New Linear π-Conjugated Diruthenium Compounds Containing Axial

Article pubs.acs.org/Organometallics

New Linear π‑Conjugated Diruthenium Compounds Containing Axial Tetrathiafulvalene-acetylide Ligands Xu-Min Cai,† Xiang-Yi Zhang,† Julia Savchenko,‡ Zhi Cao,‡ Tong Ren,*,‡ and Jing-Lin Zuo*,† †

State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing 210093, People's Republic of China ‡ Department of Chemistry, Purdue University, West Lafayatte, Indiana 47907, United States S Supporting Information *

ABSTRACT: Under the weak base conditions, diruthenium(III) tetrakis-N,N′-dimethylbenzamidinate (DMBA) nitrate (Ru2(DMBA)4(NO3)2) reacted with electroactive tetrathiafulvalene acetylene ligands, HCC−TTF1 (5-ethynyl-2-(4,5dimethyl-1,3-dithiol-2-ylidene)benzo[d][1,3]dithiole) and HCC−TTF2 (2-(5-ethynylbenzo[d][1,3]dithiol-2-ylidene)benzo[d][1,3]dithiole), to afford new compounds transRu2(DMBA)4(CC−TTF1)2 (1) and transRu2(DMBA)4(CC−TTF2)2 (2), respectively. The trans orientation and the planar nature of the ethynyltetrathiafulvalene ligands around the Ru2(III,III) core were supported by the single-crystal X-ray diffraction study of compound 1. Both compounds 1 and 2 and their TTF ligand precursors were characterized with the spectroscopic and voltammetric techniques, which revealed a minimal electronic interaction between the two TTF moieties within the same compound. The electronic structure of trans-Ru2(DMBA)4(CC−TTF)2 was analyzed based on a DFT calculation of a model compound, and the resultant distribution of valence MOs is consistent with the voltammetric results.

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INTRODUCTION Molecular materials containing tetrathiafulvalene (TTF), an organic donor, have attracted intense interest as potential organic conductors and superconductors.1,2 Similarly, metal alkynyl compounds have been explored extensively as promising candidates for molecular wires and devices.3−5 The combination of transition metals and TTF-containing alkynyls may lead to novel molecular conductors, molecular magnets, and sensors.5,6 The laboratories of Zuo and You investigated a number of metal compounds with TTF-containing ligands that exhibited interesting fluorescent, magnetic, and conducting properties.7 The laboratory of Ren investigated several families of metal-alkynyl compounds based on both the Ru2-4 and M(cyclam) (M = Cr and Fe) motifs8 and demonstrated facile charge-transfer properties in the former system through measurements conducted on both the bulk materials and the single/few molecules levels. 9 In particular, the C 2n Ru2(DMBA)4-C2n type fragments (n = 1−4; DMBA is N,N′dimethylbenzamidinate) were found to be very efficient in mediating electronic coupling between two ferrocenyls at the opposite ends of polyynyls.10−12 Recently, several mononuclear Ru(II),13 Cr(III),14 and Fe(II/III)15 compounds with different ethynyltetrathiafulvalene (TTF)-type ligands were prepared, and modest electronic coupling between the two TTF units in trans position was observed in the case of Ru(II). Reported in this contribution are the syntheses of two diruthenium-ethynylTTF compounds, trans-Ru2(DMBA)4(CC−TTFm)2 1 and 2 (Scheme 1), the X-ray structural characterization of 1, and the © 2012 American Chemical Society

electrochemical and spectroscopic studies of 1 and 2. The electronic structure of the diruthenium-ethynyl-TTF species was explored with a DFT calculation of the model compound 1′.

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RESULTS AND DISCUSSION Synthesis and Characterization. As shown in Scheme 1, the target compounds 1 and 2 were prepared by using the weak-base-assisted reaction.16,17 The TTF-containing ligands, HCC−TTF1 and HCC−TTF2, were synthesized from the corresponding iodo TTF precursors. As shown for TTF1 in Scheme 1, the Sonogashira coupling reaction between iodoTTF1 and trimethylsilylacetylene in the presence of diisopropylamine afforded Me3CC−TTF1 in 65% yield, and the ensuing deprotection with KF in MeOH/THF (v/v = 1/1) afforded HCC−TTF1 in quantitative yield. The reaction between Ru2(DMBA)4(NO3)2 and 4 equiv of HCC−TTF1 in THF and diisopropylamine afforded the red-purple compound 1 in 35% yield. Similarly, compound 2 was prepared from the reaction between Ru2(DMBA)4(NO3)2 and 2.2 equiv of HCC−TTF2 in a yield of 65%. Characterizations of compounds 1 and 2 were accomplished with 1H NMR, IR, and UV−vis absorption spectroscopic techniques. In the 1H NMR spectra of 1 and 2 (Figures S1 and S2, Supporting Information), compared with the corresponding Received: October 19, 2012 Published: December 4, 2012 8591

