Cleavage of C− H Bonds for Building Tetranuclear Half-Sandwich

May 25, 2010 - ... O, red; N, blue; C, black; H, gray) were assembled via C−H bond activation ... Ying-Feng Han , Yue-Jian Lin , T. S. Andy Hor , an...
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Organometallics 2010, 29, 2827–2830 DOI: 10.1021/om1002396

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Cleavage of C-H Bonds for Building Tetranuclear Half-Sandwich Iridium Macrocycles with Ortho-Metalated Spacers Wei-Bin Yu, Ying-Feng Han, Yue-Jian Lin, and Guo-Xin Jin* Shanghai Key Laboratory of Molecular Catalysis and Innovative Material, Department of Chemistry, Fudan University, Shanghai 200433, People’s Republic of China Received March 28, 2010 Summary: A new series of tetranuclear half-sandwich iridium macrocycles were successfully obtained via cleaving aromatic C-H bonds under mild conditions. In this context, the complexes 1-5 formed via aromatic C-H bond activation were fully characterized by IR, EA, 1H NMR, and single-crystal X-ray analysis. Thus, distorted-rectangle-shaped backbones were obviously indicated and directed to assemble nanochannel architectures via H-bonds, hydrophobic interactions, and CH 3 3 3 π stacking in complexes 1-5. Recently, cleavage of C-H bonds of aromatic compounds and alkane compounds as raw materials of synthetic processes has been intensively developed.1 In most cases, transition metals as active sites for cleaving C-H bonds have been employed in various ways.2 Since Bergman and his co-workers have successfully utilized half-sandwich iridium fragments as catalysts for activation of saturated alkane and aromatic compounds,3 numerous transition metals as catalysts of C-H bond activation have been explored one after another.4 Nevertheless, a wide range of metal-organic architectures such as metallacycles, metallaprisms, and metallaboxes have been reported based on half-sandwich fragments (Cp/Cp*) as metal centers,5 but rare

cases utilized functionalization of C-H bonds of aromatic compounds as building blocks to construct such architectures. Herein, we present several cases to construct tetranuclear halfsandwich iridium macrocycles with ortho-metalated spacers in which functionalized C-H bonds of aromatic compounds (carboxylic acid derivatives) are used as building blocks. To the best of our knowledge, nanochannel architectures assembled from organometallic macrocycles have attracted recent interest due to their facile synthetic accessibility, welldefined structures, and great potential for applications.6,7 Meanwhile, metal-organic macrocycles built from aromatic carboxylate spacer units were reported by Cotton et al.8 Hence, in this work we sought to employ rigid dicarboxylates as spacers, allowing for a control of the size of the metallacyclic tubular architectures to eventually be formed by self-assembly. However, much to our surprise the macrocycles spontaneously formed in this study were obtained with the help of an ortho-metalation reaction via C-H bond activation. In addition, ortho metalations of aromatic units via C-H bond activation have only rarely been exploited in such synthetic approaches,9 presumably due to their higher bond dissociation energies.10-15

