Carboxylate Ligand-Induced Intramolecular C−H Bond Activation of

Aug 25, 2010 - The singlet resonance of Ccarbene at δ 205.2 in the 13C NMR spectrum ..... Steady-state absorption spectra were measured using a UV−...
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Organometallics 2010, 29, 4120–4129 DOI: 10.1021/om100604u

Carboxylate Ligand-Induced Intramolecular C-H Bond Activation of Iridium Complexes with N-Phenylperimidine-Based Carbene Ligands Hayato Tsurugi,† Shingo Fujita,† Gyeongshin Choi,† Tsuneaki Yamagata,† Syoji Ito,‡ Hiroshi Miyasaka,‡ and Kazushi Mashima*,† †

Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan, and ‡Division of Frontier Materials Science, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531, Japan Received June 22, 2010

We report the synthesis and structure of iridium(I) complexes with N,N0 -disubstituted perimidine carbene ligands and halides or carboxylate ligands. Iodo-, chloro-, and acetate-Ir(carbene)(cod) complexes were selectively prepared by changing the bases and silver salts. Intramolecular C-H bond activation to prepare a cyclometalated Ir(III) complex, (C∧C:)2Ir(OAc) (6), where C∧C: is a cyclometalated perimidine carbene ligand, was achieved using a carboxylate-ligated iridium complex; otherwise, C-H activation did not proceed. Acetate-Ir(carbene)(cod) (3c) reacted with benzoic anhydride at room temperature to afford benzoate-Ir(carbene)(cod) (3d). A perimidine-carbene- and phenylpyridine-ligated Ir(III) complex, (C∧C:)(C∧N)Ir(OCOR) (8), where C∧N is a cyclometalated phenylpyridine ligand, was isolated in good yield by mixing 3c or 3d and phenylpyridine under reflux in toluene. On the basis of the formation of 1,3-cyclooctadiene from the reaction mixture, we propose the following reaction mechanism for the intramolecular C-H activation: carboxylate-induced C-H bond activation and subsequent pyridine- or carbene-directed C-H bond oxidative addition, followed by the isomerization of 1,5-cyclooctadiene and reaction with carboxylic acid produces (C∧C:)(N∧C:)Ir(OCOPh). The cyclometalated complex 6 reacts with sodium acetylacetonate to form (C∧C:)2Ir(acac) (11), which exhibits phosphorescent emission at λmax = 555 nm (τ = 0.65 μs, ΦPL = 0.0018) in CH2Cl2 solution at room temperature.

Introduction Intramolecular C-H bond activation to produce cyclometalated complexes has been intensively investigated since the first reports of nickel and platinum complexes in the 1960s.1 This research area has recently attracted increasing interest because cyclometalated organometallic compounds are involved not only in various direct functionalization *Corresponding author. E-mail: [email protected]. Fax: 81-6-6850-6245. (1) (a) Kleiman, J. P.; Dubeck, M. J. Am. Chem. Soc. 1963, 85, 1544. (b) Cope, A. C.; Siekman, R. W. J. Am. Chem. Soc. 1965, 87, 3272. (c) Cope, A. C.; Friedrich, E. C. J. Am. Chem. Soc. 1968, 90, 909. (2) For reviews see: (a) Ryabov, A. D. Chem. Rev. 1990, 90, 403. (b) Shilov, A. E.; Shul'pin, G. B. Chem. Rev. 1997, 97, 2879. (c) Kakiuchi, F.; Murai, S. Acc. Chem. Res. 2002, 35, 826. (d) Ritleng, V.; Sirlin, C.; Preffer, M. Chem. Rev. 2002, 102, 1731. (e) Kakiuchi, F.; Chatani, N. Adv. Synth. Catal. 2003, 345, 1077. (f ) Zeni, G.; Larock, R. C. Chem. Rev. 2004, 104, 3341. (g) Miura, M.; Satoh, T. Top. Organomet. Chem. 2005, 14, 55. (h) Miura, M.; Satoh, T. In Handbook of C-H Transformations; Dyker, G., Ed.; Wiley-VCH: Weinheim, 2005; Vol. 1, p 223. (i) Zeni, G.; Larock, R. C. Chem. Rev. 2006, 106, 4644. ( j) Dick, A. R.; Sanford, M. S. Tetrahedron 2006, 62, 2439. (k) Godula, K.; Sames, D. Science 2006, 312, 67. (l) Alberico, D.; Scott, M. E.; Lautens, M. Chem. Rev. 2007, 107, 174. (m) Fairlamb, I. J. S. Chem. Soc. Rev. 2007, 36, 1036. (n) Seregin, I. V.; Gevorgyan, V. Chem. Soc. Rev. 2007, 36, 1173. (o) Directed Metallation; Chatani, N., Ed.; Topics in Organometallic Chemistry, Vol. 24; Springer: Berlin, 2007. (p) Kakiuchi, F.; Kochi, T. Synthesis 2008, 3013. (q) Colby, D. A.; Bergman, R. G.; Ellman, J. A. Chem. Rev. 2009, 109, 624, and references therein. pubs.acs.org/Organometallics

Published on Web 08/25/2010

reactions of aromatic and aliphatic C-H bonds2 but also in highly efficient organometallic-based light-emitting devices possessing bis- and tris-cyclometalated structures with heavy metal ions,3 such as iridium and platinum. Thus, the cyclometalation reaction is a key step in both efficient catalysis and material synthesis, and heteroatom-directed intramolecular C-H bond activation has been considered the most straightforward synthetic strategy. The use of heteroatoms as a precoordination site before activation of a C-H bond is a general strategy, and the carbene-directed C-H bond activation reaction was recently used as a functional group suitable as a precoordination site (3) For representative examples see: (a) King, K. A.; Spellane, P. J.; Watts, R. J. J. Am. Chem. Soc. 1985, 107, 1431. (b) Baldo, M. A.; O'Brien, D. F.; You, Y.; Shoustikov, A.; Sibley, S.; Thompson, M. E.; Forrest, S. R. Nature 1998, 395, 151. (c) Baldo, M. A.; Thompson, M. E.; Forrest, S. R. Nature 2000, 403, 750. (d) Lamansky, S.; Djurovich, P.; Murphy, D.; AbdelRazzaq, F.; Lee, H.-E.; Adachi, C.; Burrows, P. E.; Forrest, S. R.; Thompson, M. E. J. Am. Chem. Soc. 2001, 123, 4304. (e) Tamayo, A. B.; Alleyne, B. D.; Djurovich, P. D.; Lamansky, S.; Tsyba, I.; Ho, N. N.; Bau, R.; Thompson, M. E. J. Am. Chem. Soc. 2003, 125, 7377. (f ) Li, J.; Djurovich, P. I.; Alleyne, B. D.; Yousufuddin, M.; Ho, N. N.; Thomas, J. C.; Peters, J. C.; Bau, R.; Thompson, M. E. Inorg. Chem. 2005, 44, 1713. (g) Sajoto, T.; Djurovich, P. I.; Tamayo, A. B.; Oxgaard, J.; Goddard, W. A., III; Thompson, M. E. J. Am. Chem. Soc. 2009, 131, 9813. For reviews see: (h) Forrest, S. R. Nature 2004, 428, 911. (i) Yersin, H. Top. Curr. Chem. 2004, 241, 1–26. ( j) Highly Efficient OLEDs with Phosphorescent Materials; Yersin, H., Ed.; WileyVCH: Berlin, 2007. (k) You, Y.; Park, S. Y. Dalton Trans. 2009, 1267, and references therein. r 2010 American Chemical Society