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Scheme 1. Reagents and Conditions: (i) Ru2(DMBA)4(NO3)2, iPr2NH, THF; (ii) Pd(PPh3)4, CuI, HC2SiMe3, iPr2NH; (iii) KF, MeOH/THF

Figure 1. Perspective drawing of the molecular structure of Me3SiCC−TTF1 (left) and side view (right). H atoms are omitted for clarity.

1.935(5) Å, which is in agreement with that in other similar Ru2(DMBA)4(CCR)2 complexes (1.95−2.00 Å). The C42− C56 distance between the two TTF moieties is 17.02 Å, which is longer than the edge−edge distance of two Fc units in Ru2(DMBA)4(CCFc)2 (11.6 Å).10−12 The extra benzene rings attenuate the coupling between two TTF moieties, as described later. The entire length of the molecule is 32.57 Å. Electrochemical and Spectroscopic Properties. The voltammetric properties of both compounds 1 and 2 and the corresponding free HCC−TTFm ligands were investigated using cyclic (CV) and differential pulse voltammogram (DPV) techniques. The CVs are shown in Figure 3 with the potential data collected in Table 4. Both HCC−TTFm ligands display two reversible one-electron oxidations, labeled as L1 and L2, which are typical for TTF moieties.1 In addition to the TTFbased couples, both compounds 1 and 2 also display two (quasi)reversible Ru2-based couples: the one-electron oxidation A and one-electron reduction B. While the assignment of both the couples A and B is unambiguous on the basis of the prior studies of the Ru2(DMBA)4(C2R)2 type compounds,4 it is noted that the couple A in 2 has the current level significantly lower than expected for a one-electron event. The cause of this apparent underoxidation remains unclear to us presently. Interestingly, the electrode potentials of both A and B are slightly more positive than those reported for transRu2(DMBA)4(C2Ph)2 (0.52 and −1.10 V, respectively), implying that both TTF1 and TTF2 are less electron donating than the phenyl group. Compound 1 also exhibited a wave C (Epa = −0.29 V) on the return sweep in the cathodic region, which is attributed to the oxidation of a Ru2(DMBA)4(CC− TTF1) intermediate derived from the dissociation of a CC− TTF1 ligand from [Ru2(DMBA)4(CC−TTF1)2]1− under highly negative potentials.20,21

free ligands, all H signals on the benzene ring of the TTF ligand for the diruthenium compound were shifted about 0.24−0.37 ppm to the higher field, which is attributed to the increase in electron density around the benzene group caused by its coordination to the electron-rich Ru2(DMBA)4 fragment. In the IR spectra, the CC band stretches in 1 (2052 cm−1) and 2 (2046 cm−1) are significantly lower than those in the free ligands HCC−TTF1 (2101 cm−1) and HCC−TTF2 (2100 cm−1). The υ(CC) stretching frequencies in 1 and 2 are among the lowest observed for the reported Ru2(DMBA)4(C2Y)2 compounds,10,11,17 suggesting a significant electronic interaction between the Ru2(III,III) core and the −CC−TTFm moiety. It may result from the loss of π(C C) electron density through its antibonding interaction with the π(Ru−Ru) orbitals.18 Crystal Structure Description. Crystal structures of the ligand Me3SiCC−TTF1 and Ru2 compound 1 are shown in Figures 1 and 2, respectively. The crystallographic and data collection parameters are given in Table 1, whereas selected bond lengths and angles are listed in Tables 2 and 3. The ligand Me3SiCC−TTF1 exhibits a planar structure, and the C9 C10 bond length is 1.203(4) Å. In compound 1, the Ru2 core is bridged by four DMBA units. The two CC−TTF1 moieties are coordinated to the Ru2 core in a trans arrangement, with the SMe substituents at the opposite sides of the TTF plane. The C37C38 bond length is 1.241(6) Å, which is slightly longer than that of Me3SiCC−TTF1. The geometric parameters around the first coordination sphere of the Ru2 core are comparable to those of other Ru 2 (DMBA) 4 (CCY) 2 compounds and exhibit the structural distortion displayed by many other Ru2(III,III) bis-alkynyls.4,19,20 The Ru−Ru bond length is 2.427(1) Å, whereas those of Ru2(DMBA)4(CCR)2 are in the range of 2.441−2.476 Å. The Ru−C bond distance is 8592

