Syntheses, Structures, and Properties of Tricarbonyl (Chloro) Rhenium

State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructures, School of Chemistry and Chemical Engineering, Nanjing ...
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Organometallics 2009, 28, 755–762

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Syntheses, Structures, and Properties of Tricarbonyl (Chloro) Rhenium(I) Complexes with Redox-Active Tetrathiafulvalene-Pyrazole Ligands Wei Liu,† Jing Xiong,† Yong Wang,‡ Xin-Hui Zhou,† Ru Wang,† Jing-Lin Zuo,*,† and Xiao-Zeng You† State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructures, School of Chemistry and Chemical Engineering, Nanjing UniVersity, Nanjing 210093, P. R. China, and Institute of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Nanjing UniVersity, Nanjing, 210093, P. R. China ReceiVed September 22, 2008

A series of new tetrathiafulvalene-substituted 3,5-dimethylpyrazole ligands, 4-[{2,6,7-tris(methylthio)TTF-3-yl}thio]-3,5-dimethylpyrazole (MTSPz*, Pz* ) 3,5-dimethylpyrazole, 4a), 4-[{6,7-benzo-2(methylthio)-TTF-3-yl}thio]-3,5-dimethylpyrazole (BTSPz*, 4b), 4-[{6,7-(ethylenedithio)-2-(methylthio)TTF-3-yl}thio]-3,5-dimethylpyrazole (ETSPz*, 4c) and 4-[{6,7-(propylenedithio)-2-(methylthio)-TTF3-yl}thio]-3,5-dimethylpyrazole (PTSPz*, 4d), have been prepared by an efficient synthetic route. Further coordination reactions of the respective ligands with Re(CO)5Cl afford new rhenium(I) tricarbonyl chloro complexes, ClRe(CO)3(MTSPz*)2 (5a), ClRe(CO)3(BTSPz*)2 (5b), ClRe(CO)3(ETSPz*)2 (5c) and ClRe(CO)3(PTSPz*)2 (5d). The crystal structures of the ligand 4d and complexes 5b-d have been determined by X-ray crystallography, showing nearly planar TTF units in these compounds, and the distorted octahedral geometry in all complexes. The absorption spectra and multiredox behaviors of these new compounds (4a-d, 5a-d) have been studied, and are rationalized based on density functional theory. The results suggest that the novel redox-active tetrathiafulvalene-pyrazole ligands are useful for the syntheses of new metal complexes. Introduction In the past decade, the synthesis and coordination chemistry of redox-active ligands containing tetrathiafulvalene (TTF) core have attracted the attention of many researchers, due to their potential applications as versatile organic-inorganic hybrid building blocks.1 The association of the TTF units with the metal ions can be achieved by covalent linkages, which provide novel perspective modulations of the molecular architecture, as well as the electronic properties. To date, a variety of mono- or polydentate coordinating functional groups, including pyridine and bipyridine,2-4 dithiolate,5,6 phosphine,7 crown ethers,8,9 * To whom correspondence should be addressed. E-mail: [email protected]. Fax: +86-25-83314502. † State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructures, School of Chemistry and Chemical Engineering, Nanjing University. ‡ Institute of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Nanjing University. (1) (a) Tanaka, H.; Okano, Y.; Kobayashi, H.; Susuki, W.; Kobayashi, A. Science 2001, 291, 285. (b) Uzelmeier, C. E.; Bartley, S. L.; Fourmigue´, M.; Rogers, R.; Grandinetti, G.; Dunbar, K. R. Inorg. Chem. 1998, 37, 6706, and references cited therein. (2) (a) Iwahori, F.; Golhen, S.; Ouahab, L.; Carlier, R.; Sutter, J.-P. Inorg. Chem. 2001, 40, 6541. (b) Ouahab, L.; Iwahori, S.; Golhen, S.; Carlier, R.; Sutter, J.-P. Synth. Met. 2003, 133, 505. (c) Setifi, F.; Ouahab, L.; Golhen, S.; Yoshida, Y.; Saito, G. Inorg. Chem. 2003, 42, 1791. (3) (a) Liu, S.-X.; Dolder, S.; Franz, P.; Neels, A.; Stoeckli-Evans, H.; Decurtins, S. Inorg. Chem. 2003, 42, 4801. (b) Liu, S.-X.; Dolder, S.; Pilkington, M.; Decurtins, S. J. Org. Chem. 2002, 67, 3160. (c) Liu, S.-X.; Dolder, S.; Rusanov, E. B.; Stoeckli-Evans, H.; Decurtins, S. C. R. Chim. 2003, 6, 657. (4) Devic, T.; Avarvari, N.; Batail, P. Chem. Eur. J. 2004, 10, 3697. (5) Kobayashi, A.; Fujiwara, E.; Kobayashi, H. Chem. ReV. 2004, 104, 5243. references cited therein.