Article Chart 1. Cyclometalated Iridium Complexes with Five-Membered N-Heterocyclic Carbenes

to prepare phosphorescent cyclometalated iridium complexes that possess a five-membered N-heterocyclic carbene framework (Chart 1, A-C).4,5 Richeson et al. reported that six-membered perimidine-based carbene ligands increase steric congestion and electron-donating ability compared to five-membered carbene ligands.6 Together with the fact that the heteroaromatic-directed C-H bond activation reaction highly depends on the ring size of the heteroaromatics,7 we anticipated that perimidine carbene ligands would affect the intramolecular C-H bond activation reaction of iridium complexes as well as the phosphorescent properties of the resulting cyclometalated iridium complexes. In fact, most iridium complexes with cyclometalated phenylcarbene ligands are prepared in a one-pot manner: simple treatment of IrCl3 or Ir(I) species with silver salt, carbenium salt, and base in 2-ethoxyethanol produces bis-/ tris(cyclometalated) iridium complexes with five-membered carbene complexes,4b,c whereas cyclometalation of perimidine carbene ligands is not achieved in a one-pot procedure. Herein we report the synthesis of iridium complexes supported by six-membered perimidine carbene ligands and their intramolecular C-H bond activation reaction. In contrast to the previously reported five-membered imidazole-based carbene complexes, introduction of a carboxylate ligand to the iridium atom was indispensable for the C-H bond activation reaction, consistent with recent studies of direct coupling reactions via C-H bond activation where the anionic ligands attached to the metal center significantly (4) (a) Hitchcock, P. B.; Lappert, M. F.; Terreros, P. J. Organomet. Chem. 1982, 239, C26. (b) Sajoto, T.; Djurovich, P. I.; Tamayo, A.; Yousufuddin, M.; Bau, R.; Thompson, M. E.; Holmes, R. J.; Forrest, S. R. Inorg. Chem. 2005, 44, 7992. (c) Tsuchiya, K.; Yagai, S.; Kitamura, A.; Karatsu, T.; Endo, K.; Mizukami, J.; Akiyama, S.; Yabe, M. Eur. J. Inorg. Chem. 2010, 6, 926. (5) Chien, C.-H.; Fujita, S.; Yamoto, S.; Hara, T.; Yamagata, T.; Watanabe, M.; Mashima, K. Dalton Trans. 2008, 916. (6) (a) Bazinet, P.; Yap, G. P. A.; Richeson, D. S. J. Am. Chem. Soc. 2003, 125, 13314. (b) Bazinet, P.; Ong, T.-G.; O'Brien, J. S.; Lavoie, N.; Bell, E.; Yap, G. P. A.; Korobkov, I.; Richeson, D. S. Organometallics 2007, 26, 2885. (7) Desai, L. V.; Stowers, K. J.; Sanford, M. S. J. Am. Chem. Soc. 2008, 130, 13285, and references therein. (8) (a) Davis, D. L.; Al-Duaij, O.; Fawcett, J.; Giardiello, M.; Hilton, S. T.; Russell, D. R. Dalton Trans. 2003, 4132. (b) Davis, D. L.; Donald, S. M. A.; Al-Duaij, O.; Macgregor, S. A.; P€olleth, M. J. Am. Chem. Soc. 2006, 128, 4210. (c) Davis, D. L.; Donald, S. M. A.; Al-Duaij, O.; Fawcett, J.; Little, C.; Macgregor, S. A. Organometallics 2006, 25, 5976. (d) Li, L.; Brennessel, W. W.; Jones, W. D. J. Am. Chem. Soc. 2008, 130, 12414. (e) Li, L.; Brennessel, W. W.; Jones, W. D. Organometallics 2009, 28, 3492. (f ) Ryabov, A. D.; Sakodinskaya, I. K.; Yatsimirsky, A. K. J. Chem. Soc., Dalton Trans. 1985, 2629. (g) Davis, D. L.; Donald, S. M. A.; Macgregor, S. A. J. Am. Chem. Soc. 2005, 127, 13754. (h) Lafrance, M.; Rowley, C. N.; Woo, T. K.; Fagnou, K. J. Am. Chem. Soc. 2006, 128, 8754. (i) Lafrance, M.; Fagnou, K. J. Am. Chem. Soc. 2006, 128, 16496. ( j) Stuart, D. R.; Villemure, E.; Fagnou, K. J. Am. Chem. Soc. 2007, 129, 12072. (k) Lafrance, M.; Gorelsky, S. I.; Fagnou, K. J. Am. Chem. Soc. 2007, 129, 14570. (l) Liegault, B.; Lapointe, D.; Caron, L.; Vlassova, A.; Fagnou, K. J. Org. Chem. 2009, 74, 1826.

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Scheme 1. Preparation of Dissymmetric Peridinium Salts

accelerated the heteroaromatic-directed C-H bond activation reaction.8 To clarify the reaction mechanism for the formation of bis(cyclometalated)iridium complexes, (C∧C:)2IrX (C∧C: = a cyclometalated perimidine carbene ligand), we conducted a reaction of carboxylate-Ir(MeNPhNcarbene)(cod) with phenylpyridine, which led to a perimidine-carbene- and phenylpyridine-ligated Ir(III) complex, (C∧C:)(C∧N)Ir(OCOR), where C∧N is a cyclometalated phenylpyridine ligand. Furthermore, we prepared an acetylacetonate derivative, (C∧C:)2Ir(acac) (acac = acetylacetonato), that exhibited phosphorescent emission at room temperature.

Results and Discussion Synthesis of Perimidinium Salts as Precursors of N-Heterocyclic Carbene Ligands. The synthesis of dissymmetric perimidinium salts is outlined in Scheme 1. Because the perimidine motif has two types of nitrogen atoms, amine and imine atoms, stepwise substitution reactions at two nitrogen atoms were easily conducted. A Cu-catalyzed N-phenylation reaction afforded N-phenylperimidine,9 which was treated with MeI and iPrI to give the corresponding salts 1a and 1b. On the other hand, N-benzyl-N-methyl derivative 2 was synthesized in a one-pot reaction of the first N-methylation in the presence of KOH followed by N-benzylation by PhCH2Cl under refluxing conditions. Both reactions produced perimidinium salts 1 and 2 in moderately good yields, which were spectroscopically characterized. Synthesis and Characterization of Halide-Ir(carbene)(cod) Complexes. The general synthesis method of late transition metal carbene complexes is based on the pregeneration of neutral carbene ligands using an appropriate base or silver carbene complexes as carbene transfer reagents by treatment with silver oxide before complexation to the metals.10 According to the reported procedure for forming perimidinebased carbenes,6 we conducted the reaction of [IrCl(cod)]2 with LiN(SiMe3)2 in the presence of excess perimidinium salt 1a in THF at room temperature. After extraction with CH2Cl2, an iridium complex with the perimidine carbene (9) deLange, B.; Lambers-Verstappen, M. H.; van de Vondervoort, L. S.; Sereinig, N.; de Rijk, R.; de Vries, A. H. M.; de Vries, V. J. G. Synlett 2006, 18, 3105. (10) (a) Bourissou, D.; Guerret, O.; Gabbai, F. P.; Bertrand, G. Chem. Rev. 2000, 100, 39. (b) Díez-Gonzalez, S.; Marion, N.; Nolan, S. P. Chem. Rev. 2009, 109, 3612.

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Scheme 2. Synthesis of (Iodo)- and (Chloro)Ir(carbene)(cod) Complexes

Figure 1. ORTEP drawing of the molecular structures of 3a (a) and 3b (b). All hydrogen atoms are omitted for clarity. Table 1. Selected Bond Distances (A˚) and Angles (deg.) of 3a and 3b

ligand was isolated in good yield (Scheme 2). The iridium center possessed an iodide anion as the halogen ligand. The singlet resonance of Ccarbene at δ 205.2 in the 13C NMR spectrum provided direct spectral evidence for the formation of 3a. The lower field shift of the carbene carbon signal compared to the unsaturated five-membered carbene carbon resonances was ascribed to the strong electron-donating character of the six-membered carbene ligand in 3a.6,11 Similar to other carbene transfer reactions using silver carbene complexes, the silver complex of the perimidine carbene acted as a carbene transfer reagent to the iridium atom: the reaction of [IrCl(cod)]2 with excess perimidinium salt 1a in the presence of Ag2O in toluene, followed by the removal of the silver salt and purification by column chromatography, yielded yellow powders of 4a in good yield (Scheme 2). In contrast to the use of LiN(SiMe3)2, FAB-MS and elemental analysis confirmed the halogen ligand of 4a was chloride. The difference in the halide ligand was probably due to the different solubility of LiI and AgI, which were formed during the complexation reaction. Iridium complexes with a more bulky perimidine carbene ligand derived from 1b were synthesized in a similar manner to 3a [LiN(SiMe3)2 as the base] and 4a (Ag2O method), giving the iodo-Ir(carbene)(cod) complex 3b and its chloro derivative 4b, respectively. In the 1H NMR spectra of 3b and 4b, the proton signal of the NCHMe2 group appeared at a lower field (δ 6.63 for 3b; 6.93 for 4b) than that of 1b, probably due to the proximity of the isopropyl group to the electron-rich metal center.6 The molecular structures of the iridium complexes 3a, 3b, 4a, and 4b were determined by X-ray crystallographic analyses. Figure 1 shows the molecular structures of iodide complexes 3a and 3b, and their bond distances and angles (11) (a) Hermann, W. A.; Elison, M.; Fisher, J.; K€ ocher, C.; Artus, G. R. J. Chem.;Eur. J. 1996, 2, 772. (b) Vazquez-Serrano, L. D.; Owens, B. T.; Buriak, J. M. Chem. Commun. 2002, 21, 2518. (c) Voutchkova, A. M.; Appelhans, L. N.; Chianese, A. R.; Crabtree, R. H. J. Am. Chem. Soc. 2005, 127, 17624. (d) Prinz, M.; Veiros, L. F.; Calhorda, M. J.; Ramao, C. C.; Herdtweck, E.; Kuehn, F. E.; Hermann, W. A. J. Organomet. Chem. 2006, 691, 4446. (e) Frey, G. D.; Rentzsch, C. F.; von Preysing, D.; Scherg, T.; Muhlhofer, M.; Herdtweck, E.; Hermann, W. A. J. Organomet. Chem. 2006, 691, 5725. (f ) Kelly, R. A., III; Clavier, H.; Giudice, S.; Scott, N. M.; Stevens, E. D.; Bordner, J.; Samardjiev, I.; Hoff, C. D.; Cavallo, L.; Nolan, S. P. Organometallics 2008, 27, 202. (g) Kownacki, I.; Kubicki, M.; Szubert, K.; Marciniec, B. J. Organomet. Chem. 2008, 693, 321. (h) Tapu, D.; Dixon, D. A.; Roe, C. Chem. Rev. 2009, 109, 3385.

