Synthesis, Characterization, and Electrochemical Properties of

ARTICLE pubs.acs.org/Organometallics

Synthesis, Characterization, and Electrochemical Properties of Diruthenium Complexes Bridged by Anthraquinones Fei Li,† Jie Cheng,† Xiaohong Chai,† Shan Jin,*,† Xianghua Wu,† Guang-Ao Yu,† Sheng Hua Liu,*,† and George Z. Chen‡ †

Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan 430079, People's Republic of China ‡ School of Chemical, Environmental and Mining Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, U.K.

bS Supporting Information ABSTRACT: We have prepared four isomeric binuclear ruthenium complexes, in which two ruthenium units have been attached to the 1,4(4a), 1,5- (4b), 1,8- (4c), or 2,6-positions (4d) of a central anthraquinone (Aq) moiety, leading to packed (4c) or extended (4a,b,d) topologies. All of these bimetallic complexes were fully characterized by elemental analysis, 1 H, 13C{1H}, and 31P NMR{1H} spectrometry, and UV/vis spectrophotometry. Moreover, the structures of 4a,b were established by X-ray crystallography. The electrochemical properties of the stable binuclear ruthenium complexes 4a
d were investigated, revealing that the two metal centers in 4a
c could interact with each other through an anthraquinone bridge, suggesting that the electron-withdrawing carbonyl chain actually functions as an effective bridge.

’ INTRODUCTION There is growing interest in understanding and controlling electron transport properties through molecular wires for the purpose of developing molecular electronic devices.1 In particular, linear compounds with two redox-active organometallic termini linked by an unsaturated conjugated bridging ligand have received great attention as models for “molecular wires” that allow electron transfer. The redox-active metal centers act as donor and acceptor sites for the transfer. If one of the metal centers is oxidized or reduced, the complex can then generate a mixed-valence state. Here, it is possible to probe the degree of electron delocalization and the rate at which the odd electron and the charge generated during the redox process are transmitted between the two redox-active termini groups.2 Electron transfer in these molecular wires can be perturbed differently by electroactive end groups and bridging ligands, depending on, to a great extent, the medium, the molecular topology, the nature of the metal complex, and the nature of the connecting bridge groups (electron rich or deficient, long or short chain).3
7 Therefore, molecular wires can exhibit quite particular electronic properties by careful control of these parameters. Considerable attention has been paid during the last two decades to studying bimetallic polyynediyl complexes7e,8
14 and polyylenediyl complexes15 because of their facile accessibility and high efficiency for electron delocalization. The study of [RuCl(CO)(PMe3)3]2(μ-CHdCH
Ar
CHdCH) type compounds in our laboratory revealed that electronic coupling between two Ru centers could be tuned by modification of a 1,4-diethenylphenylene bridging ligand and that the attachment of an electron-donating substituent facilitated electron coupling.7i,k r 2011 American Chemical Society

Recently, several groups have attempted to further tune the coupling through the modification of carbon-rich chains by the introduction of carborane,16 silylene,17 or metal moieties such as metallocene,18
22 [Ru(dppm)2],23
25 [Pt2(dppm)],26 and most especially [Ru2(DMBA)4]12d,e (DMBA = N,N0 -dimethylbenzamidinate). However, these results illustrate that the insertion of metal units can be utilized to enhance (or weaken) electronic coupling across a carbon-rich backbone, not to fine-tune electronic coupling between two termini groups. In seeking to control the rate of through-bond electron transfer, it seems appropriate to enhance the capability of the bridge to fine-tune the electronic properties. For such a purpose, bridging ligands that possess structural bistability controlled by an external stimulus are required. Potential candidates of the stimulus are electromagnetic radiation, photons, electronic potential, and chemical gradients. So far, several proposals for the bridging unit as controllable switches have been put forward, including dithienylethene derivatives and biphenylene crown ethers. For example, a photoswitchable dithienylethene unit as a redox-active diiron27,28 or ruthenium29,30 complex linker has been shown to be capable of switching on and off the electronic interaction between the two metal centers. Many molecular rods comprising a central biphenylene-based crown ether subunit have been reported. The magnitude of electronic coupling between the terminal chromophores shows a precise dependence on the dihedral angle around a bridging biphenyl group by selection of the bound substrates.31 Recently, an anthraquinone Received: September 28, 2010 Published: March 14, 2011 1830

