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Heteroditopic ligands containing a 2,2′-bipyridine and a 2,2′:6′,2″-Terpyridine moiety and their ruthenium tris(bipyridine)-like complexes
Inorganic Chemistry Communications 5 (2002) 5–8 www.elsevier.com/locate/inoche
Heteroditopic ligands containing a 2; 20-bipyridine and a 2; 20: 60 ; 200 -terpyridine moiety and their ruthenium tris(bipyridine)-like complexes Bruno Galland, Daniele Limosin, Helene Laguitton-Pasquier, Alain Deronzier
*
Laboratoire d’Electrochimie Organique et de Photochimie Redox, UMR CNRS 5630, Universit e Joseph Fourier Grenoble 1, BP 53, 38041 Grenoble C edex 9, France Received 8 September 2001; accepted 29 September 2001
Abstract Two novel heteroditopic ligands in which the bidentate 2; 20 -bipyridine (bpy) ligand is covalently linked to one or two 2; 20 : 60 ; 200 terpyridine (terpy) terdentate ligands have been prepared and characterized. The synthesis and the physico-chemical features of their corresponding complexes in which the bpy site is complexed by a ruthenium moiety are also reported. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: 2; 20 -bipyridine; 2; 20: 60 ; 200 -terpyridine ligand; Ruthenium complexes; Supramolecular structure
1. Introduction The design of molecular structures, able to mimicking at the molecular level functions performed by a natural system or by artificial macroscopic devices, is currently of great interest. Construction of molecular assemblies effecting energy transfer, electron transfer and/or photocatalysis is an important theme of this chemistry [1–3]. A peculiar interesting design of such assemblies is based on a bimetallic complex where the two coordination sites are bridged by an alkyl chain preventing alteration of the individual properties of the both sites. Most examples contain bridged two identical diimine liganding sites like 2; 20 -bipyridine (bpy) derivatives. Typically a ½RuðbpyÞ3 2þ chromophor moiety is connected to another chromophor (Ru [4–7], Os [8], Fe [9–11], Re [12,13] bipyridine complexes) or to an electron acceptor or donor (Co [14], Pt [15], Rh [16], Mn [17], bipyridine complexes). In view of having access to a new kind of bimetallic complex with dissymetrical coordination sites we have synthesized two new heteroditopic ligands 1, 2 *
Corresponding author. Tel.: +33-4-76-51-46-83; fax: +33-4-76-5142-67. E-mail address: [email protected] (A. Deronzier).
(Scheme 1) noted bpy–terpy and bpy–terpy2 , respectively, in which the bidentate 2; 20 -bipyridine ligand is bridged to one or two terdentate ligands such as a 2; 20: 60 ; 200 -terpyridine one (terpy). Examples of such types of ligands are extremely rare [18–20]. We report also the synthesis and the main feature of their corresponding complexes 3, 4 noted ½Ruðbpy–terpyÞðbpyÞ2 2þ and ½Ruðbpy–terpy2 ÞðbpyÞ2 2þ , respectively, in which the bpy site is complexed by a ruthenium moiety forming a RuðbpyÞ2þ 3 -like core.
2. Experimental 2.1. Physical measurements UV–Visible spectra were obtained using a Cary 1 absorption spectrophotometer on 1 cm path length quartz cells. The steady-state emission spectra were recorded on a Photon Technology International (PTI) SE900M spectrofluorimeter. Emission quantum yield /L was determined at 25 °C in deoxygenated acetonitrile solutions with a CH3 CN solution of ½RuðbpyÞ3 ðPF6 Þ2 as a standard (/ref L ¼ 0:062 [21] at 25 °C) according to Eq. (1):
1387-7003/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 7 - 7 0 0 3 ( 0 1 ) 0 0 3 2 8 - 8
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B. Galland et al. / Inorganic Chemistry Communications 5 (2002) 5–8
Scheme 1.
