Diruthenium Complexes of Axial Ferrocenyl−Polyynyl Ligands: The

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Organometallics 2009, 28, 2338–2341

Diruthenium Complexes of Axial Ferrocenyl-Polyynyl Ligands: The Cases of C6Fc and C8Fc Bin Xi, Guo-Lin Xu, Phillip E. Fanwick, and Tong Ren* Department of Chemistry, Purdue UniVersity, West Lafayette, Indiana 47907 ReceiVed December 31, 2008 Summary: Four Ru2(Y-DMBA)4(C2nFc)2 type compounds with n ) 3, 4 and Y-DMBA ) N,N’-dimethylbenzamidinate, N,N’dimethyl-3-methoxybenzamidinate were prepared using a weakbase protocol and characterized using Voltammetry and singlecrystal X-ray diffraction. Structural studies yielded Fc-Fc (edge-edge) separations of 22.0 and 27.1 Å for n ) 3, 4, respectiVely. The potential differences between two Fc oxidation couples were determined Via Voltammetric studies as 0.24 and 0.22 V for n ) 3, 4, respectiVely, implying the retention of strong interferrocene electronic couplings oVer extended distances. Understanding of charge-transfer processes on the nano scale has attracted intense interest from various disciplines in recent years.1-5 Conjugated organometallic compounds have been thoroughly studied as model compounds for such exploration,6-9 and extensive electronic delocalization was demonstrated for polyyn-diyl compounds capped by various transition-metal units.10,11 Prior work from our laboratory also revealed both electron (reduction) and hole (oxidation) delocalization across the polyyn-diyl bridges between diruthenium termini.12 The utility of conjugated organometallics as both molecular wires and active species of molecular devices has been explored as well.13

* To whom correspondence should be addressed. E-mail: [email protected]. Tel. 1-765-494-5466. Fax: 1-765-494-0239. (1) Barbara, P. F.; Meyer, T. J.; Ratner, M. A. J. Phys. Chem. 1996, 100, 13148. (2) Creutz, C.; Brunschwig, B. S.; Sutin, N. ComprehensiVe Coordination Chemistry II: From Biology to Nanotechnology; Elsevier/Pergamon: Oxford, U.K., and New York, 2004. (3) Adams, D. M.; Brus, L.; Chidsey, C. E. D.; Creager, S.; Creutz, C.; Kagan, C. R.; Kamat, P. V.; Lieberman, M.; Lindsay, S.; Marcus, R. A.; Metzger, R. M.; Michel-Beyerle, M. E.; Miller, J. R.; Newton, M. D.; Rolison, D. R.; Sankey, O.; Schanze, K. S.; Yardley, J.; Zhu, X. Y. J. Phys. Chem. B 2003, 107, 6668. (4) Nitzan, A.; Ratner, M. A. Science 2003, 300, 1384. (5) Albinsson, B.; Martensson, J. J. Photochem. Photobiol. C: Photochem. ReV. 2008, 9, 138. (6) Paul, F.; Lapinte, C. Coord. Chem. ReV. 1998, 178-180, 431. (7) Bruce, M. I.; Low, P. J. AdV. Organomet. Chem. 2004, 50, 179. (8) Ren, T. Organometallics 2005, 24, 4854. (9) Wong, W.-Y.; Ho, C.-L. Coord. Chem. ReV. 2006, 250, 2627. (10) Szafert, S.; Gladysz, J. A. Chem. ReV. 2003, 103, 4175. (11) (a) LeNarvor, N.; Toupet, L.; Lapinte, C. J. Am. Chem. Soc. 1995, 117, 7129. (b) Dembinski, R.; Bartik, T.; Bartik, B.; Jaeger, M.; Gladysz, J. A. J. Am. Chem. Soc. 2000, 122, 810. (c) Bruce, M. I.; Low, P. J.; Costuas, K.; Halet, J. F.; Best, S. P.; Heath, G. A. J. Am. Chem. Soc. 2000, 122, 1949. (d) Kheradmandan, S.; Heinze, K.; Schmalle, H. W.; Berke, H. Angew. Chem., Int. Ed. 1999, 38, 2270. (e) Rigaut, S.; Olivier, C.; Costuas, K.; Choua, S.; Fadhel, O.; Massue, J.; Turek, P.; Saillard, J.-Y.; Dixneuf, P. H.; Touchard, D. J. Am. Chem. Soc. 2006, 128, 5859. (12) (a) Ren, T.; Zou, G.; Alvarez, J. C. Chem. Commun. 2000, 1197. (b) Xu, G. L.; Zou, G.; Ni, Y. H.; DeRosa, M. C.; Crutchley, R. J.; Ren, T. J. Am. Chem. Soc. 2003, 125, 10057. (c) Shi, Y.; Yee, G. T.; Wang, G.; Ren, T. J. Am. Chem. Soc. 2004, 126, 10552.