acetylacetonate,10 Schiff-base,11a and DNA11b have been attached to the TTF moiety, and the corresponding metal complexes have been reported. Monodentate pyrazole group, a unique two-nitrogen heterocycle, could act as versatile ligands as well as intra- or intermolecular hydrogen-bonding donors.12 In addition, the (6) Wen, H. R.; Li, C. H.; Song, Y.; Zuo, J. L.; Zhang, B.; You, X. Z. Inorg. Chem. 2007, 46, 6837. (7) (a) Fourmigue´, M.; Batail, P. Bull. Soc. Chim. Fr. 1992, 129, 29. (b) Fourmigue´, M.; Uzelmeier, C. E.; Boubekeur, K.; Bartley, S. L.; Dunbar, K. R. J. Organomet. Chem. 1997, 529, 343. (c) Smucker, B. W.; Dunbar, K. R. J. Chem. Soc., Dalton Trans. 2000, 1309. (d) Cerrada, E.; Diaz, C.; Diaz, M. C.; Hursthouse, M. B.; Laguna, M.; Light, M. E. J. Chem. Soc., Dalton Trans. 2002, 1104. (e) Avarvari, N.; Martin, D.; Fourmigue´, M. J. Organomet. Chem. 2002, 643-644, 292. (f) Pellon, P.; Gachot, G.; Le Bris, J.; Marchin, S.; Carlier, R.; Lorcy, D. Inorg. Chem. 2003, 42, 2056. (g) Devic, T.; Batail, P.; Fourmigue´, M.; Avarvari, N. Inorg. Chem. 2004, 43, 3136. (h) Avarvari, N.; Fourmigue´, M. Chem. Commun. 2004, 1300, and references cited therein. (8) Le Derf, F.; Mazari, M.; Mercier, N.; Levillain, E.; Trippy, G.; Riou, A.; Richomme, P.; Becher, J.; Garin, J.; Orduna, J.; Gallego-Planas, N.; Gorgues, A.; Sally, M. Chem. Eur. J. 2001, 7, 447. (9) (a) Ji, Y.; Zhang, R.; Li, Y. J.; Li, Y. Z.; Zuo, J. L.; You, X. Z. Inorg. Chem. 2007, 46, 866. (b) Liu, W.; Lu, J. H.; Ji, Y.; Zuo, J. L.; You, X. Z. Tetrahedron Lett. 2006, 47, 3431. (10) (a) Massue, J.; Bellec, N.; Chopin, S.; Levillain, E.; Roisnel, T.; Cle´rac, R.; Lorcy, D. Inorg. Chem. 2005, 44, 8740. (b) Zhu, Q.-Y.; Bian, G.-Q.; Zhang, Y.; Dai, J.; Zhang, D.-Q.; Lu, W. Inorg. Chim. Acta 2006, 359, 2303. (c) Bellec, N.; Massue, J.; Roisnel, T.; Lorcy, D. Inorg. Chem. Commun. 2007, 10, 1172. (d) Bellec, N.; Lorcy, D. Tetrahedron Lett. 2001, 42, 3189. (11) (a) Wu, J.-C.; Liu, S.-X.; Keene, T. D.; Neels, A.; Mereacre, V.; Powell, A. K.; Decurtins, S. Inorg. Chem. 2008, 47, 3452. (b) Bouquin, N.; Malinovskii, V. L.; Gue´gano, X.; Liu, S.-X.; Decurtins, S.; Ha¨ner, R. Chem. Eur. J. 2008, 14, 5732. (12) Pe´rez, J.; Riera, L. Chem. Commun. 2008, 533, and references cited therein.

10.1021/om800919u CCC: $40.75  2009 American Chemical Society Publication on Web 01/06/2009

756 Organometallics, Vol. 28, No. 3, 2009 Scheme 1. Structures of Ligands 4a-d

deprotonated forms of pyrazole, namely pyrazolato anions, usually serve as bridging ligand to construct polynuclear complexes.13 Therefore, the TTF derivatives fused with such type of groups can be favorable ligands for exploring hybrid molecule materials with the combination of different physical properties, and we call them as multifunctional materials. However, to the best of our knowledge, there is no TTF-pyrazole metal complex reported so far. The tricarbonyl (chloro) rhenium(I) complexes are wellknown to be air stable and display unique photophysical and photochemical properties.14-20 Recently, we have successfully prepared a series of luminescent sulfur-rich metal complexes, which combine metal-to-ligand charge transfer (MLCT) luminophores of rhenium(I) system with 1,3-dithiole-2-ylidene (13) See for examples: (a) Murray, H. H.; Raptis, R. G.; Fackler, J. P., Jr Inorg. Chem. 1988, 27, 26. (b) Umakoshi, K.; Yamauchi, Y.; Nakamiya, K.; Kojima, T.; Yamasaki, M.; Kawano, H.; Onishi, M. Inorg. Chem. 2003, 42, 3907, and references cited therein. (14) See for examples: (a) Wrighton, M.; Morse, D. L. J. Am. Chem. Soc. 1974, 96, 998. (b) Lucia, L. A.; Abboud, K.; Schanze, K. S. Inorg. Chem. 1997, 36, 6224. (c) Stufkens, D. J.; Vlcˇek, A., Jr Coord. Chem. ReV. 1998, 177, 127. (d) Tapolsky, G.; Duesing, R.; Meyer, T. J. Inorg. Chem. 1990, 29, 2285. (e) Wallace, L.; Woods, C.; Rillema, D. P. Inorg. Chem. 1995, 34, 2875. (f) Yam, V. W. W.; Lau, V. C. Y.; Cheung, K. K. J. Chem. Soc., Chem. Commun. 1995, 259. (g) Yam, V. W. W.; Lo, W. Y.; Lam, C. H.; Fung, W. K. M.; Wong, K. M. C.; Lau, V. C. Y.; Zhu, N. Coord. Chem. ReV. 2003, 245, 39. (h) Gabrielsson, A.; Hartl, F.; Zhang, H.; Lindsay Smith, J. R.; Towrie, M.; Vlcˇek, A., Jr.; Perutz, R. N. J. Am. Chem. Soc. 2006, 128, 4253. (i) Berger, S.; Klein, A.; Kaim, W.; Fiedler, J. Inorg. Chem. 1998, 37, 5664. (15) See for examples: (a) Lo, K. K. W.; Tsang, K. H. K.; Zhu, N. Organometallics 2006, 25, 3220. (b) Busby, M.; Matousek, P.; Towrie, M.; Clark, I. P.; Motevalli, M.; Hartl, F.; Vlcˇek, A., Jr Inorg. Chem. 2004, 43, 4523. (c) Wei, L.; Babich, J. W.; Ouellette, W.; Zubieta, J. Inorg. Chem. 2006, 45, 3057. (d) Wang, K. Z.; Huang, L.; Gao, L. H.; Jin, L. P.; Huang, C. H. Inorg. Chem. 2002, 41, 3353. (e) Yam, V. W. W.; Ko, C. C.; Zhu, N. J. Am. Chem. Soc. 2004, 126, 12734. (16) See, for examples: (a) Koike, K.; Okoshi, N.; Hori, H.; Takeuchi, K.; Ishitani, O.; Tsubaki, H.; Clark, I. P.; George, M. W.; Johnson, F. P. A.; Turner, J. J. J. Am. Chem. Soc. 2002, 124, 11448. (b) Tsubaki, H.; Sekine, A.; Ohashi, Y.; Koike, K.; Takeda, H.; Ishitani, O. J. Am. Chem. Soc. 2005, 127, 15544. (c) Marti, N.; Spingler, B.; Breher, F.; Schibli, R. Inorg. Chem. 2005, 44, 6082. (d) de Silva, A. P.; Gunaratne, N.; Gunnlaugsson, T.; Huxley, A. J. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T. E. Chem. ReV. 1997, 97, 1515. (e) Stufkens, D. J.; Vlcˇek, A., Jr. Coord. Chem. ReV. 1998, 117, 127. (f) Lees, A. J. Chem. ReV. 1987, 87, 711. and further references therein. (17) See, for examples: (a) Pomestchenko, I. E.; Polyansky, D. E.; Castellano, F. N. Inorg. Chem. 2005, 44, 3412. (b) Lam, S. C. F.; Yam, V. W. W.; Wong, K. M. C.; Cheng, E. C. C.; Zhu, N. Organometallics 2005, 24, 4298. (c) Gabrielsson, A.; Hartl, F.; Zhang, H.; Lindsay Smith, J. R.; Towrie, M.; Vle˘k, A., Jr.; Perutz, R. N. J. Am. Chem. Soc. 2006, 128, 4253. (d) Coe, B. J.; Curati, N. R. M.; Fitzgerald, E. C.; Coles, S. J.; Horton, P. N.; Light, M. E.; Hursthouse, M. B. Organometallics 2007, 26, 2318. (18) See, for examples: (a) Reger, D. L.; Watson, R. P.; Smith, M. D.; Pellechia, P. J. Organometallics 2005, 24, 1544. (b) Wei, Q. H.; Yin, G. Q.; Zhang, L. Y.; Chen, Z. N. Inorg. Chem. 2006, 45, 10371. (c) Cattaneo, M.; Fagalde, F.; Katz, N. E. Inorg. Chem. 2006, 45, 6884. (d) de Wolf, P.; Waywell, P.; Hanson, M.; Heath, S. L.; Meijer, A. J. H. M.; Teat, S. J.; Thomas, J. A. Chem. Eur. J. 2006, 12, 2188.

