Stepwise Formation of Half-Sandwich Iridium-Based Rectangles

May 12, 2009 - Alexandra I. Gaudette , Ie-Rang Jeon , John S. Anderson , Fernande Grandjean , Gary J. Long , and T. David Harris. Journal of the Ameri...
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Organometallics 2009, 28, 3459–3464

3459

Stepwise Formation of Half-Sandwich Iridium-Based Rectangles Containing 2,5-Diarylamino-1,4-benzoquinone Derivatives Linkers Wei-Guo Jia, Ying-Feng Han, Yue-Jian Lin, Lin-Hong Weng, and Guo-Xin Jin* Shanghai Key Laboratory of Molecular Catalysis and InnoVatiVe Material, Department of Chemistry, AdVanced Materials Laboratory, Fudan UniVersity, 200433, Shanghai, P. R. China ReceiVed February 27, 2009

Binuclear complexes [Cp*2Ir2(µ-DB)Cl2] (1-5) (Cp* ) η5-C5Me5, DB ) 2,5-diarylamino-1,4benzoquinone derivatives) were obtained by the reactions of [Cp*Ir(µ-Cl)Cl]2 with 2,5-diarylamino-1,4benzoquinone derivatives in the presence of base. Treatments of [Cp*2Ir2(µ-DB)Cl2] with bidentate ligands (L) such as pyrazine, 4,4′-bipyridine (bpy) in the presence of Ag(OTf) (OTf ) CF3SO3) in CH3OH solution gave the corresponding tetranuclear complexes, with the general formulas [Cp*4Ir4(µ-DB)2(µL)2](OTf)4 [1a,b-5a,b: DB ) 2,5-dianilino-1,4-benzoquinone (DABQ), L ) pyrazine (1a); DB ) DABQ, L ) bpy (1b); DB ) 2,5-dianilino-3,6-dichloro-1,4-benzoquinone (DCBQ), L ) pyrazine (2a); DB ) DCBQ, L ) bpy (2b); DB ) 2,5-bis(4′-chloroanilino)-3,6-dichloro-1,4-benzoquinone (BCBQ), L ) pyrazine (3a); DB ) BCBQ, L ) bpy (3b); DB ) 2,5-bis(4′-bromoanilino)-3,6-dichloro-1,4-benzoquinone (BBBQ), L ) pyrazine (4a); DB ) BBBQ, L ) bpy (4b); DB ) 2,5-bis(4′-methoxyanilino)-3,6-dichloro1,4-benzoquinone (BMBQ), L ) pyrazine (5a); DB ) BMBQ, L ) bpy (5b)]. The molecular structures of [Cp*2Ir2(µ-DABQ)Cl2] (1), [Cp*2Ir2(µ-DCBQ)Cl2] (2), [Cp*4Ir4(µ-BCBQ)2(µ-bpy)2](OTf)4 (3b), and [Cp*4Ir4(µ-BBBQ)2(µ-bpy)2](OTf)4 (4b) have been determined by single-crystal X-ray analysis. Introduction The metal-directed self-assembly of supramolecular architectures is currently attracting considerable attention, largely because of their potential for porosity and their consequent use in applications in various fields, including host-guest chemistry,1 gas separation and storage,2 ion recognition or ion exchange,3 and optoelectronics or photovoltaics,4 as well as catalysis.5 In recent years, supramolecular chemistry with organometallic half-sandwich complexes based on Ir, Rh, and Ru fragments has received considerable attention, because the complexes show a number of interesting characteristics; for example, they can be severed as specific receptors for small cations and anions.3a-c * Corresponding author. Tel: +86-21-65643776. Fax: +86-21-65641740. E-mail: [email protected]. (1) (a) Yamauchi, Y.; Yoshizawa, M.; Fujita, M. J. Am. Chem. Soc. 2008, 130, 5832–5833. (b) Takamizawa, S.; Nakata, E.; Akatsuka, T. Angew. Chem., Int. Ed. 2006, 45, 2216–2221. (c) Tanaka, D.; Masaoka, S.; Horike, S.; Furukawa, S.; Mizuno, M.; Endo, K.; Kitagawa, S. Angew. Chem., Int. Ed. 2006, 45, 4628–4631. (d) Ono, K.; Yoshizawa, M.; Kato, T.; Watanabe, K.; Fujita, M. Angew. Chem., Int. Ed. 2007, 46, 1803–1806. (e) Yamaguchi, T.; Fujita, M. Angew. Chem., Int. Ed. 2008, 47, 2067–2069. (2) (a) Rowsell, J. L. C.; Spencer, E. C.; Eckert, J.; Howard, J. A. K.; Yaghi, O. M. Science 2005, 309, 1350–1354. (b) Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O’Keeffe, M.; Yaghi, O. M. Science 2002, 295, 469–472. (c) Dincaˇ, M.; Long, J. R. Angew. Chem., Int. Ed. 2008, 47, 6766–6779. (d) Matsuda, R.; Kitaura, R.; Kitagawa, S.; Kubota, Y.; Belosludov, R. V.; Kobayashi, T. C.; Sakamoto, H.; Chiba, T.; Takata, M.; Kawazoe, Y.; Mita, Y. Nature 2005, 436, 238–241. (e) Kitagawa, S. Nature. 2006, 441, 584–585. (f) Chatterjee, B.; Noveron, J. C.; Resendiz, M. J. E.; Liu, J.; Yamamoto, T.; Parker, D.; Cinke, M.; Nguyen, C. V.; Arif, A. M.; Stang, P. J. J. Am. Chem. Soc. 2004, 126, 10645–10656. (g) Farha, O. K.; Spokoyny, A. M.; Mulfort, K. L.; Hawthorne, M. F.; Mirkin, C. A.; Hupp, J. T. J. Am. Chem. Soc. 2007, 129, 12680–10681. (3) (a) Lehaire, M.-L.; Scopelliti, R.; Piotrowski, H.; Severin, K. Angew. Chem., Int. Ed. 2002, 41, 1419–1422. (b) Piotrowski, H.; Polborn, K.; Hilt, G.; Severin, K. J. Am. Chem. Soc. 2001, 123, 2699–2700. (c) Grote, Z.; Scopelliti, R.; Severin, K. J. Am. Chem. Soc. 2004, 126, 16959–16972. (d) Shvareva, T. Y.; Skanthakurmar, S.; Soderholm, L.; Clearfield, A.; AlbrechtSchmitt, T. E. Chem. Mater. 2007, 19, 132–134.