In probing the degree of charge delocalization across a molecular fragment -X-, the use of ferrocenyl as the capping unit has been an effective method applicable to -X- as both organic and inorganic species.14,15 Strong electronic couplings between two ferrocene centers across a Ru2 unit were concluded on the basis of voltammetric and spectroelectrochemical studies of the Fc(CtC)n[Ru2(DMBA)4](CtC)mFc type compounds, where DMBA is N,N’-dimethylbenzamidinate and n, m ) 1, 2.16,17 The proven capacity of diruthenium units in mediating strong electronic coupling is significant for the pursuit of extended molecular wires on the basis of oligomeric [Ru2(CtC)n-]k species.8 Most significantly, the (adiabatic) electronic coupling Had was found to be ca. 2400 cm-1 for the compound with n, m ) 2, where the two Fc centers were separated by 16.6 Å.17 To further explore the distance dependence of such strong couplings, it is necessary to prepare Fc(CtC)n[Ru2(DMBA)4](CtC)mFc type compounds with n, m > 2. Reported in this contribution are the synthesis and characterization of the symmetric Fc(CtC)n[Ru2(Y-DMBA)4](CtC)nFc compounds with n ) 3 (1), 4 (2), and benzo substituent Y defined in Scheme 1.

(13) (a) Schull, T. L.; Kushmerick, J. G.; Patterson, C. H.; George, C.; Moore, M. H.; Pollack, S. K.; Shashidhar, R. J. Am. Chem. Soc. 2003, 125, 3202. (b) Blum, A. S.; Ren, T.; Parish, D. A.; Trammell, S. A.; Moore, M. H.; Kushmerick, J. G.; Xu, G.-L.; Deschamps, J. R.; Pollack, S. K.; Shashidhar, R. J. Am. Chem. Soc. 2005, 127, 10010. (c) Kim, B.; Beebe, J. M.; Olivier, C.; Rigaut, S.; Touchard, D.; Kushmerick, J. G.; Zhu, X.Y.; Frisbie, C. D. J. Phys. Chem. C 2007, 111, 7521. (d) Gauthier, N.; Argouarch, G.; Paul, F.; Humphrey, M. G.; Toupet, L.; Ababou-Girard, S.; Sabbah, H.; Hapiot, P.; Fabre, B. AdV. Mater. 2008, 20, 1952. (e) Mahapatro, A. K.; Ying, J.; Ren, T.; Janes, D. B. Nano Lett. 2008, 8, 2131. (f) Liu, K.; Wang, X. H.; Wang, F. S. ACS Nano 2008, 2, 2315. (14) Barlow, S.; O’Hare, D. Chem. ReV. 1997, 97, 637. (15) (a) Colbert, M. C. B.; Lewis, J.; Long, N. J.; Raithby, P. R.; White, A. J. P.; Williams, D. J. J. Chem. Soc., Dalton Trans. 1997, 99. (b) Jones, N. D.; Wolf, M. O.; Giaquinta, D. M. Organometallics 1997, 16, 1352. (c) Wong, W. Y.; Lu, G. L.; Choi, K. H.; Guo, Y. H. J. Organomet. Chem. 2005, 690, 177. (d) Kuo, C. K.; Chang, J. C.; Yeh, C. Y.; Lee, G. H.; Wang, C. C.; Peng, S. M. Dalton Trans. 2005, 3696. (e) Sakamoto, R.; Murata, M.; Nishihara, H. Angew. Chem., Int. Ed. 2006, 45, 4793. (f) Wei, Q. H.; Yin, G. Q.; Zhang, L. Y.; Chen, Z. N. Organometallics 2006, 25, 4941. (g) Bruce, M. I.; Humphrey, P. A.; Jevric, M.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 2007, 692, 2564. (h) Monreal, M. J.; Carver, C. T.; Diaconescu, P. L. Inorg. Chem. 2007, 46, 7226. (i) Diez, A.; Fernandez, J.; Lalinde, E.; Moreno, M. T.; Sanchez, S. Dalton Trans. 2008, 4926. (j) Koridze, A. A.; Sheloumov, A. M.; Dolgushin, F. M.; Ezernitskaya, M. G.; Rosenberg, E.; Sharmin, A.; Ravera, M. Organometallics 2008, 27, 6163. (k) Venkatasubbaiah, K.; Doshi, A.; Nowik, I.; Herber, R. H.; Rheingold, A. L.; Jakle, F. Chem. Eur. J. 2008, 14, 444. (l) Xu, G.-L.; Xi, B.; Updegraff, J. B.; Protasiewicz, J. D.; Ren, T. Organometallics 2006, 25, 5213. (m) Adams, R. D.; Qu, B.; Smith, M. D.; Albright, T. A. Organometallics 2002, 21, 2970. (16) Xu, G. L.; DeRosa, M. C.; Crutchley, R. J.; Ren, T. J. Am. Chem. Soc. 2004, 126, 3728. (17) Xu, G. L.; Crutchley, R. J.; DeRosa, M. C.; Pan, Q. J.; Zhang, H. X.; Wang, X. P.; Ren, T. J. Am. Chem. Soc. 2005, 127, 13354.