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derivatives.21 We are also interested in the further studies on the possible incorporation of redox-active TTF units, which exhibit more delocalized structures than the 1,3-dithiole-2ylidene precursors. It is envisaged that the π-electron donating TTF units included in complexes would retain two reversible consecutive one-electron redox processes with very accessible potentials. In this paper, a new class of TTF-pyrazole type ligands (Scheme 1), MTSPz* (4a), BTSPz* (4b), ETSPz* (4c), and PTSPz* (4d), have been successfully synthesized. The reactions of the respective ligands with Re(CO)5Cl afford new tricarbonyl (chloro) rhenium(I) complexes, ClRe(CO)3(MTSPz*)2 (5a), ClRe(CO)3(BTSPz*)2 (5b), ClRe(CO)3(ETSPz*)2 (5c), and ClRe(CO)3(PTSPz*)2 (5d). Herein, we present the syntheses, spectroscopic and electrochemical properties of these new compounds, and describe the structures of some typical complexes.

Experimental Section General Procedures. The IR spectra were taken on a Vector22 Bruker spectrophotometer (400-4000 cm-1) with KBr pellets. Absorption spectra were measured on a UV-3100 spectrophotometer. Elemental Analyses for C, H, and N were performed on a Perkin-Elmer 240C analyzer. Cyclic voltammetry was performed on a CHI660b electrochemical analytical instrument, with platinum as the working and counter electrodes, Ag/Ag+ as the reference electrode, and n-Bu4NClO4 (0.2 M for 4 and 0.1 M for 5) as the supporting electrolyte. 1H NMR spectra were measured on a Bruker AM 500 spectrometer. ESI-MS spectra were recorded on a Varian MAT 311A instrument. 2,6,7-tris(methylthio)-3-(cyanoethylthio)-1,4,5,8-tetrathiafulvalene (2a), 2-(methylthio)-3-(cyanoethylthio)-6,7-benzo-1,4,5,8-tetrathiafulvalene (2b), 2-(methylthio)-3-(cyanoethylthio)-6,7-(ethylenedithio)-1,4,5,8-tetrathiafulvalene (2c), 2-(methylthio)-3-(cyanoethylthio)-6,7-(propylenedithio)-1,4,5,8-tetrathiafulvalene (2d), 3-[{2,6,7-tris(methylthio)-TTF-3-yl}thio]pentane-2,4-dione (3a), 3-[{6,7-benzo-2-(methylthio)-TTF-3-yl}thio]pentane-2,4-dione (19) See, for examples: (a) Wong, K. M. C.; Lam, S. C. F.; Ko, C. C.; Zhu, N.; Yam, V. W. W.; Roue´, S.; Lapinte, C.; Fathallah, S.; Costuas, K.; Kahlal, S.; Halet, J. F. Inorg. Chem. 2003, 42, 7086. (b) Azo´car, M. I.; Mikelsons, L.; Ferraudi, G.; Moya, S.; Guerrero, J.; Aguirre, P.; Martinez, C. Organometallics 2004, 23, 5967. (20) See, for examples: (a) Kennedy, F.; Shavaleev, N. M.; Koullourou, T.; Bell, Z. R.; Jeffery, J. C.; Faulkner, S.; Ward, M. D. J. Chem. Soc., Dalton Trans. 2007, 1492. (b) Shavaleev, N. M.; Accorsi, G.; Virgili, D.; Bell, Z. R.; Lazarides, T.; Calogero, G.; Armaroli, N.; Ward, M. D. Inorg. Chem. 2005, 44, 61. (c) Ku¨hn, F. E.; Zuo, J. L.; Fabrizi de Biani, F.; Santos, A. M.; Zhang, Y.; Zhao, J.; Sandulachea, A.; Herdtweck, E. New. J. Chem. 2004, 28, 43. (21) (a) Liu, W.; Wang, R.; Zhou, X. H.; Zuo, J. L.; You, X. Z. Organometallics 2008, 27, 126. (b) Liu, W.; Chen, Y.; Wang, R.; Zhou, X. H.; Zuo, J. L.; You, X. Z. Organometallics 2008, 27, 2990. (22) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision B.04; Gaussian, Inc.: Wallingford, CT, 2004. (23) (a) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 37, 785. (b) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989, 157, 200. (c) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.