ref S 1 10OD I L /ref ; /SL ¼ ref IL ð1 10OD Þ L
ð1Þ
where IL , the emission intensity, was calculated from the R spectrum area Ið mÞ d m, OD represents the optical density at the excitation wavelength (454 nm). The superscripts ‘‘S’’ and ‘‘ref’’ refer, respectively, to the sample and the standard. Time-resolved studies were performed on a PTI Quanta-Master luminescence lifetime spectrometer. It consists of a nanosecond flash lamp (fwhm of 5 ns) coupled to a lens-based T-format sample compartment that has a stroboscopic detector. The detailed description of the instrument and procedures has been previously reported [22]. Electrochemical experiments were run under an inert atmosphere in a glovebox at room temperature. Acetonitrile (CH3 CN, Rathburn, HPLC grade) was used as received and stocked under an argon atmosphere in the glovebox. The supporting electrolyte, tetra-n-butylammonium perchlorate (TBAP), was purchased from Fluka, recrystallized from ethyl acetate–cyclohexane and dried under vacuum at 80 °C for 3 days. Cyclic voltammetry was performed using a PAR model 273 potentiostat/galvanostat. The standard three-electrode electrochemical cell was used. Potentials are referred to an Agj10 mM AgNO3 reference electrode in CH3 CN þ 0:1 M TBAP. Potentials referenced to this system can be converted to the ferrocene/ferricinium couple by adding 70 mV. The working electrode was a glassy carbon disk (3 mm diameter) polished with 1 lm diamond paste. 1 H NMR spectra were recorded on a Brucker AC 250 spectrometer. Mass spectra were obtained on an AIE Kratos MS 50 spectrometer fitted with an Ion Tech. Gun at the mass spectrometry service UJF-CNRS, CERMAV, Grenoble, France. Elemental analyses were
performed by the Service Central d’Analyse du CNRS at Vernaison (France).
3. Synthesis 3.1. Ligands Ligand 1 was synthesized by the reaction in dry THF between 40 -(p-bromomethyl-phenyl)-2; 20: 60 ; 200 -terpyridine (1.10 g, 2.74 mmol) prepared as in [23] and 4; 40 dimethyl-2; 20 -bipyridine anion synthesized following a known procedure [24]. In a typical reaction a solution of 4; 40 -dimethyl2; 20 -byridine (0.420 g, 2.28 mmol) in dry THF ð10 cm3 Þ was cooled to )60 °C under nitrogen and a slight excess of LDA (3 mmol) was added over 1 h. After stirring at )60 °C for 15 min a slight excess of 40 (p-bromomethyl-phenyl)-2; 20: 60 ; 200 -terpyridine (1.10 g, 2.74 mmol) was added to dry THF (50 cm3 ) and the reaction allowed to slowly warm to temperature while stirring overnight. The reaction was quenched with water ð10 cm3 Þ and the mixture was extracted with dichloromethane ð3 200 cm3 Þ. The organic phase was dried over anhydrous sodium sulfate and filtered. Following the removal of the solvent the yellow residue was purified by chromatography on a silica column (CH2 Cl2: ðC2 H5 Þ2 O; 90:10) eluted with increasing amount of ðC2 H5 Þ2 O and finally with a (C2 H5 Þ2 O : C2 H5 OH, 90:10 mixture followed by an increasing amount of C2 H5 OH. 1 is obtained as a while solid (0.521 g; yield 45%). 1 H NMR ðCDCl3 Þ d 8.69–8.62 (6H, m), 8.53 (1H, d), 8.51 (1H, d), 8.26 (1H, s), 8.19 (1H, s), 7.88–7.78 (4H, m), 7.35–7.28 (4H, m), 7.12–7.06 (2H, m), 3.08 (4H, s), 2.41 (3H, s). Anal. found: C, 80.38; H, 5.39; N, 13.64. Calc. for C34 H27 N5 : C, 80.77; H, 5.38; N, 13.85%. MS, m=z 505.
