Organometallics 2010, 29, 283–285 DOI: 10.1021/om9007604
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A Rigidity-Modulated Approach toward the Construction of Metallacycles from a Flexible Tetratopic Ligand Chuan-Hung Chuang,† Malaichamy Sathiyendiran,† Yi-Hsiu Tseng,†,‡ Jing-Yun Wu,† Kung-Chung Hsu,‡ Chen-Hsiung Hung,† Yuh-Sheng Wen,† and Kuang-Lieh Lu*,† †
Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan and ‡Department of Chemistry, National Taiwan Normal University, Taipei 106, Taiwan Received August 31, 2009
Summary: Conformation control of a flexible tetratopic ligand by modulation of the length of the rigid bridging ligand is achieved during the self-assembly of metallacycles. The ability to control the conformation of the flexible ligand using an ancillary rigid ligand provides a new method for the preparation of novel metallacycles that contain both flexible and rigid modules with highly accurate prediction of the final structures. Precise control of supramolecular metallacycles requires a rational design of molecular components, because the information that determines the specific assembly should be encoded in the molelcular architecture.1 Recently, the use of flexible motifs to construct metallacycles has increased because of the advantages associated with their use, such as *To whom correspondence should be addressed. Fax: Int. code þ8862-27831237. E-mail:
[email protected]. (1) (a) Lehn, J. M. Supramolecular Chemistry, Concepts and Perspectives; VCH: Weinheim, Germany, 1995. (b) Leininger, S.; Olenyuk, B.; Stang, P. J. Chem. Rev. 2000, 100, 853–908. (c) Jones, C. J. Chem. Soc. Rev. 1998, 27, 289–300. (d) Swiegers, G. F.; Malefetse, T. J. Chem. Rev. 2000, 100, 3483–3538. (e) Fujita, M.; Umemoto, K.; Yoshizawa, M.; Fujita, N.; Kusukawa, T.; Biradha, K. Chem. Commun. 2001, 509–518. (f) Holliday, B. J.; Mirkin, C. A. Acc. Chem. Res. 2005, 38, 825–837. (g) Cotton, F. A.; Lin, C.; Murillo, C. A. Acc. Chem. Res. 2001, 34, 759–771. (h) Caulder, D. L.; Raymond, K. N. Acc. Chem. Res. 1999, 32, 975–982. (i) Dinolfo, P. H.; Hupp, J. T. Chem. Mater. 2001, 13, 3113–3125. (j) Thanasekaran, P.; Liao, R. T.; Liu, Y. H.; Rajendran, T.; Rajagopal, S.; Lu, K. L. Coord. Chem. Rev. 2005, 249, 1085–1110. (k) Sathiyendiran, M.; Thanasekaran, P.; Luo, T. T.; Venkataramanan, N. S.; Lee, G. H.; Peng, S. M.; Lu, K. L. Inorg. Chem. 2006, 45, 10052–10054. (l) Ghosh, K.; Hu, J.; Yang, H.-B.; Northrop, B. H.; White, H. S.; Stang, P. J. J. Org. Chem. 2009, 74, 4828–4833. (2) (a) Sauvage, J.-P. Acc. Chem. Res. 1998, 31, 611–619. (b) Fujita, M.; Ogura, K. Bull. Chem. Soc. Jpn. 1996, 69, 1471–1482. (c) Carlucci, L.; Ciani, G.; Proserpio, D. M. CrystEngComm 2003, 5, 269–279. (d) Hoskin, B. F.; Robson, R.; Slizys, D. A. J. Am. Chem. Soc. 1997, 119, 2952–2953. (e) Chen, C. L.; Kang, B. S.; Su, C. Y. Aust. J. Chem. 2006, 59, 3–18. (f) Wang, C.-G.; Xing, Y.-H.; Li, Z.-P.; Li, J.; Zeng, X.-Q.; Ge, M.-F.; Niu, S.-Y. Cryst. Growth Des. 2009, 9, 1525–1530. (3) (a) Hartshorn, C. M.; Steel, P. J. Chem. Commun. 1997, 541–542. (b) James, S. L.; Mingos, D. M. P.; White, A. J. P.; Williams, D. J. Chem. Commun. 