Tricarbonyl (Chloro) Rhenium(I) Complexes

Organometallics, Vol. 28, No. 3, 2009 757

Scheme 2. Synthetic Routes to Complexes 5a-d

Table 1. Crystallographic Data for Complexes 4d, 5b-d empirical formula Mr cryst syst space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z Fc (g cm-3) F(000) T/K µ(Mo KR)/ mm-1 index ranges GOF (F2) R1a, wR2b (I > 2σ(I)) R1a, wR2b (all data) a

4d · CH3OH

5b

5c · 2H2O

5d · H2O

C16H20N2OS8 512.82 triclinic P1j 7.9103(13) 12.213(2) 12.503(2) 85.206(3) 80.115(3) 71.614(3) 1128.7(3) 2 1.509 532 293(2) 0.802 -9 e h e 8 -13 e k e 14 -14 e l e 13 1.058 0.0647, 0.1267 0.0912, 0.1358

C35H28ClN4O3ReS12 1158.98 triclinic P1j 13.3502(11) 13.4076(11) 13.5947(11) 76.8690(10) 68.1570(10) 87.3180(10) 2197.7(3) 2 1.751 1148 293(2) 3.436 -6 e h e 16 -16 e k e 16 -16 e l e 16 1.098 0.0329, 0.0817 0.0349, 0.0825

C31H32ClN4O5ReS16 1275.22 triclinic P1j 14.886(3) 15.115(3) 24.448(5) 78.393(4) 78.397(4) 72.951(4) 5091.9(17) 4 1.663 2536 293(2) 3.135 -17 e h e 17 -17 e k e 16 -28 e l e 13 0.964 0.0744, 0.1581 0.2184, 0.1798

C33H34ClN4O4ReS16 1285.25 monoclinic P21/c 15.888(2) 30.026(4) 13.2625(17) 90.000 90.204(2) 90.000 6326.9(14) 4 1.349 2560 293(2) 2.523 -18 e h e 18 -33 e k e 35 -15 e l e 15 1.029 0.0821, 0.2273 0.1207, 0.2473

R1 ) Σ|C| - |Fc|/ΣFo|. b wR2 ) [Σw(Fo2 - Fc2)2/Σw(Fo2)]1/2.

Table 2. Selected Bond Distances (Å) and Angles (deg) for 4d C(4)-C(5) C(8)-C(9) C(12)-N(1) C(14)-N(2) C(8)-S(7)-C(10)

1.344(6) 1.334(6) 1.333(6) 1.332(5) 101.7(3)

C(6)-C(7) C(11)-C(12) N(1)-N(2) C(11)-C(14) C(11)-S(8)-C(9)

1.339(6) 1.404(6) 1.349(5) 1.383(7) 103.8(2)

(3b), and 3-[{6,7-(ethylenedithio)-2-(methylthio)-TTF-3-yl}thio]pentane-2,4-dione (3c) were synthesized in high yields according to literature methods.10

3-[{6,7-(Propylenedithio)-2-(methylthio)-TTF-3-yl}thio]pentane2,4-dione (3d). Under a nitrogen atmosphere, to a solution of 2d (964 mg, 2.5 mmol) in 25 mL of THF, a solution of CsOH · H2O (403 mg, 3 mmol) in 6 mL of CH3OH was added dropwise at room temperature. The mixture was allowed to stir for 30 min and 3-chloro-2,4-pentanedione (0.36 mL, 3 mmol) was added. The reaction mixture was stirred overnight. Then the solvent was evaporated, and the orange residue was extracted with CH2Cl2 and washed with water. The organic extract was purified by column chromatography (CH2Cl2/petroleum ether) on silica gel. After

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Figure 1. ORTEP view of compound 4d with an atom-numbering scheme. The thermal ellipsoids are drawn at the 30% probability level. Table 3. Selected Bond Distances (Å) and Angles (deg) for 5b Re(1)-N(1) Re(1)-C(1) Re(1)-C(3) N(1)-N(2) C(10)-C(11) C(14)-C(15) C(16)-C(17) C(18)-C(19) C(26)-C(27) N(3)-Re(1)-N(1) C(2)-Re(1)-N(3)

2.222(4) 1.899(4) 2.195(3) 1.360(5) 1.327(6) 1.399(6) 1.377(7) 1.379(7) 1.342(6) 84.51(13) 173.99(16)

Re(1)-N(3) Re(1)-C(2) Re(1)-Cl(1) N(3)-N(4) C(12)-C(13) C(15)-C(16) C(17)-C(18) C(14)-C(19) C(28)-C(29) C(1)-Re(1)-N(1) C(3)-Re(1)-Cl(1)

2.195(3) 1.916(5) 2.4996(11) 1.367(5) 1.333(6) 1.381(6) 1.373(7) 1.393(6) 1.334(6) 176.02(16) 177.48(14)

Table 4. Selected Bond Distances (Å) and Angles (deg) for 5c Re(1)-N(1) Re(2)-N(5) Re(1)-C(1) Re(1)-C(3) Re(2)-C(32) Re(2)-C(34) N(3)-Re(1)-N(1) C(2)-Re(1)-N(1) N(7)-Re(2)-N(5) C(33)-Re(2)-N(5)

2.172(13) 2.239(14) 1.91(2) 1.82(3) 1.72(3) 1.72(3) 83.0(5) 174.5(9) 81.7(5) 175.1(8)

Re(1)-N(3) Re(2)-N(7) Re(1)-C(2) Re(1)-Cl(1) Re(2)-C(33) Re(2)-Cl(2) C(1)-Re(1)-N(3) C(3)-Re(1)-Cl(1) C(32)-Re(2)-N(7) C(34)-Re(2)-Cl(2)

2.149(15) 2.188(15) 1.77(2) 2.472(6) 1.98(2) 2.478(6) 177.0(7) 177.5(7) 177.7(11) 178.0(9)

Table 5. Selected Bond Distances (Å) and Angles (deg) for 5d Re(1)-N(2) Re(1)-C(16) Re(1)-C(18) N(1)-N(2) C(4)-C(5) C(8)-C(9) C(27)-C(28) C(16)-Re(1)-Cl(1) C(18)-Re(1)-N(3)

2.184(9) 1.817(13) 1.888(18) 1.382(12) 1.338(13) 1.304(14) 1.331(15) 179.5(6) 172.9(5)