B. Galland et al. / Inorganic Chemistry Communications 5 (2002) 5–8
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Table 1 em MLCT absorption band maxima ðkabs max Þ luminescence maxi ðkmax Þ, emission quantum yield ð/Þ and lifetime (s) of the excited states of 3 and 4 at 298 K, in deoxygenated CH3 CN solution Complexes
1 cm1 Þ kabs max ðeÞ ðnm=M
kem max
/
s ðlsÞ
3 4
455 (14 300) 455 (12 900)
609 609
0.054 0.046
0.997 1.014
2 was synthesized by a method similar to 1 except that dianion of the 4; 40 -dimethyl-2; 20 -bipyridine was first prepared in THF instead of the monoanion using a larger amount of LDA (6 mmol). Purification of 2 was accomplished by two successive chromatographies on an alumina column. The first one was eluted with pentane:ethyl acetate, 50:50 and the second one with toluene: CH3 OH, 95:5 and furnished 2 as a white solid (735 mg; yield 36 %). A small amount of 1 is also obtained first (58 mg; yield 5%). 1 H NMR ðCDCl3 Þ d 8.71–8.63 (12H, m), 8.57 (2H, d), 8.20 (2H, s), 7.89–7.81 (8H, m), 7.36–7.29 (8H, m), 7.09 (2H, d), 3.06 (8H, s). Anal. found: C, 81.12; H, 5.17; N, 13.21. Calc. for C56 H42 N8 : C, 81.33; H, 5.12; N, 13.55. MS, m=z 826. Scheme 2.
3.2. Complexes 3. A slight excess of ligand 1 (0.110 g, 0.18 mmol) was added to 0.155 mmol of RuðbpyÞ2 Cl2 , 2H2 O prepared as in [25] and heated in 30 cm3 of EtOH under reflux for 3 h under argon atmosphere. The solution was cooled to room temperature and a solution of KPF6 (0.29 g) in 25 cm3 of water was added to precipitate the complex 1. After filtration 1 is washed with H2 O and dried under vacuum. Yield 82% (0.173 g). 1 H NMR ðCD3 CNÞ d 8.74–8.63 (6H, m), 8.55–8.48 (4H, m), 8.14–7.96 (8H, m), 7.78–7.66 (6H, m), 7.51– 7.42 (4H, m), 7.39–7.32 (4H, m), 7.19 (2H, d), 7.13–7.06 (2H, m), 3.14 (4H, m), 2.43 (3H, s). Anal. found: C, 53.71; H, 3.56; N, 10.18. Calc. for C54 H43 N9 RuP2 F12 : C, 53.65; H, 3.58; N, 10.43. FAB: m=z (positive mode), C2þ , þ PF 6 , 1064 C , 918. 4. This complex was prepared in a similar fashion by the reaction of ligand 2 with RuðbpyÞ2 Cl2 , 2H2 O. Yield: 97%. 1 H NMR ðCD2 Cl2 Þ d 8.68–6.53 (12H, m), 8.47– 8.21 (6H, m), 8.04–7.81 (12H, m), 7.72–7.45 (6H, m), 7.39–7.36 (8H, m), 7.15–7.08 (6H, m), 3.03 (8H, s). Anal.
found: C, 59.30; H, 3.82; N, 11.09. Calc. for C76 H58 N12 RuP2 F12 : C, 59.65; H, 3.82; N, 10.98. FAB: þ m=z (positive mode), C2þ , PF 6 , 1383, C , 12.37.
4. Results and discussion The bridging ligands 1 and 2 were prepared by the reaction of 40 -(p-bromomethyl-phenyl)-,20: 60 ; 200 -terpyridine with chemically prepared solution of mono and bis anion of 4; 40 -dimethyl-2; 20 -bipyridine (Scheme 2). Obtention of pure samples of 1 and 2 with moderate yields (45% and 36%, respectively) required careful chromatography workup (see Section 2). Selective complexation of the bpy site of the ligands was easily accomplished by reaction with RuðbpyÞ2 Cl2 and furnished the expected complexes 3 and 4 isolated as their PF 6 salts with good yields (82% and 97%, respectively).
Table 2 Redox potentials of ligands 1, 2 and complexes 3, 4 in CH3 CN (0.1 M TBAP) Compounds
E1=2 ðDEp Þ=V Oxidation
1 2a 3 4 a
– – 0.94 (0.07) 0.92 (0.07)
Reduction – – )1.67 (0.06) )1.67 (0.06)
This compound is poorly soluble in CH3 CN.