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Scheme 1

(AQ) was proposed by van Dijk and Nishihara as a bridge in molecular wires becasue its redox states were expected to be able to control the extent of electronic delocalization and thus to strongly affect the electric transparency.32 In order to investigate how two metal centers bridged by anthraquinone units interact with each other, a series of conjugated binuclear ruthenium vinyl complexes have been designed and synthesized in this work. The four isomers only differ in the connecting positions of the ruthenium units to the central AQ moiety (i.e., 1,4, 1,5, 1,8, and 2,6), which leads to distinct relative topological configurations of the binuclear ruthenium complexes. The electrochemical properties of these complexes have been investigated.

’ RESULTS AND DISCUSSION Syntheses and Characterization. The synthesis of 3a
d required two steps from diiodoanthraquinones 1a
d that proceeded

in 32
62% overall yield: (PPh3)2PdCl2-catalyzed coupling with trimethylsilylacetylene, affording the bis((trimethylsilyl)ethynyl)anthraquinones 2a
d, and K2CO3
MeOH or fluoridemediated cleavage of the protecting groups. The general synthetic route for the preparation of binuclear ruthenium vinyl complexes is outlined in Scheme 1. Diethynylanthraquinones 3a
d were reacted with the ruthenium hydride complex [RuHCl(CO)(PPh3)3] to give the insertion products [(PPh 3 )2 Cl(CO)Ru]2 (μ-CHdCH
Aq
CHdCH), which were not isolated because they were air-sensitive, especially in solution. PMe3 was then added to give the corresponding sixcoordinated complexes 4a
d. These complexes were characterized by NMR. The PMe3 ligands in 4 are meridionally coordinated to ruthenium, as indicated by an AM2 pattern in the 31P{1H} NMR spectrum. The 1H NMR spectrum (in CDCl3) of 4a features two Ru
CH proton signals at δ 8.30 ppm (4b, δ 8.40; 4c, δ 8.47; 4d, δ 8.82). The chemical shift is higher than that found in 1831

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Figure 1. Molecular structure of 4a.

Figure 2. Molecular structure of 4b.

[RuCl(CO)(PMe3)3]2(μ-(CHdCH)n). The vinylic proton has a trans geometry, and the acetylene is cis-inserted into the Ru
H bond, as confirmed by the X-ray structures of 4a,b (Figures 1 and 2). X-ray Structures of 4a,b. Single crystals of compounds 4a,b suitable for X-ray analysis were obtained by slow diffusion of hexane into a solution of dichloromethane. The crystallographic details are given in Table 1. Selected bond distances and angles for 4a,b are presented in Tables S1 and S2, respectively (Supporting Information). The molecular structures of 4a,b are depicted in Figures 1 and 2, respectively. The linear-conjugated complex 4a and cross-conjugated32 complex 4b consist of two (PMe3)3Cl(CO)Ru end -groups linked by a anthraquinone carbon chain through Ru
C σ-bonding. In 4a, the two double bonds are in the cis configuration, and the two ruthenium units are located on the same side of the anthraquinone moieties. Another interesting feature lies in the nonplanar anthraquinone skeleton of 4a, which is in sharp contrast to the planar skeleton of 4b. The two phenyl rings in the anthraquinone moiety form a V shape intersecting at C(19) and C(22) with a dihedral angle of 28.5°, where O(2) and O(3) are obviously bent out of the anthraquinone plane, as shown in Figure 1. These results indicate a considerable twist of the anthraquinone framework. The molecular structure of 4b is centrosymmetric, as shown in Figure 2. The compound contains two Ru centers linked by a