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Figure 2. Perspective drawing of the molecular structure of 1 (top) and side view (bottom). H atoms and interstitial solvent molecules are omitted for clarity. Ru, purple; S, yellow; N, blue; C, green.

Table 1. Crystallographic Data for Compounds Me3SiC C−TTF1 and 1 empirical formula Mr cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z ρc (g cm−3) F(000) T (K) μ(Mo−Kα) (mm−1) index range

data/restraints/params GOF (F2) R1a, wR2b (I > 2σ(I)) a

Me3SiCC−TTF1

1·THF·1/4H2O

C17H18S6Si 442.76 triclinic Pi ̅ 5.606(9) 12.453(4) 15.351(5) 87.330(6) 82.746(6) 82.964(5) 1054.8(5) 2 1.394 460 120 0.703 −3 ≤ h ≤ 6 −15 ≤ k ≤15 −18 ≤ l ≤18 4070/0/222 1.019 0.0464, 0.1313

C68H70.50N8O1.25Ru2S12 1606.68 triclinic Pi ̅ 10.741(3) 17.988(5) 18.789(6) 92.293(5) 92.391(6) 90.340(5) 3623.9(2) 2 1.472 1649 120 0.811 −12 ≤ h ≤13 −22 ≤ k ≤22 −23 ≤ l ≤21 13779/4/805 1.056 0.0598, 0.1241

Table 2. Selected Bond Distances (Å) and Angles (deg) for Me3SiCC−TTF1 C9−C10 C2−S6 Si1−C9 Si1−C9−C10 S1−C4−S2 S5−C7−C2

1.203(4) 1.743(2) 1.832(3) 175.3(3) 114.73(14) 123.7(2)

C4−C6 C7−S5

1.349(4) 1.748(3)

C9−C10−C5 S3−C6−S4 S6−C2−C7

175.6(3) 115.64(14) 124.4(2)

Table 3. Selected Bond Distances (Å) and Angles (deg) for 1 Ru1−Ru2 Ru2−C51 C51−C52 C59−C60 C52−C53 C37−Ru1−Ru2 C38−C37−Ru1 N1−Ru1−Ru2 N5−Ru1−Ru2

2.4274(7) 1.939(5) 1.239(6) 1.374(8) 1.407(1) 159.73(15) 167.5(5) 97.21(12) 79.82(12)

Ru1−C37 C37−C38 C45−C46 C38−C39

1.935(5) 1.241(6) 1.358(7) 1.409(1)

Ru1−Ru2−C51 Ru2−C51−C52 N3−Ru1−Ru2 N7−Ru1−Ru2

160.57(15) 175.3(5) 80.29(11) 96.48(13)

The redox behavior of two TTF units in each of compounds 1 and 2 is relatively unremarkable: two reversible 2e − oxidations at electrode potentials nearly identical to those of the corresponding free ligand. Differential pulse voltammograms of compound 1 were also measured under the conditions stipulated by Richardson and Taube22 in order to determine if

R1 = ∑||C| − |Fc||/ΣFo|. bwR2 = [∑w(Fo2 − Fc2)2/∑w(Fo2)2]1/2.

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Figure 3. (top) Cyclic voltammograms for 1 and HCC−TTF1; (bottom) cyclic voltammograms for 2 and HCC−TTF2 at a scan rate of 100 mV/s in 0.2 M THF solution of (Bu4N)PF6. Figure 4. Absorption spectra of HCC−TTF1, Ru2(DMBA)4(NO3)2, and compound 1 in CH2Cl2.