The organic π-ligands of (cyclopentadienyl)M (M ) Rh, Ir) or (arene)Ru complexes and their derivatives can be used as building block to construct metallamacrocyclic complexes as well as coordination cages. Using this kind of half-sandwich complexes as building block offers a variety of advantages: (i) the starting materials can be synthesized easily by reactions of metal chlorides with cyclopentadienyl or arene groups, respectively; (ii) the staring materials are remarkably robust toward air and well-soluble in normal organic solvents such as THF, CH2Cl2, CHCl3; (iii) Cp* or substituted benzene groups of η6 ligands shield hemisphere of the metals on the octahedron, benefiting building a bond between the metal and donor atom, such as N, S, O, P, or carbene donor groups; (iv) introducing substituents on the cyclopentadienyl ring can also enhance solubility and the redox properties of the complexes. Many tri-, tetra-, hexa-, and octanuclear metallamacrocycles of halfsandwich complexes were studied extensively by Severin,6,3a-c Fish,7 Rauchfuss,8 Therrien,9 and our groups.10 We were interested in supramolecular complexes based on quasioctahedral geometries that bear cyclopentadienyl or arene groups and their derivatives, since a new type of supramolecular series has been developed by introduction (4) (a) Halder, G. J.; Kepert, C. J.; Moubaraki, B.; Murray, K. S.; Cashion, J. D. Science 2002, 298, 1762–1765. (b) Alvaro, M.; Carbonell, E.; Ferrer, B.; Llabre´s i Xamena, F. X.; Garica, H. Chem.sEur. J. 2007, 13, 5106–5112. (c) Yang, H.-B.; Ghosh, K.; Zhao, Y.; Northrop, B. H.; Lyndon, M. M.; Muddiman, D. C.; White, H. S.; Stang, P. J. J. Am. Chem. Soc. 2008, 130, 839–841. (d) Dinolfo, P. H.; Hupp, J. T. J. Am. Chem. Soc. 2004, 126, 16814–16819. (5) (a) Seo, J. S.; Whang, D.; Lee, H.; Jun, S. I.; Oh, J.; Jin, Y.; Kim, K. Nature 2000, 404, 982–986. (b) Zou, R. Q.; Sakurai, H.; Xu, Q. Angew. Chem., Int. Ed. 2006, 45, 2542–2546. (c) Wu, C.-D.; H, A.; Zhang, L.; Lin, W. B. J. Am. Chem. Soc. 2005, 127, 8940–8941. (d) Llabre´s i Xamena, F. X.; Abad, A.; Corma, A.; Garcia, H. J. Catal. 2007, 250, 294–298. (6) (a) Severin, K. Chem. Commun. 2006, 3859–3867. (b) Severin, K. Coord. Chem. ReV. 2003, 245, 3–10. (7) (a) Fish, R. H.; Jaouen, G. Organometallics 2003, 22, 2166–2177. (b) Fish, R. H. Coord. Chem. ReV. 1999, 185-186, 569–584.

10.1021/om900160t CCC: $40.75  2009 American Chemical Society Publication on Web 05/12/2009

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Scheme 1. Synthesis of Binuclear Iridium Complexes 1-5