3a Ir-I Ir-C19 Ir-C23 C1-N1 C1-Ir-I Ir-C1-N2 C1-N2-C18

2.6746(3) 2.162(4) 2.096(4) 1.366(6) 89.32(12) 123.9(3) 119.0(3)

Ir-C1 Ir-C20 Ir-C24 C1-N2 Ir-C1-N1 C1-N1-C12

2.035(4) 2.213(4) 2.140(4) 1.353(5) 119.1(3) 117.6(3)

3b Ir-I Ir-C21 Ir-C25 C1-N1 C1-Ir-I Ir-C1-N2 C1-N2-C18

2.6845(2) 2.173(3) 2.117(3) 1.368(3) 87.57(7) 123.88(19) 116.0(2)

Ir-C1 Ir-C22 Ir-C26 C1-N2 Ir-C1-N1 C1-N1-C12

2.038(3) 2.210(3) 2.129(3) 1.357(3) 119.02(19) 118.3(2)

are listed in Table 1 (structures of 4a and 4b are given in the Supporting Information). The coordination environments around the iridium center of 3a and 3b are essentially the same, and each iridium atom possesses a square-planar geometry. The distances of Ir-Ccarbene for 3a and 3b are 2.035(4) and 2.038(3) A˚, respectively, which are within the range observed for (X)Ir(carbene)(cod) complexes.11b,d,e,g The longer distances of Ir-C(19) and Ir-C(20) compared to those of Ir-C(23) and Ir-C(24) for 3a reflect the strong trans influence of the carbene ligand. The dihedral angles of the perimidine ring and phenyl ring attached to the nitrogen atom are 82.7° for 3a and 76.9° for 3b, and thus, the iridium atom and the hydrogen atom of the phenyl ring do not interact in these complexes. Ortho C-H Bond Activation: Preparation of a Cyclometalated Ir Complex. We examined an ortho C-H bond activation of the phenyl ring attached to a nitrogen atom of the perimidine ligand to prepare a cyclometalated complex. We previously reported the ortho-metalation of imidazoliumbased carbene ligands by iridium, following the similar reaction conditions for the synthesis of 3b and 4b.5 The different reactivity toward the C-H bond activation for the perimidine carbene ligands was ascribed to the stability of complexes 3 and 4, and the toluene solutions of 3 and 4 were stable under refluxing conditions. We also prepared an iridium complex with an N-benzylsubstituted perimidine ligand 2 to reduce the steric repulsion between the nitrogen substituent and the iridium metal

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ring,11 and we thus tried to prepare an acetate-Ir(carbene) complex. When [IrCl(cod)]2, perimidinium salt, and silver acetate were mixed in toluene, the product was a complicated reaction mixture, and no single component was isolated. The acetate-Ir(carbene) complex was successfully prepared by treatment with [IrCl(cod)]2, perimidinium salt, LiN(SiMe3)2, and excess silver acetate in THF at room temperature (eq 2). The analytically pure compound 3c was obtained by recrystallization from saturated hexane solution. The signal of the carbonyl carbon was observed at δ 176.9 in the 13C NMR, clearly indicating the presence of the acetate ligand. The molecular structure and selected bond distances and angles are listed in Figure 3 and Table S2, respectively. Similar to the halide-Ir(carbene)(cod) complexes, the iridium atom possesses a square-planar geometry and the acetate ligand attaches to the iridium in an η1-coordination mode.

Figure 2. ORTEP drawing of the molecular structure of 5. All hydrogen atoms are omitted for clarity.

Compared with the halide-Ir(carbene)(cod) complexes, the acetate derivative 3c was unstable under toluene refluxing conditions, but isolation and characterization of any reaction product failed. Ortho C-H bond activation of the phenyl group attached to the nitrogen atom of the perimidine proceeded by treatment of complex 3c with 1a, LiN(SiMe3)2, and a slight excess of silver acetate. The cyclometalated product, (C∧C:)2Ir(OAc) (6), was isolated in quantitative yield, where C∧C: is a cyclometalated perimidine carbene ligand (eq 3).

Figure 3. ORTEP drawing of the molecular structure of 3c. All hydrogen atoms are omitted for clarity.

center. The corresponding iridium complex 5 was prepared in a similar manner to the synthesis of 3b and 4b (eq 1). Crystallographic analysis to determine the molecular structure of 5 (Figure 2 and Table S1) revealed that the phenyl moiety of the benzyl group was positioned far from the metal center due to the flexibility of the benzyl methylene group. The toluene solution of 5 was stable under refluxing conditions, and no C-H bond activation was observed for 5.

Several research groups recently reported that the carboxylate group attached to the metal center is effective for the intra- and intermolecular C-H activation of the aromatic

During purification of the crude product 6 by silica gel chromatography, a small amount of 6 was decomposed to give a chloride-bridged dinuclear Ir complex, [(C∧C:)2Ir(μ-Cl)]2 (7). In the 1H NMR of 7, the resonance corresponding to the acetate ligand disappeared and a new set of signals assignable to the perimidine ligand was observed. The formation of 7 from the acetate derivative 3c is probably due to the preferential coordination of the halide ligand to the metal center over that of the acetate ligand, which was also observed for Cp*MX2 (M = Rh, Ir) complexes.11a,e A single crystal was grown from the CH2Cl2/hexane solution, and the molecular structure of 7 was clarified by X-ray crystallographic analysis. The molecular structure and selected bond distances and angles are listed in Figure 4 and Table S3, respectively. Both of the iridium atoms have a distorted octahedral geometry, and two cyclometalated perimidine carbene ligands coordinate to the metal center. Similar to the previously reported [(pypi)2Ir(μ-Cl)]2 (pypi = pyridyl[1,2-a]{2phenylimidazol}-3-ylidene) complex, the chloride atoms are

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with 3c and benzoic anhydride produced benzoate-Ir(MeNPhNcarbene)(cod) (3d) in good yield via an exchange reaction of the carboxylate group (eq 4). Carboxylate derivatives 3c and 3d were reacted with phenylpyridine in refluxing toluene to give 8c and 8d in good yield (eq 5). The 1H NMR spectrum of 8 showed one set of the perimidine-based carbene ligand, phenylpyridine, and carboxylate groups, whereas the resonances corresponding to the cod ligand were not observed. The X-ray analysis of 8d indicates the formation of (C∧C:)(C∧N)Ir(OCOPh), where C∧N is a cyclometalated phenylpyridine ligand (Figure 5; selected bond distances and angles are listed in Table S4; structure of 8c is given in the Supporting Information).

Figure 4. ORTEP drawing of the molecular structure of 7. All hydrogen atoms are omitted for clarity.

1

Figure 5. ORTEP drawing of the molecular structure of 8d. All hydrogen atoms are omitted for clarity.

positioned trans to the Caryl donor atoms, indicating a stronger trans influence of Caryl than that of Ccarbene.5 The distances of Ir-Ccarbene are similar to that in the monomeric iridium complexes 3 and 4. The ortho position of the phenyl ring attached to one of two nitrogen atoms of the perimidine ring is metalated to form a five-membered metallacycle. The distances of Ir-Caryl for Ir1-C13 and Ir1-C31 are 1.992(13) and 2.019(12) A˚, respectively, which are within the range typically observed for ortho-metalated iridium complexes.3e,4,5,11a,11d,11e The planarity of the perimidine backbone is slightly distorted due to the formation of the ortho-metalated structure. Preparation of a Perimidine-carbene- and PhenylpyridineLigated Cyclometalated Ir Complex and the Mechanistic Study. To clarify the reaction mechanism for the C-H bond activation of the phenyl group of the perimidine carbene ligand, we perfomed a controlled experiment: mixing 3c with the perimidinium salt 1a and LiN(SiMe3)2 without silver acetate afforded iodo-Ir(MeNPhNcarbene)(cod) (3a) in 60% yield due to the strong affinity of the halide ligand to the metal center. Thus, we examined the reaction of 3a with aromatic substrates having carbonyl or pyridyl groups as linkers to the central metal, instead of the perimidinium salt. Although the reaction of 3c with methyl benzoate or phenylpyridine did not proceed at room temperature, treatment