Re(1)-N(3) Re(1)-C(17) Re(1)-Cl(1) N(3)-N(4) C(6)-C(7) C(25)-C(26) C(29)-C(30) C(17)-Re(1)-N(2) N(2)-Re(1)-N(3)

2.208(9) 1.916(13) 2.499(4) 1.365(11) 1.286(13) 1.342(15) 1.267(15) 177.3(5) 82.6(3)

evaporation of solvent, pure orange red oil was collected (yield: 1.04 g, 86%). IR (KBr, cm-1): 3449, 1560, 1549, 1410, 1273, 1015, 889, 766. 1H NMR (500 MHz, CDCl3, ppm): δ 2.41-2.46 (m, 11H), 2.70 (s, 4H), 17.21 (s, 1H). ESI-MS: m/z 483.9 [M+]. Anal. Calcd for C15H16O2S8: C, 37.16; H, 3.33. Found: C, 37.23; H, 3.23. 4-[{2,6,7-Tris(methylthio)-TTF-3-yl}thio]-3,5-dimethylpyrazole (4a, MTSPz*, Pz* ) 3,5-dimethylpyrazole). To a suspension of 3a (565 mg, 1.2 mmol) in 25 mL of ethanol, was added hydrazine hydrate (0.18 mL, 3.6 mmol) at room temperature with stirring. The reaction mixture was refluxed for 5 h and the clear orange red solution was cooled to room temperature. The orange crystalline solids of 4a were filtered, washed with Et2O and dried in a vacuum.

Figure 2. ORTEP view of compound 5b with an atom-numbering scheme. The thermal ellipsoids are drawn at the 30% probability level. Yield: 340 mg (60%). IR (KBr, cm-1): 3441, 3103, 2967, 2916, 2854, 1629, 1425, 1314, 1046, 889, 769. 1H NMR (500 MHz, CDCl3, ppm): δ 2.42-2.60 (m, 15H). ESI-MS: m/z 468.0 [M+]. Anal. Calcd for C14H16N2S8: C, 35.87; H, 3.44; N, 5.98. Found: C, 35.71; H, 3.31; N, 5.88. ClRe(CO)3(MTSPz*)2 (5a). Under a nitrogen atmosphere, a mixture of Re(CO)5Cl (54.2 mg, 0.15 mmol) and 4a (140 mg, 0.3 mmol) was refluxed in 10 mL of toluene for 50 min. The solvent was removed to obtain the orange crude product. Purification was achieved by flash chromatography on a silica gel column using CH2Cl2 as eluent. Yield: 143 mg (77%). IR (KBr, cm-1): 2025, 1917, 1889 (νCtO). 1H NMR (500 MHz, CDCl3, ppm): δ 2.44-2.46 (m, 30 H), 11.36 (s, 2H). ESI-MS: m/z 1239.9 [M+]. Anal. Calcd for C31H32ClN4O3ReS16: C, 29.95; H, 2.59; N, 4.51. Found: C, 29.83; H, 2.47; N, 4.46. 4-[{6,7-Benzo-2-(methylthio)-TTF-3-yl}thio]-3,5-dimethylpyrazole (4b, BTSPz*). Orange compound 4b was obtained with similar procedures for synthesizing 4a by using 3b instead of 3a. Yield: 61%. IR (KBr, cm-1): 3426, 3195, 3100, 2964, 2915, 2815, 1633, 1430, 1312, 1119, 1036, 769, 738. 1H NMR (500 MHz, CDCl3, ppm): δ 2.45 (s, 6H), 2.48 (3H, s), 7.11 (t, 2H), 7.21-7.25 (m, 2H). ESI-MS: m/z 425.9. Anal. Calcd for C16H14N2S6: C, 45.04; H, 3.31; N, 6.56. Found: C, 44.89; H, 3.17; N, 6.47. ClRe(CO)3(BTSPz*)2 (5b). Pure orange solid of 5b was obtained by a method similar to the preparation of 5a. Orange crystals suitable for X-ray diffraction were obtained from evaporation of the solution of CH2Cl2 and CH3CN mixture. Yield: 86%. IR (KBr, cm-1): 2024, 1918, 1890 (νCtO). 1H NMR (500 MHz, CDCl3, ppm): δ 2.18-2.50 (m, 18 H), 7.08-7.21 (m, 8H), 11.40 (s, 2H). ESI-MS: m/z 1156.08 [M+]. Anal. Calcd for C35H28ClN4O3ReS12: C, 36.27; H, 2.43; N, 4.83. Found: C, 36.18; H, 2.34; N, 4.75. 4-[{6,7-(Ethylenedithio)-2-(methylthio)-TTF-3-yl}thio]-3,5-dimethylpyrazole (4c, ETSPz*). To a suspension of 3c (375 mg, 0.8 mmol) in 20 mL of ethanol was added hydrazine hydrate (0.12 mL, 2.4 mmol) at room temperature with stirring. The reaction mixture was refluxed for 6 h, and a clear orange solution appeared. The solution was then cooled and filtrated to remove a small amount of white precipitate. The solvent was removed under reduced pressure and Et2O was added to get an orange solid. Pure crystalline solids of 4c were obtained from evaporation of the CH2Cl2 and CH3CN mixture. Yield: 303 mg (81%). IR (KBr, cm-1): 3422, 3184, 3094, 2916, 2854, 1636, 1559, 1408, 1309, 1283, 1116, 1033, 886, 769. 1H NMR (500 MHz, CDCl3, ppm): δ 2.39-2.44 (m, 9H), 3.28 (s, 4H). ESI-MS: m/z 465.9 [M+]. Anal. Calcd for C14H14N2S8: C, 36.02; H, 3.02; N, 6.00. Found: C, 35.93; H, 2.89; N, 5.88.

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Organometallics, Vol. 28, No. 3, 2009 759

Figure 3. Crystal structure of complex 5c. 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 least-squares methods on F2 using SHELXTL-97. All non-hydrogen atoms were found in alternating difference Fourier syntheses and least-squares 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. Computational Details. All calculations were carried out with Gaussian03 programs.22 We employed the density functional theory (DFT) and time-dependent DFT (TDDFT) with no symmetry constraints to investigate the optimized geometries, HOMOs, and LUMOs with the three-parameter hybrid functional (B3LYP),23 with a 6-31G* basis set for C, H, O, N, S, and Cl atoms and the effective core potentials (ECP) such as LANL2DZ for Re atoms.