of these organic moieties. We have reported a series of tetra-, hexa-, and octanuclear Ir, Rh, and Ru supramolecules bearing Cp* ligands in coordination with two different types of spacer ligands.10 The most used multifunctional ligands are oxalate (C2O42-), 1,4-dihydroxybenzoquinon (C6H4O4) or its homologues (C6H2X2O4), and pyridyl derivatives. In contrast, the tetradentate ligands containing 2,5-diarylamino-1,4-benzoquinone derivatives (C6X2O2N2R2; X ) H, or Cl) are still underdeveloped. In consideration that these ligands show good electrochemistry properties,11-13 the organometallic complexes containing these organic linkers are worth studying. Herein, we report the stepwise formation of tetranuclear iridium complexes bearing pentamethylcyclopentadienyl ligands and C6X2O2N2R2 bridges, connected by two pyridyl-based subunits. Binuclear complexes {[Cp*2Ir2(µ-DABQ)Cl2] (1) and [Cp*2Ir2(µ-DCBQ)Cl2] (2)} and tetranuclear complexes {[Cp*4Ir4(µ-BCBQ)2(µ-bpy)2](OTf)4 (3b) and [Cp*4Ir4(µBBBQ)2(µ-bpy)2] (OTf)4 (4b)} were confirmed by X-ray analyses [Cp* ) η5-C5Me5; DABQ ) 2,5-dianilino-1,4benzoquinone; DCBQ ) 2,5-dianilino-3,6-dichloro-1,4-benzoquinone; BCBQ ) (2,5-bis(4′-chloroanilino)-3,6-dichloro(8) (a) Boyer, J. L.; Ramesh, M.; Yao, H.; Rauchfuss, T. B.; Wilson, S. R. J. Am. Chem. Soc. 2007, 129, 1931–1936. (b) Klausmeyer, K. K.; Rauchfuss, T. B.; Wilson, S. R. Angew. Chem., Int. Ed. 1998, 37, 1694– 1696. (c) Contakes, S. M.; Rauchfuss, T. B.; Wilson, S. R. Angew. Chem., Int. Ed. 2000, 39, 1984–1986. (d) Klausmeyer, K. K.; Wilson, S. R.; Rauchfuss, T. B. J. Am. Chem. Soc. 1999, 121, 2705–2711. (e) Kuhlman, M. L.; Rauchfuss, T. B. J. Am. Chem. Soc. 2003, 125, 10084–10092. (9) (a) Mattsson, J.; Govindaswamy, P.; Furrer, J.; Sei, Y.; Yamaguchi, K.; Su¨ss-Fink, G.; Therrien, B. Organometallics 2008, 27, 4346–4356. (b) Govindaswamy, P.; Furrer, J.; Su¨ss-Fink, G.; Therrien, B. Z. Anorg. Allg. Chem. 2008, 634, 1349–1352. (c) Barry, N. P. E.; Govindaswamy, P.; Furrer, J.; Su¨ss-Fink, G.; Therrien, B. Z. Inorg. Chem. Commun. 2008, 11, 1300– 1303. (d) Govindaswamy, P.; Su¨ss-Fink, G.; Therrien, B. Organometallics 2007, 26, 915–924. (10) (a) Han, Y. F.; Lin, Y. J.; Weng, L. H.; Berke, H.; Jin, G.-X. Chem. Commun. 2008, 350–352. (b) Han, Y. F.; Lin, Y. J.; Jia, W. G.; Weng, L. H.; Jin, G.-X. Organometallics 2007, 26, 5848–5853. (c) Han, Y. F.; Jia, W. G.; Lin, Y. J.; Jin, G.-X. Organometallics 2008, 27, 5002–5008. (d) Han, Y. F.; Lin, Y. J.; Jia, W. G.; Jin, G.-X. Organometallics 2008, 27, 4088–4097. (e) Han, Y. F.; Lin, Y. J.; Jia, W. G.; Wang, G. L.; Jin, G.-X. Chem. Commun. 2008, 1807–1809. (f) Han, Y. F.; Jia, W. G.; Lin, Y. J.; Jin, G.-X. J. Organomet. Chem. 2008, 693, 546–550. (g) Wang, J. Q.; Ren, C. X.; Jin, G.-X. Organometallics 2006, 25, 74–81. (11) Braunstein, P.; Siri, O.; Taquet, J.; Rohmer, M.; Be´nard, M.; Welter, R. J. Am. Chem. Soc. 2003, 125, 12246–12256. (12) (a) Zhang, D.; Jin, G.-X. Organometallics 2003, 22, 2851–2854. (b) Bergman, J.; Wahlstro¨m, N.; Yudina, L. N.; Tholander, J.; Lidgren, G. Tetrahedron 2002, 58, 1443–1452. (13) Batra, M.; Kriplani, P.; Batra, C.; Ojha, K. G. Bioorg. Med. Chem. 2006, 14, 8519–8526.

1,4-benzoquinone); BBBQ ) 2,5-bis(4′-bromoanilino)-3,6dichloro-1,4-benzoquinone; bpy ) 4,4′-bipyridyl; OTf ) CF3SO3].

Results and Discussion The five potentially tetradentate N2O2 donorssDABQ,12 DCBQ,13 BCBQ,13 BBBQ, and BMBQ (2,5-bis(4′-methoxyanilino)-3,6-dichloro-1,4-benzoquinone)12shave been achieved by condensing monosubstituted anilines with 2,5-dihydroxy-pbenzoquinone or tetrachloro-p-benzoquinone according to the procedures described in the literature, respectively. As shown in Scheme 1, when [Cp*Ir(µ-Cl)Cl]2 was treated with five tetradentate N2O2 donors: (DABQ, DCBQ, BCBQ, BBBQ, and BMBQ) in the presence of excess NEt3 in CH2Cl2 at room temperature, the purple prismatic crystals of binuclear complexes (1-5) were isolated in moderate yields, respectively, after recrystallization. The binuclear half-sandwich iridium complexes 1-5 were characterized by IR, 1H NMR, and elemental analysis. For complex 1, the 1H NMR spectrum in CDCl3 shows signals at δ 1.38, 5.62, 7.18, and 7.36 ppm, which can be assigned to the methyl groups of Cp*, olefinic protons of DABQ ligand, and olefinic protons of the aromatic rings, respectively. These spectroscopic data and the combustion analyses for C and H indicate a dimeric structure in which the Ir centers are connected by 2,5-diarylamino-1,4-benzoquinone derivatives. Crystals suitable for X-ray crystallography of 1 and 2 were obtained by slow diffusion of diethyl ether into concentrated solution of the complexes in dichloromethane solution. The crystallographic data for complexes 1 and 2 are summarized in Table 1. As shown in Figure 1, the crystal structure of 1 consists of binuclear units, connected by DABQ ligand, and each iridium atom can be described as a three-legged piano stool, which is common in Cp*Ir complexes, and the iridium atom was coordinated by O and N atoms of DABQ ligand and one Cl atom. The molecular structures confirm the six-coordinate geometry about the metal atom, assuming that the Cp* ring serves as a three-coordinated ligand. The Ir-O bond distance is 2.089 Å, which is shorter than the iridium binuclear complex containing chloranilate as bis-bidenate ligand (2.116 and 2.140 Å).10d The Ir-N bond distance is 2.077 Å, which is shorter than the normal Ir-N distance due to the conjugate effect of the five-membered ring. Along the b-axis direction, the two molecular structures are parallel to each other, the intradimer Ir · · · Ir separation is 7.793 Å, and there does not appear to be