μ-CHdCH
Aq
CHdCH bridge (Aq = 1,5-anthraquinone). The two Ru centers are related by a pseudo-C2 rotation axis. The Ru1 3 3 3 Ru1a distance in complex 4b is 13.926 Å, which is longer than that in complex 4a, for which the Ru1 3 3 3 Ru2 distance is 11.477 Å. The carbon atoms of the μ-CHdCH
Aq
CHdCH units are nearly coplanar. The two double bonds are in the trans configuration. The overall geometry of the two ruthenium centers in 4b closely resembles that in the bimetallic ruthenium complexes [RuCl(CO)(PMe3)3]2(μ-(CHdCH)n).7i,k It is worth noting that the vinyl groups are essentially coplanar with Cl
Ru
CO. Such coplanarity of the vinyl group and CO is expected from the strong π-interaction between these ligands and the metal centers in this conformation. The two complexes adopt the same crystal system and space group, as can be seen in Table 1. Electronic Absorption Spectroscopy. The electronic properties of the series of vinyl bimetallic complexes in dichloromethane are shown in Figure 3. The strongest band near 250 nm is known to be due to π
π* transitions with benzenoid character.33,34 The other characteristic peaks are at 392 and 540 nm for 4a, 352 and 485 nm for 4b, and 346 and 482 nm for 4c. Those of 4d are at 362 and 451 nm (Table 2), corresponding to n
π* and MLCT bands, respectively. For these anthraquinone-bridged bimetallic complexes, the main broad transition in the visible region is expected to arise from the allowed transition 1832

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Table 1. Crystal Data, Data Collection, and Refinement Parameters for 4a,b 4a

4b

formula

C39H68Cl4O5P6Ru2

C39H68Cl4O5P6Ru2

fw temp (K)

1146.69 295(2)

1146.69 298(2)

cryst syst

monoclinic

monoclinic

space group

P21/c

P21/c

a (Å)

17.8930(9)

11.6537(14)

b (Å)

17.5966(9)

13.3040(15)

c (Å)

18.3564(9)

18.220(2)

β (deg)

109.0400(10)

103.271(2)

V (Å
3) Z

5463.4(5) 4

2749.3(6) 2

Dcalcd (g cm
3)

1.394

1.261

F(000)

2352

1072

θ range (deg)

1.80
27.00

1.91
28.31

no. of rflns collected

33 199

6782

no. of indep rflns

11 902 (0.0511)

6782 (0.0511)

no. of data/restraints/params

11 902/0/523

6782/0/245

final R Rwa

0.0636 0.1412

0.0527 0.1112

R (all date)

0.0855

0.0704

0.1519

0.1175

Rw (all date) goodness of fit/F

2

a

1.127

Figure 3. UV
vis absorption spectral changes of compounds 4a
d (1  10
5 mol/L) in CH2Cl2.

Table 2. UV
Vis Data for [RuCl(CO)(PMe3)3]2(CHdCH
Aq
CHdCH) Complexes 4a
d in CH2Cl2

1.082

compd

λmax, nm (10
4ε, dm3 mol
1 cm
1)

4a

256 (4.02), 296 (1.9), 392 (1.42), 540 (0.40)

4b

252 (6.35), 352 (2.50), 485 (1.04)

4c

252 (0.50), 346 (1.42), 482 (0.45)

4d

252 (3.68), 311 (3.28), 362 (3.57), 451 (2.40)