Table 4. Electrochemical Data (E (V), vs Ag/AgCl) compounds HCC−TTF1 HCC−TTF2 1 2

E(B)

−0.98 −0.91

E(A)

E(L1)

E(L2)

0.61 0.55

0.80 0.80 0.79 0.80

0.98 1.00 0.99 1.00

of 1, the optimized Ru−Ru bond (2.548 Å) is longer than the experimental value (2.427 Å), which is attributed to the underestimation of weak metal−metal interactions by the DFT method, as discussed in a prior publication.10 The order of Ru2based MOs in 1′ is consistent with the previous DFT results on the Ru2(DMBA)4(CC−R) type compounds.24,28,29 Hence, the emphasis of the current study lies in the orbital interactions between the −CC−TTF ligands and Ru2 core in 1′. All the computed energies and counter plots of the most relevant MOs are given in Figure 5.

the appearance of the 2e− waves is the result of coalescence of two closely spaced 1e− waves. The result, provided in the Supporting Information (Figure S3), clearly shows that this is not the case. The simultaneous oxidation of both TTF units clearly indicates the absence of a significant electronic interaction between the pair, similar to the behavior observed for trans-[CrCyclam(CC-5-methyl-4′,5′-ethylenedithioTTF)2]+.14 It is worth noting that a weak electronic coupling was detected between two TTF-ethynyl ligands that are in trans positions across a mononuclear Ru center, where the ethynyl is directly attached to the tetrathiafulvalene ring.13 It is plausible that the additional benzene ring stabilizes a localized radical cation and prevents interunit coupling. The UV−vis absorption spectra of ligand HCC−TTF1, Ru2(DMBA)4(NO3)2, and compound 1 are shown in Figure 4. The intense absorptions of 1 relating to the intraligand (π → π*) transition are observed in the range of 300−400 nm, which were red-shifted (ca. 60 nm) compared with the free ligand HCC−TTF1. This is reasonable since ΔE(π→π*) is lowered upon coordination to Ru2(III).23 The absorption spectrum of 1 also features two broad and weak peaks at ca. 505 nm (ε ∼ 7000 M−1 cm−1) and 700−900 nm (ε ∼ 2000 M−1 cm−1). On the basis of the comparison with Ru2(DMBA)4(NO3)2, the high-energy transition is attributed to the ligand-to-metal charge transfer from the amidinate π(N) → δ*(Ru−Ru), whereas the low-energy transition is likely assigned to the πyz*(Ru−Ru) → δ*(Ru−Ru).24 To gain further insight into the electronic interaction between the −CC−TTF1 ligands and the Ru2 core, density functional calculations at the BP8625/LanL2DZ26 level (Gaussian 03 program)27 were performed on the model compound 1′, where the terminal methylthiol groups of the −CC−TTF1 in 1 were replaced by −SH groups. While most of the optimized bond lengths and angles (see the Supporting Information) are in good agreement with the crystal structure

Figure 5. Molecular orbital diagrams for 1′ obtained from DFT calculations.

It is clear from Figure 5 that the two highest occupied MOs, namely, HOMO-1 and HOMO, are predominantly the antibonding combinations of π(Ru2) and π(CC). The HOMO-1 is the antibonding combination of πyz(Ru−Ru) and two π(CC), while the HOMO is the antibonding combination of πyz*(Ru−Ru) and two π(CC). It is noteworthy that, although formally antibonding, the πyz*8594

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(Ru−Ru) component in HOMO displays significant σ-type overlap due to the severe distortion of the equatorial coordination sphere, as noted in the prior study from our laboratory.28 The HOMO-3 and HOMO-2 are predominantly the delocalized π(TTF) orbitals with secondary contributions from πxz(Ru−Ru) and πxz*(Ru−Ru), respectively. Two π(TTF) orbitals are out-of-phase in HOMO-3, and in-phase in HOMO-2. The LUMO is dominated by δ*(Ru−Ru) and contains no contribution from −CC−TTF due to the orbital orthogonality. The LUMO+1 is mostly the contribution of two σ*(Ru−C) bonds, where two Ru dz2 have an appearance of σbonding interaction. The computed HOMO−LUMO gap is about 1.76 eV, which is comparable to that of transRu2(DMBA)4(C2Fc)2 (1.84 eV).10 Importantly, the energetic order of the occupied MOs is consistent with the assignment of redox couples in 1 and 2. The first reduction corresponds to the addition of an electron to the LUMO, the δ*(Ru2) orbital, while the second reduction would place an electron into the σ (Ru−C) orbital (LUMO+1), triggering degradation of the Ru2 species via the dissociation of the axial alkynyl ligand. The first oxidation removes an electron from the Ru2-centered HOMO, and the resultant positive charge significantly stabilizes the HOMO-1 that is also Ru2centered. Consequently, the ensuing oxidations remove the electrons from the HOMO-2 and HOMO-3, both of which are TTF-based. It should be noted that, while the calculated HOMO-2 and HOMO-3 are fully delocalized over two TTF ligands, the voltammetric studies revealed the π electrons being localized on individual TTF units. This is possibly due to the overestimation of electronic delocalization of the generalized gradient approximation (GGA) in the prediction of extended conjugated metal complexes.30