– )1.86 (0.07) )1.87 (0.07)
– – )2.12 (0.07) )2.19 (0.10)
)2.38 (0.08) – )2.35 (0.08) )2.39 (0.10)
)2.57 (0.12) – )2.60 (0.10) )2.64 (0.12)
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B. Galland et al. / Inorganic Chemistry Communications 5 (2002) 5–8
All these new compounds were fully characterized by elemental analysis, NMR spectroscopy and mass spectrometry (EI for ligands and FABþ for complexes; see Section 2). Complexes 3 and 4 exhibit the regular spectroscopic features of ruthenium-tris(bipyridine)-like compounds. The MLCT absorption and the emission bands have been red-shifted from their position in the parent complex RuðbpyÞ2þ and are closed to those of 3 ½RuðdmbpyÞ3 2þ (dmbpy ¼ 4; 40 -dimethyl-2; 20 -bipyridine). These two complexes give also a value of the emission quantum yield ð/4 Þ slightly higher than that of ½RuðbpyÞ3 2þ at room temperature. The decay curves are single-exponential. All the data are summarized in Table 1. The redox potentials of the ligand 1 and complexes 3 and 4 determined by cyclic voltammetry in CH3 CN are reported in Table 2. As for the parent 40 -tolyl-2, 20 :60 ; 200 terpyridine compound, 1 is reduced by a quasi-reversible one-electron process followed by an irreversible one [23]. The poor solubility of 2 in CH3 CN prevents any accurate determination of its redox potentials. The cyclic voltammogram obtained with complex 3 is shown in Fig. 1. At negative potentials, four reversible one-electron processes are observed. The three first ones correspond to the successive ligand-localized reduction of the RuðbpyÞ2þ 3 -like complex. The next process is due to the first reduction of the metal-free terpy part of the molecule. An irreversible wave is also observed at a more negative potential corresponding to the second reduc-
Fig. 1. Cyclic voltammogram at a glassy carbon electrode of 103 M 1 in CH3 CN þ 0:1 M TBAP, m ¼ 0:1 V s1 .
tion of the terpy group (not shown in Fig. 1). At positive potential the typical reversible one-electron couple of peaks of the metal oxidation ðRu2þ =Ru3þ Þ is shown as expected. A similar cyclic voltammogram is obtained with complex 4. However in the negative potential region waves are more or less distorted by some electroprecipitation–redissolution phenomena due to the poor solubility of the reduced forms of the complex. We have are currently investigating the complexation of the terpy part of 3 and 4 with cation metal centers like Fe2þ and Mn2þ in view of obtaining heterobimetallic complexes. With ligand 4 the formation of soluble polymeric complexes is greatly expected.
References [1] V. Balzani, A. Juris, M. Venturi, S. Campagna, S. Serroni, Chem. Rev. 96 (1996) 759. [2] C.A. Bignozzi, J.R. Schoonover, F. Scandola, Special volum molecular level artificial photosynthetic materials, in: G.J. Meyer, K.D. Karlin (Eds.), Progress in Inorganic Chemistry, vol. 44, Wiley, New York, 1997, p. 1. [3] L. De Cola, P. Beloer, Coord. Chem. Rev. 177 (1998) 301. [4] M. Furue, N. Kuroda, S.I. Nozakura, Chem. Lett. (1986) 1209. [5] B.R. Serr, K.A. Andersen, C.M. Elliot, O.P. Anderson, Inorg. Chem. 27 (1998) 4499. [6] M. Furue, N. Kuroda, S. Sano, J. Macromol. Sci. Chem. A 25 (1998) 1263. [7] A. Macatangay, G.Y. Zheng, D.P. Rillema, D.C. Jackman, J.W. Merkert, Inorg. Chem. 35 (1996) 6823. [8] M. Furue, T. Yoshidzumi, S. Kinoshita, T. Kushida, S.I. Nozakura, M. Kamachi, Bull. Chem. Soc. Jpn. 64 (1991) 1632. [9] S.L. Larson, S.M. Hendrickson, S. Ferrere, D.L. Derr, C.M. Elliot, J. Am. Chem. Soc. 117 (1995) 5881. [10] C.M. Elliot, D.L. Derr, D.V. Matynshow, M.O. Newton, J. Am. Chem. Soc. 120 (1998) 11714. [11] M.