w = 1/[σ (Fo) þ (aP) þ bP], where P = (Fo þ Fc )/3. 2

2

2

2

2

Table 3. Electrochemical Data for Compounds 4a
d from one of the metal-based HOMOs to an unoccupied ligandbased orbital (MLCT), the latter probably being mainly delocalized over the anthraquinone-based bridge ligand. The lowenergy absorptions of complex 4a, showing a notable red shift, indicated that there was a higher degree of conjugation, perhaps related to the fact that 4a also has the strongest Ru
Ru interaction, in comparison with the other complexes 4b
d. Electrochemistry. The extent of the interaction between the two metal termini bridged by anthraquinone was examined by electrochemical methods. The redox behavior of the binuclear complexes 4a
d (1 mM in CH2Cl2) has been investigated by cyclic voltammetry and square-wave voltammetry with 0.1 M n-Bu4NPF6 as the supporting electrolyte. The electrochemical data are compiled in Table 3. Cyclic and square-wave voltammograms (CVs and SWVs) for complexes 4a
d are depicted in Figure 4. As shown in Figure 4a,b, the CV and SWV of the linear-conjugated complex 4a exhibit two separated one-electron oxidation waves, most likely originating from successive oxidation of RuII,II to RuII,III and RuII,III to RuIII,III, respectively. The peak separation of the two oxidation waves, ΔE, for complex 4a was about 114 mV, suggesting a weak electronic interaction between the two metal centers. Due to the strong electron-withdrawing effect of the quinone moiety, the ΔE value in 4a with 1,4-anthraquinone is obviously smaller than that in [RuCl(CO)(PMe3)3]2(μ-CHdCH
Ar
CHdCH) with 4,40 diethynylphenyl as the spacer,7i for which the ΔE value is 296 mV. The cross-conjugated complex 4b showed a broad oxidation wave (not shown), and on the basis of the results of simulation, the separation of the two redox processes was estimated to be 75 mV.6k Interestingly, for the typical cross-conjugated complex 4c, a weak but appreciable electronic interaction between the metal centers is still observed (Figure 4c,d). The ΔE value for complex

complex

Ep1 (V)a

Ep2 (V)a

4E (mV)b

4a 4c

0.388 0.612

0.502 0.712

114 100

4b

0.572

0.647

75

4d

0.680c

a From square-wave voltammetry in 0.1 M CH2Cl2/nBu4NPF6 solutions at 10 Hz for SWV. Potentials are vs Fcþ/Fc. b Peak potential differences ΔE = Ep2
Ep1. c Anodic peak potential Ep for a one-step two-electron process.

4c was found to be 100 mV, suggesting the electron-withdrawing carbonyl chain actually functioned as an effective bridge. Conversely, the CV and SWV of 4d (Figure 4e,f) showed only one irreversible oxidation wave at Ep,a = þ0.680 V with no clear sign of peak separation. This result indicates that there is little, if any, electronic interaction between the metal centers in complex 4d. This can be attributed to the fact that (1) the electron-withdrawing carbonyl decreases the electronic interaction between the two metal centers and (2) increasing the distance between the two metal centers leads to decreasing interaction.

’ CONCLUSION We have prepared four isomeric binuclear ruthenium systems, in which two ruthenium units have been attached to the 1,4- (4a), 1,5- (4b), 1,8- (4c), or 2,6-positions (4d) of a central anthraquinone (Aq) moiety, leading to folded (4c) or extended (4a,b,d) topologies. Electrochemical studies have shown that the two metal centers could interact with each other through an anthraquinone 1833

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Figure 4. Cyclic voltammograms (CV) of complexes (a) 4a (c) 4c, and (e) 4d in CH2Cl2/Bu4NPF6 at v = 0.1 V s
1 and square-wave voltammograms (SWV) of complexes (b) 4a, (d), 4c, and (f) 4d at f = 10 Hz. Potentials are given relative to the Ag/Agþ standard.

bridge, suggesting that the electron-withdrawing carbonyl chain actually functioned as an effective bridge. In a forthcoming paper, we will examine the role of the metal ion and proton in finetuning the electronic interaction in such systems.

’ EXPERIMENTAL SECTION General Materials. All manipulations were carried out at room temperature under a nitrogen atmosphere using standard Schlenk techniques, unless otherwise stated. Solvents were predried, distilled and degassed prior to use, except those for spectroscopic measurements, which were of spectroscopic grade. The starting materials RuHCl(CO)(PPh3)3,35 1,4diiodoanthraquinone (1a),36 1,5-diiodoanthraquinone (1b),37 1,8-diiodoanthraquinone (1c),38 2,6-diiodoanthraquinone (1d)39,40 were prepared by the procedures described in literature methods.