Half-Sandwich Iridium-Based Rectangles

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Table 1. Crystallographic Data and Structure Refinement Parameters for Complexes 1, 2, 3b, and 4b empirical formula formula weight crystal syst, space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) volume (Å3), Z Dc (mg/m3) µ(Mo KR) (mm-1) F(000) θ range (deg) limiting indices reflections/unique [R(int)] completeness to θ (deg) data/restraints/parameters goodness-of-fit on F2 R1, wR2 [I > 2σ(I)]a R1, wR2 (all data) largest diff peak/hole (e/Å-3) a

1

2

3b

4b

C40H46Cl6Ir2N2O2 1183.89 monoclinic, P2(1)/n 17.16(8) 7.79(4) 17.82(8) 90 107.79(6) 90 2269(18), 2 1.733 6.245 1144 1.98-27.00 -21, 20; -9, 9; -22, 11 8702/4755 [0.0444] 27.00 (96.2%) 4755/0/240 0.927 0.0323, 0.0686 0.0455, 0.0707 1.300/-1.111

C38H38Cl4Ir2N2O2 1080.90 triclinic, P1j 7.848(3) 9.483(4) 13.381(6) 95.108(5) 96.797(5) 106.129(5) 942.1(7), 1 1.905 7.374 518 1.55-26.01 -9,7; -11, 11; -12, 16 4278/3592 [0.0284] 26.01 (96.9%) 3592/0/221 0.994 0.0287, 0.0683 0.0315, 0.0689 1.289/-1.248

C100H92Cl8F12Ir4N8O16S4 3070.46 orthorhombic, Pbca 24.014(6) 31.496(8) 35.049(9) 90 90 90 26509(12), 8 1.539 4.299 11936 1.21-25.00 -28, 28; -30, 37; -41, 31 106921/23322 [0.1234] 25.00 (99.9%) 23322/83/1346 0.885 0.0993, 0.2493 0.1845, 0.2833 4.089/-0.780

C100H92Br4Cl4F12Ir4N8O16S4 3248.30 orthorhombic, Pbca 24.131(17) 31.70(2) 35.12(2) 90 90 90 26860(32), 8 1.607 5.353 12512 1.21-25.01 -28, 28; -26, 37; -41, 35 108513/23678 [0.1265] 25.01 (100.0%) 23678/33/1334 0.871 0.0807, 0.1795 0.1720, 0.2109 2.279/-1.160

R1 ) ∑|Fo| - |Fc|/∑|Fo|; wR2 ) [∑w(|Fo2| - |Fc2|)2/∑w|Fo2|2]1/2.

Figure 1. Molecular structure of 1 with thermal ellipsoids drawn at the 30% level; all hydrogen atoms are omitted for clarity. Selected lengths (Å) and angles (deg): Ir(1)-O(1), 2.089(9); Ir(1)-N(1), 2.077(9); Ir(1)-Cl(1), 2.408(10); O(1)-C(2), 1.289(7); N(1)-C(3), 1.316(8); N(1)-C(4), 1.424(8); N(1)-Ir(1)-O(1), 76.5(2); N(1)Ir(1)-Cl(1), 84.7(3); O(1)-Ir(1)-Cl(1), 85.5(2).

Figure 2. Molecular structure of 2 with thermal ellipsoids drawn at the 30% level; all hydrogen atoms are omitted for clarity. Selected lengths (Å) and angles (deg): Ir(1)-O(1), 2.075(4); Ir(1)-N(1), 2.100(4); Ir(1)-Cl(3), 2.3889(16); O(1)-C(1), 1.278(6); N(1)-C(2), 1.309(6); N(1)-C(7), 1.433(7); O(1)-Ir(1)-N(1), 75.64(15); O(1)-Ir(1)-Cl(3), 86.45(12); N(1)-Ir(1)-Cl(3), 82.92(12).

any interaction between the dimers. In addition, the two Cl atoms are oriented in a trans manner. (See Supporting Information.) The isostructural dimeric iridium complexes 2 are shown in Figure 2; the Ir-O and Ir-N distances are 2.075 and 2.100 Å, respectively. These values are similar to those of 1, indicating that the substituted Cl atoms on 1,4-benzoquinone ring have little effect on the molecular structure. As shown in Scheme 2, treatments of [Cp*2Ir2(µ-DB)Cl2] (1-5) with bidentate ligands (L) such as pyrazine and 4,4′bipyridine (bpy) in the presence of Ag(OTf) in CH3OH solution gave the corresponding tetranuclear complexes, with the general formulas [Cp*4Ir4(µ-DB)2(µ-L)2](OTf)4 (1a-5a and 1b-5b) in moderate yields, respectively. The 1H NMR spectra in 1a-5a and 1b-5b consist of two characteristic singlets at ca. δ ) 1.32 and 5.30, 7.20, 8.70 ppm due to methyl groups of Cp* ligands and aniline and pyrazine or bipyridine ligands, suggesting symmetric tetranuclear structures. Complexes 1a-5a and 1b-5b are air- and moisture-stable, and they are quite soluble in common polar organic solvents, such as CH2Cl2, CH3OH, DMF, and CH3CN.