H NMR and GC-MS monitoring of the reaction sequence revealed the generation of 1,3-cod, but we did not observe an intermediate for the formation of 8. To gain further insight into the reaction mechanism, we perfomed deuterium labeling experiments (Scheme 3). First, we prepared a perimidinium salt (1a-d5) and an iridium complex (3d-d5), where the C6D5 group was attached to the nitrogen atom of the perimidine ring. Under the same conditions in which 8d was formed, one deuterium atom was incorporated into 1,3-cod (79% d0 þ 21% d1). 1,3-Cod (82% d0 þ 18% d1) was also detected by the reaction of 3d with phenylpyridined5, indicating that the deuterium atom of 1,3-cod was due to the C6D5 group attached to the perimidine and pyridine ring. On the basis of the deuterium labeling experiments, we propose the reaction pathway for the formation of 8 shown in Scheme 4. Due to the thermal instability of the carboxylate complexes 3c and 3d compared with the halide complexes 3a and 3b, carboxylate-induced intramolecular C-H bond activation may occur at the ortho position of the phenyl group bound to pyridine or perimidine in the first step to give 9, via a sterically less hindered, acetate-chelated, six-membered transition state.8b As observed for the oxidative addition of the C-H bond of R,β-unsaturated imines to rhodium compounds,12 oxidative addition of the C-H bond of the other phenyl group affords intermediate 10. Due to the (12) (a) Colby, D. A.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc. 2006, 128, 5604. (b) Colby, D. A.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc. 2008, 130, 3645.

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Scheme 3. Deuterium Labeling Experiment for the Formation of 8d

Scheme 4. Proposed Mechanism for the Formation of 8

Figure 6. ORTEP drawing of the molecular structure of 11. All hydrogen atoms are omitted for clarity. Table 2. Selected Bond Distances (A˚) and Angles (deg.) of 11 Ir-C1 Ir-C13 Ir-O1 C1-Ir-C19 C1-Ir-C31 C1-Ir-O2 C13-Ir-O1 O1-Ir-O2 O2-C40-C39

detection of 1,3-cod from the reaction mixture, isomerization of 1,5-cyclooctadiene seems to proceed via migratory insertion of Ir-H to cyclooctadiene and subsequent β-hydrogen elimination. Because hydrogen-accepted products by cyclooctadienes, cyclooctene, or cyclooctane, were not detected in the 1H NMR and GC-MS analyses, we assume that the in situ generated (13) (a) Kim, J. I.; Shin, I.-S.; Kim, H.; Lee, J.-K. J. Am. Chem. Soc. 2005, 127, 1614. (b) Thomas, K. R. J.; Velusamy, M.; Lin, J. T.; Chien, C.-H.; Tao, Y.-T.; Wen, Y. S.; Hu, Y.-H.; Chou, P.-T. Inorg. Chem. 2005, 44, 5677. (c) Huang, Y.-T.; Chuang, T.-H.; Shu, Y.-L.; Kuo, Y.-C.; Wu, P.-L.; Yang, C.-H.; Sun, I.-W. Organometallics 2005, 24, 6230. (d) Zhen, H.; Jiang, C.; Yang, W.; Jiang, J.; Huang, F.; Cao, Y. Chem.;Eur. J. 2005, 11, 5007. (e) Zhao, A.; Jiang, C.-Y.; Shi, M.; Li, F.-Y.; Yi, T.; Cao, Y.; Huang, C.-H. Organometallics 2006, 25, 3631. (f ) Zhang, X.; Gao, J.; Yang, C.; Zhu, L.; Li, Z.; Zhang, K.; Qin, J.; You, Y.; Ma, D. J. Organomet. Chem. 2006, 691, 4312. (g) Yang, C.-H.; Chen, C.-H.; Sun, I.-W. Polyhedron 2006, 25, 2407. (h) Li, W.; Chen, Z.; Zhao, Q.; Shen, L.; Li, F.; Yi, T.; Cao, Y.; Huang, C. Inorg. Chem. 2007, 46, 5518. (i) Chen, H.; Zhao, Q.; Wu, Y.; Li, F.; Yang, H.; Yi, T.; Huang, C. Inorg. Chem. 2007, 46, 11075. ( j) Shin, I.-S.; Kim, J. I.; Kwon, T.-H.; Hong, J.-I.; Lee, J.-K.; Kim, H. J. Phys. Chem. C 2007, 111, 2280. (k) Velusamy, M.; Thomas, K. R. J.; Chen, C.-H.; Lin, J. T.; Wen, Y. S.; Hsieh, W.-T.; Lai, C.-H.; Chou, P.-T. Dalton Trans. 2007, 3025. (l) Coughlin, F. J.; Westrol, M. S.; Oyler, K. D.; Byme, N.; Kraml, C.; Zysman-Colman, E.; Lowry, M. S.; Bernhard, S. Inorg. Chem. 2008, 47, 2039. (m) Bronstein, H. A.; Finlayson, C. E.; Kirov, K. R.; Friend, R. H.; Williams, C. K. Organometallics 2008, 27, 2980. (n) Agarwal, N.; Nayak, P. K. Tetrahedron Lett. 2008, 49, 2710.

2.057(4) 2.000(4) 2.162(3) 174.43(13) 96.34(14) 83.49(12) 175.60(12) 87.41(10) 126.5(4)

Ir-C19 Ir-C31 Ir-O2 C1-Ir-C13 C1-Ir-O1 C13-Ir-C32 C13-Ir-O2 O1-C38-C39 C38-C39-C40

2.069(4) 1.990(4) 2.164(3) 78.84(15) 99.36(13) 95.44(14) 88.38(12) 126.4(4) 128.6(4)

carboxylic acid directly reacts with Ir-H species to form 8 and dihydrogen in the final step. We presume that (C∧C:)2Ir(OAc) (6) was obtained in same manner, and the excess AgOAc was an acetate anion source for the reaction. Preparation of (C∧C:)2Ir(acac) and the Photophysical Properties. Homoleptic and heteroleptic cyclometalated phenylpyridine complexes and phenylcarbene complexes of Ir(III) are strong phosphorescent molecules.3f,i,j,4,13 We thus attempted to prepare tris(C∧C:)Ir to study the photophysical properties of perimidine-based carbene iridium complexes, but the preparation of tris(C∧C:)Ir complexes failed under the reaction conditions, in which 6 was formed in the presence of excess perimidinium salt. However, an acetylacetonato ligand was successfully introduced to 6, affording (C∧C:)2Ir(acac) (11). The mixed-ligated complex 11 was prepared in a successive manner from [IrCl(cod)]2 by the in situ generation of 6, followed by the addition of acetylacetone and Na2CO3 (eq 6). In the 1H NMR of 11, the olefinic proton of the acetylacetonate ligand was observed at δ 5.01. The olefinic proton of the acetylacetonate ligand and the methyl protons attached to the perimidine ligand were observed in 1:6 ratio, indicating that one acetylacetonate and two perimidine ligands were bound to the iridium atom. The molecular structure was clarified by X-ray analysis of single crystals of 11 (Figure 6 and Table 2). The iridium center has a distorted octahedral geometry, and acetylacetonate attaches to the iridium through a η2-(O,O) coordination mode. The distances of Ir-O1 (2.162(4) A˚) and Ir-O2 (2.162(4) A˚) are within the range observed for other Ir(acac) complexes.3f,4,13b,13c,13e,13g,13k The coordination geometry of

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carboxylate group bound to the iridium atom, and subsequent oxidative addition of the other C-H bonds of the phenyl group was key to producing complex 8. The acacligated complex 11 exhibited phosphorescent emission at λmax = 555 nm (τ = 0.65 μs, ΦPL = 0.0018) in CH2Cl2 solution at room temperature.

Experimental Section

Figure 7. Absorption and emission spectra (excited at 350 nm) of 11. Both spectra were measured in CH2Cl2 at room temperature.

the perimidine ligand to iridium is similar to the chlorobridged dimer 7.

The absorption and emission spectra for 11 were measured in CH2Cl2 at room temperature (Figure 7). The absorption spectrum shows an intense band at λmax = 234 nm (ε ≈ 5.8  104 M-1 cm-1) assignable to the π-π* transition of the cyclometalated perimidine ligand and a weaker band at around 300-450 nm (λmax = 349 nm, ε ≈ 2.6  104 M-1 cm-1), which is assigned to MLCT transition. Both absorptions are typically observed for cyclometalated Ir(III) complexes.3 The complex 11 was luminescent at room temperature with emission characteristics of phosphorescence at λmax = 555 nm (τ = 0.65 μs)14 in CH2Cl2 solution. The excitation spectrum of 11 matches the absorption spectrum with a maximum efficiency at π-π* and MLCT transition bands (Figure S4 in Supporting Information). The nonradiative decay rates are comparable to those of the other cyclometalated Ir(III) complexes, although the radiative decay rate is lower (kr = 2.8  103 s-1, knr = 1.5  106 s-1).14 Therefore, the quantum efficiency of 11 (ΦPL = 0.0018) is very low compared to the phenylpyridine- and phenylcarbene-based Ir complexes.