Synthesis of Bis((trimethylsilyl)ethynyl)-9,10-anthraquinones. 1,4-Bis((trimethylsilyl)ethynyl)-9,10-anthraquinone (2a)39. To a stirred solution of diiodoanthraquinone 1a (2 g, 4.3 mmol), CuI (0.08 g, 0.43 mmol), and (PPh3)2PdCl2 (0.15 g, 0.22 mmol) in triethylamine (50 mL) and THF (50 mL) under an argon atmosphere was added (trimethylsilyl)acetylene (0.59 g, 6 mmol), and the mixture at 40 °C was refluxed for 18 h. The cold solution was filtered through a bed of Celite. The filtrate was evaporated under reduced pressure and purified by silica gel column chromatography (petroleum ether/dichloromethane 3/1) to give a yellow solid (1.09 g, 63%). 1H NMR (400 MHz, CDCl3): δ (ppm) 0.36 (s, 18H, SiCH3), 7.77 (dd, 3J = 5.4 Hz, 2H, H-6, H-7), 7.80 (s, 2H, H-2, H-3), 8.29 (dd, 3J = 5.8 Hz, 2H, H-5, H-8). 1,5-Bis((trimethylsilyl)ethynyl)-9,10-anthraquinone (2b)41. The procedure of 2b was similar to that for 2a, with THF being replaced by toluene: 1834

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Organometallics 1b (1.5 g, 3.2 mmol), CuI (0.06 g, 0.32 mmol), (PPh3)2PdCl2 (0.11 g, 0.16 mmol), triethylamine (80 mL) and toluene (40 mL), (trimethylsilyl) acetylene (1.86 g, 19.2 mmol). Yield: 0.96 g (74%) of a yellow solid. 1H NMR (400 MHz, CDCl3): δ (ppm) 0.35 (s, 18H, SiCH3), 7.70 (t, 3J = 7.6 Hz, 2H, H-3, H-7), 7.91 (dd, 3J = 7.6 Hz, 2H, H-2, H-6), 8.34 (dd, 3 J = 7.6 Hz, 2H, H-4, H-8). 1,8-Bis((trimethylsilyl)ethynyl)-9,10-anthraquinone (2c)41. The procedure of 2c was similar to that for 2a, with THF being replaced by toluene: 1c (2 g, 4.3 mmol), CuI (0.08 g, 0.43 mmol), (PPh3)2PdCl2 (0.14 g, 0.22 mmol), triethylamine (80 mL) and toluene (40 mL), (trimethylsilyl)acetylene (2.55 g, 25.98 mmol). Yield: 1.09 g (63%) of a yellow solid. 1H NMR (400 MHz, CDCl3): δ (ppm) 0.35 (s, 18H, SiCH3), 7.67 (t, 3J = 7.6 Hz, 2H, H-3, H-6), 7.94 (dd, 3J = 7.6 Hz, 2H, H-2, H-7), 8.26 (dd, 3J = 7.6 Hz, 2H, H-4, H-5). 2,6-Bis((trimethylsilyl)ethynyl)-9,10-anthraquinone (2d)41. The procedure of 2d was similar to that for 2a, with THF being replaced by toluene: 1d (1.56 g, 3.38 mmol), CuI (0.06 g, 0.34 mmol), (PPh3)2PdCl2 (0.12 g, 0.17 mmol), triethylamine (80 mL) and toluene (40 mL), (trimethylsilyl)acetylene (1.99 g, 20.28 mmol). Yield: 0.18 g (27%) of a yellow solid. 1H NMR (400 MHz, CDCl3): δ (ppm) 0.29 (s, 18H, SiCH3), 7.84 (dd, 3J = 8.2 Hz, 2H, H-3, H-7), 8.25 (d, 3J = 8.2 Hz, 2H, H-4, H-8), 8.36 (d, 4J = 1.6 Hz, 2H, H-1, H-5). Synthesis of Biethynyl-9,10-anthraquinone41. 1,4-Diethynyl-9,10-anthraquinone (3a). 