*To whom correspondence should be addressed. E-mail: gxjin@ fudan.edu.cn. Fax: (þ86)-21-65643776. (1) (a) Ledger, A. E. W.; Mahon, M. F.; Whittlesey, M. K.; Williams, J. M. J. Dalton Trans. 2009, 6941. (b) Meiners, J.; Friedrich, A.; Herdtweck, E.; Schneider, S. Organometallics 2009, 28, 6331. (c) Oblad, P. F.; Bercaw, J. E.; Hazari, N.; Labinger, J. A. Organometallics 2010, 29, 789. (d) Sun, C. -L.; Li, B. -J.; Shi, Z.-J. Chem. Commun. 2010, 46, 677. (e) Nishikata, T.; Abela, A. R.; Lipshutz, B. H. Angew. Chem., Int. Ed. 2010, 49, 781. (f) Feng, Y.; Chen, G. Angew. Chem., Int. Ed. 2010, 49, 958. (g) Nadeau, E.; Ventura, D. L.; Brekan, J. A.; Davies, H. M. L. J. Org. Chem. 2010, 75, 1927. (2) (a) Johansson, L.; Tilset, M. J. Am. Chem. Soc. 2001, 123, 739. (b) Thomas, J. C.; Peters, J. C. J. Am. Chem. Soc. 2001, 123, 5100. (c) Johansson, L.; Ryan, O. B.; Rømming, C.; Tilset, M. J. Am. Chem. Soc. 2001, 123, 6579. (d) Ritleng, V.; Sirlin, C.; Pfeffer, M. Chem. Rev. 2002, 102, 1731. (e) Whited, M. T.; Grubbs, R. H. Acc. Chem. Res. 2009, 42, 1607. (f) Grounds, H.; Anderson, J. C.; Hayter, B.; Blake, A. J. Organometallics 2009, 28, 5289. (3) (a) Janowicz, A. H.; Bergman, R. G. J. Am. Chem. Soc. 1983, 105, 3929. (b) Periana, R. A.; Bergman, R. G. J. Am. Chem. Soc. 1984, 106, 7272. (c) Stoutland, P. O.; Bergman, R. G. J. Am. Chem. Soc. 1985, 107, 4581. (d) Klein, D. P.; Hayes, J. C.; Bergman, R. G. J. Am. Chem. Soc. 1988, 110, 3704. (e) Lee, S. Y.; Bergman, R. G. J. Am. Chem. Soc. 1995, 117, 5877. (f) Thalji, R. K.; Ahrendt, K. A.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc. 2001, 123, 9692. (g) Tan, K. L.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc. 2002, 124, 3202. (h) Bergman, R. G. Nature 2007, 446, 391. (4) (a) Frey, P. A. Chem. Rev. 1990, 90, 1343. (b) Boutry, O.; Poveda, M. L.; Carmona, E. J. Organomet. Chem. 1997, 528, 143. (c) Ritleng, V.; Sirlin, C.; Pfeffer, M. Chem. Rev. 2002, 102, 1731. (d) Yamamoto, Y.; Takahashi, A.; Sunada, Y.; Tatsumi, K. Inorg. Chim. Acta 2004, 357, 2833. (e) Lersch, M.; Tilset, M. Chem. Rev. 2005, 105, 2471. (f) Davies, D. L.; Donald, S. M. A.; Al-Duaij, O.; Macgregor, S. A.; P€ olleth, M. J. Am. Chem. Soc. 2006, 128, 4210. (g) Oxgaard, J.; Tenn, W. J., III; Nielsen, R. J.; Periana, R. A.; Goddard, W. A., III Organometallics 2007, 26, 1565.

