by anions via N—H⋯F interactions.

Related literature

For related literature, see: Gillaizeau-Gauthier et al. (2001 ▶); Ozawa & Sakai (2007 ▶); Ozawa et al. (2006 ▶, 2007 ▶); Sakai & Ozawa (2007 ▶); Sakai et al. (1993 ▶). For discussion of attractive interactions between negatively-charged atoms and alpha C atoms from heterocyclic rings, see: Schottel et al. (2008 ▶).

Experimental

Crystal data

[Ru(C₁₀H₈N₂)₂(C₂₁H₁₈N₄O₄)](PF₆)₂
M _r = 1093.77
Monoclinic,
a = 18.400 (3) Å
b = 13.187 (2) Å
c = 18.863 (3) Å
β = 111.344 (2)°
V = 4262.9 (11) Å³
Z = 4
Mo Kα radiation
μ = 0.55 mm⁻¹
T = 100 (s.u.?) K
0.20 × 0.10 × 0.03 mm

Data collection

Bruker APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ▶) T _min = 0.717, T _max = 0.986
23329 measured reflections
9357 independent reflections
6405 reflections with I > 2σ(I)
R _int = 0.047

Refinement

R[F ² > 2σ(F ²)] = 0.043
wR(F ²) = 0.113
S = 1.00
9357 reflections
614 parameters
H-atom parameters constrained
Δρ_max = 0.79 e Å⁻³
Δρ_min = −0.48 e Å⁻³

Data collection: APEX2 (Bruker, 2006 ▶); cell refinement: APEX2; data reduction: SAINT (Bruker, 2004 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: KENX (Sakai, 2004 ▶); software used to prepare material for publication: SHELXL97, TEXSAN (Molecular Structure Corporation, 2001 ▶), KENX and ORTEPII (Johnson, 1976 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809002360/kp2198sup1.cif

e-65-0m228-sup1.cif^{(38KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809002360/kp2198Isup2.hkl

e-65-0m228-Isup2.hkl^{(473.4KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected bond lengths (Å).

Ru1—N1	2.077 (3)
Ru1—N2	2.070 (3)
Ru1—N3	2.076 (3)
Ru1—N4	2.065 (3)
Ru1—N5	2.051 (3)
Ru1—N6	2.038 (3)

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Table 2. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N7—H7⋯F2ⁱ	0.86	2.34	3.181 (4)	168
N8—H8B⋯F10ⁱ	0.86	2.29	2.999 (5)	139

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Symmetry code: (i) Inline graphic .

Acknowledgments

This work was in part supported by a Grant-in-Aid for Scientific Research (A) (No. 17205008), a Grant-in-Aid for Specially Promoted Research (No. 18002016), and a Grant-in-Aid for the Global COE Program (‘Science for Future Molecular Systems’) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

supplementary crystallographic information

Comment

Continuous efforts have been made to elucidate the molecular catalysis of platinum(II) complexes in photochemical hydrogen production from water (Sakai et al., 1993; Sakai & Ozawa, 2007; Ozawa et al., 2007; Ozawa & Sakai, 2007). The results obtained so far suggest that destabilization of the HOMO, which generally corresponds to the filled Pt^IId_z2 orbital, gives rise to the higher H₂-evolving activity of the complexes (Sakai & Ozawa, 2007). It has also been ascertained that the amidate-bridged dinuclear platinum(II) complexes having a strong metal–metal interaction exhibit considerably higher H₂-evolving activity in comparison with the mononuclear complexes, which has been attributed to their highly destabilized HOMOs arising from the anti-bonding couple of the filled Pt^IId_z2 orbitals (Sakai & Ozawa, 2007). Moreover, the first effective model of a `photo-hydrogen-evolving' molecular device possessing both a light-harvesting capability and an H₂-evolving activity was developed in our group (Ozawa & Sakai, 2006). Since this molecular device is made up of a photosensitizing tris(2,2'-bipyridine)ruthenium(II) derivative and a mononuclear (4-carbamoyl-4'-carboxy-2,2'-bipyridine)dichloroplatinum(II) fragment, it is important to develop an amidate-bridged diplatinum(II) complex tethered to tris(2,2'-bipyridine)ruthenium(II) photosensitizers. In order to develop such systems, tris(2,2'-bipyridine)ruthenium(II) derivatives having an uncoordinated amide group must be prepared as a synthetic precursor. The title compound has been prepared as one of such precursor compounds. The actual application of this complex ligand will be separately reported elsewhere.