grams were recorded in 0.2 M (n-Bu)4NPF6 solution (THF, N2degassed) on a CHI620A voltammetric analyzer with a glassy carbon working electrode (diameter = 2 mm), a Pt-wire auxiliary electrode, and a Ag/AgCl reference electrode. The concentration of Ru2 species is always 1.0 mM. Synthesis of (2-(2-(4,5-Bis(methylthio)-1,3-dithiolan-2ylidene)benzo[d][1,3]dithiol-5-yl)ethynyl)trimethylsilane (Me3SiCC−TTF1). The iodo-TTF1 (507 mg, 1.07 mmol), Pd(PPh3)4 (73 mg, 0.21 mmol), CuI (38 mg, 0.21 mmol), and the trimethylsilylacetylene (0.28 mL, 2 mmol) were added to diisopropylamine (80 mL). The reaction mixture was stirred at 50 °C overnight. The solvent was removed under vacuum, and the product was purified on a silica gel column using CH2Cl2/petroleum ether (v/v = 1/20) as eluent. Me3SiCC−TTF1 was obtained as orange crystals in 65% yield. Single crystals were obtained by slow evaporation of Me3SiC C−TTF1 in CH2Cl2/MeOH (v/v = 1/1). IR (KBr, υ(CC), cm−1): 2154. 1H NMR (500 MHz, CD2Cl2, δ): 7.11 (m, 3H, benzene), 2.378 (s, 3H, SMe), 2.381 (s, 3H, SMe), 0.15 (s, 9H,TMS). EI-MS, m/z (relative intensity): 442.0 ([M]+, 100), 427.0 ([M − Me(SMe)]+, 15). Anal. Calcd for C17H18S6Si: C, 46.11; H, 4.10. Found: C, 46.33; H, 3.88. Synthesis of (2-(2-(Benzo[d][1,3]dithiol-2-ylidene)benzo[d][1,3]dithiol-5-yl)ethynyl)trimethylsilane. Yellow product Me3SiCC−TTF2 was obtained with a similar procedure as that for synthesizing Me3SiCC−TTF1 by using iodo TTF2 instead of iodo TTF1. Yield: 40%. IR (KBr, υ(CC), cm−1): 2152. 1H NMR (500 MHz, CD2Cl2, δ): 7.32 (s, 1H, benzene), 7.23 (m, 6H, benzene), 0.16 (s, 9H,TMS). EI-MS, m/z (relative intensity): 400.0 ([M]+, 100). Anal. Calcd for C19H16S4Si: C, 56.95; H, 4.02. Found: C, 57.26; H, 3.86. Synthesis of 2-(4,5-Bis(methylthio)-1,3-dithiol-2-ylidene)-5ethynylbenzo[d][1,3]dithiole (HCC−TTF1). To a solution of Me3SiCC−TTF1 (175 mg, 0.4 mmol) in 40 mL of MeOH/THF (v/v = 1/1) was added KF (139.2 mg, 2.4 mmol). The solution was stirred overnight at room temperature, and the solvent was removed under vacuum. The product was purified by silica gel column chromatography using CH2Cl2 as eluent. HCC−TTF1 was obtained as an orange powder in quantitative yield. IR (KBr, υ(C C), cm−1): 2101. 1H NMR (500 MHz, CD2Cl2, δ): 7.28 (d, 1H, J = 1.0 Hz, benzene), 7.17 (d, 1H, J = 8.0 Hz, benzene), 7.04 (dd, J = 8.0 Hz, 1.0 Hz, 1H, benzene), 3.77 (s, 1H, −CC−H), 2.483 (s, 3H, SMe), 2.480 (s, 3H, SMe). EI-MS, m/z (relative intensity): 369.9 ([M]+, 100), 354.9 ([M − Me(SMe)]+, 13). Anal. Calcd for C14H10S6: C, 45.37; H, 2.72. Found: C, 45.54; H, 2.93. Synthesis of 2-(5-Ethynylbenzo[d][1,3]dithiol-2-ylidene)benzo[d][1,3]dithiole (HCC−TTF2). Yellow powder HCC− TTF2 was obtained with a similar procedure as that for synthesizing HCC−TTF1 by using Me3SiCC−TTF2 instead of Me3SiCC− TTF1. Yield: 80%. IR (KBr, υ(CC), cm−1): 2102. 1H NMR (500 MHz, CD2Cl2, δ): 7.30 (s, 1H, benzene), 7.21−7.08 (m, 6H, benzene), 3.09 (s, 1H, −CC−H). EI-MS, m/z (relative intensity): 328.0 ([M]+, 100). Anal. Calcd for C14H10S6: C, 58.50; H, 2.45. Found: C, 58.80; H, 2.32. Synthesis of Compound 1. Ru2(DMBA)4(NO3)2 (45.7 mg, 0.05 mmol) and HCC−TTF1 (74 mg, 0.2 mmol) were added in a 50 mL Schlenk flask. THF (24 mL) and iPr2NH (4 mL) were then added into the solids under N2. The color of the solution changed rapidly from orange/green to red purple. The reaction mixture was stirred overnight. The solvent was removed under reduced pressure, and the residue was purified by silica gel column chromatography using THF/ hexane (v/v = 1/5) as eluent under N2. Compound 1 was obtained as a red-purple powder in 35% yield. Single crystals were obtained by slow diffusion of hexane into a concentrated solution of 1 in THF under N2. Data for 1: Rf = 0.5 (THF/hexane, 1/5, v/v). 1H NMR (500 MHz, CD2Cl2, δ): 7.34−7.40 (m, 12H, benzene), 6.91−6.78 (m, 12H, benzene), 6.78 (d, 2H, benzene), 3.19 (s, 24H, −NCH3), 2.32 (s, 12H, SMe). Anal. Calcd for C68H70.50N8O1.25S12Ru2: C, 50.79; H, 4.39; N, 6.97. Found: C, 51.02; H, 4.11; N, 7.18. HR-nESI-MS: [M + H]+ 1529.977, (calcd 1529.984). Visible spectra λmax (nm, ε (M−1 cm−1): 800(2000), 505(7000). FT-IR (cm−1): υ(CC), 2052 (s). Cyclic