(5) (a) Lehaire, M.-L.; Scopelliti, R.; Herdeis, L.; Polborn, K.; Mayer, P.; Severin, K. Inorg. Chem. 2004, 43, 1609. (b) de Biani, F. F.; Corsini, M.; Zanello, P.; Yao, H.; Bluhm, M. E.; Grimes, R. N. J. Am. Chem. Soc. 2004, 126, 11360. (c) Grote, Z.; Scopelliti, R.; Severin, K. J. Am. Chem. Soc. 2004, 126, 16959. (d) Das, N.; Arif, A. M.; Stang, P. J.; Sieger, M.; Sarkar, B.; Fiedler, W. K. Inorg. Chem. 2005, 44, 5798. (e) Sadhukhan, N.; Patra, S. K.; Sana, K.; Bera, J. K. Organometallics 2006, 25, 2914. (f) Mimassi, L.; Cordier, C.; Guyard-Duhayon, C.; Mann, B. E.; Amouri, H. Organometallics 2007, 26, 860. (g) Moussa, J.; Guyard-Duhayon, C.; Boubekeur, K.; Amouri, H.; Yip, S.-K.; Yam, V. W. W. Cryst. Growth Des. 2007, 7, 962. (h) Liu, Y.; Hou, H.; Chen, Q.; Fan, Y. Cryst. Growth Des. 2008, 8, 1435. (i) Mirtschin, S.; Krasniqi, E.; Scopelliti, R.; Severin, K. Inorg. Chem. 2008, 47, 6375. (j) Bar, A. K.; Chakrabarty, R.; Mukherjee, P. S. Organometallics 2008, 27, 3806. (k) Herbert, D. E.; Gilroy, J. B.; Chan, W. Y.; Chabanne, L.; Staubitz, A.; Lough, A. J.; Manners, I. J. Am. Chem. Soc. 2009, 131, 14958. (l) Wang, G.-L.; Lin, Y.-J.; Berke, H.; Jin, G.-X. Inorg. Chem. 2010, 49, 2193. (6) (a) Grave, C.; Schl€ uter, A. D. Eur. J. Org. Chem. 2002, 3075. (b) H€oger, S. Chem. Eur. J. 2004, 10, 1320. (c) Oh, M.; Carpenter, G. B.; Sweigart, D. A. Acc. Chem. Res. 2004, 37, 1. (d) Reingold, J. A.; Son, S. U.; Kim, S. B.; Dullaghan, C. A.; Oh, M.; Frake, P. C.; Carpenter, G. B.; Sweigart, D. A. Dalton Trans. 2006, 2385. (e) Zhang, W.; Moore, J. S. Angew. Chem., Int. Ed. 2006, 45, 4416. (f) Zheng, Y.-R.; Stang, P. J. J. Am. Chem. Soc. 2009, 131, 3487. (7) (a) Leininger, S.; Olenyuk, B.; Stang, P. J. Chem. Rev. 2000, 100, 853. (b) Holliday, B. J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2001, 40, 2022. (c) Li, G.; Yu, W.; Cui, Y. J. Am. Chem. Soc. 2008, 130, 4582. (8) Cotton, F. A.; Lin, C.; Murillo, C. A. Acc. Chem. Res. 2001, 34, 759. (9) (a) Davies, H. M. L.; Beckwith, R. E. J. Chem. Rev. 2003, 103, 2861. (b) Han, S. B.; Kim, I. S.; Krische, M. J. Chem. Commun. 2009, 7278. (10) Dı´ az-Requejo, M. M.; Perez, P. J. Chem. Rev. 2008, 108, 3379. (11) Blanksby, S. J.; Ellison, G. B. Acc. Chem. Res. 2003, 36, 255. (12) Kranenburg, M.; Ciriano, M. V.; Cherkasov, A.; Mulder, P. J. Phys. Chem. A 2000, 104, 915. (13) (a) Cruickshank, F. R.; Benson, S. W. J. Am. Chem. Soc. 1969, 91, 1289. (b) Burkey, T. J.; Castelhano, A. L.; Griller, D.; Lossing, F. P. J. Am. Chem. Soc. 1983, 105, 4701. (c) Tian, Z.; Fattahi, A.; Lis, L.; Kass, S. R. J. Am. Chem. Soc. 2006, 128, 17087.

r 2010 American Chemical Society

Published on Web 05/25/2010

pubs.acs.org/Organometallics

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Yu et al.

Scheme 1. Preparation of Organometallic Complexes 1-5

We report here the assembly of the nanotubular crystalline complexes (Cp*)4Ir4[p-C6H2(CO2)2]2(pyr)2 (1; Cp*=η5Me5C5, pyr= pyrazine), (Cp*)4Ir4[p-C6H2(CO2)2]2(bpy)2 (2; bpy =4,40 -biprydine), (Cp*)2Ir2[C6H2(CO2)]2(pyr) (3), (Cp*)4Ir4[2,6-C10H4(CO2)2]2(pyr)2 (4), and (Cp*)4Ir4[4,40 -C12H6(CO2)2]2(pyr)2 (5), which are metallacycles (Scheme 1) forming molecular squares with ortho-metalated spacers and chelate-enhanced rigidity. By analogy to our previous work, these “flat” squares stack in the solid state, eclipsing these units and forming channels with sizes of the square holes.16

Figure 1. Views of (a) the structure of an Ir4 cycle in 1, (b) its space-filling model, (c) the packing of the Ir4 macrocycles to generate a nanotube, and (d) a space-filling model demonstrating the open channels along the a axis within the 3D structure of 1. Guest molecules and hydrogen atoms are omitted for clarity. Legend: bright green, iridium; black, carbon; red, oxygen; blue, nitrogen.