Crystals suitable for X-ray crystallography of 3b and 4b were obtained by slow diffusion of diethyl ether into a concentrated solution of 3b and 4b in methanol solution, and the selected bond lengths and angles are listed in Table 2. As shown in Figures 3 and 4, respectively, complexes cations of 3b and 4b have remarkably similar molecular structures. As tetranuclear complex 4b, for example, bears the 4,4′-bipyridine ligand and is formulated as [Cp*4Ir4(µ-BBBQ)2(µ-bpy)2](OTf)4. The complex cation of 4b possesses a rectangular structure bridged by two BBBQ and two bpy molecules. The crystal structure of 4b is composed of one [Cp*4Ir4(µ-BBBQ)2(µ-bpy)2]4+ cation and four triflate counteranions located outside of the metallacycle. Each Ir atom is coordinated by one nitrogen atom of 4,4′bipyridine and one nitrogen, one oxygen of BBBQ ligands, resulting in a tetranuclear rectangle structure, with the dimension 11.31 × 8.07 Å, as defined by the iridium centers, and the Ir(1) · · · Ir(4) and Ir(2) · · · Ir(3) diagonal lengths in the rectangular structure are 13.65 and 14.01 Å, respectively. The rectangle dimension is larger than those of the tetranuclear iridium complexes {[Cp*4Ir4(µ-bpy)2(CA)2](OTf)4 (11.24 × 8.03)10e and

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Scheme 2. Synthesis of Tetranuclear Iridium Complexes 1a-5a and 1b-5b

Table 2. Selected Bond Distances and Angles for 3b and 4b bond distance (Å) in 3b Ir(1)-O(1) Ir(1)-N(5) Ir(2)-N(2) Ir(3)-O(3) Ir(3)-N(6) Ir(4)-N(4)

2.060(11) 2.106(12) 2.137(16) 2.048(11) 2.116(14) 2.092(15)

Ir(1)-N(1) Ir(2)-O(2) Ir(2)-N(7) Ir(3)-N(3) Ir(4)-O(4) Ir(4)-N(8)

1,4-benzoquinone derivatives as bis-bidentate ligands are used, it will be possible to synthesize supramolecules with prism or

2.101(14) 2.042(12) 2.140(17) 2.059(17) 2.089(12) 2.126(16)

bond angle (deg) in 3b O(1)-Ir(1)-N(1) N(1)-Ir(1)-N(5) O(2)-Ir(2)-N(7) O(3)-Ir(3)-N(3) N(3)-Ir(3)-N(6) O(4)-Ir(4)-N(8)

77.7(5) 87.9(6) 82.4(6) 75.3(6) 88.3(6) 83.1(6)

O(1)-Ir(1)-N(5) O(2)-Ir(2)-N(2) N(2)-Ir(2)-N(7) O(3)-Ir(3)-N(6) O(4)-Ir(4)-N(4) N(4)-Ir(4)-N(8)

82.6(5) 77.6(6) 87.6(6) 84.7(6) 77.2(6) 89.9(6)

bond distance (Å) in 4b Ir(1)-O(1) Ir(1)-N(5) Ir(2)-N(2) Ir(3)-O(3) Ir(3)-N(6) Ir(4)-N(4)

2.088(8) 2.173(10) 2.110(13) 2.078(9) 2.144(9) 2.132(12)

Ir(1)-N(1) Ir(2)-O(2) Ir(2)-N(7) Ir(3)-N(3) Ir(4)-O(4) Ir(4)-N(8)

2.131(12) 2.093(10) 2.170(11) 2.118(10) 2.105(9) 2.151(11)

bond angle (deg) in 4b O(1)-Ir(1)-N(1) N(1)-Ir(1)-N(5) O(2)-Ir(2)-N(7) O(3)-Ir(3)-N(3) N(3)-Ir(3)-N(6) O(4)-Ir(4)-N(8)

73.8(4) 88.0(4) 82.8(4) 77.0(4) 88.4(4) 84.6(4)

O(1)-Ir(1)-N(5) O(2)-Ir(2)-N(2) N(2)-Ir(2)-N(7) O(3)-Ir(3)-N(6) O(4)-Ir(4)-N(4) N(4)-Ir(4)-N(8)

Figure 3. Complex cation of 3b with thermal ellipsoids drawn at the 30% level; all hydrogen atoms are omitted for clarity.