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CONCLUSION Linear π-conjugated Ru2(DMBA)4 compounds containing axial ethynyltetrathiafulvalenes, 1 and 2, were prepared and characterized. The electronic interactions between the Ru 2 (III) core and TTF moieties were explored with voltammetry, spectroscopy, and a DFT calculation. The latter revealed strong antibonding interactions between π(Ru−Ru) and π(CC). Voltammetric studies also showed that the interaction between two TTF units across the Ru2 core is negligible due to the presence of extra benzene units. Likely, the use of ethynyltetrathiafulvalene ligands without a fused benzo group, such as −CC−TTF* (TTF* = 4,5,4′trimethyl-TTF),15 may lead to a much enhanced electronic interaction across the diruthenium core, and this hypothesis is being examined in our laboratories.

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EXPERIMENTAL SECTION

General Procedure and Materials. All reactions were carried out using Schlenk techniques. THF and diisopropylamine were distilled under a N2 atmosphere prior to use. 2-(4,5-Bis(methylthio)-1,3dithiolan-2-ylidene)-5-iodobenzo[d][1,3]dithiole (iodo TTF1) and Ru2(DMBA)4(NO3)2 were synthesized according to the literature.16,31 The IR spectra were taken on either a Vector22 Bruker spectrophotometer (400−4000 cm−1) with KBr pellets or a JASCO FT/IR-6300 spectrometer with neat samples. Elemental analyses for C, H, and N were performed on a PerkinElmer 240C analyzer. 1H NMR spectra were measured on a Bruker AM 500 spectrometer. The HR-nESI-MS spectra were performed on a modified QqTOF tandem mass spectrometer in CH2Cl2 (QSTAR XL; Applied Biosystems/MDS Sciex, Concord, ON, Canada). UV−vis spectra were measured on a UV-3100 spectrophotometer. Cyclic and differential pulse voltammo8595