1,4-Bis((trimethylsilyl)ethynyl)-9,10-anthraquinone (2a; 0.3 g, 0.75 mmol) was dissolved in a mixture of THF and methanol (40 mL, 1/1, v/v). Powdered potassium carbonate (1.04 g, 7.5 mmol) was added, and the reaction mixture was stirred at room temperature for 12 h. The reaction mixture was diluted with dichloromethane and washed with brine. The organic layer was dried over NaSO4, and the solvent was removed in vacuo. The crude product was purified by chromatography (petroleum ether/dichloromethane 2/1). Yield: 0.03 g (15%) of a light yellow solid. 1,5-Diethynyl-9,10-anthraquinone (3b). 1,5-Bis((trimethylsilyl) ethynyl)-9,10-anthraquinone (2b; 0.47 g, 1.2 mmol) was dissolved in chloroform (50 mL) and heated at reflux. To this mixture was added a solution of tetrabutylammonium fluoride (7.5 mL, 7.5 mmol, 1 M solution) dropwise over 1 h. After 12 h, water was added and the organic layer was washed with brine and with water. After removal of the solvent, the solid residue was thoroughly washed with methanol and vacuum-dried to afford a gray solid. Yield: 0.26 g (84%). 1H NMR (400 MHz, CDCl3): δ (ppm) 3.62 (s, 2H, tCH), 7.77 (t, 3J = 7.6 Hz, 2H, H-3, H-7), 7.96 (dd, 3J = 7.6 Hz, 2H, H-2, H-6), 8.38 (dd, 3J = 7.6 Hz, 2H, H-4, H-8). 1,8-Diethynyl-9,10-anthraquinone (3c). The procedure of 3c was similar to that for 3b: 2c (0.43 g, 1.07 mmol), n-Bu4NF (5.4 mL, 5.4 mmol), CHCl3 (50 mL). Yield: 0.11 g (41%) of a brown solid. The crude product was purified by chromatography (petroleum ether/dichloromethane 3/1). 2,6-Diethynyl-9,10-anthraquinone (3d). The procedure of 3d was similar to that for 3b: 2d (0.3 g, 1.07 mmol), n-Bu4NF (4.5 mL, 4.5 mmol), CHCl3 (50 mL). Yield: 0.14 g (74%) of a light brown solid. 1H NMR (400 MHz, CDCl3): δ (ppm) 3.38 (s, 2H, tCH), 7.88 (dd, 3J = 8.2 Hz, 2H, H-3, H-7), 8.28 (d, 3J = 8.2 Hz, 2H, H-4, H-8), 8.41 (d, 4J = 1.6 Hz, 2H, H-1, H-5). General Synthesis of Binuclear Ruthenium Complexes. To a suspension of RuHCl(CO)(PPh3)3 (0.31 g, 0.33 mmol) in CH2Cl2 (20 mL) was slowly added a solution of the corresponding diethynyl9,10-anthraquinone (0.047 g, 0.18 mmol) in CH2Cl2 (5 mL). The reaction mixture was stirred for 30 min to give a red solution. Then a 1 M THF solution of PMe3 (1.8 mL, 1.8 mmol) was added to the red solution. The mixture was stirred for another 20 h. The solution was filtered through a column of Celite. The volume of the filtrate was reduced to ca. 2 mL under vacuum. Addition of hexane (30 mL) to the residue produced a black solid, which was collected by filtration, washed with hexane, and dried under vacuum.