84.6(4) 76.2(5) 89.8(5) 82.4(4) 76.6(4) 88.6(4)

[Cp*4Ir4(µ-bpy)2(µ-η4-C2O4)2] (OTf)4 (11.10 × 5.56)10b} bridged by chloranilate (CA) and oxalate ligands. The average Ir-Nbpy, Ir-NBBBQ, and Ir-O bond distances are 2.160, 2.123, and 2.091 Å, respectively. There are no π-π interactions between independent molecules, and the molecular stacking cannot form rectangle channels due to the bulky asymmetry structure of BBBQ ligand. (See Supporting Information.) In conclusion, a new series of bi- and tetranuclear halfsandwich iridium complexes containing 2,5-diarylamino-1,4benzoquinone derivatives has been synthesized and characterized. The molecular structures indicate that the tetranuclear iridium complexes are rectangles connected with two different multifunctional ligands. We believe that when 2,5-diarylamino-

Figure 4. Complex cation of 4b with thermal ellipsoids drawn at the 30% level; all hydrogen atoms are omitted for clarity.

Half-Sandwich Iridium-Based Rectangles

cubic frameworks following this general strategy, and this work is in progress.

Experimental Section General Data. All manipulations were carried out under nitrogen using standard Schlenk and vacuum-line techniques. All solvent were purified and degassed by standard procedures. The starting materials, [Cp*Ir(µ-Cl)Cl]2,14 2,5-dianilino-1,4benzoquinone (DABQ),12 2,5-dianilino-3,6-dichloro-1,4-benzoquinone (DCBQ),13 2,5-bis(4′-chloroanilino)-3,6-dichloro-1,4benzoquinone (BCBQ),13 2,5-bis(4′-bromoanilino)-3,6-dichloro-1,4benzoquinone (BBBQ),13 and 2,5-bis(4′-methoxyanilino)-3,6dichloro-1,4-benzoquinone (BMBQ)13 were synthesized according to the procedures described in the literature. The 1H NMR spectra were measured on a VAVCE-DMX 400 spectrometer. IR (KBr) spectra were recorded on a Niclolet FT-IR spectrometer. Elemental analyses were performed on an Elementar vario EL III Analyzer. General Procedure for Preparation of Binuclear Complexes 1-5. To a stirred suspension of 2,5-diarylamino-1,4-benzoquinone derivatives (0.1 mmol) and excess NEt3 in CH2Cl2 (30 mL) was added [Cp*Ir(µ-Cl)Cl]2 (80 mg, 0.1 mmol). The mixture was stirred for 10 h and then filtered using abundant CH2Cl2; the solvent was then evaporated to dryness under vacuum. The product was washed with H2O to give corresponding binuclear complex. [Cp*2Ir2(µ-DABQ)Cl2] (1). Brick red, 76 mg, 68%. Anal. Calcd for C38H42N2O2Cl2Ir2: C 44.96, H 2.76, N 5.68. Found: C 44.63, H 2.64, N 5.57. 1H NMR (400 MHz CDCl3): δ (ppm) ) 1.38 (s, Cp*, 30H), 5.62 (s, aromatic, 2H), 7.18 (m, aromatic, 2H), 7.36 (m, aromatic, 8H). IR (KBr cm-1): 2980 (w), 2917 (w), 1558 (w), 1520 (vs), 1393 (m), 1309 (w), 1258 (m), 1197 (w), 1029 (m), 812 (w), 730 (m), 697 (m). [Cp*2Ir2(µ-DCBQ)Cl2] (2). Purple, 64 mg, 59%. Anal. Calcd for C38H40N2O2Cl4Ir2: C 42.14, H 3.73, N 2.59. Found: C 41.96, H 3.35, N 2.68. 1H NMR (400 MHz CDCl3): δ (ppm) ) 1.39 (s, Cp*, 30H), 5.65 (s, aromatic, 2H), 6.95-7.30 (m, aromatic, 8H). IR (KBr cm-1): 2976 (w), 2914 (w), 1586 (w), 1486 (vs), 1361 (m), 1305 (m), 1195 (m), 1029 (m), 902 (m), 759 (w), 703 (m). [Cp*2Ir2(µ-BCBQ)Cl2] (3). Purple, 86 mg, 75%. Anal. Calcd for C38H38N2O2Cl6Ir2: C 39.65, H 3.33, N 2.44. Found: C 39.78, H 3.62, N 2.47. 1H NMR (400 MHz CDCl3): δ (ppm) ) 1.37 (s, Cp*, 30H), 6.99 (s, aromatic, 4H), 7.52 (s, aromatic, 4H). 2975 (w), 2920 (w), 1623 (w), 1484 (vs), 1377 (m), 1303 (m), 1203 (m), 1086 (m), 1032 (m), 905 (m), 784 (w). [Cp*2Ir2(µ-BBBQ)Cl2] (4). Purple, 83 mg, 67%. Anal. Calcd for C38H38N2O2Br2Cl4Ir2: C 36.84, H 3.09, N 2.26. Found: C 36.75, H 3.28, N 2.40. 1H NMR (400 MHz CDCl3): δ (ppm) ) 1.37 (s, Cp*, 30H), 7.01 (s, aromatic, 4H), 7.52 (s, aromatic, 4H). IR (KBr cm-1): 2977 (w), 2918 (w), 1622 (w), 1482 (vs), 1366 (m), 1301 (m), 1202 (m), 1168 (m), 1030 (m), 904 (m), 760 (w), 725 (m). [Cp*2Ir2(µ-BMBQ)Cl2] (5). Purple, 85 mg, 74%. Anal. Calcd for C40H44N2O4Cl4Ir2: C 42.03, H 3.88, N 2.45. Found: C 42.33, H 3.66, N 2.38. 1H NMR (400 MHz CDCl3): δ (ppm) ) 1.38 (s, Cp*, 30H), 3.82 (s, 2CH3, 6H), 6.89 (m, aromatic, 4H), 7.49 (m, aromatic, 4H). IR (KBr cm-1): 2918 (w), 1606 (w), 1484 (vs), 1362 (m), 1302 (m), 1240 (m), 1200 (m), 1167 (m), 1028 (m), 906 (w), 764 (w). General Procedure for Preparation of Tetranuclear Complexes 1a-5b. Ag(OTf) (51 mg, 0.2 mmol) was added to a solution of binuclear complex (0.1 mmol) in CH3OH (30 mL) at room temperature and stirred for 8 h, followed by filtration to remove insoluble materials. Pyrazine (8 mg, 0.1 mmol) or 4,4′-dipyridyl (16 mg, 0.1 mmol) was added to the filtrate, which stirred for 16 h. The mixture was filtered and the filtrate was concentrated to about (14) White, C.; Yates, A.; Maitlis, P. M. Inorg. Synth. 1992, 29, 228– 234.