Conclusion In summary, we successfully prepared iridium(I) complexes with N,N0 -disubstituted perimidine carbene ligands. In contrast to other five-membered carbene analogues, the use of carboxylate ligands is necessary for the perimidinecarbene-directed C-H bond activation reaction. Investigation of the formation of (C∧C:)(C∧N)Ir(OCOR) (8) revealed the dissociation of 1,3-cyclooctadiene from the iridium center during the C-H bond activation reaction. On the basis of the deuterium labeling experiments for the formation of 8, a C-H bond of the phenyl group bound to the perimidine carbene or pyridine ligand was activated by the (14) See Supporting Information.

General Procedures. All manipulations involving air- and moisture-sensitive organometallic compounds were operated using the standard Schlenk techniques under argon. Perimidine,15 [IrCl(cod)]2,16 and phenylpyridine-d517 were prepared according to the literature. Other chemicals were purchased and used without further purification. Hexane, THF, toluene, and ether were dried and deoxygenated by distillation over sodium benzophenone ketyl under argon. Benzene-d6, toluene-d8, CDCl3, CD2Cl2, and DMSO-d6 were degassed and stored under Ar. 1H NMR (300 MHz, 400 MHz) and 13C NMR (75 MHz, 100 MHz) spectra were measured on Varian Unity Inova-300 and Bruker Avance III-400 spectrometers. Assignments for 1H and 13C NMR peaks for some of the complexes were aided by 2D 1H-1H COSY, 2D 1H-1H NOESY, 2D 1H-13C HETCOR, and/or 2D 1H-13C HMBC spectra. The elemental analyses were recorded by using a Perkin-Elmer 2400 at the Faculty of Engineering Science, Osaka University. GC-MS measurement was carried out using a DB-1 capillary column (0.25 mm  30 m) on a Shimadzu GCMSQP2010Plus. All melting points were measured in sealed tubes under an argon atmosphere. Steady-state absorption spectra were measured using a UV-vis spectrophotometer (Hitachi, U-3500). Steady-state emission and excitation spectra were measured with a spectrofluorometer (Hitachi, F850E). The emission lifetime of the iridium complexes was measured using a time-correlated single photon counting (TCSPC) method. The experimental setup for TCSPC measurement was described previously.18 Synthesis of N-Phenylperimidine. Perimidine (3.364 g, 20.0 mmol), Cs2CO3 (6.519 g, 20.0 mmol), and CuCl (0.595 g, 6.01 mmol) were placed in a Schlenk, and a mixture of acetylacetone (1.512 g, 15.1 mmol) and bromobenzene (4.102 g, 26.2 mmol) in NMP (40 mL) was added. The reaction mixture was degassed and heated at 130 °C for 18 h under an argon atmosphere. The suspension was cooled to ambient temperature, and saturated NaHCO3(aq) (800 mL) was added. The mixture was filtered, and the filtrate was washed with saturated NaHCO3(aq) (800 mL). The organic product was extracted with methylene chloride, and the solvent was evaporated. Purification by flash column chromatography on silica gel using CH2Cl2-MeOH as the eluent (v/v = 40:1) gave a brown solid of N-phenylperimidine in 58% yield (2.826 g, 11.6 mmol), mp 96 °C. 1H NMR (CDCl3, 300 MHz, 35 °C): δ 5.90 (d, J = 7.4 Hz, 1H), 6.87 (d, J = 7.1 Hz, 1H), 6.96 (t, J = 8.0 Hz, 1H), 7.09 (d, J = 8.2 Hz, 1H), 7.15-7.30 (m, 3H), 7.35-7.65 (m, 5H). 13C NMR (CDCl3, 75.5 MHz, 35 °C): δ 102.5, 115.5, 119.8, 121.0, 122.7, 127.1, 127.5, 128.8, 129.1, 130.7, 135.5, 139.2, 139.3, 142.9, 147.4. IR (NaCl film, cm-1): ν~ 3053, 1629, 1580, 1493, 1395, 1370, 1321, 1278, 1217, 1200, 1165, 823, 767, 698. HRMS (EI): m/z calcd for C17H12N2 244.1001; found 244.1016. Synthesis of N-Methyl-N-phenylperimidinium Iodide ([MeNPhNcarbene-H][I], 1a). Methyl iodide (42 mL, 7.0  102 mmol) was added to a Schlenk containing N-phenylperimidine (1.671 g, 6.84 (15) Herbert, J. M.; Woodgate, P. D.; Denny, W. A. J. Med. Chem. 1987, 30, 2081. (16) Herde, J. H.; Lambert, J. C.; Senoff, C. V. Inorg. Synth. 1974, 15, 18. (17) Kozhushkov, S. I.; Yufit, D. S.; Ackermann, L. Org. Lett. 2008, 10, 3409. (18) Nagasawa, Y.; Itoh, T.; Yasuda, M.; Ishibashi, Y.; Ito, S.; Miyasaka, H. J. Phys. Chem. B 2008, 112, 15758.

Article mmol). The Schlenk was covered with Al foil, and the mixture was stirred for 67 h at room temperature. After removal of excess methyl iodide, the resulting orange solid was washed with ether (50 mL  5) and dried in vacuo to give 1a in 91% yield (2.413 g, 6.25 mmol), mp 255 °C. 1H NMR (CDCl3, 300 MHz, 35 °C): δ 3.77 (s, 3H, CH3), 6.34 (d, J = 7.7 Hz, 1H), 6.85 (d, J = 7.5 Hz, 1H), 7.21-7.27 (m, 1H), 7.40-7.55 (m, 3H), 7.58-7.70 (m, 3H), 7.81-7.87 (m, 2H), 9.58 (s, 1H, NCHN). 13C NMR (CDCl3, 75.5 MHz, 35 °C): δ 39.9, 108.0, 109.3, 121.2, 124.4, 124.9, 127.5, 128.0, 128.4, 131.0, 131.3, 133.0, 134.3, 134.9, 135.4, 151.7. IR (KBr tablet, cm-1): ν~ 3061, 3035, 3009, 2948, 1660, 1605, 1587, 1491, 1421, 1379, 817, 760, 693. HRMS (FAB) for [MeNPhNcarbene-H]þ: m/z calcd for C18H15N2 259.1235; found 259.1202. Synthesis of N-Isopropyl-N-phenylperimidinium Iodide ([iPrNPhNcarbene-H][I], 1b). Isopropyl iodide (6.847 g, 40.3 mmol) was added to a Schlenk containing N-phenylperimidine (0.726 g, 2.97 mmol). The Schlenk was covered with Al foil, and the mixture was refluxed for 48 h. After removal of excess isopropyl iodide, the resulting yellow solid was purified by flash chromatography on silica gel using CH2Cl2-MeOH as the eluent (v/v = 20:1) to give a yellow powder of 1b in 65% yield (0.800 g, 1.93 mmol), mp 247 °C. 1 H NMR (CDCl3, 300 MHz, 35 °C): δ 1.78 (d, J = 6.5 Hz, 6H, CH(CH3)2), 4.75, (sept, J = 6.5 Hz, 1H, CH(CH3)2), 6.25 (d, J = 7.7 Hz, 1H), 7.11 (d, J = 7.4 Hz, 1H), 7.21 (t, J = 8.4 Hz, 1H), 7.41-7.53 (m, 3H), 7.54-7.66 (m, 3H), 7.84-7.90 (m, 2H), 8.69 (s, 1H, NCHN). 13C NMR (CDCl3, 75.5 MHz, 35 °C): δ 19.9, 54.8, 108.9, 109.1, 121.4, 124.2, 124.5, 127.5, 127.6, 128.1, 130.7, 131.0, 131.3, 133.9, 134.8, 135.5, 148.7. IR (NaCl film, cm-1): ν~ 3033, 3009, 2979, 1655, 1604, 1586, 1493, 1466, 1427, 1387, 1377, 1343, 1271, 820, 768, 731, 697. HRMS (FAB) for [iPrNPhNcarbene-H]þ: m/z calcd for C20H19N2 287.1548, found 287.1548. Synthesis of N-Methylperimidine. To an ethanol solution (36 mL) containing KOH (0.794 g, 12.0 mmol) was added perimidine (1.688 g, 10.0 mmol), and the reaction mixture was stirred for 1 h at room temperature. Methyl iodide (0.75 mL, 12.0 mmol) was added, and the mixture was refluxed for 3 h. After removal of the solvent and methyl iodide, the organic compound was extracted with CH2Cl2. All the solvent was evaporated to give a brown powder of N-methylperimidine in 61% yield (1.120 g, 6.15 mmol), mp 118 °C. 1H NMR (CDCl3, 300 MHz, 35 °C): δ 3.12 (s, 3H, NCH3), 6.05-6.14 (m, 1H), 6.83 (d, J = 7.0 Hz, 1H), 7.10-7.28 (m, 5H). 13C NMR (CDCl3, 75.5 MHz, 35 °C): δ 35.7, 100.1, 114.7, 119.2, 120.0, 122.5, 127.1, 128.4, 135.0, 138.2, 143.2, 148.2. IR (NaCl film, cm-1): ν~ 3093, 3049, 3007, 2958, 2919, 2855, 2818, 1628, 1588, 1334, 1256, 1152, 1083, 822, 768. HRMS (EI): m/z calcd for C12H10N2 182.0845, found 182.0844. Synthesis of N-Benzyl-N-methylperimidinium Chloride ([MeNBnNcarbene-H][Cl], 2). Benzyl chloride (11.0 mmol) was added to a Schlenk containing N-methylperimidine (1.149 g, 6.31 mmol). The reaction mixture was refluxed for 22 h. After cooling to room temperature, hexane (40 mL) was added and a yellow-brown precipitate was filtered and washed with hexane (40 mL  2) and ether (40 mL  3). The solid was dried in vacuo to give a yellowbrown powder of 2 in 99% yield (1.927 g, 6.24 mmol), mp 232 °C. 1 H NMR (CDCl3, 300 MHz, 35 °C): δ 3.90 (s, 3H, CH3), 5.51 (s, 2H, CH2), 6.78 (d, J = 7.6 Hz, 1H), 6.82 (d, J = 7.6 Hz, 1H), 7.26-7.56 (m, 9H), 11.5 (s, 1H, NCHN). 13C NMR (DMSO-d6, 75.5 MHz, 35 °C): δ 54.1, 55.1, 108.0, 108.7, 120.9, 123.5, 123.8, 127.6, 128.1, 128.4, 128.4, 128.9, 131.6, 132.8, 133.1, 134.1, 154.1. IR (KBr tablet, cm-1): ν~ 3030, 2933, 2900, 2820, 1990, 1664, 1604, 1589, 1497, 1466, 1454, 1427, 1377, 1347, 1257, 1231, 1163, 1137, 1081, 1052, 978, 818, 767, 711, 642. HRMS (FAB) for [MeNBnNcarbeneH]þ: m/z calcd for C19H17N2 273.1392, found 273.1402. Synthesis of Iodo-Ir(MeNPhNcarbene)(cod) (3a). THF (5.5 mL) was added to a Schlenk containing LiN(SiMe3)2 (32.0 mg, 1.9  10-1 mmol), [IrCl(cod)]2 (64.0 mg, 9.5  10-2 mmol), and 1a (73.0 mg, 1.9  10-1 mmol) at room temperature. The reaction mixture was stirred for 6 h at room temperature, and the solvent was evaporated. The iridium compound was extracted with CH2Cl2 and then purified by flash chromatography on silica