-N. Collomb, A. Deronzier, K. Gorgy, J.-C. Lepr^etre, New J. Chem. 24 (2000) 455. [12] S.W. Wallendael, D.P. Rillema, J. Chem. Soc., Chem. Commun. (1990) 1081. [13] S.W. Wallendael, M.W. Perkovic, D.P. Rillema, Inorg. Chem. Acta 213 (1993) 253. [14] X. Song, Y. Lei, S. Van Wallendal, M.W. Perlovic, D.C. Jackman, J.F. Endiicott, D.P. Rillema, J. Phys. Chem. 97 (1993) 3225. [15] R. Sahai, D.A. Baucom, D.P. Rillema, Inorg. Chem. 25 (1986) 3843. [16] M.T. Indelli, C.A. Bignozzi, A. Harriman, J.R. Schoonover, F. Scandola, J. Am. Chem. Soc. 116 (1994) 3768. [17] L. Sun, L. Hammarstr€ om, B. Akermark, S. Styring, Chem. Soc. Rev. 30 (2001) 36. [18] A.M.W. Cargill Thompson, Coord. Chem. Rev. 160 (1997) 1. [19] A. Harriman, R. Ziessel, J. Chem. Soc., Chem. Commun. (1996) 1707. [20] E.C. Constable, C.E. Housecroft, I. Poleschark, Inorg. Chem. Commun. 2 (1999) 565. [21] J.V. Caspar, T.J. Meyer, J. Am. Chem. Soc. 105 (1983) 5583. [22] H. Laguitton-Pasquier, A. Martre, A. Deronzier, J. Phys. Chem. B 105 (2001) 4801. [23] J.-P. Collin, A. Jouaiti, J.-P. Sauvage, J. Electroanal. Chem. 286 (1990) 75. [24] T. Spiro, P. Gosh, J. Am. Chem. Soc. 102 (1980) 5543. [25] B.P. Sullivan, D.J. Salmon, T.J. Meyer, Inorg. Chem. 17 (1978) 3384.
Heteroditopic ligands containing a 2; 20-bipyridine and a 2; 20: 60 ; 200 -terpyridine moiety and their ruthenium tris(bipyridine)-like complexes Bruno Galland, Daniele Limosin, Helene Laguitton-Pasquier, Alain Deronzier
*
Laboratoire d’Electrochimie Organique et de Photochimie Redox, UMR CNRS 5630, Universit e Joseph Fourier Grenoble 1, BP 53, 38041 Grenoble C edex 9, France Received 8 September 2001; accepted 29 September 2001
Abstract Two novel heteroditopic ligands in which the bidentate 2; 20 -bipyridine (bpy) ligand is covalently linked to one or two 2; 20 : 60 ; 200 terpyridine (terpy) terdentate ligands have been prepared and characterized. The synthesis and the physico-chemical features of their corresponding complexes in which the bpy site is complexed by a ruthenium moiety are also reported. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: 2; 20 -bipyridine; 2; 20: 60 ; 200 -terpyridine ligand; Ruthenium complexes; Supramolecular structure
1. Introduction The design of molecular structures, able to mimicking at the molecular level functions performed by a natural system or by artificial macroscopic devices, is currently of great interest. Construction of molecular assemblies effecting energy transfer, electron transfer and/or photocatalysis is an important theme of this chemistry [1–3]. A peculiar interesting design of such assemblies is based on a bimetallic complex where the two coordination sites are bridged by an alkyl chain preventing alteration of the individual properties of the both sites. Most examples contain bridged two identical diimine liganding sites like 2; 20 -bipyridine (bpy) derivatives. Typically a ½RuðbpyÞ3 2þ chromophor moiety is connected to another chromophor (Ru [4–7], Os [8], Fe [9–11], Re [12,13] bipyridine complexes) or to an electron acceptor or donor (Co [14], Pt [15], Rh [16], Mn [17], bipyridine complexes). In view of having access to a new kind of bimetallic complex with dissymetrical coordination sites we have synthesized two new heteroditopic ligands 1, 2 *
Corresponding author. Tel.: +33-4-76-51-46-83; fax: +33-4-76-5142-67. E-mail address: [email protected] (A. Deronzier).