Organometallics, Vol. 28, No. 12, 2009 3463 3 mL. Diethyl ether was added slowly to the solution, giving the corresponding tetranuclear complex. [Cp*4Ir4(µ-DABQ)2(µ-pyrazine)2](OTf)4 (1a). Dark red, 71 mg, 54%. Anal. Calcd for C88H92F12Ir4N8O16S4: C 39.99, H 3.51, N 4.24. Found: C 39.85, H 3.42, N 4.30. 1H NMR (400 MHz CD3OD): δ (ppm) ) 1.31 (s, Cp*, 60H), 5.20 (m, aromatic, 4H), 7.21 (m, aromatic, 4H), 7.46-7.63 (m, aromatic, 16H), 8.68 (m, pyrazine, 8H). IR (KBr cm-1): 2922 (m), 2853 (m), 1629 (m), 1556 (w), 1519 (s), 1391 (m), 1260 (vs), 1162 (m), 1031 (s), 825 (m), 638 (m). [Cp*4Ir4(µ-DABQ)2(µ-bpy)2](OTf)4 (1b). Brick red, 82 mg, 57%. Anal. Calcd for C100H100F12Ir4N8O16S4: C 42.97, H 3.61, N 4.01. Found: C 42.77, H 3.62, N 4.41. 1H NMR (400 MHz CD3OD): δ (ppm) ) 1.32 (s, Cp*, 60H), 5.42 (m, aromatic, 4H), 7.25 (m, aromatic, 4H), 7.50-7.87 (m, aromatic, 16H), 8.02-8.69 (m, pyridyl, 16H). IR (KBr cm-1): 2923 (m), 2852 (m), 1613 (m), 1561 (w), 1520 (s), 1393 (m), 1255 (vs), 1163 (m), 1031 (s), 820 (m), 639 (m). [Cp*4Ir4(µ-DCBQ)2(µ-pyrazine)2](OTf)4 (2a). Violet, 81 mg, 58%. Anal. Calcd for C88H88Cl4F12Ir4N8O16S4: C 38.01, H 3.19, N 4.03. Found: C 37.86, H 3.34, N 4.26. 1H NMR (400 MHz CD3OD): δ (ppm) ) 1.29 (s, Cp*, 60H), 5.49 (m, aromatic, 4H), 7.31-7.70 (m, aromatic, 16H), 8.99 (m, pyrazine, 8H). IR (KBr cm-1): 2919 (m), 2850 (m), 1627 (m), 1550 (w), 1479 (s), 1359 (m), 1267 (s), 1154 (m), 1032(s), 910 (m), 758 (m). [Cp*4Ir4(µ-DCBQ)2(µ-bpy)2](OTf)4 (2b). Violet, 95 mg, 63%. Anal. Calcd for C100H96Cl4F12Ir4N8O16S4: C 40.95, H 3.30, N 3.82. Found: C 40.60, H 3.22, N 3.65. 1H NMR (400 MHz CD3OD): δ (ppm) ) 1.31 (s, Cp*, 60H), 7.24 (m, aromatic, 4H), 7.44-7.84 (m, aromatic, 16H), 8.69-8.77 (m, pyridyl, 16H). IR (KBr cm-1): 2921 (m), 2852 (m), 1611 (m), 1479 (vs), 1359 (m), 1266 (s), 1156 (m), 1030(m), 906 (m), 758 (m). [Cp*4Ir4(µ-BCBQ)2(µ-pyrazine)2](OTf)4 (3a). Violet, 69 mg, 47%. Anal. Calcd for C88H84Cl8F12Ir4N8O16S4: C 36.22, H 2.90, N 3.84. Found: C 36.35, H 2.67, N 3.56. 1H NMR (400 MHz CD3OD): δ (ppm) ) 1.30 (s, 20CH3, 60H), 7.15-7.49 (m, aromatic, 16H), 8.69 (s, pyrazine, 8H). IR (KBr cm-1): 2925 (m), 2850 (m), 1630 (m), 1481 (s), 1353 (m), 1260 (s), 1174 (m), 1032(m), 912 (m), 768 (m). [Cp*4Ir4(µ-BCBQ)2(µ-bpy)2](OTf)4 (3b). Violet, 91 mg, 58%. Anal. Calcd for C100H92Cl8F12Ir4N8O16S4: C 39.12, H 3.02, N 3.65. Found: C 39.20, H 2.87, N 3.62. 1H NMR (400 MHz CD3OD): δ (ppm) ) 1.32 (s, Cp*, 60H), 7.25-7.68 (m, aromatic, 16H), 8.71 (m, pyridyl, 16H). IR (KBr cm-1): 2919 (m), 2850 (m), 1612 (m), 1480 (vs), 1360 (m), 1265 (s), 1156 (m), 1087 (m), 1030 (m), 901 (m), 638 (m). [Cp*4Ir4(µ-BBBQ)2(µ-pyrazine)2](OTf)4 (4a). Violet, 78 mg, 50%. Anal. Calcd for C88H84Br4Cl4F12Ir4N8O16S4: C 34.14, H 2.73, N 3.62. Found: C 34.21, H 2.50, N 3.74. 1H NMR (400 MHz CD3OD): δ (ppm) ) 1.31 (s, Cp*, 60H), 7.10-7.65 (m, aromatic, 16H), 8.64 (s, pyrazine, 8H). IR (KBr cm-1): 2921 (m), 2851 (m), 1633 (m), 1480 (s), 1390 (m), 1254 (s), 1168 (m), 10313(s), 908 (m), 640 (m). [Cp*4Ir4(µ-BBBQ)2(µ-bpy)2](OTf)4 (4b). Violet, 103 mg, 62%. Anal. Calcd for C100H92Br4Cl4F12Ir4N8O16S4: C 36.98, H 2.85, N 3.45. Found: C 36.67, H 2.59, N 3.50. 1H NMR (400 MHz CD3OD): δ (ppm) ) 1.31 (s, Cp*, 60H), 7.19-7.83 (m, aromatic, 16H), 8.71 (m, pyridyl, 16H). IR (KBr cm-1): 2922 (m), 2851 (m), 1612 (m), 1478 (vs), 1360 (m), 1265 (s), 1155 (m), 1030(m), 908 (m), 758 (m). [Cp*4Ir4(µ-BMBQ)2(µ-pyrazine)2](OTf)4 (5a). Violet, 81 mg, 56%. Anal. Calcd for C92H96Cl4F12Ir4N8O20S4: C 38.09, H 3.34, N 3.86. Found: C 38.24, H 3.53, N 3.57. 1H NMR (400 MHz CD3OD): δ (ppm) ) 1.33 (s, 20CH3, 60H), 3.92 (s, 4CH3, 12H), 7.05-7.55 (m, aromatic, 16H), 8.64 (s, pyrazine, 8H). IR (KBr cm-1): 2922 (m), 2853 (m), 1610 (m), 1482 (s), 1382 (m), 1254 (s), 1164 (m), 1033 (m), 819 (m), 641 (m). [Cp*4Ir4(µ-BMBQ)2(µ-bpy)2](OTf)4 (5b). Violet, 94 mg, 60%. Anal. Calcd for C104H104Cl4F12Ir4N8O20S4: C 40.92, H 3.43, N 3.67.