1998, 2323–2324. (c) Fleming, J. S.; Mann, K. L. V.; Carrez, C.-A.; Psillakis, E.; Jeffrey, J. C.; McCleverty, J. A.; Ward, M. D. Angew. Chem., Int. Ed. 1998, 37, 1279–1281. (4) (a) Raehm, L.; Mimassi, L.; Cuyard-Duhayon, C.; Amouri, H. Inorg. Chem. 2003, 42, 5654–5659. (b) Su, C. Y.; Cai, Y. P.; Chen, C. L.; Smith, M. D.; Kaim, W.; zur Loye, H. C. J. Am. Chem. Soc. 2003, 125, 8595–8613. (c) Dobrzanska, L.; Lioyd, G. O.; Raubenheimer, H. G.; Barbour, L. J. J. Am. Chem. Soc. 2005, 127, 13134–13135. (d) Dobrzanska, L.; Lioyd, G. O.; Raubenheimer, H. G.; Barbour, L. J. J. Am. Chem. Soc. 2006, 128, 698–699. (e) Chatterjee, B.; Noveron, J. C.; Resendiz, M. J. E.; Liu, J.; Yamamoto, T.; Parker, D.; Cinke, M.; Nguyen, C. V.; Ariff, A. M.; Stang, P. J. J. Am. Chem. Soc. 2004, 126, 10645–10656. (5) (a) Cai, Y. P.; Su, C. Y.; Zhang, H. X.; Zhou, Z. Y.; Zhu, L. X.; Chan, A. S. C.; Liu, H. Q.; Kang, B. S. Z. Anorg. Allg. Chem. 2002, 628, 2321–2328. (b) Chen, C. L.; Tan, H. Y.; Yao, J. H.; Wan, Y. Q.; Su, C. Y. Inorg. Chem. 2005, 44, 8510–8520. (c) Baker, M. V.; Bosnich, M. J.; Brown, D. H.; Byrne, L. T.; Hesler, V. J.; Skelton, B. W.; White, A. H.; Williams, C. C. J. Org. Chem. 2004, 69, 7640–7652. r 2009 American Chemical Society
adaptive recognition properties and breathing ability in the solid state.2-5 Flexible organic components are generally less predictable during self-assembly and have a tendency to generate [2]catenanes2 or oligomers upon reaction with metal ions. Prior research in this area has focused on the use of di- and tritopic flexible N-donors to construct both ionic and neutral metallacycles.2-6 The synthesis and use of semirigid tetratopic N-donors as structural components for metallacycles is rare because of their higher conformational flexibility, which must be restricted to obtain well-preorganized subunits.7 Herein, we report an effective rigiditymodulated approach for the design of neutral metallacycles. The rigid anionic linker responsible for determination of M 3 3 3 M separation allows for conformational control of the flexible motif with simultaneous use of a rigid bis(chelator), tetratopic flexible N-donors, and fac-Re(CO)3 cores during self-assembly (Scheme 1). In this study, the flexible ligand 1,2,4,5-tetrakis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene (TXyBim) and two rigid moieties, 2,20 -bis(benzimidazolyl) (H2-Bim)8 and chloranilic acid (H2-CA), were explored as basic building units. In the case of TXyBim, four benzimidazoles are connected via flexible methylene groups to an arene core. This flexibility permits TXyBim to adopt several possible conformations because of the orientation of the four benzimidazolyl arms (Chart S1 in the Supporting Information).9 Compound 1 was assembled from Re2(CO)10, TXyBim, and H2-Bim in toluene in 68% yield under solvothermal conditions (Scheme 2).10 The resulting yellow product is airand moisture-stable and slightly soluble in polar solvents. The IR spectrum of 1 exhibited strong bands at 2018, 1914, and 1900 cm-1, characteristic of fac-Re(CO)3. The structure of compound 1 was determined by X-ray crystallographic analysis, which revealed that metallacycle 1 contains four fac-Re(CO)3 cores, two Bim groups, and one TXyBim moiety, as shown in Figure 1.10 The coordination geometry around the Re centers is a distorted octahedron with a C3N3donor environment. The dianionic Bim is coordinated in a (6) Sathiyendiran, M.; Chang, C. H.; Chuang, C. H.; Luo, T. T.; Wen, Y. S.; Lu, K. L. Dalton Trans. 