Results and Discussion To build the squared moieties, pyrazine or bpy was reacted first with [Cp*IrCl2]2 in dichloromethane, producing binuclear [Cp*IrCl2]2(pyrazine) and [Cp*IrCl2]2(bpy) complexes. In two consecutive steps first AgOTf and then after 3 h H2BDC/benzoic acid/H2NDC/4,40 -dibenzoic acid with TEA was added to the reaction solution, and the mixture was stirred for 10 h. In all cases, complexes 1-5 were obtained in pure form and in good yields after chromatography over neutral alumina. Single crystals of the complexes 1-5 were obtained by diffusion of ether into their methanol solutions. The structures of complexes 1-5 were confirmed by their 1H NMR and IR spectra, and the elemental analyses were in agreement with their compositions. The molecular structures of complexes 1-5 were determined by X-ray diffraction studies.17 The structures of 1-5 consist of rectangular structures with Ir 3 3 3 Ir edges. Complex 1 crystallizes in the space group P21/n and exhibits a tubular architecture (Figure 1c). The iridium fragments adopt a three-legged piano-stool geometry with the three legs formed from N, C, and O donor atoms of one pyrazine linker and a perpendicular chelating benzene-1,4-dicarboxylate-2-yl ligand forming a cyclic tetramer as shown in Figure 1a. The outer diameter of the square is 1.53 nm with a (14) Janowicz, A. H.; Bergman, R. G. J. Am. Chem. Soc. 1982, 104, 352. (15) (a) Mobley, T. A.; Bergman, R. G. J. Am. Chem. Soc. 1998, 120, 3253. (b) Wiedemann, S. H.; Lewis, J. C.; Ellman, J. A.; Bergman, R. G. J. Am. Chem. Soc. 2006, 128, 2452. (c) Lewis, J. C.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc. 2007, 129, 5332. (d) Lewis, J. C.; Berman, A. M.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc. 2008, 130, 2493. (16) (a) Han, Y.-F.; Lin, Y.-J.; Jia, W.-G.; Wang, G.-L.; Jin, G.-X. Chem. Commun. 2008, 1807. (b) Han, Y.-F.; Jia, W.-G.; Lin, Y.-J.; Jin, G.-X. Angew. Chem., Int. Ed. 2008, 48, 6234. (c) Han, Y.-F.; Lin, Y.-J.; Jia, W.-G.; Jin, G.-X. Dalton Trans. 2009, 2077. (d) Han, Y.-F.; Jia, W.-G.; Yu, W.-B.; Jin, G.-X. Chem. Soc. Rev. 2009, 38, 3419. (17) The crystal structure of complex 5 has been determined by singlecrystal X-ray diffraction at 203 K.

Figure 2. Intermolecular CH 3 3 3 π interactions between the Ir4 macrocycles in the compounds.

thickness of 1.30 nm and an inner pore diameter of 0.98 nm. The square of 1 is slightly distorted with Ir 3 3 3 Ir diagonal lengths of 9.7911 and 9.6378 A˚. The dihedral angle between the (Ir,C,O) and pyrazine planes is 87.92°. Two diagonal pairs of Cp* groups of iridium centers are organized in a manner such that they partially cover the two sides of the cyclic equatorial Ir4 planes, thus generating four hydrophobic pockets while producing intermolecular CH 3 3 3 π interactions between the Ir4 macrocycles in the complexes which link discrete macrocycles with each other (see Figure 2). Additionally, a similar structure is observed in complex 2 (see the Supporting Information). The same coordinating surroundings of Ir atoms of complex 2 utilized as center consist of the distorted-rectangular structure, whose width and length are about 7.0331 and 11.3973 A˚, respectively. The layers of the macrocycles in 1 interact via hydrogen bonding between free carbonyl groups of the [p-C6H2(CO2)2]4ligands and methanol guests and free water molecules (see Figure 3). Actually, these hydrogen bonds involving methanol