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gel using CH2Cl2 as the eluent to give a yellow powder of 3a in 74% yield (97.0 mg, 1.4  10-1 mmol), mp 265 °C (dec). 1H NMR (CDCl3, 300 MHz, 35 °C): δ 0.79-0.95 (m, 1H, CH2 of cod), 1.10-1.49 (m, 4H, CH2 of cod), 1.69-1.94 (m, 2H, CH2 of cod), 2.14-2.29 (m, 1H, CH2 of cod), 2.50-2.59 (m, 1H, dCH of cod), 3.31-3.37 (m, 1H, dCH of cod), 4.16 (s, 3H, CH3), 4.45-4.64 (m, 2H, dCH of cod), 5.98 (d, J = 8.1 Hz, 1H, Ar), 6.72 (m, 1H, Ar), 7.12 (t, J = 7.8 Hz, 1H, Ar), 7.29 (d, J = 8.1 Hz, 1H, Ar), 7.33-7.41 (m, 3H, Ar), 7.48-7.62 (m, 3H, Ar), 8.15-8.20 (m, 1H, Ar). 13C NMR (CDCl3, 75.5 MHz, 35 °C): δ 26.5 (CH2 of cod), 27.9 (CH2 of cod), 32.2 (CH2 of cod), 36.4 (CH2 of cod), 43.6 (NCH3), 54.8 (dCH of cod), 56.2 (dCH of cod), 80.8 (dCH of cod), 84.0 (dCH of cod), 104.7 (N-Ph), 106.7 (CH, perimidine ring), 119.4, 120.7 (CH, permidine ring), 121.3 (CH, N-Ph), 127.5 (CH, perimidine ring), 127.9 (CH), 128.2 (CH), 128.5 (CH, N-Ph), 128.7 (CH, N-Ph), 129.6 (CH, perimidine ring), 134.3, 134.7 (CH, perimidine ring), 136.1, 137.7, 139.1, 205.2 (IrdC). IR (KBr tablet, cm-1): ν~ 3058, 3041, 3008, 2955, 2935, 2906, 2873, 2826, 1633, 1583, 1492, 1426, 1378, 1399, 1120, 1083, 1074, 814, 767, 759, 696. MS (FAB): m/z 686 (Mþ). Anal. Calcd for C26H26IIrN2: C, 45.55; H, 3.82; N, 4.09. Found: C, 45.43; H, 3.47; N, 4.05. Iodo-Ir(iPrNPhNcarbene)(cod) (3b) was prepared in a similar manner to 3a. Yield: 60%, mp 242 °C (dec). 1H NMR (CDCl3, 300 MHz, 35 °C): δ 0.68-0.82 (m, 1H, CH2 of cod), 0.97-1.25 (m, 3H, CH2 of cod), 1.34-1.47 (m, 1H, CH2 of cod), 1.57-1.86 (m, 2H, CH2 of cod), 1.75 (d, J = 6.9 Hz, 3H, CHMe2), 1.79 (d, J = 6.9 Hz, 3H, CHMe2), 2.04-2.20 (m, 1H, CH2 of cod), 2.50-2.60 (m, 1H, dCH of cod), 3.39-3.46 (m, 1H, dCH of cod), 4.27-4.37 (m, 1H, dCH of cod), 4.49-4.57 (m, 1H, dCH of cod), 5.76 (d, J = 8.1 Hz, 1H, Ar), 6.56 (sep, J = 6.9 Hz, 1H, CHMe2), 6.91-7.02 (m, 2H, Ar), 7.15 (d, J = 8.4 Hz, 1H, Ar), 7.20-7.29 (m, 3H, Ar), 7.38-7.52 (m, 3H, Ar), 8.14 (d, J = 7.1 Hz, 1H, Ar). 13C NMR (CDCl3, 75.5 MHz, 35 °C): δ 18.1, 21.3, 26.3, 28.0, 31.9, 36.5, 55.5, 55.6, 60.7, 79.1, 83.2, 106.5, 108.0, 120.71, 120.73, 120.9, 127.2 (2C), 128.25, 128.32, 128.6, 129.3, 133.4, 134.8, 135.4, 137.3, 138.9, 205.1 (IrdC). IR (NaCl film, cm-1): ν~ 3060, 2933, 2909, 2877, 2830, 1633, 1580, 1491, 1424, 1375, 1335, 1323, 1265, 1229, 1159, 816, 768, 736, 699. MS (FAB): m/z 714 (Mþ). Anal. Calcd for C28H30IIrN2: C, 47.12; H, 4.24; N, 3.93. Found: C, 46.89; H, 4.03; N, 3.88. Synthesis of Chloro-Ir(MeNPhNcarbene)(cod) (4a). Toluene (3 mL) was added to a Schlenk containing Ag2O (47.0 mg, 2.0  10-1 mmol), [IrCl(cod)]2 (35.0 mg, 5.2  10-2 mmol), and 1a (77.0 mg, 2.0  10-1 mmol) at room temperature. The reaction mixture was stirred for 1 h at room temperature and then refluxed for 24 h. After evaporation of all the solvent, the iridium compound was extracted with CH2Cl2 and purified by flash chromatography on silica gel using CH2Cl2-MeOH as the eluent (v/v = 80:1) to give a yellow powder of 4a in 91% yield (56.0 mg, 9.5  10-2 mmol), mp >270 °C. 1 H NMR (CDCl3, 300 MHz, 35 °C): δ 0.93-1.09 (m, 1H, CH2 of cod), 1.16-1.46 (m, 3H, CH2 of cod), 1.59-1.85 (m, 2H, CH2 of cod), 1.88-2.02 (m, 1H, CH2 of cod), 2.23-2.35 (m, 1H, CH2 of cod), 2.35-2.48 (m, 1H, dCH of cod), 3.17-3.24 (m, 1H, dCH of cod), 4.21-4.31 (m, 1H, dCH of cod), 4.28 (s, 3H, CH3), 4.39-4.47 (m, 1H, dCH of cod), 6.06 (d, J = 7.5 Hz, 1H, Ar), 6.67-6.75 (m, 1H, Ar), 7.12 (t, J = 7.8 Hz, 1H, Ar), 7.29 (d, J = 8.4 Hz, 1H, Ar), 7.33-7.40 (m, 3H, Ar), 7.50-7.68 (m, 3H, Ar), 8.08-8.13 (m, 1H, Ar). 13C NMR (CDCl3, 75.5 MHz, 35 °C): δ 26.5 (CH2 of cod), 29.4 (CH2 of cod), 30.6 (CH2 of cod), 36.1 (CH2 of cod), 42.9 (NCH3), 51.0 (dCH of cod), 54.3 (dCH of cod), 82.2 (dCH of cod), 85.6 (dCH of cod), 104.8 (CH, N-Ph), 106.8 (CH, permidine ring), 119.5, 120.8 (CH, perimidine ring), 121.3 (CH, N-Ph), 127.5 (CH, permidine ring), 127.7 (CH, N-Ph), 127.9 (CH, N-Ph), 128.5 (CH), 128.6 (CH), 129.9 (CH, permidine ring), 134.2 (CH, permidine ring), 134.3, 136.0, 137.5, 139.7, 204.7 (IrdC). IR (KBr tablet, cm-1): ν~ 3060, 3041, 3011, 3000, 2952, 2934, 2909, 2874, 2828, 1634, 1583, 1491, 1428, 1378, 1350, 1340, 1121, 1082, 813, 764, 695. MS (ESI): m/z 594 (Mþ). Anal. Calcd for C26H26ClIrN2: C, 52.56; H, 4.41; N, 4.71. Found: C, 52.94; H, 4.08; N, 4.68.