10.1021/om801227q CCC: $40.75  2009 American Chemical Society Publication on Web 03/18/2009

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Figure 1. Structural plots of [Ru2(DMBA)4](C6Fc)2 (1a) and [Ru2(DMBA)4](C8Fc)2 (2a). Scheme 1. (FcC2n)-[Ru2(Y-DMBA)4]-(C2nFc) Compounds

Scheme 2. Weak Base Protocol for Alkylnylation

Results and Discussion Synthesis. Due to the instability of H(CtC)nFc (n g 3),18 the preparation of Ru2(Y-DMBA)4(C2nFc)2 (1, n ) 3; 2, n ) 4) was based on the weak-base protocol for alkylnylation (Scheme 2),19-21 which is different from the synthesis of [Ru2(Y-DMBA)4](C2R)2 based on the reaction between Ru2(Y-DMBA)4Cl2 and LiC2R.16,17 Reactions between Ru2(Y-DMBA)4(NO3)2 and terminal alkynes H(CtC)3Fc and H(CtC)4Fc in slight excess in the presence of Et3N afforded the symmetric compounds Ru2(Y-DMBA)4(C6Fc)2 (1a,b) and Ru2(Y-DMBA)4(C8Fc)2 (2a,b), respectively, as dark red crystalline solids in excellent yields. Symmetric compounds 1 and 2 are diamagnetic and display well-resolved 1H NMR spectra. Molecular Structures. The less soluble Ru2(DMBA)4-based compounds 1a and 2a were easier to crystallize than the m-MeOsubstituted analogues 1b and 2b, and the structures of the former compounds were determined using single-crystal X-ray diffraction. Structural plots of compounds 1a and 2a are shown in Figure 1, and the selected bond lengths and angles are given in Table 1. Compounds 1a and 2a exhibit Ru2 coordination spheres nearly identical with those of the previously reported Ru2(DMBA)4(C2nFc)2 (n ) 1, 2).16,17 The Ru-Ru bond lengths are 2.4725(6) and 2.473(2) Å for compounds 1a and 2a, respectively, which are slightly longer than those reported for Ru2(DMBA)4(C2Fc)2 (2.4386(9) Å) and Ru2(DMBA)4(C4Fc)2 (18) Adams, R. D.; Qu, B.; Smith, M. D. Organometallics 2002, 21, 3867. (19) Xu, G. L.; Jablonski, C. G.; Ren, T. Inorg. Chim. Acta 2003, 343, 387. (20) Xu, G. L.; Jablonski, C. G.; Ren, T. J. Organomet. Chem. 2003, 683, 388. (21) Hurst, S. K.; Ren, T. J. Organomet. Chem. 2003, 670, 188.