3464 Organometallics, Vol. 28, No. 12, 2009 Found: C 40.75, H 3.46, N 3.88. 1H NMR (400 MHz CD3OD): δ (ppm) ) 1.33 (s, Cp*, 60H), 3.93 (s, 4CH3, 12H), 7.08-8.09 (m, aromatic, 16H), 8.76 (m, pyridyl, 16H). IR (KBr cm-1): 2923 (m), 2854 (m), 1606 (m), 1480 (vs), 1358 (m), 1253 (s), 1162 (m), 1031 (m), 907 (m), 812 (m). X-ray Structure Determination. Diffraction data of 1, 2, 3b, and 4b were collected on a Bruker Smart APEX CCD diffractometer with graphite-monochromated Mo KR radiation (λ ) 0.710 73 Å). All the data were collected at room temperature and the structures were solved by direct methods and subsequently refined on F2 by using full-matrix least-squares techniques (SHELXL),15 and SADABS16 absorption corrections were applied to the data. All calculation was performed using the Bruker Smart program. There were disordered solvent molecules in the crystal structures of 3b and 4b, which cannot be refined properly. New data sets corresponding to omission of them were generated with the SQUEEZE algorithm17 and then the structures were refined to convergence. (15) Sheldrick. G. M. SHELXL-97, Program for the Refinement of Crystal Structures, Universita¨t Gto¨tingen: Germany, 1997. (16) Sheldrick. G. M. SADABS (2.01), Bruker/Siemens Area Detector Absorption Correction Program; Bruker AXS: Madison, WI, 1998. (17) van der Sluis, P.; Spek, A. L. Acta Crystallogr. 1990, A46, 194.

Jia et al. In complexes 1 and 2, all non-hydrogen atoms were refined anisotropically, and hydrogen atoms were located at calculated positions. In complexes 3b and 4b, non-hydrogen atoms except O14, O15, O16, F10, F11, F12, and C100 (in 3b) and F4, F5, F6, F10, F11, F12, Cl7, C99, and C100 (in 4b) were refined anisotropically and hydrogen atoms were concluded in calculated positions. A summary of the crystallographic data and structure refinement parameters are listed in Table 1.

Acknowledgment. This work was supported by the National Science Foundation of China (20531020, 20721063, 20771028), Shanghai Science and Technology Committee (08DZ2270500, 08DJ1400103), Shanghai Leading Academic Discipline Project (B108), and the National Basic Research Program of China (2009CB825300). Supporting Information Available: The crystallographic data for 1, 2, 3b, and 4b, including UV-vis absorption spectra of 4 and 1-5b and cyclic voltammogram of 4 and 4b. This material is available free of charge via the Internet at http://pubs.acs.org. OM900160T