Note

Figure 3. Hydrogen bonds between the guest methanol, free water, and the carbonyls of the ligand molecules, Ir4 macrocycles directly assemble into nanotubes along the crystallographic a axis. The methanol guests are indicated by a spacefilling model. Legend: bright green, iridium; black, carbon; red, oxygen; blue, nitrogen.

molecules and water molecules to assemble H-bond nets are the cause for the packing of the metallacycles in a vertical direction along the crystallographic a axis, creating the nanochannel architectures (Figure 1c). The structure is further enforced by intermolecular CH 3 3 3 π interactions between Cp* groups of one macrocycle with that of another perpendicular unit (ranging from 2.870 to 3.448 A˚), as shown in Figure 1d. Furthermore, the layers of the macrocycles of 2 indicated features similar to those in the macrocycles of 1. However, their stacking interaction is different. Complex 1 has a CH 3 3 3 π interaction, while complex 2 has π 3 3 3 π stacking (Supporting Information, Figure S2). In order to determine in other substrates whether the formation of macrocyclic complexes 1 and 2 was accompanied by C-H bond activation or not, a benzoic acid ligand replaced the terephthalic acid ligand in reactions under the same conditions. As a result, the binuclear complex 3 was formed via activation of C-H bonds from benzyl groups. Therefore, it is unambiguously suggested that the C-H bond activation played a dominant role in the formation of these complexes. Furthermore, longer ligands such as naphthalene-2,6-dicarboxylic acid (H2NDA) and 4,40 -biphenyldicarboxylic acid (H2BDA) substituted for both of the above ligands in the reaction. Successively, complexes 4 and 5 were obtained successfully following the process. Additionally, these complexes were fully characterized by single-crystal X-ray diffraction (Figure 4). With structures similar to those of 1 and 2, the macrocycles 4 and 5 have longer edges, at 9.1854 A˚ (Ir- - -carboxylate- - -Ir separation) and 9.9511 A˚ (Ir- - -carboxylate- - -Ir separation) forming channels with 11.4580 and 12.2345 A˚ inside diameter in the solid state, respectively. Meanwhile, C-H bond activation occurred in 4 and 5, which played an important role in the construction of these metallamacrocycles. In conclusion, a concise method has been carried out to functionalize C-H bonds under milder conditions, which can assemble supramolecular nanochannel architectures via C-H activation. The series of complexes 1-5 were fully characterized, and in order to further determine their structures, single-crystal X-ray diffraction was carried out. Structural analysis indicates that the formation of tetranuclear macrocycles can employ hydrocarbon activation. Furthermore, the molecular structure of complex 3 has powerfully supported the notion that the formation of macrocycles in the other complexes could not play a vital role in C-H bond

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Figure 4. Molecular structures of complexes 3-5. Guest molecules, free molecules, and hydrogen atoms are omitted for clarity. Legend: bright green, iridium; black, carbon; red, oxygen; blue, nitrogen.

activation. Further studies on the application of C-H activation based on the iridium fragment system are in progress.