(2.4472(5) Å).17 The elongation of the Ru-Ru bond is attributed to the enhanced electron deficiency at the Ru2 center with the increasing number of acetylene units. Other notable structural features include the following: (1) two ferrocenyl groups occupy the opposite axial positions, and the edge-edge distances between two Fc centers (Cω · · · Cω′) are calculated as 21.98 and 27.05 Å for compounds 1a and 2a, respectively; (2) the relative orientation between two Fc units is either close to orthogonal (1a) or almost cis to each other (2a); (3) there are structural distortions around the Ru2 core from an idealized D4h geometry that are attributed to a second-order Jahn-Teller effect.22 Voltammetric Properties of Compounds 1b and 2b. Both the cyclic voltammograms (CV) and differential pulse voltammograms (DPV) of the more soluble compounds 1b and 2b recorded in THF are shown in Figure 2, accompanied by those for the previously reported Ru2(m-MeODMBA)4(C2Fc)2 and Ru2(m-MeODMBA)4(C4Fc)2 for comparison purposes.17 The CVs and DPVs of compounds 1a and 2a are very similar to those of 1b and 2b and are presented in the Supporting Information. As discussed in the prior report, Ru2(m-MeODMBA)4(C2Fc)2 undergoes three successive one-electron oxidations, which were assigned as Ru2 based (C) and Fc based (B and A) on the basis of spectroelectrochemical studies.16,17 Upon the extension of both axial ligands by one CtC unit, the oxidation couples C and B in Ru2(m-MeODMBA)4(C4Fc)2 merged into a pseudotwo-electron couple (B + C). The same anodic behavior was observed for compounds 1b and 2b. All Ru2(mMeODMBA)4(C2nFc)2 compounds display at least one oneelectron reduction that is Ru2 based (D). It is clear from Figure 2 that this couple is progressively shifted in the anodic direction with an increase of n, reflecting the increase in electron deficiency at the Ru2 core with the increasing number of CtC units. In the case of compounds 1b and 2b, the second Ru2based reduction (E) becomes accessible in the potential window allowed by the solvent. These assignments are summarized in Scheme 3, and the related potential data are collected in Table 2. Of particular interest to us is the potential difference between couples A and B + C (∆E in Table 2). The ∆E values calculated for both 1b and 2b are comparable to those reported for shorter Ru2(m-MeODMBA)4(C2nFc)2 compounds with n ) 1, 2 (0.2-0.3 V), implying that the strong electronic coupling between two Fc groups is retained over the extended distances. However, both compounds 1b and 2b were unstable over the time scale required for spectroelectrochemical measurements, which prevented quantitative assessment of the electronic couplings (Had) in compounds 1 and 2. In conclusion, we prepared and characterized two new diruthenium compounds bearing extended ferrocenyl-polyynyl axial ligands with Fc · · · Fc separations up to 27 Å. Significant interferrocene electronic coupling was inferred from the voltammetric data of compounds 1 and 2, which validates the proposal of achieving molecular wires based on dirutheniumalkynyl oligomers.

Experimental Section Ru2(DMBA)4(NO3)2 and Ru2(m-MeODMBA)4(NO3)2 were prepared as previously described.19,23 1-Ferrocenyl-6-(triethylsilyl)1,3,5-hexatriyne (FcC6SiEt3) and 1-ferrocenyl-8-(triethylsilyl)1,3,5,7-octatetrayne (FcC8SiEt3) were prepared using the Cadiot(22) Lin, C.; Ren, T.; Valente, E. J.; Zubkowski, J. D. J. Chem. Soc., Dalton Trans. 1998, 571. (23) Xu, G.-L.; Campana, C.; Ren, T. Inorg. Chem. 2002, 41, 3521.