2007, 1872–1874. (7) (a) Reger, D. L.; Semeniuc, R. F.; Silaghi-Dumitrescu, I.; Smith, M. D. Inorg. Chem. 2003, 42, 3751–3764. (b) Reger, D. L.; Semeniuc, R. F.; Little, C. A.; Smith, M. D. Inorg. Chem. 2006, 45, 7758–7769. (c) Reger, D. L.; Foley, E. A.; Semeniuc, R. F.; Smith, M. D. Inorg. Chem. 2007, 46, 11345–11355. (8) Rezende, M. C.; Dall’Oglio, E. L. Tetrahedron Lett. 1996, 37, 5265–5268. (9) Wu, J. Y.; Lin, Y. F.; Chuang, C. H.; Tseng, T. W.; Wen, Y. S.; Lu, K. L. Inorg. Chem. 2008, 47, 10349–10356. Published on Web 12/29/2009
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Scheme 1. Self-Assembly of Metallacycles via Conformational Selection from Various Conformers (Center: Ortho (Top), Meta (Middle), Para (Bottom)) of the Tetratopic Flexible Liganda
a
The short rigid bridging ligand resulted in the ortho conformer, and the long rigid bridger produced the meta conformer.
Scheme 2
symmetrical tetradentate manner through its four nitrogens to two rhenium centers. The Re 3 3 3 Re distance is 5.74 A˚. The TXyBim ligand adopts a syn,anti,syn,anti conformation mode (see the Supporting Information), with both o-benzimidazole arms on the same side, serving as two molecular clips. The two benzimidazolyl units are almost parallel, with a dihedral angle of 23.5°. The distance between the two parallel benzimidazole rings ranges from 4.05 to 4.11 A˚, suggesting a weak π 3 3 3 π stacking interaction. The phenylene plane is perpendicular to the two benzimidazole arms (dihedral angles 86.9 and 69.7°). In addition, the phenylene of TXyBim is sandwiched within the cleft of two benzimidazolyls of Bim at (10) A mixture of Re2(CO)10 (153 mg, 0.23 mmol), H2-Bim (57 mg, 0.24 mmol), and TXyBim (83 mg, 0.11 mmol) in toluene/ethanol (13:2 mL) in a Teflon flask was placed in a steel bomb. The bomb was placed in an oven maintained at 160 °C for 72 h and then cooled to 25 °C. Good-quality pale yellow single crystals of 1 (183 mg, 68%) were obtained. The crystals were separated by filtration and washed with hexane. Anal. Calcd for C86H62N16O12Re4 3 2C7H8: C, 49.21; H, 3.22; N, 9.18. Found: C, 48.87; H, 3.38; N, 8.92. FT-IR νmax(THF)/cm-1: 2018, 1914, and 1900 (CO). FABMS: m/z 2256 (Mþ, C86H62N16O12Re4 requires 2256.34). Crystal data for 1: C86H62N16O12Re4 3 2C7H8, M = 2440.58, monoclinic, P21/c, a = 12.130(2) A˚, b = 17.621(5) A˚, c = 22.118(7) A˚, β = 102.21(17)°, V = 4620 (3) A˚3, Z = 2, Fcalcd = 1.754 Mg m-3, μ = 5.294 mm-1, F(000) = 2372, T = 200 K. A total of 28 398 reflections were collected in the range θ = 1.49-24.97°, of which 7738 were unique (Rint = 0.0492). Final R indices: R1 = 0.0332, wR2 = 0.0727 for 6284 reflections (I > 2σ(I)); R1 = 0.0476, wR2 = 0.0777 for 7738 independent reflections (all data) and 595 parameters, GOF = 1.045.