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voltammogram [E1/2/V, ΔEp/V, ibackward/iforward]: L1, 0.79, 0.050, 0.66; L2, 0.99, 0.078, 1.20; A, 0.61, 0.053, 0.43; B, −0.98, 0. 058, 0.52. Synthesis of Compound 2. To a 50 mL Schlenk flask with 69.0 mg (0.075 mmol) of Ru2(DMBA)4(NO3)2 and 55 mg (0.165 mmol) of HCC−TTF2 was added 10 mL of distilled THF and 1.0 mL of Et2NH. The solution became wine red rapidly, and the reaction mixture was stirred overnight under N2. The solution was filtered through a Celite plug, and the solvents were removed on a rotovap. Compound 2 was isolated as a red solid (70 mg, 0.016 mmol, 65%) after being recrystallized from THF/MeOH. Data for 2: Rf = 0.6 (THF/hexane, 1/2, v/v). 1H NMR: 7.45 (d − 12 H, PhH), 7.10 (6H, PhH). 7.03 (d − 8H, PhH), 6.91 (2H, PhH), 7.05 (4H, PhH), 3.29 (24H, NCH3). HR-nESI-MS: [M + H]+ 1446.040 (calcd 1446.064). Visible spectra, λmax (nm, ε (M−1 cm−1): 785(5000), 499(16000). FTIR (cm−1): υ(CC), 2046 (s). Cyclic voltammogram [E1/2/V, ΔEp/ V, ibackward/iforward]: L1, 0.80, 0.057, 0.50; L2, 1.0, 0.070, 0.50; A, 0.55, 0.047, 0.30; B, −0.91, 0. 12, 1.0. Computational Methods. Ground-state geometry of model compound 1′ was fully optimized using the density functional method, generalized gradient approximation, Becke’s nonlocal correction to exchange, and Perdew’s nonlocal correction to correlation (BP86).25 Model compound 1′ was assembled based on the truncated crystal structure of compound 1. Both −SCH3 ligands in 1 were replaced by −SH, followed by full optimization. The basis set used was the LanL2DZ effective core potential26 for the metal centers and 6-31G(d,p)32 for the ligand atoms. All the calculations were performed using the Gaussian 03 program package.27 No negative frequency was observed in the vibrational frequency analysis, which indicates that these phenylacetylenic-TTF-substituted diruthenium complexes are stable equilibrium structures. Crystal Structure Determination. The data were collected on a Bruker Smart Apex CCD diffractometer equipped with graphite monochromated Mo Kα radiation (λ = 0.71073 Å) using a ω-2θ scan mode at 120 K. The highly redundant data sets were reduced using SAINT and corrected for Lorentz and polarization effects. Absorption corrections were applied using SADABS supplied by Bruker. The structure was solved by direct methods and refined by full-matrix leastsquares methods on F2 using SHELXTL-97. All non-hydrogen atoms were found in alternating difference Fourier syntheses and leastsquares refinement cycles and, during the final cycles, refined anisotropically. Hydrogen atoms were placed in calculated positions and refined as riding atoms with a uniform value of Uiso.

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preparation of this manuscript. We also thank Prof. Yi-Zhi Li for his assistance on crystallographic work.

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ASSOCIATED CONTENT

S Supporting Information *

1

H NMR spectra of compounds 1 and 2, DPVs of compound 1, DFT calculations for model compound 1′, and X-ray crystallographic details (CIF) of 1 and Me3SiCC−TTF1. This material is available free of charge via the Internet at http://pubs.acs.org.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (J.-L.Z.), [email protected] (T.R.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported, in part, by the Major State Basic Research Development Program (2013CB922101 and 2011CB808704) and the National Natural Science Foundation of China (51173075) to Nanjing University, and the National Science Foundation (CHE 1057621) and the USAF Asian Office of Aerospace Research & Development (Grant FA238612-1-4006) to Purdue University. T.R. acknowledges the IR/D support from the U.S. National Science Foundation during the 8596

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