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Notes

Table 1. Selected Bond Lengths (Å) and Angles (deg) for Compounds 1a and 2a 1a

2a

Ru1-Ru2 Ru1-N214 Ru1-N224 Ru1-N234 Ru1-N244 Ru1-C1 C1-C2 C2-C3 C3-C4 C4-C5 C5-C6 Cω · · · Cω′a

2.4725(6) 1.984(4) 2.201(4) 2.133(4) 2.067(4) 1.937(5) 1.231(7) 1.379(7) 1.196(7) 1.382(8) 1.197(8) 21.98

Ru2-N212 Ru2-N222 Ru2-N232 Ru2-N242 Ru2-C7 C7-C8 C8-C9 C9-C10 C10-C11 C11-C12

2.104(4) 2.084(4) 1.989(4) 1.987(4) 1.953(5) 1.227(7) 1.377(7) 1.203(7) 1.372(7) 1.204(7)

C1-Ru1-Ru2 N214-Ru1-Ru2 N224-Ru1-Ru2 N234-Ru1-Ru2 N244-Ru1-Ru2

162.9(2) 94.0(1) 90.2(1) 82.8(1) 77.6(1)

C7-Ru2-Ru1 N212-Ru2-Ru1 N222-Ru2-Ru1 N232-Ru2-Ru1 N242-Ru2-Ru1

165.3(2) 78.6(1) 82.0(1) 94.5(1) 90.2(1)

N212-Ru2-Ru1-N214 N222-Ru2-Ru1-N224 N232-Ru2-Ru1-N234 N242-Ru2-Ru1-N244

20.9(2) 21.0(2) 21.8(2) 18.4(2)

a

Ru1-Ru2 Ru1-N1 Ru1-N3 Ru1-N5 Ru1-N7 Ru1-C1 C1-C2 C2-C3 C3-C4 C4-C5 C5-C6 C6-C7 C7-C8 Cω · · · Cω′

2.473(2) 1.99(1) 2.06(1) 2.02(1) 2.08(1) 1.89(2) 1.21(2) 1.49(2) 1.19(2) 1.29(2) 1.25(2) 1.38(3) 1.17(2) 27.05

Ru2-N2 Ru2-N4 Ru2-N6 Ru2-N8 Ru2-C9 C9-C10 C10-C11 C11-C12 C12-C13 C13-C14 C14-C15 C15-C16

2.08(1) 1.99(1) 2.08(1) 2.03(1) 1.96(2) 1.25(2) 1.34(2) 1.17(2) 1.30(2) 1.27(2) 1.40(3) 1.17(2)

C1-Ru1-Ru2 N1-Ru1-Ru2 N3-Ru1-Ru2 N5-Ru1-Ru2 N7-Ru1-Ru2

167.0(5) 92.5(4) 81.8(4) 92.2(4) 81.1(3)

C9-Ru2-Ru1 N2-Ru2-Ru1 N4-Ru2-Ru1 N6-Ru2-Ru1 N8-Ru2-Ru1

166.5(4) 81.0(4) 92.1(4) 80.8(3) 91.3(4)

N1-Ru1-Ru2-N2 N3-Ru1-Ru2-N4 N5-Ru1-Ru2-N6 N7-Ru1-Ru2-N8

19.2(5) 17.4(5) 19.6(5) 20.4(5)

Cω and Cω′ denote the Cp carbon atoms covalently bonded to the CtC unit.

Scheme 3. Assigment of Redox Couples Observed in [Ru2(Y-DMBA)4](C2nFc)2

Table 2. Electrode Potentials (V) of 1b and 2b from DPV Measurements

Chodkiewicz coupling reaction (see the Supporting Information).24,25 THF was distilled over Na/benzophenone under an N2 atmosphere prior to use. 1H NMR spectra were recorded on a Varian 300 NMR spectrometer with chemical shifts (δ) referenced to the residual

[Fc-Fc]+2/+ Ru27+/6+ Ru26+/5+ Ru25+/4+ E(A) (A) and [Fc-Fc]+/0 (B + C) (D) (E) E(B + C) 1b 2b