Experimental Details General Procedures. All manipulations were performed under an atmosphere of nitrogen using standard Schlenk techniques. Dichloromethane and methanol were distilled. The starting materials [Cp*IrCl(μ-Cl)]2 were prepared according to the literature methods,18 while other chemicals were obtained commercially and used without further purification. Elemental analyses were performed on an Elementar III Vario EI analyzer. 1 H NMR (400 MHz) spectra were obtained on a Bruker DMX500 spectrometer in [D6]DMSO solution. IR spectra were measured on a Nicolet Avatar-360 spectrophotometer (as KBr pellets). Thermogravimetric analyses (TGA) were carried out under an N2 atmosphere with a heating rate of 8 °C/min on a STA449C integration thermal analyzer. Synthesis of 1-5. To a solution of [Cp*IrCl(μ-Cl)]2 (80 mg, 0.1 mmol) in CH2Cl2 (20 mL) was added pyrazine (8 mg, 0.1 mmol)/4,40 -bipyridine (10 mg, 0.1 mmol) at room temperature. After vigorous stirring for 3 h, AgOTf (102 mg, 0.4 mmol) was then added to the solution and the reaction was carried out in the dark. Finally, terephthalic acid (16.6 mg, 0.1 mmol)/ benzoic acid (12.2 mg, 0.1 mmol)/naphthalene-2,6-dicarboxylic acid (21.6 mg, 0.1 mmol)/4,40 -dibenzoic acid (24.2 mg, 0.1 mmol) was added to the solution with TEA (0.5 mL), and vigorous stirring was continued for 10 h. After the reaction was complete, the solution was filtered to remove undissolved compounds. The filtrate was concentrated and further purified via neutral alumina gel chromatography (CHCl2, CH3OH). Red compounds were obtained by concentration via vacuum: 1, 54.2 mg (52%); obtained complex 2, 51 mg (50%); complex 3, 55 mg (56%); complex 4, 46 mg (48%); complex 5, 67 mg (60%). Red needlelike crystals of 1 were obtained by slowly diffusing ether into the solution for several days. Complexes 2-5 were obtained via the same process as complex 1. Data for complex 1 are as follows. Anal. Calcd for C66H92Ir4N4O16: C, 40.31; H, 4.72; N, 2.85. Found: C, 40.52; H, 4.74;N, 2.84. 1H NMR (400 MHz, [D6]DMSO): δ 1.65 (s, 15H, CH3 Cp*), 7.48 (d, 2H, terephthalate), 8.66 (s, 4H, pyrazinyl).13C NMR (150 MHz, CDCl3): δ 8.514 (CH3 Cp*), 45.911 (C Cp*), 94.058, 136.102, and 141.679 (benzenyl), 144.926 (pyrazine), (18) White, C.; Yates, A.; Maitles, P. M. Inorg. Synth. 1992, 29, 228.