ARTICLE

4a: yield 0.11 g, 65%. Anal. Calcd for C38H64Cl2O3P6Ru2: C, 43.73; H, 6.18. Found: C, 43.37; H, 6.04. 31P NMR (160 MHz, CDCl3): δ (ppm)
20.81 (t, J = 22.56 Hz),
8.92 (d, J = 22.56 Hz). 1H NMR (400 MHz, CDCl3): δ (ppm) 1.47 (t, J = 3.4, 36H, PMe3), 1.50 (d, J = 6.8, 18H, PMe3), 7.64 (dd, 3J = 5.6 Hz, 2H, H-6, H-7), 7.66
7.70 (m, 2H, Ar
CHd), 7.83 (s, 2H, H-2, H-3), 8.30 (dd, 3J = 5.8 Hz, 2H, H-5, H-8), 8.26
8.34 (m, 2H, Ru
CHd). 13C NMR (100 MHz, CDCl3): δ (ppm) 16.71 (t, J = 14.45 Hz, PMe3), 20.02 (d, J = 20.50 Hz, PMe3), 126.13, 127.59, 132.28, 132.34, 134.86, 135.03, 140.96 (d, J = 8 Hz, Aq
CHd), 172.78 (Ru
CHd), 186.49 (Aq
CO), 202.13 (CO). 4b: yield 0.06 g, 32%. Anal. Calcd for C38H64Cl2O3P6Ru2: C, 43.73; H, 6.18. Found: C, 43.23; H, 6.60. 31P NMR (160 MHz, CDCl3): δ (ppm)
20.73 (t, J = 22.6 Hz),
8.87 (d, J = 22.6 Hz). 1H NMR (400 MHz, CDCl3): δ (ppm) 1.46 (t, J = 3.2, 36H, PMe3), 1.50 (d, J = 6.8, 18H, PMe3), 7.52 (t, 3J = 7.6 Hz, 2H, H-3, H-7), 7.78
7.85 (m, 2H, Ar
CHd), 7.88 (dd, 3J = 7.6 Hz, 2H, H-2, H-6), 7.99 (dd, 3J = 7.6 Hz, 2H, H-4, H-8). 8.36
8.44 (m, 2H, Ru
CHd). 13C NMR (100 MHz, CDCl3): δ (ppm) 16.75 (t, J = 15.2 Hz, PMe3), 20.04 (d, J = 20.5 Hz, PMe3), 126.37, 127.34, 132.61, 133.95, 136.80, 137.30, 143.48 (d, J = 32.7 Hz, Aq
CHd), 175.00 (Ru
CHd), 186.40 (Aq
CO), 202.00 (CO). 4c: yield 0.05 g, 33%. Anal. Calcd for C38H64Cl2O3P6Ru2: C, 43.73; H, 6.18. Found: C, 43.23; H, 6.49. 31P NMR (160 MHz, CDCl3): δ (ppm)
20.69 (t, J = 20.96 Hz),
8.85 (d, J = 20.96 Hz). 1H NMR (400 MHz, CDCl3): δ (ppm) 1.45 (t, J = 3.4, 36H, PMe3), 1.49 (d, J = 6.8, 18H, PMe3), 7.49 (t, 3J = 7.8 Hz, 2H, H-3, H-6), 7.63
7.7.69 (m, 2H, Ar
CHd), 7.97 (t, 3J = 7 Hz, 4H, H-2, H-7, H-4, H-5), 8.45
8.49 (m, 2H, Ru
CHd).13C NMR (100 MHz, CDCl3): δ (ppm) 16.67 (t, J = 10.4 Hz, PMe3), 19.95 (d, PMe3), 124.99, 128.36, 128.49, 129.43, 131.97, 132.06, 132.89, 133.57, 184.66 (Aq
CO), 201.86 (CO). 4d: yield 0.18 g, 95%. Anal. Calcd for C38H64Cl2O3P6Ru2: C, 43.73; H, 6.18. Found: C, 43.99; H, 6.57. 31P NMR (160 MHz, CDCl3): δ (ppm)
19.19 (t, J = 21.84 Hz),
7.61 (d, J = 21.84 Hz). 1H NMR (400 MHz, CDCl3): δ (ppm) 1.40 (t, J = 3, 36 Hz, PMe3), 1.49 (d, J = 6.8 Hz, 18H, PMe3), 6.84
6.88 (m, 2H, Aq
CHd), 7.74 (dd, 3J = 8.0 Hz, 2H, H-3, H-7), 8.03 (dd, 3J = 8.0 Hz, 2H, H-4, H-8), 8.18 (d, 4J = 1.6 Hz, 2H, H-1, H-5), 8.79
8.85 (m, 2H, Ru
CHd). 13C NMR (100 MHz, CDCl3): δ (ppm) 16.56 (t, J = 15.2 Hz, PMe3), 19.82 (d, J = 21.3 Hz, PMe3), 122.66, 127.65, 128.02, 129.62, 134.15, 134.53, 145.70 (Aq
CHd), 178.43 (d, J = 77.6 Hz, Ru
CHd), 183.54 (Aq
CO), 201.91 (CO). Crystallographic Details. Crystals suitable for X-ray diffraction were grown from a dichloromethane solutions of 4a,b layered with hexane. Crystals with approximate dimensions of 0.20  0.10  0.10 mm3 for 4a,b were mounted on glass fibers for diffraction experiments. Intensity data were collected on a Nonius Kappa CCD diffractometer with Mo KR radiation (0.710 73 Å) at room temperature. The structures were solved by a combination of direct methods (SHELXS-97)42 and Fourier difference techniques and refined by full-matrix least squares (SHELXL-97).43 All non-H atoms were refined anisotropically. The hydrogen atoms were placed in the ideal positions and refined as riding atoms. Further crystal data and details of the data collection are summarized in Table 1. Selected bond distances and angles are given in Tables S1 and S2, respectively, in the Supporting Information. Physical Measurements. Elemental analyses (C, H, N) were performed with a Vario ElIII Chnso instrument. 1H, 13C{1H}, and 31 1 P{ H} NMR spectra were collected on a Varian MERCURY Plus 400 spectrometer (400 MHz) or on a Varian MERCURY Plus 600 spectrometer (600 MHz). 1H and 13C NMR chemical shifts are relative to TMS, and 31P NMR chemical shifts are relative to 85% H3PO4. IR spectra were recorded on a Nicolet AVATAR 360 FT-IR spectrophotometer using KBr disks. UV
vis spectra were recorded on a PDA spectrophotometer by quartz cells with a path length of 1.0 cm. The electrochemical measurements were performed on a CHI 660C potentiostat 1835