Results and Discussion Figure 4. Crystal structure of complex 5d. ClRe(CO)3(ETSPz*)2 (5c). Complex 5c was prepared by procedures similar to those for 5a. Orange red crystals of 5c were obtained from diffusion of Et2O into CHCl3 solution. Yield: 78%. IR (KBr, cm-1): 2023, 1910, 1893 (νCtO). 1H NMR (500 MHz, CDCl3, ppm): δ 2.42-2.46 (m, 18H), 3.29 (s, 8H), 11.41(s, 2H). ESI-MS: m/z 1239.0 [M+]. Anal. Calcd for C31H32ClN4O5ReS16: C, 29.20; H, 2.53; N, 4.39. Found: C, 29.09; H, 2.63; N, 4.31. 4-[{6,7-(propylenedithio)-2-(methylthio)-TTF-3-yl}thio]-3,5-dimethylpyrazole (4d, PTSPz*). Compound 4d was obtained under the same condition as described for 4a, by using 3d instead of 3a. It was isolated as a yellow crystalline solid in 64% yield. Orange yellow crystals suitable for X-ray diffraction were obtained from evaporation of the solution of THF and CH3OH mixture. IR (KBr, cm-1): 3434, 3189, 3097, 2967, 2917, 2873, 1627, 1579, 1411, 1309, 1275, 1239, 1187, 1124, 1035, 968, 886, 767. 1H NMR (500 MHz, CDCl3, ppm): δ 2.39 (s, 9H), 2.44 (s, 2H), 2.68 (s, 4H). ESI-MS: m/z 480.0 [M+]. Anal. Calcd for C15H16N2S8: C, 37.47; H, 3.35; N, 5.83. Found: C, 37.33; H, 3.21; N, 5.69. ClRe(CO)3(PTSPz*)2 (5d). Complex 5d was prepared by similar procedures to those for 5a. Orange crystals were obtained from diffusion Et2O into CHCl3 solutions. Yield: 80%. IR (KBr, cm-1): 2025, 1918, 1890 (νC≡O). 1H NMR (500 MHz, CDCl3, ppm): δ 2.42-2.47 (m, 22H), 3.46-3.50 (m, 8H), 11.39 (s, 2H). ESI-MS: m/z 1266.9 [M+]. Anal. Calcd for C33H34ClN4O4ReS16: C, 30.83; H, 2.67; N, 4.36. Found: C, 30.71; H, 2.61; N, 4.28. Crystal Structure Determination. The data were collected on a Bruker Smart Apex CCD diffractometer equipped with graphitemonochromated Mo KR (λ ) 0.71073 Å) radiation using a ω-2θ scan mode at 293 K. The highly redundant data sets were reduced

Synthesis and Characterization. As shown in Scheme 2, the direct reaction of tetrathiafulvalene-fused acetylacetonate with hydrazine hydrate (N2H4 · H2O) in ethanol affords novel π-conjugated redox-active ligands, 3,5-dimethylpyrazole substituted by tetrathiafulvalene, MTSPz* (4a), BTSPz* (4b), ETSPz* (4c) and PTSPz* (4d). All new compounds are soluble (24) See, for examples: (a) Jørgensen, M.; Lestrup, K. A.; Bechgaard, K. J. Org. Chem. 1991, 56, 5684. (b) Bryce, M. R.; Marshallsay, G. J.; Moore, A. J. J. Org. Chem. 1992, 57, 4859. (c) Sudmale, I. V.; Tormos, G. V.; Khodorkovsky, V. Y.; Edzina, A. S.; Neilands, O. J.; Cava, M. P. J. Org. Chem. 1993, 58, 1355. (d) Adam, K.; Mu¨llen, K. AdV. Mater. 1994, 6, 439. (e) Khodorkovsky, V.; Becker, J. Y. In Organic Conductors: Fundamentals and Applications; Farges, J.-P., Ed.; Marcel Dekker: New York, 1994. (f) Lahlil, K.; Moradpour, A.; Merienne, C.; Bowlas, C. J. Org. Chem. 1994, 59, 8030. (g) Avarvari, N.; Fourmigue´, M. Chem. Commun. 2004, 2794. (k) Bendikov, M.; Wudl, F.; Perepichka, D. F. Chem. ReV. 2004, 104, 4891. (h) Iyoda, M.; Hasegawa, M.; Miyake, Y. Chem. ReV. 2004, 104, 5085. (i) Loosli, C.; Jia, C. Y.; Liu, S-X.; Haas, M.; Dias, M.; Levillain, E.; Neels, A.; Labat, G.; Hauser, A.; Decurtins, S. J. Org. Chem. 2005, 70, 4988. (j) Segura, J. L.; Martı´n, N. Angew. Chem., Int. Ed. 2001, 40, 1372. (25) (a) Natsuaki, K.; Nakano, M.; Matsubayashi, G.; Arakawa, R. Inorg. Chim. Acta 2000, 299, 112. (b) Kubo, K.; Nakano, M.; Tamura, H.; Matsubayashi, G.; Nakamoto, M. J. Organomet. Chem. 2003, 669, 141. (c) Kawabata, K.; Nakano, M.; Tamura, H.; Matsubayashi, G. Eur. J. Inorg. Chem. 2004, 2137. (26) (a) Biaso, F.; Geoffroy, M.; Canadell, E.; Auban-Senzier, P.; Levillain, E.; Fourmigu, M.; Avarvari, N. Chem. Eur. J. 2007, 13, 5394. (b) Hudhomme, P.; Le Moustarder, S.; Durand, C.; Gallego-Planas, N.; Mercier, N.; Blanchard, P.; Levillain, E.; Allain, M.; Gorgues, A.; Riou, A. Chem. Eur. J. 2001, 7, 5070. (c) Jia, C.; Liu, S-X.; Tanner, C.; Leiggener, C.; Neels, A.; Sanguinet, L.; Levillain, E.; Leutwyler, S.; Hauser, A.; Decurtins, S. Chem. Eur. J. 2007, 13, 3804. (d) Díaz, M. C.; Illescas, B. M.; Martín, N.; Viruela, R.; Viruela, P. M.; Ortí, E.; Brede, O.; Zilbermann, I.; Guldi, D. M. Chem. Eur. J. 2004, 10, 2067.