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183.534 (carbonyl). IR (KBr, cm-1): 3439 (m), 2914 (m), 2566 (w), 1618 (s), 1594 (s), 1458 (m), 1415 (m), 1373 (s), 1299 (s), 1155 (m), 1030 (s), 832 (w), 793 (m), 641 (m), 520 (w). Data for complex 2 are as follows. Anal. Calcd for C76H92Ir4N4O14: C, 44.43; H, 4.51; N, 2.73. Found: C, 44.51; H, 4.48; N, 2.71. 1H NMR (400 MHz, [D6]DMSO): δ 2.15 (s, 15H, CH3 Cp*), 7.55 (d, 2H, terephthalate), 7.90 (m, 4H, dipyridyl), 8.80 (m, 4H, dipyridyl). 13C NMR (150 MHz, CDCl3): δ 7.628 (CH3 Cp*), 45.709 (C Cp*), 93.363, 115.254, and 118.439 (benzyl), 121.623, 124.754, and 151.028 (4,40 -bipyridine), 183.159 (carbonyl). IR (KBr, cm-1): 3430 (m), 2960 (w), 2914 (m), 1618 (s), 1595 (s), 1480 (w), 1452 (w), 1408 (w), 1372 (s), 1289 (s), 1225 (m), 1157 (m), 1032 (m), 818 (m), 784 (m), 639 (m), 516 (m). Data for complex 3 are as follows. Anal. Calcd for C38H42Ir2N2O4: C, 46.80; H, 4.34; N, 2.87. Found: C, 46.38; H, 4.30; N, 2.89. 1H NMR (400 MHz, [D6]DMSO): δ 1.67(d, 30H, CH Cp*), 7.03 (m, 2H, benenzyl), 7.24 (m, 4H, benzenyl), 7.56 (d, 2H, benzenyl), 8.66(s, 4H, pyrazinyl). 13C NMR (150 MHz, CDCl3): δ 8.763 (CH3, Cp*), 46.021 (Cp*), 88.204, 119.726, 123.615, 129.299, and 132.981 (benzenyl), 149.972 (pyrazine), 184.789 (carbonyl). IR (KBr, cm-1): 3108 (w), 3052 (w), 2986 (w), 2914 (w), 2484 (w), 1618 (s), 1449 (m), 1386 (w), 1342 (m), 1256 (s), 1163 (s), 1029 (s), 804 (w), 743 (w), 635 (s). Data for complex 4 are as follows. Anal. Calcd for C72H76Ir4N4O8: C, 45.65; H, 4.04; N, 2.96. Found: C, 45.92; H, 4.02; N, 2.94. 1 H NMR (400 MHz, [D6]DMSO): δ 1.64(d, 15H, CH3 Cp*), 6.95(s, 2H, naphthalate), 7.08 (s, 2H, naphthalate), 7.80 (d, 4H, pyrazinyl). 13C NMR (150 MHz, CDCl3): δ 8.015 (CH3, Cp*), 46.039 (Cp*), 99.814, 115.603, 118.788, 121.953, and 125.138 (naphthalenyl), 131.011 (pyrazine), 166.709 (carbonyl). IR (KBr, cm-1): 3447 (m), 2926 (m), 2848 (w), 1950 (s), 1458 (w), 1338 (m), 1279 (s), 1252 (s), 1159 (s), 1030 (s), 789 (w), 641 (m), 516 (w). Data for complex 5 are as follows. Anal. Calcd for C84H116Ir4N4O18: C, 45.07; H, 5.22; N, 2.50. Found: C, 45.30; H, 5.18; N, 2.48. 1 H NMR (400 MHz, [D6]DMSO): δ 1.70 (d, 15H, CH3 Cp*),

Yu et al. 7.36(m, 2H, benzenyl), 7.80 (m, 2H, benzenyl), 8.03 (m, 2H, benzenyl), 8.66 (d, 4H, pyrazinyl). 13C NMR (150 MHz, CDCl3): δ 7.593 (CH3 Cp*), 45.674 (Cp*), 93.709, 101.737, 115.086, 118.404, 121.416, and 135.814 (benzenyl), 146.607 (pyrazine), 173.685 (carbonyl). IR (KBr, cm-1): 2976 (w), 2914 (w), 2484 (w), 1706 (w), 1583 (s), 1450 (w), 1373 (m), 1322 (w), 1271 (m), 1158 (w), 1102 (w), 1030 (m), 840 (w), 779 (w), 702 (w), 635 (w). X-ray Crystallography. Single-crystal XRD data of the compounds were collected on a Bruker Smart 1000 CCD diffractometer with Mo KR radiation (λ = 0.710 73 A˚) at room temperature. The empirical absorption correction was applied by using the SADABS program.19 The structure was solved using direct methods and refined by full-matrix least squares on F2.20 In crystal 1, the guest molecules and H atoms were refined isotropically, while all other atoms were refined anisotropically.

Acknowledgment. This work was supported by the National Science Foundation of China (Nos. 20721063, 20771028), the Shanghai Leading Academic Discipline Project (No. B108), the Shanghai Science and Technology Committee (No. 08dj1400100), and the National Basic Research Program of China (No. 2009CB825300). Supporting Information Available: CIF files giving crystal data and figures giving ORTEP diagrams of complexes 1-5 and a figure giving TGA data for complex 1. This material is available free of charge via the Internet at http://pubs.acs.org. (19) Sheldrick, G. M. SADABS, Program for Empirical Absorption Correction of Area Detector Data; University of G€ottingen, G€ottingen, Germany, 1996. (20) Sheldrick, G. M. SHELXL-97; University of G€ottingen, G€ottingen, Germany, 1997.