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Chloro-Ir(iPrNPhNcarbene)(cod) (4b) was prepared in a similar manner to 4a. Yield: 80%, mp 250 °C (dec). 1H NMR (CDCl3, 300 MHz, 35 °C): δ 0.84-1.03 (m, 1H, CH2 of cod), 1.08-1.42 (m, 3H, CH2 of cod), 1.55-1.69 (m, 1H, CH2 of cod), 1.77-1.99 (m, 2H, CH2 of cod), 1.79 (d, J = 7.1 Hz, 3H, CHMe2), 1.88 (d, J = 7.1 Hz, 3H, CHMe2), 2.18-2.33 (m, 1H, CH2 of cod), 2.42-2.51 (m, 1H, dCH of cod), 3.29-3.36 (m, 1H, dCH of cod), 4.13-4.22 (m, 1H, dCH of cod), 4.37-4.45 (m, 1H, dCH of cod), 5.94 (d, J = 8.0 Hz, 1H, Ar), 6.93 (sep, J = 7.1 Hz, 1H, CHMe2), 6.98-7.09 (m, 2H, Ar), 7.22 (d, J = 8.1 Hz, 1H, Ar), 7.27-7.37 (m, 3H, Ar), 7.48-7.65 (m, 3H, Ar), 8.10-8.15 (m, 1H, Ar). 13C NMR (CDCl3, 75.5 MHz, 35 °C): δ 17.7, 21.0, 26.1, 29.4, 30.3, 36.4, 51.7, 53.3, 61.5, 80.3, 84.7, 106.5, 107.9, 120.7, 120.8, 120.9, 127.1, 127.2, 127.8, 128.35, 128.42, 129.6, 133.3, 134.6, 134.9, 137.0, 139.4, 204.4 (IrdC). IR (NaCl film, cm-1): ν~ 3060, 2970, 2935, 2909, 2877, 2830, 1633, 1581, 1492, 1423, 1375, 1339, 1327, 1230, 1160, 817, 768, 735, 698. MS (FAB): m/z 622 (Mþ). Anal. Calcd for C28H30ClIrN2: C, 54.05; H, 4.86; N, 4.50. Found: C, 54.26; H, 4.63; N, 4.57. Chloro-Ir(MeNBnNcarbene)(cod) (5) was prepared in a similar manner to 4a. Yield: 55% , mp 255 °C (dec). 1H NMR (CDCl3, 300 MHz, 35 °C): δ 1.25-1.49 (m, 1H, CH2 of cod), 1.64-1.86 (m, 4H, CH2 of cod), 2.08-2.38 (m, 3H, CH2 of cod), 2.90-2.99 (m, 1H, dCH of cod), 3.13-3.22 (m, 1H, dCH of cod), 4.38 (s, 3H, CH3), 4.59-4.71 (m, 2H, dCH of cod), 6.46 (d, J = 7.5 Hz, 1H, Ar), 6.72 (dd, J = 2.4 and 6.0 Hz, 1H, Ar), 7.13 (t, J = 8.1 Hz, 1H, Ar), 7.18-7.41 (m, 8H, Ar and CH2 of Bn). 13C NMR (CDCl3, 75.5 MHz, 35 °C): δ 28.6 (CH2 of cod), 29.7 (CH2 of cod), 32.3 (CH2 of cod), 33.8 (CH2 of cod), 42.8 (NCH3), 54.0, 54.9, 59.2, 84.0, 84.8, 104.6, 107.3, 119.9, 120.7, 121.2, 126.3, 127.1, 127.6, 128.6, 134.3, 134.4, 135.3, 135.6, 205.4 (IrdC). IR (NaCl film, cm-1): ν~ 3062, 3029, 2958, 2913, 2879, 2831, 1634, 1585, 1429, 1384, 1338, 815, 764, 731. MS (EI): m/z 608 (Mþ). Anal. Calcd for C27H28ClIrN2(CH2Cl2)0.33: C, 51.58; H, 4.54; N, 4.40. Found: C, 51.52; H, 4.17; N, 4.46. Synthesis of Acetate-Ir(MeNPhNcarbene)(cod) (3c). THF (30 mL) was added to a Schlenk containing LiN(SiMe3)2 (0.167 g, 1.0 mmol), [IrCl(cod)]2 (0.336 g, 5.0  10-1 mmol), 1a (0.389 g, 1.0 mmol), and AgOAc (1.669 g, 10 mmol) at room temperature. The reaction mixture was stirred for 6 h at room temperature, and the solvent was evaporated. The iridium compound was extracted with CH2Cl2, and the extract was concentrated. The resulting solid was washed with hexane (30 mL  2) to give a yellow powder of 3c in 80% yield (0.496 g, 8.0  10-1 mmol), mp 185 °C (dec). 1H NMR (CDCl3, 300 MHz, 35 °C): δ 1.03-1.59 (m, 5H, CH2 of cod), 1.83-2.04 (m, 2H, CH2 of cod), 1.98 (s, 3H, CH3COO), 2.27-2.43 (m, 2H, CH2 and dCH of cod), 2.87-2.96 (m, 1H, dCH of cod), 4.08-4.17 (m, 2H, dCH of cod), 4.29 (s, 3H, NCH3), 6.01 (d, J = 7.5 Hz, 1H, Ar), 6.69 (dd, J = 1.8 and 6.9 Hz, 1H), 7.08 (t, J = 8.1 Hz, 1H, Ar), 7.22-7.45 (m, 4H, Ar), 7.51-7.64 (m, 3H, Ar), 7.68-7.76 (m, 1H, Ar). 13C NMR (CDCl3, 75.5 MHz, 35 °C): δ 23.6 (OCCH3), 26.5 (CH2 of cod), 29.2 (CH2 of cod), 29.9 (CH2 of cod), 35.5 (CH2 of cod), 43.2 (NCH3), 48.5 (dCH of cod), 53.3 (dCH of cod), 81.2 (dCH of cod), 85.7 (dCH of cod), 104.6 (CH, N-Ph), 106.3 (CH, permidine ring), 119.4, 120.3 (CH), 120.7 (CH), 127.2 (CH, perimidine ring), 127.7 (CH), 127.8 (CH), 128.5 (CH), 128.6 (CH), 129.9 (CH), 131.3 (CH, permidine ring), 134.3, 136.0, 137.5, 140.1, 176.9 (CdO), 205.5 (IrdC). IR (NaCl film, cm-1): ν~ 3061, 2962, 2933, 2911, 2879, 2831, 1635, 1584, 1528, 1493, 1426, 1380, 1342, 1120, 1082, 815, 760, 719, 697, 669. Anal. Calcd for C28H29IrN2O2(CH2Cl2)0.33: C, 52.67; H, 4.63; N, 4.34. Found: C, 52.78; H, 4.39; N, 4.38. Synthesis of (C∧C:)2Ir(OAc) (C:∧C = C∧MeNPhNcarbene, 6). 1 H NMR (CDCl3, 300 MHz, 35 °C): δ 1.81 (s, 6H, CH3COO), 3.97 (s, 12H, NCH3), 6.52 (dd, J = 7.1 and 7.4 Hz, 2H, Ar), 6.67-6.76 (m, 4H, Ar), 6.86 (dd, J = 1.5 and 6.3 Hz, 2H, Ar), 7.40-7.51 (m, 8H, Ar), 7.68 (d, J = 7.8 Hz, 2H, Ar), 7.78 (dd, J = 2.7 and 5.4 Hz, 2H, Ar). 13C NMR (CDCl3, 75.5 MHz, 35 °C): δ 24.5 (OCCH3), 42.4 (NCH3), 106.3, 110.4, 112.0, 120.5, 121.0, 121.4, 122.2, 124.0,