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Liu et al.

Figure 5. Packing diagram of compound 5d (the dotted line representing the S · · · S nonbonded contacts less than 3.7 Å).

Figure 7. UV-vis absorption spectra for 4a-d (4 × 10-5 M) and 5a-d (2 × 10-5 M), in the presence of varying amounts of TCNQ, measured in CH2Cl2. Figure 6. Cyclic voltammogram (solid line) and differential pulse voltammogram (dash-dotted line) for compounds 5a and 5d (5 × 10-4 M), measured in CH2Cl2 (vs Fc/Fc+). The scan rate for CV measurements was 100 mV/s; the step increment and pulse width for DPV measurements were 4 mV and 0.05 s, respectively. Table 6. Cyclic Voltammetry Data (/V) for Compounds 4a-d and 5a-d compound

E11/2 (1e-)

E21/2 (1e-)

compound

E11/2 (1e-)

E21/2 (1e-)

E31/2 (2e-)

E4ox (1e-)

4a 4b 4c 4d

0.11 0.16 0.12 0.13

0.41 0.52 0.44 0.45

5a 5b 5c 5d

0.08 0.13 0.08 0.10

0.19 0.24 0.22 0.22

0.36 0.46 0.36 0.42

1.07 1.16 1.13

in most organic solvents, and air stable in both fluid solution and solid state. Reactions of Re(CO)5Cl with two equivalents of the ligands 4a-d, and subsequent chromatographic separation of the crude products on silica gel give the respective ReI complexes with high yields. Characterization of all these complexes has been accomplished by IR, 1H NMR, UV-vis and mass spectrometry. Typical three bands for ReI complexes 5a-d, which indicate facial arrangement of the three coordinated C≡O in the CO stretching region are observed in IR spectra. In the 1H NMR

spectra for 5a-d, the presence of the single set (ca. 11.39 Hz) of pyrazole signals indicates the equivalence of the two ligands in each complex. The results confirm the versatile coordination ability of the above tetrathiafulvalene-pyrazole ligands. Crystal Structure. The crystal structures of compounds 4d and 5b-d were determined by single-crystal X-ray diffraction. The crystallographic and data collection parameters are given in Table 1; selected bond lengths and angles are listed in Tables 2-5. Figure 1 gives the ORTEP view of 4d with atomic numbering. The TTF core is nearly planar and almost perpendicular to the plane formed by appended pyrazole group, with a dihedral angle of 83.9°. Atoms C1, C2, C3, C4, C5, S1, and S2 form a seven-membered ring, which adopts a chair conformation and is tilted from the central TTF plane. Intermolecular short S · · · S contacts (S2 · · · S2, 3.516 Å) are observed in the crystal structure (Figure S1). The structures of complexes 5b-d are very similar and each distorted octahedral rhenium(I) complex has two tetrathiafulvalene-pyrazole ligands in a cis configuration (Figures 2-4). The average Re-N bond length is 2.208(8), 2.187(1), and 2.196(9) Å for 5b-d, respectively. Two different molecule conformers are present for complex 5c and the two N-Re-N

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Organometallics, Vol. 28, No. 3, 2009 761

Figure 8. The energy (eV) and graphical representation for molecular orbitals of complex 5a, in the neutral, radical cation, dication, trication and tetracation states. Table 7. Main Experimental and Calculated Optical Transitions for 5a and Its Corresponding Oxidized States 5a 5a•+ 5a2+ 5a•3+ 5a4+ a

orbital excitationsa

character

279 f 283 278 f 282 274β f 279β 273β f 279β 274 f 279

ICT πf πf ICT ICT πf πf πf πf

273 f 279 270R f 279R 273 f 278

π* π* π* π* π* π*

calcd/nm

fb

exptl/nm

388 375 923 829 926

0.0336 0.0426 0.0788 0.0627 0.1929

333

922 1060 882

0.1160 0.0292 0.3561

The molecular orbital no. involved in each transition. strength.

823 822 822 821 b

Oscillator

angles are 83.0° and 81.7°, while the N-Re-N angles are 84.5 and 82.6° for 5b and 5d, respectively. Noncovalent interactions in the structures of 5b-d are similar (Figures S2-S4), and detailed descriptions here are presented for complex 5d only. Short intramolecular S · · · S contacts are observed in 5d between the two TTF units, being equal to 3.569 Å (S3 · · · S12). Besides, noticeable intermolecular S · · · S interactions (S3 · · · S4, 3.596 Å; S4 · · · S13, 3.626 Å) have been found in the crystal, forming the “dimer” structure (Figure 5). In addition, intramolecular hydrogen bonds are present between the pyrazole NH (donor) and the coordinated chloride atom (acceptor) (N1-H1 · · · Cl1, N to Cl distance 3.103(8) Å, N-H · · · Cl angle 115.16°; N4-H4 · · · Cl1, N to Cl distance 3.056(9) Å, N-H · · · Cl angle 111.11°). The adjacent “dimers” are arranged to 1D chains through intermolercular N-H · · · Cl hydrogen bonds between NH of the pyrazole ring and the coordinated Cl atom (N · · · Cli, i ) 2 - x, 1 - y, 1 - z). The separation of N · · · Cli is 3.213(9) with the angle of N-H · · · Cl as 155.64 °. Electrochemical and Spectroscopic Properties. The electrochemical behaviors of compounds 4a-d and 5a-d were