(Scheme 1) noted bpy–terpy and bpy–terpy2 , respectively, in which the bidentate 2; 20 -bipyridine ligand is bridged to one or two terdentate ligands such as a 2; 20: 60 ; 200 -terpyridine one (terpy). Examples of such types of ligands are extremely rare [18–20]. We report also the synthesis and the main feature of their corresponding complexes 3, 4 noted ½Ruðbpy–terpyÞðbpyÞ2 2þ and ½Ruðbpy–terpy2 ÞðbpyÞ2 2þ , respectively, in which the bpy site is complexed by a ruthenium moiety forming a RuðbpyÞ2þ 3 -like core.
2. Experimental 2.1. Physical measurements UV–Visible spectra were obtained using a Cary 1 absorption spectrophotometer on 1 cm path length quartz cells. The steady-state emission spectra were recorded on a Photon Technology International (PTI) SE900M spectrofluorimeter. Emission quantum yield /L was determined at 25 °C in deoxygenated acetonitrile solutions with a CH3 CN solution of ½RuðbpyÞ3 ðPF6 Þ2 as a standard (/ref L ¼ 0:062 [21] at 25 °C) according to Eq. (1):
1387-7003/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 7 - 7 0 0 3 ( 0 1 ) 0 0 3 2 8 - 8
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B. Galland et al. / Inorganic Chemistry Communications 5 (2002) 5–8
Scheme 1.
ref S 1 10OD I L /ref ; /SL ¼ ref IL ð1 10OD Þ L
ð1Þ
where IL , the emission intensity, was calculated from the R spectrum area Ið mÞ d m, OD represents the optical density at the excitation wavelength (454 nm). The superscripts ‘‘S’’ and ‘‘ref’’ refer, respectively, to the sample and the standard. Time-resolved studies were performed on a PTI Quanta-Master luminescence lifetime spectrometer. It consists of a nanosecond flash lamp (fwhm of 5 ns) coupled to a lens-based T-format sample compartment that has a stroboscopic detector. The detailed description of the instrument and procedures has been previously reported [22]. Electrochemical experiments were run under an inert atmosphere in a glovebox at room temperature. Acetonitrile (CH3 CN, Rathburn, HPLC grade) was used as received and stocked under an argon atmosphere in the glovebox. The supporting electrolyte, tetra-n-butylammonium perchlorate (TBAP), was purchased from Fluka, recrystallized from ethyl acetate–cyclohexane and dried under vacuum at 80 °C for 3 days. Cyclic voltammetry was performed using a PAR model 273 potentiostat/galvanostat. The standard three-electrode electrochemical cell was used. Potentials are referred to an Agj10 mM AgNO3 reference electrode in CH3 CN þ 0:1 M TBAP. Potentials referenced to this system can be converted to the ferrocene/ferricinium couple by adding 70 mV. The working electrode was a glassy carbon disk (3 mm diameter) polished with 1 lm diamond paste. 1 H NMR spectra were recorded on a Brucker AC 250 spectrometer. Mass spectra were obtained on an AIE Kratos MS 50 spectrometer fitted with an Ion Tech. Gun at the mass spectrometry service UJF-CNRS, CERMAV, Grenoble, France. Elemental analyses were
performed by the Service Central d’Analyse du CNRS at Vernaison (France).