0.972 1.008

0.732 0.788

-0.752 -0.648

-1.688 -1.528

0.240 0.220

CHCl3. Vis-NIR spectra were acquired in THF using a JASCO V-670 UV-vis-NIR spectrophotometer. Infrared spectra were recorded on a JASCO FT/IR-ATR 6300 spectrometer. Elemental analysis was performed by Atlantic Microlab, Norcross, GA. Both cyclic and differential pulse voltammograms were recorded in 0.20 M (n-Bu)4NPF6 solution (THF, N2 degassed) 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 diruthenium species is always 1.0 mM. The ferrocenium/ferrocene couple was observed at 0.568 V (vs Ag/AgCl) under experimental conditions. Preparation of Ru2(DMBA)4(C6Fc)2 (1a). To a 30 mL THF/ CH3OH (2/1 v/v) solution of FcC6SiEt3 (0.075 g, 0.20 mmol) was added K2CO3 (0.5 g), and the mixture was stirred for 20 min, followed by the addition of 40 mL of a THF solution of Ru2(DMBA)4(NO3)2 (0.070 g, 0.077 mmol) and Et3N (ca. 1 mL) to yield a dark red solution. The reaction mixture was stirred in air for 1 h and then filtered through a 2 cm silica gel pad. After the solvent removal, the residue was washed with copious amount of hexanes and dried under vacuum to yield 0.096 g of red powder (96% based on Ru). Data for 1a are as follows. Rf 0.45 (THF/ hexanes/Et3N ) 1/2/0.1); Anal. Found (calcd) for C68H62Fe2N8Ru2: C, 62.58 (62.58); H, 4.91 (4.75); N, 8.37 (8.59). MS-FAB (m/e, based on 101Ru): 1305 [M+]. 1H NMR: 7.41 (s, 12H, benzene), 6.95-6.92 (m, 8H, benzene), 4.38 (s, 4H, Fc), 4.15 (s, 14H, Fc), 3.21 (s, 24H, CH3N). Vis-NIR (λmax, nm (ε, M-1 cm-1)): 888 (4500), 523 (35 800). IR (ν(CtC), cm-1): 2109 (s), 1995 (s). Figure 2. DPVs (thick lines) and CVs (thin lines) of Ru2(mMeODMBA)4(C2nFc)2 (n ) 1-4) recorded in 0.20 M THF solutions of Bu4NPF6. All CVs were recorded at the same scan rate of 100 mV/s.

(24) Siemsen, P.; Livingston, R. C.; Diederich, F. Angew. Chem., Int. Ed. 2000, 39, 2632. (25) Bartik, B.; Dembinski, R.; Bartik, T.; Arif, A. M.; Gladysz, J. A. New J. Chem. 1997, 21, 739.

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Organometallics, Vol. 28, No. 7, 2009 2341

Table 3. Crystallographic Parameters for Compounds 1a · 1.5C4H8O and 2a · 0.79C6H4Cl2 empirical formula formula wt space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z dcalcd (g cm-3) µ (mm-1) T (K) no. of data/restraints/ params R1, wR2

1a · 1.5C4H8O

2a · 0.79C6H4Cl2

C74H74Fe2N8O1.50Ru2 1413.30 P1j 17.2957(13) 19.5103(14) 21.763(3) 88.027(7) 84.001(4) 85.140(4) 7274.8(12) 4 1.290 0.835 150 24 964/0/1592

C76.78H65.16Cl1.58Fe2N8Ru2 1469.32 P1j 11.0311(7) 18.9355(16) 21.081(2) 70.969(9) 80.291(5) 78.288(3) 4051.1(6) 2 1.204 0.802 150 7511/6/787