distances ranging from 3.81 to 4.76 A˚, suggesting weak π 3 3 3 π stacking interactions. When the H2Bim assembly unit was replaced by H2CA, which has a longer rigid bridging length, and TXyBim was used as the flexible ligand, compound 2 formed in 65% yield.11 The dark green product 2 was air- and moisture-stable and insoluble. FAB-MS showed a molecular ion peak at m/z 2205.6. A single-crystal X-ray diffraction analysis showed that compound 2 adopts a tetrametallic bicyclic metallacyclic structure (Figure 2).11 The coordination geometry around the Re centers is a distorted octahedron with a C3NO2-donor environment. The dianion (CA2-) of chloranilic acid chelates two rhenium(I) atoms through four oxygen atoms and acts as (11) A mixture of Re2(CO)10 (151 mg, 0.23 mmol), TXyBim (82 mg, 0.11 mmol), and H2-CA (48 mg, 0.23 mmol) in toluene (16 mL) in a Teflon flask was placed in a steel bomb. The bomb was placed in an oven maintained at 160 °C for 48 h and then cooled to 25 °C. Good-quality dark green single crystals of 2 (165 mg, 65%) were obtained. Anal. Calcd for C70H46Cl4N8O20Re4: C, 38.12; H, 2.10; N, 5.08. Found: C, 38.45; H, 2.64; N, 5.10. FAB-MS m/z 2205.6 (Mþ, C70H46Cl4N8O20Re4 requires 2205.17). Crystal data for 2: C70H46Cl4N8O20Re4, M = 2205.75, monoclinic, P21/c, a = 18.0124(7) A˚, b = 13.2976(5) A˚, c = 15.5995(6) A˚, β = 101.9280(10)°, V = 3655.7(2) A˚3, Z = 2, Fcalcd = 2.004 Mg m-3, μ = 6.825 mm-1, F(000) = 2100, T = 296(2) K, A total of 24 860 reflections were collected in the range θ = 1.92-27.47°, of which 7437 were unique (Rint = 0.0733). Final R indices: R1 = 0.0507, wR2 = 0.0933 for 4123 reflections (I > 2σ(I)); R1 = 0.1149, wR2 = 0.1133 for 7437 independent reflections (all data) and 482 parameters, GOF = 0.985.
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Organometallics, Vol. 29, No. 2, 2010
Figure 1. Ball and stick representation of the crystal structure of 1. Atomic labels with “A” represent equivalent atoms generated from the symmetry code -x, -y þ 2, -z. Hydrogen atoms are omitted for clarity.
a tetradentate ligand. The CA unit is planar with π-electron delocalization confined to the upper and lower regions of the ligand: i.e., the two halves. The C7-C8 and C10-C11 bond lengths are 1.497 and 1.512 A˚, indicative of negligible conjugation between the halves of the ligand. The Re 3 3 3 Re distance across the rigid anionic bridging unit is 8.141 A˚, approximately 2.9 A˚ longer than that found in compound 1. The flexible TXyBim ligand adopts an anti,syn,anti,syn conformation mode with both metal-benzimidazole arms on the same side, serving as two molecular clips. Unlike compound 1, the m-benzimidazolyls are orientated in a head-to-head syn conformation, utilizing the benzimidazoline N atoms to bridge the bis-chelated dirhenium unit. These results indicate that the length of the rigid bridging ligand is the primary structure-directing influence on the conformation of the flexible building units during the self-assembly of metallacycles. This rigidity-modulated approach to conformation control is highly effective not only for flexible ditopic ligands6 but also for flexible tetratopic ligands. To the best of our knowledge, this is the first 2-
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Figure 2. Ball and stick representation of the crystal structure of 2. Atomic labels with “A” represent equivalent atoms generated from the symmetry code -x þ 2, -y þ 1, -z þ 1. Hydrogen atoms and methyl groups are omitted for clarity.
report on conformation control of a flexible tetratopic building unit using a rigid motif during the self-assembly of metallacycles. The ability to control the conformation of the flexible ligand using an ancillary rigid ligand provides a new method for the preparation of novel metallacycles that contain both flexible and rigid modules with highly accurate prediction of the final structures.
Acknowledgment. We thank the Academia Sinica and the National Science Council of Taiwan for financial support. Supporting Information Available: Chart S1, giving possible conformers for a flexible ligand, TXyBim, in solution, and CIF files giving details of the X-ray structural analysis and crystallographic data for 1 and 2. This material is available free of charge via the Internet at http://pubs.acs.org.