3. Synthesis 3.1. Ligands Ligand 1 was synthesized by the reaction in dry THF between 40 -(p-bromomethyl-phenyl)-2; 20: 60 ; 200 -terpyridine (1.10 g, 2.74 mmol) prepared as in [23] and 4; 40 dimethyl-2; 20 -bipyridine anion synthesized following a known procedure [24]. In a typical reaction a solution of 4; 40 -dimethyl2; 20 -byridine (0.420 g, 2.28 mmol) in dry THF ð10 cm3 Þ was cooled to )60 °C under nitrogen and a slight excess of LDA (3 mmol) was added over 1 h. After stirring at )60 °C for 15 min a slight excess of 40 (p-bromomethyl-phenyl)-2; 20: 60 ; 200 -terpyridine (1.10 g, 2.74 mmol) was added to dry THF (50 cm3 ) and the reaction allowed to slowly warm to temperature while stirring overnight. The reaction was quenched with water ð10 cm3 Þ and the mixture was extracted with dichloromethane ð3 200 cm3 Þ. The organic phase was dried over anhydrous sodium sulfate and filtered. Following the removal of the solvent the yellow residue was purified by chromatography on a silica column (CH2 Cl2: ðC2 H5 Þ2 O; 90:10) eluted with increasing amount of ðC2 H5 Þ2 O and finally with a (C2 H5 Þ2 O : C2 H5 OH, 90:10 mixture followed by an increasing amount of C2 H5 OH. 1 is obtained as a while solid (0.521 g; yield 45%). 1 H NMR ðCDCl3 Þ d 8.69–8.62 (6H, m), 8.53 (1H, d), 8.51 (1H, d), 8.26 (1H, s), 8.19 (1H, s), 7.88–7.78 (4H, m), 7.35–7.28 (4H, m), 7.12–7.06 (2H, m), 3.08 (4H, s), 2.41 (3H, s). Anal. found: C, 80.38; H, 5.39; N, 13.64. Calc. for C34 H27 N5 : C, 80.77; H, 5.38; N, 13.85%. MS, m=z 505.
B. Galland et al. / Inorganic Chemistry Communications 5 (2002) 5–8
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Table 1 em MLCT absorption band maxima ðkabs max Þ luminescence maxi ðkmax Þ, emission quantum yield ð/Þ and lifetime (s) of the excited states of 3 and 4 at 298 K, in deoxygenated CH3 CN solution Complexes
1 cm1 Þ kabs max ðeÞ ðnm=M
kem max
/
s ðlsÞ
3 4
455 (14 300) 455 (12 900)
609 609
0.054 0.046
0.997 1.014
2 was synthesized by a method similar to 1 except that dianion of the 4; 40 -dimethyl-2; 20 -bipyridine was first prepared in THF instead of the monoanion using a larger amount of LDA (6 mmol). Purification of 2 was accomplished by two successive chromatographies on an alumina column. The first one was eluted with pentane:ethyl acetate, 50:50 and the second one with toluene: CH3 OH, 95:5 and furnished 2 as a white solid (735 mg; yield 36 %). A small amount of 1 is also obtained first (58 mg; yield 5%). 1 H NMR ðCDCl3 Þ d 8.71–8.63 (12H, m), 8.57 (2H, d), 8.20 (2H, s), 7.89–7.81 (8H, m), 7.36–7.29 (8H, m), 7.09 (2H, d), 3.06 (8H, s). Anal. found: C, 81.12; H, 5.17; N, 13.21. Calc. for C56 H42 N8 : C, 81.33; H, 5.12; N, 13.55. MS, m=z 826. Scheme 2.
3.2. Complexes 3. A slight excess of ligand 1 (0.110 g, 0.18 mmol) was added to 0.155 mmol of RuðbpyÞ2 Cl2 , 2H2 O prepared as in [25] and heated in 30 cm3 of EtOH under reflux for 3 h under argon atmosphere. The solution was cooled to room temperature and a solution of KPF6 (0.29 g) in 25 cm3 of water was added to precipitate the complex 1. After filtration 1 is washed with H2 O and dried under vacuum. Yield 82% (0.173 g). 1 H NMR ðCD3 CNÞ d 8.74–8.63 (6H, m), 8.55–8.48 (4H, m), 8.14–7.96 (8H, m), 7.78–7.66 (6H, m), 7.51– 7.42 (4H, m), 7.39–7.32 (4H, m), 7.19 (2H, d), 7.13–7.06 (2H, m), 3.14 (4H, m), 2.43 (3H, s). Anal. found: C, 53.71; H, 3.56; N, 10.18. Calc. for C54 H43 N9 RuP2 F12 : C, 53.65; H, 3.58; N, 10.43. FAB: m=z (positive mode), C2þ , þ PF 6 , 1064 C , 918. 4. This complex was prepared in a similar fashion by the reaction of ligand 2 with RuðbpyÞ2 Cl2 , 2H2 O. Yield: 97%. 1 H NMR ðCD2 Cl2 Þ d 8.68–6.53 (12H, m), 8.47– 8.21 (6H, m), 8.04–7.81 (12H, m), 7.72–7.45 (6H, m), 7.39–7.36 (8H, m), 7.15–7.08 (6H, m), 3.03 (8H, s). Anal.
found: C, 59.30; H, 3.82; N, 11.09. Calc. for C76 H58 N12 RuP2 F12 : C, 59.65; H, 3.82; N, 10.98. FAB: þ m=z (positive mode), C2þ , PF 6 , 1383, C , 12.37.