0.059, 0.137

0.089, 0.211

Preparation of Ru2(m-MeODMBA)4(C6Fc)2 (1b). Compound 1b was prepared using the same procedure as for 1a with Ru2(DMBA)4(NO3)2 being replaced by Ru2(m-MeODMBA)4(NO3)2 in a yield of 90%. Data for 1b are as follows. Rf 0.54 (THF/hexanes/ Et3N ) 1/1/0.1). Anal. Found (calcd) for C72H70Fe2N8O4Ru2 · 3H2O: C, 58.13 (58.65); H, 5.18 (5.16); N, 8.17 (7.60). MS-ESI (m/e, based on 101Ru): 1426 [M+]. 1H NMR: 7.37 (t, 4H, benzene), 6.98-6.95 (m, 4H, benzene), 6.55-6.47 (m, 8H, benzene), 4.41 (t, 4H, Fc), 4.18-4.17 (m, 14H, Fc), 3.83 (s, 12H, OCH3), 3.24 (s, 24H, CH3N. Vis-NIR (λmax, nm (ε, M-1 cm-1)): 884 (1900), 521 (15 700). IR (ν(CtC), cm-1): 2113 (s), 1997 (s). Preparation of Ru2(DMBA)4(C8Fc)2 (2a). To a 30 mL THF/ CH3OH (2/1, v/v) solution of FcC8SiEt3 (0.080 g, 0.20 mmol) was added K2CO3 (0.5 g), and the mixture was stirred for 20 min, followed by the addition of 40 mL of a THF solution of Ru2(DMBA)4(NO3)2 (0.070 g, 0.077 mmol) and Et3N (1 mL) to yield a dark red solution. The reaction mixture was stirred in air for 1 h and then filtered through a 2 cm silica gel pad. After the solvent removal, the residue was washed with copious amount of hexanes and dried under vacuum to yield 0.070 g of red powder (68% based on Ru). Data for 2a: are as follows. Rf 0.35 (THF/ hexanes/Et3N ) 1/2/0.1). Anal. Found (calcd) for C72H62Fe2N8Ru2: C, 63.59 (63.91); H, 4.65 (4.59); N, 8.12 (8.29). 1H NMR: 7.47-7.44 (m, 12H, benzene), 6.98-6.94 (m, 8H, benzene), 4.46

(t, 4H, Fc), 4.23 (s, 10H, Fc), 4.21 (t, 4H, Fc), 3.22 (s, 24H, CH3N). Vis-NIR (λmax, nm (ε, M-1 cm-1)): 873 (2870), 520 (31 300). IR (ν(CtC), cm-1): 2175 (m), 2110 (w), 2072 (s), 1977 (s). Preparation of Ru2(m-MeODMBA)4(C8Fc)2 (2b). Compound 2b was prepared using the same procedure as for 2a with Ru2(DMBA)4(NO3)2 being replaced by Ru2(m-MeODMBA)4(NO3)2 in a yield of 80%. Data for 2b are as follows. Rf 0.49 (THF/hexanes/ Et3N ) 1/1/0.1). Anal. Found (calcd) for C76H70Fe2N8O4Ru2 · 2H2O: C, 60.89 (60.97); H, 4.83 (4.90); N, 7.25 (7.42). 1H NMR: 7.39 (t, 4H, benzene), 6.98-6.96 (m, 3H, benzene), 6.55-6.47 (m, 11H, benzene), 4.48 (t, 8H, Fc), 4.24-4.23 (m, 10H, Fc), 3.84-3.81 (m, 12H, OCH3), 3.23 (s, 24H, CH3N). Vis-NIR (λmax, nm (ε, M-1 cm-1)): 872 (1600), 515 (17 400). IR (ν(CtC), cm-1): 2174 (m), 2111 (w), 2070 (s), 1974 (s). X-ray Data Collection, Processing, and Structure Analysis and Refinement. Single crystals were grown Via slow diffusion of a THF solution with hexanes and slow evaporation of a dichlorobenzene solution for 1a and 2a, respectively. The X-ray intensity data were collected at 150 K on a Nonius KappaCCD X-ray diffractometer system using Mo KR radiation (λ ) 0.710 73 Å). The structures were solved by direct methods using SIR2004 and refined using SHELX-97 in the space group P1j for both 1a and 2a.26 The occupancy of dichlorobenzene in 2a was refined using a free variable and refined to 0.790(10). Relevant information on the data collection and the figures of merit of final refinement are given in Table 3.

Acknowledgment. Financial support from the National Science Foundation (Grant No. CHE 0715404) and Purdue University is gratefully acknowledged. We also thank Prof. R. J. Crutchley for a preliminary examination of the spectroelectrochemical behaviors of compounds 1b and 2b. Supporting Information Available: Text and figures giving preparations of FcC6SiEt3 and FcC8SiEt3 and vis-NIR spectra and voltammograms of compounds 1a,b and 2a,b and CIF files giving X-ray crystallographic data for the structure determinations of compounds 1a and 2a. This material is available free of charge via the Internet at http://pubs.acs.org. OM801227Q (26) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112.