investigated in CH2Cl2 by cyclic voltammetry (CV) and differential pulse votammetry (DPV). As expected, all ligands 4a-d exhibit two reversible one-electron redox couples, the first ones ranging from 0.11 to 0.16 V and the second ones at 0.41-0.52 V, which correspond to the formation of their radical cation and dication species, respectively (Figure S6 and Table 6). Compared with 4a-d, the redox waves for complexes 5a-d are ligand-centered, and each shows three reversible systems (E11/2 ) 0.08-0.13 V, E21/2 ) 0.19-0.24 V, E31/2 ) 0.36-0.46 V, Table 6). Since the first two redox waves are not fully separated, differential pulse votammetry has been performed. The CV and DPV waves for 5a and 5d are shown in Figure 6 as representatives. For each complex, the first two well-defined peaks with low potentials indicate two sequential one-electron steps, while the third one at higher potential position is a twoelectron process. In the previously described reported compounds involving two TTF moieties, the interactions between the donor cores were electrochemically evidenced.10b,24 While in the present system, the two TTFs are linked by a Re(SPz*)2 bridge, which is favorable for interactions through bonds. Moreover, short intra- and intermolecular S · · · S contacts observed in the structure indicate the close proximity of the redox cores. Therefore, the splitting of the first oxidation waves for 5a-d can be attributed to the sizable interactions between two TTF moieties through bonds. Additionally, one peak for irreversible oxidation of ReI/ReII in the range of 1.07-1.16 V (vs Fc/Fc+) was observed in each cyclic volammogram of 5a, 5b, and 5d, while no obvious wave was found in that of 5c. Among the four complexes, complex 5b exhibits the highest redox potentials, indicating a less delocalized structure. In 5a, 5c, and 5d, there are more sulfur atoms, which extend the conjugated system and make the molecules to be oxidized more easily.

762 Organometallics, Vol. 28, No. 3, 2009

Intense absorption bands around ca. 245-390 nm for 5a-d can be assigned to intraligand (IL) transitions, since similar absorptions are observed for uncoordinated ligands 4a-d. However, no obvious absorption band with metal-to-ligand charge transfer (MLCT) character was observed for complexes 5a-d. These new TTF-pyrazole type compounds with low oxidation potentials can be oxidized by TCNQ and I2. Upon addition of TCNQ, the absorption bands around 400 nm for 4a-d and 5a-d emerge, and the intensities increase gradually (Figure 7), suggesting the intermolecular electron transfer between the classical electron-acceptor TCNQ and the compounds containing electron-donor TTF unit during the titration. As shown in Figure S5, in the presence of the oxidizing I2, a broadband assigning to one-electron-oxidized species for each compound appears at around 830 nm; the intensity increases and reaches the maxima after the formation of two-electronoxidized and four-electron-oxidized species for ligands 4a-d and complexes 5a-d, respectively. Such spectral changes were very similar to those observed at high wavelengths for those TTF-containing compounds, such as [Ru(bpy)2(C8H4S8)],25a [Au(ppy)(C8H4S8)],25b and [Rh(η5-C5Me5)(C8H4S8)].25c Computational Studies. Theoretical calculations were carried out by using density functional theory (DFT) and time-dependent DFT (TDDFT) for complexes 5a-d, in the neutral, radical cation, dication, trication and tetracation states. The optimized geometries are in good agreement with the experimental structures, reproducing the boat-like conformation of the TTF moieties in the neutral molecules and the planar symmetry of those in cation states (Figure S7). As expected, the orbital energies of 5a-d vary slightly as the peripheral substitute of the TTF core changes, and the successive oxidations all lead to stabilizations of the HOMO level. Since the spatial distributions of the frontier orbitals are similar for 5a-d, no detailed discussions are presented here for 5b-d. For complex 5a, the HOMO orbital in neutral state is mostly localized on one TTF unit, and the single occupied molecular orbital (SOMO) is on the other TTF unit in the radical cation state (Figure 8). Such observations further support the redox behaviors. First, stable monoradical cations are generated through one-electron oxidation process from one TTF core. Then the second electron is removed from the other donor core as a result of the Coulombic repulsion.10b,24,26a For the di- and trication species, the HOMO orbitals mainly consist of the delocalized π orbitals on both TTF units, and the contribution from the bridging Re(SPz*)2 is negligible. While for the tetracation state, the main contribution belongs only to the Re(SPz*)2. The important orbital changes from the di- to tetracation states provide the further evidence on the simultaneous removal of the two electrons from both electroactive TTF(+) centers, which is consistent with the results from electrochemical studies. Additionally, it is noteworthy that the two TTFs are more apart from each other as the oxidation state

Liu et al.

increases, which implies the enhancement of the electrostatic repulsion between the cationic species. As shown in Tables 7 and S1, the energies of calculated spinallowed electronic transitions match with the experimental ones for complex 5a and its different oxidized states. According to the calculations, the experimentally observed absorption band (around 333 nm) for complex 5a in the neutral state mainly originates from a mixed transition of HOMO f LUMO+3 and HOMO-1 f LUMO+2. Such transition can be assigned to intramolecular charge transfer (ICT) and π f π* character, due to their orbital characters of the corresponding starting and arriving states.26b-d For radical cation state (5a•+), the calculated transitions are well consistent with the new highenergy UV-vis band at 800 nm which emerges upon addition the oxidizing agent I2. As for the di-, tri- and tetracation states of 5a, the calculations reveal that the absorptions all follow the experimental trends.

Conclusion In summary, a series of TTF-pyrazole ligands have been successfully prepared for the first time and their coordination ability has been confirmed by the formation of tricarbonyl (chloro) rhenium(I) complexes. The interesting redox active properties for the new compounds have been evidenced by electrochemical studies and theoretical calculations. The results demonstrate that the novel tetrathiafulvalene-pyrazole ligands are useful for the syntheses of new metal complexes with interesting properties. Further investigations on the binding of TTF-pyrazole type ligands to various transition metal ions are now in progress in our group.

Acknowledgment. This work was supported by the Major State Basic Research Development Program (2006CB806104 and 2007CB925103), the National Science Fund for Distinguished Young Scholars of China (Grant 20725104) and the National Natural Science Foundation of China (Grant 20721002). Note Added after ASAP Publication. The version of this paper published on January 6, 2009, contained an error in Table 1. The version published on January 12, 2009 contains the correct information. Supporting Information Available: X-ray crystallographic data for 4d, 5b, 5c, and 5d in CIF format, a table giving the main optical transitions for 5a-d and their corresponding oxidized states, and figures showing packing diagrams for 4d and 5b-d; UV-vis absorption spectra for 4a-d and 5a-d, CVs and DPVs for 4a and 4b, and frontier orbitals for complexes 5b-d. This material is available free of charge via the Internet at http://pubs.acs.org. OM800919U