4. Results and discussion The bridging ligands 1 and 2 were prepared by the reaction of 40 -(p-bromomethyl-phenyl)-,20: 60 ; 200 -terpyridine with chemically prepared solution of mono and bis anion of 4; 40 -dimethyl-2; 20 -bipyridine (Scheme 2). Obtention of pure samples of 1 and 2 with moderate yields (45% and 36%, respectively) required careful chromatography workup (see Section 2). Selective complexation of the bpy site of the ligands was easily accomplished by reaction with RuðbpyÞ2 Cl2 and furnished the expected complexes 3 and 4 isolated as their PF 6 salts with good yields (82% and 97%, respectively).
Table 2 Redox potentials of ligands 1, 2 and complexes 3, 4 in CH3 CN (0.1 M TBAP) Compounds
E1=2 ðDEp Þ=V Oxidation
1 2a 3 4 a
– – 0.94 (0.07) 0.92 (0.07)
Reduction – – )1.67 (0.06) )1.67 (0.06)
This compound is poorly soluble in CH3 CN.
– )1.86 (0.07) )1.87 (0.07)
– – )2.12 (0.07) )2.19 (0.10)
)2.38 (0.08) – )2.35 (0.08) )2.39 (0.10)
)2.57 (0.12) – )2.60 (0.10) )2.64 (0.12)
8
B. Galland et al. / Inorganic Chemistry Communications 5 (2002) 5–8
All these new compounds were fully characterized by elemental analysis, NMR spectroscopy and mass spectrometry (EI for ligands and FABþ for complexes; see Section 2). Complexes 3 and 4 exhibit the regular spectroscopic features of ruthenium-tris(bipyridine)-like compounds. The MLCT absorption and the emission bands have been red-shifted from their position in the parent complex RuðbpyÞ2þ and are closed to those of 3 ½RuðdmbpyÞ3 2þ (dmbpy ¼ 4; 40 -dimethyl-2; 20 -bipyridine). These two complexes give also a value of the emission quantum yield ð/4 Þ slightly higher than that of ½RuðbpyÞ3 2þ at room temperature. The decay curves are single-exponential. All the data are summarized in Table 1. The redox potentials of the ligand 1 and complexes 3 and 4 determined by cyclic voltammetry in CH3 CN are reported in Table 2. As for the parent 40 -tolyl-2, 20 :60 ; 200 terpyridine compound, 1 is reduced by a quasi-reversible one-electron process followed by an irreversible one [23]. The poor solubility of 2 in CH3 CN prevents any accurate determination of its redox potentials. The cyclic voltammogram obtained with complex 3 is shown in Fig. 1. At negative potentials, four reversible one-electron processes are observed. The three first ones correspond to the successive ligand-localized reduction of the RuðbpyÞ2þ 3 -like complex. The next process is due to the first reduction of the metal-free terpy part of the molecule. An irreversible wave is also observed at a more negative potential corresponding to the second reduc-
Fig. 1. Cyclic voltammogram at a glassy carbon electrode of 103 M 1 in CH3 CN þ 0:1 M TBAP, m ¼ 0:1 V s1 .
tion of the terpy group (not shown in Fig. 1). At positive potential the typical reversible one-electron couple of peaks of the metal oxidation ðRu2þ =Ru3þ Þ is shown as expected. A similar cyclic voltammogram is obtained with complex 4. However in the negative potential region waves are more or less distorted by some electroprecipitation–redissolution phenomena due to the poor solubility of the reduced forms of the complex. We have are currently investigating the complexation of the terpy part of 3 and 4 with cation metal centers like Fe2þ and Mn2þ in view of obtaining heterobimetallic complexes. With ligand 4 the formation of soluble polymeric complexes is greatly expected.
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