In (I) (Fig. 1), the coordination bonds from the 4,4'-substituted bipyridine ligand [Ru1—N5 = 2.051 (3) and Ru1—N6 = 2.038 (3) Å] are meaningfully shorter than those from the non-substituted 2,2'-bipyridine ligands [Ru1—N1 = 2.077 (3), Ru1—N2 = 2.070 (3), Ru1—N3 = 2.076 (3), and Ru1—N4 = 2.065 (3) Å] (Table 1). This can be interpreted in terms of the stronger backdonation in the former bonds due to the electron-withdrawing effects of the carbamoyl and ethoxycarbonyl groups in the 4,4'-substituted bipyridyl ligand.

All the three bipyridyl units do not form a planar geometry but the two pyridyl planes within each bipyridyl unit are tilted with each other as follows. Two pyridyl planes consisting of N1→C5 and N2→C10 are only slightly tilted at an angle of 1.5 (2)°. On the other hand, the dihedral angles between the N3→C15 and N4→C20 planes and that between the N5→C25 and N6→-C30 planes are somewhat larger: 6.3 (3) and 8.7 (2)°, respectively. The six-atom r.m.s. deviations given in the best-plane calculations for the N1→C5, N2→C10, N3→C15, N4→C20, N5→C25, and N6→C30 planes are 0.0053, 0.0038, 0.0079, 0.0019, 0.0181, and 0.0129, respectively.

On the other hand, the plane defined by atoms C31, O1, and O2 from the ethoxycarbonyl unit is slightly tilted with respect to the connecting pyridyl plane (N5→C25) at an angle of 4.5 (4)°. The carbamoyl plane defined with atoms C34, O3, and N7 is even more tilted with respect to the connecting pyridyl plane (N6→C30) at an angle of 15.1 (5)°. The aromatic plane consisting of atoms C35—C40 is tilted with respect to the above-mentioned carbamoyl unit (C34/O3/N7) at an angle of 26.6 (3)°, where the six-atom r.m.s. deviation given in the best-plane calculation for the C35–C40 plane was 0.0056. The C35–C40 plane is also tilted with regard to the terminal carbamoyl unit (C41/O4/N8) at an angle of 7.9 (2)°.

The crystal packing is stabilized with van der Waals interactions with contributions of the hydrogen bonds formed between the F atoms of PF₆^- and the N—H units of carbamoyl groups (Table 2). Short intermolecular contacts [F4—C11 = 2.965 (4) Å and F3—C10 = 2.946 (5) Å] may be assigned as relatively weak hydrogen bonds. The other two short intermolecular contacts [O4—C1 = 2.974 (6) Å and O4—C26 = 3.010 (5) Å] may be due to attractive interactions between negatively-charged atoms and alpha C atoms from heterocyclic rings (Schottel et al., 2008).

Experimental

As described below, the ligand L was synthesized in three steps and was finally reacted with cis-RuCl₂(bpy)₂.2H₂O to give the final product (I).

First, 4,4'-diethoxycarbonyl-2,2'-bipyridine was prepared according to the literature (Gillaizeau-Gauthier et al., 2001).

Next, 4-carboxy-4'-ethoxycarbonyl-2,2'-bipyridine monohydrate was prepared from the partial hydrolysis of 4,4'-diethoxycarbonyl-2,2'-bipyridine as follows. To a solution of 4,4'-diethoxycarbonyl-2,2'-bipyridine (1.50 g, 5.0 mmol) in absolute dichloromethane (200 ml) was dropwisely added a solution of potassium hydroxide (0.23 g, 5.00 mmol) in ethanol (50 ml) at 273 K over 1 h. This procedure was carried out under Ar atmosphere. The reaction mixture was further stirred for 1 d, during which the temperature of the solution was gradually raised to room temperature. The colourless solid precipitated was collected by filtration and washed with ethyl acetate. The ethyl acetate washing was evaporated to dryness to collect the unreacted 4,4'-diethoxycarbonyl-2,2'-bipyridine (0.525 g, 35%). The colourless precipitate was re-dissolved in water and acidified by 1 N hydrochloric acid to give the product as a colourless solid, which was collected by filtration and dried in vacuo (yield 0.812 g, 60%). Anal. Calcd for C₁₄N₂H₁₄O₅: C, 57.92; H, 4.86; N, 9.65. Found: C, 57.27; H, 4.68; N, 9.67. ¹H NMR (300.27 MHz, d-DMSO): δ 1.38 (t, 3H, J = 7.0 Hz), 4.42 (q, 2H, J = 7.0 Hz), 7.93 (m, 2H), 8.84 (s, 2H), 8.93 (t, 2H, J = 4.6 Hz), 13.84 (s, 1H).