dx.doi.org/10.1021/om100932u |Organometallics 2011, 30, 1830–1837

Organometallics (CHI USA). A three-electrode one-compartment cell was used to contain the solution of the compound and supporting electrolyte in dry CH2Cl2. Deaeration of the solution was achieved by argon bubbling through the solution for about 10 min before measurement. The ligand and electrolyte (Bu4NPF6) concentrations were typically 0.001 and 0.1 mol dm
3, respectively. A 500 μm diameter platinum-disk working electrode, a platinum-wire counter electrode, and an Ag/Agþ reference electrode were used. The Ag/Agþ reference electrode contained an internal solution of 0.01 mol dm
3 AgNO3 in acetonitrile and was incorporated into the cell with a salt bridge containing 0.1 mol dm
3 Bu4NPF6 in CH2Cl2. All electrochemical experiments were carried out under ambient conditions.

’ ASSOCIATED CONTENT

bS

Supporting Information. Tables of bond distances and angles and CIF files giving X-ray crystallographic files for [(PPh3)2Cl(CO)Ru]2(μ-CHdCH
Aq
CHdCH) (4a; Aq = 1,4-anthraquinone) and [(PPh3)2Cl(CO)Ru]2(μ-CHdCH
Aq
CHdCH) (4b). This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected] (S.J.); [email protected]. edu.cn (S.H.L.).

’ ACKNOWLEDGMENT We acknowledge financial support from the National Natural Science Foundation of China (Nos. 20931006, 21072070, 20803027), Program for Changjiang Scholars and Innovative Research Team in University (No. IRT0953), and the Natural Science Foundation of Hubei Province (No. 2008CDB019). ’ REFERENCES (1) Joachim, C.; Gimzewski, J. K.; Aviram, A. Nature 2000, 408, 541. (2) Launay, J. P. Chem. Soc. Rev. 2001, 30, 386. (3) Schwab, P. F. H.; Levin, M. D.; Michl, J. Chem. Rev. 1999, 99, 1863. (4) (a) de Montigny, F.; Argouarch, G.; Roisnel, T.; Toupet, L.; Lapinte, C.; Lam, S. C. F.; Tao, C. H.; Yam, V. W. W. Organometallics 2008, 27, 1912. (b) Paul, F.; da Costa, G.; Bondon, A.; Gauthier, N.; Sinbandhit, S.; Toupet, L.; Costuas, K.; Halet, J. F.; Lapinte, C. Organometallics 2007, 26, 874. (c) Samoc, M.; Gauthier, N.; Cifuentes, M. P.; Paul, F.; Lapinte, C.; Humphrey, M. G. Angew. Chem., Int. Ed. 2006, 45, 7376. (d) Cifuentes, M. P.; Humphrey, M. G.; Morall, J. P.; Samoc, M.; Paul, F.; Roisnel, T.; Lapinte, C. Organometallics 2005, 24, 4280. (e) Paul, F.; Lapinte, C. Coord. Chem. Rev. 1998, 178
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