As the final step in the synthesis of ligand L, 4-carboxy-4'-ethoxycarbonyl-2,2'-bipyridine monohydrate (397 mg, 1.46 mmol), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC.HCl, 337 mg, 1.76 mmol) and 1-hydroxybenzotriazole (HOBT.H₂O, 280 mg, 1.77 mmol) were dissolved in DMF (dimethylformamide) (40 ml). To a solution of 4-aminobenzamide (235 mg, 1.72 mmol) and N-methylmorpholine (0.3 ml) in DMF (20 ml) was dropwisely added the former solution at 273 K over 20 min. The reaction mixture was further stirred for 1 d in Ar, during which the temperature of the mixture was gradually raised to room temperature. The reaction mixture was then evaporated to a total volume of 5 ml followed by addition of water (200 ml). The white solid precipitated was collected by filtration and washed with water (20 ml), with an aqueous 5% NaHCO₃ solution (20 ml), with an aqueous 5% citric acid solution (20 ml), and finally with water (20 ml). The white solid was dried in vacuo (yield 208 mg, 36.5%). The washing from the aqueous 5% NaHCO₃ solution was acidified by HCl to give the unreacted starting bpy derivative (147.3 mg 37.1%). Anal. Calcd for L, C₂₁H₁₈N₄O₄: C, 64.61; H, 4.65; N, 14.35. Found: C, 64.17; H, 4.84; N, 13.89. ¹H NMR (300.27 MHz, d-DMSO): δ 1.39 (t, 3H), 4.42 (q, 2H), 7.31 (s, broad), 7.87 (s, broad), 7.90 (s, 4H), 7.96 (d, 1H), 8.00 (d, 1H), 8.89 (d, 2H), 8.97 (t, 2H), 10.96 (s, 1H).

Compound (I) [RuL(bpy)₂](PF₆)₂ was prepared as follows. A solution of ligand L (0.396 g, 1.02 mmol) and cis-RuCl₂(bpy)₂.2H₂O (0.545, 1.05 mmol) in ethanol (150 ml) was refluxed for 12 h followed by filtration for the removal of insoluble materials. The filtrate was evaporated to dryness. The residue was redissolved in water (2–3 ml) followed by filtration for the removal of insoluble materials. To the filtrated was added an aqueous saturated NH₄PF₆ solution (2 ml). The dark red solid precipitated was collected by filtration and washed with a minimum amount of cold water. The crude product (1.08 g) was recrystallized twice from a 1:1 mixture of ethanol and water (yield, 0.60 g, 55%). Anal. Calcd for [RuL(bpy)₂](PF₆)₂, C₄₁H₃₄N₈O₄RuP₂F₁₂: C, 45.02; H, 3.13; N, 10.24. Found: C, 44.95; H, 3.25; N, 10.18. ¹H NMR (300.27 MHz, CD3CN): δ 1.40 (t, 3H, J = 7.0 Hz), 4.46 (q, 2H, J = 7.0 Hz), 5.98 (s, broad, 1H), 6.74 (s, broad, 1H) 7.42 (m, 4H), 7.71 (t, 4H, J = 5.5 Hz), 7.84 (m, 2H), 7.88 (s, 4H), 7.95 (d, 1H, J = 5.8 Hz), 7.96 (d, 1H, J = 5.8 Hz), 8.09 (m, 4H), 8.52 (d, 4H, J = 7.7 Hz), 9.03 (s, 2H), 9.10 (s, 2H), 9.30 (s, 1H). ESI-TOF MS (m/z): 402 ([RuL(bpy)₂]²⁺), 949 ({[RuL(bpy)₂](PF₆)}⁺).