Tsurugi et al. 124.3, 127.26, 127.30, 132.6, 134.6, 134.9, 138.6, 151.7, 184.9 (CdO), 207.8 (IrdC). IR (NaCl film, cm-1): ν~ 3051, 2963, 2925, 2850, 1681, 1633, 1585, 1571, 1526, 1480, 1455, 1419, 1383, 1349, 1320, 1264, 1223, 1108, 1078, 817, 744, 673. MS (FAB): m/z 707 ([M - OAc]þ). Characterization of [(C∧C:)2Ir(μ-Cl)]2 (7). Mp > 270 °C. 1H NMR (CDCl3, 300 MHz, 35 °C): δ 3.69 (s, 12H, CH3), 5.69 (d, J = 7.8 Hz, 4H, Ar), 6.37 (t, J = 7.5 Hz, 4H, Ar), 6.49 (dd, J = 1.2 and 7.2 Hz, 4H, Ar), 6.61 (t, J = 6.9 Hz, 4H, Ar), 7.05 (t, J = 7.8 Hz, 4H, Ar), 7.39-7.61 (m, 20H, Ar). 13C NMR (CDCl3, 75.5 MHz, 35 °C): δ 42.6 (NCH3), 106.1, 109.8, 110.9, 120.6, 120.9, 121.1, 121.3, 123.5, 127.2, 127.4, 128.4, 132.6, 134.1, 134.2, 138.1, 151.7, 209.9 (IrdC). IR (KBr tablet, cm-1): ν~ 3053, 2955, 2925, 1632, 1586, 1570, 1525, 1479, 1455, 1442, 1420, 1381, 1350, 1315, 1265, 1216, 1107, 1075, 1031, 816, 768, 743. MS (FAB): m/z 707 ([M - Cl]þ). Synthesis of Benzoate-Ir(MeNPhNcarbene)(cod) (3d). THF (30 mL) was added to a Schlenk containing 3c (0.57 g, 9.2  10-1 mmol) and benzoic anhydride (0.21 g, 9.22  10-1 mmol) at room temperature. The reaction mixture was stirred for 24 h at room temperature, and the solvent was evaporated. The solid was washed with ether (15 mL  2) and hexane (15 mL) to give a yellow powder of 3d in 90% yield (0.59 g, 8.5  10-1 mmol), mp 218 °C (dec). 1H NMR (C6D6, 400 MHz, 35 °C): δ 1.11-1.15 (m, 1H, CH2 of cod), 1.22-1.30 (m, 1H, CH2 of cod), 1.53-1.58 (m, 2H, CH2 of cod) 1.61-1.67 (m, 1H, CH2 of cod), 1.91-2.01 (m, 2H, CH2 of cod), 2.35-2.42 (m, 2H, CH2 and dCH of cod), 2.92-2.96 (m, 1H, dCH of cod), 4.11 (s, 3H, NCH3), 4.52-4.57 (m, 2H, dCH of cod), 5.93 (d, J = 7.4 Hz, 1H, Ar), 6.24 (d, J = 7.4 Hz, 1H, Ar), 6.75 (t, J = 7.8 Hz, 1H, Ar), 6.99-7.09 (m, 4H, Ar), 7.13-7.21 (m, 6H, Ar), 7.95-7.97 (m, 1H, Ar), 8.44-8.47 (m, 2H, Ar). 13C NMR (C6D6, 100 MHz, 35 °C): δ 27.2 (CH2 of cod), 30.4 (CH2 of cod), 30.8 (CH2 of cod), 36.7(CH2 of cod), 43.7(NCH3), 49.0 (dCH of cod), 54.2 (dCH of cod), 82.2 (dCH of cod), 86.6 (dCH of cod), 105.3 (CH), 107.0 (CH), 120.3, 120.8 (CH), 121.2 (CH), 127.7 (CH), 127.9 (CH), 128.9 (CH), 129.2 (CH), 130.8 (CH), 130.8 (CH), 131.0 (CH), 132.3 (CH), 135.3, 137.0, 137.2, 138.4, 141.1, 172.0 (OCOPh), 206.8 (IrdC). IR (KBr tablet, cm-1): ν~ 3447, 3060, 2960, 2912, 2879, 2831, 1635, 1583, 1492, 1426, 1380, 1338, 1121, 1081, 815, 763, 713. Synthesis of (C∧C:)(C∧N)Ir(OAc) (8c). Toluene (30 mL) was added to a Schlenk containing 3d (0.174 g, 2.8  10-1 mmol) and 2-phenylpyridine (0.043 g, 7.5  10-1 mmol) at room temperature. The reaction mixture was heated at 120 °C for 24 h under an argon atmosphere. The mixture was cooled to ambient temperature, and the solvent was evaporated. The resulting solid was washed with hexane (15 mL) and ether (15 mL) to give a yellow powder of 8c in 96% yield (0.178 g, 2.7  10-1 mmol), mp >270 °C (dec). 1H NMR (C6D6, 400 MHz, 35 °C): δ 1.87 (s, 3H, CH3COO), 3.90 (s, 3H, NCH3), 6.22 (d, J = 7.2 Hz, 1H, perimidine ring), 6.42 (d, J = 7.1 Hz, 1H, N-Ph), 6.58 (t, J = 6.2 Hz, 1H, py), 6.59 (t, J = 7.3 Hz, 1H, N-Ph), 6.72 (t, J = 6.2 Hz, 1H, N-Ph), 6.74 (t, J = 6.6 Hz, 1H, py-Ph), 6.86 (t, J = 7.4 Hz, 1H, py), 6.96-7.00 (m, 4H, 3H for perimidine ring; 1H for py-Ph), 7.01 (t, J = 6.7 Hz, 1H, perimidine ring), 7.11 (t, J = 5.8 Hz, 1H, py-Ph), 7.34 (d, J = 6.6 Hz, 1H, py), 7.41 (d, J = 7.9 Hz, 1H, perimidine ring), 7.46 (d, J = 6.6 Hz, 1H, Ph-py), 7.61 (d, J = 7.9 Hz, 1H, N-Ph), 8.82 (d, J = 5.5 Hz, 1H, py). 13C NMR (C6D6, 100 MHz, 35 °C): δ 23.3 (OCH3), 42.9 (NCH3), 106.7 (CH, perimidine ring), 110.6, 112.6, 118.9 (py), 121.2 (CH, perimidine ring), 121.6 (py), 122.0, 122.2, 122.3, 123.9, 124.9, 125.2, 127.6, 127.7, 129.7, 129.9, 130.4, 133.6, 133.8, 135.2, 135.5, 135.8, 137.1 (py), 138.0 (N-Ph), 138.7 (N-Ph), 147.6 (py), 150.0 (N-Ph), 166.0 (py), 191.2 (IrdC); some carbon resonances are overlapped with C6D6 signals. Synthesis of (C∧C:)(C∧N)Ir(OC(O)Ph) (8d). Toluene (30 mL) was added to a Schlenk containing 3d (0.508 g, 7.5  10-1 mmol) and 2-phenylpyridine (0.115 g, 7.5  10-1 mmol) at room temperature. The reaction mixture was heated at 120 °C for 24 h under an argon atmosphere. The mixture was cooled to

Article ambient temperature, and the solvent was evaporated. The resulting solid was washed with hexane (15 mL) and ether (15 mL) to give a yellow powder of 8d in 94% yield (0.517 g, 7.1  10-1 mmol), mp >270 °C (dec). 1H NMR (C6D6, 400 MHz, 35 °C): δ 3.91 (s, 3H, NCH3), 6.10 (d, J = 7.5 Hz, 1H, perimidine ring), 6.36 (t, J = 6.4 Hz, 1H, py), 6.49 (d, J = 7.5 Hz, 1H, N-Ph), 6.62 (t, J = 7.5 Hz, 1H, N-Ph), 6.74 (t, J = 7.5 Hz, 1H, py-Ph), 6.76 (t, J = 7.5 Hz, 1H, N-Ph), 6.87 (t, J = 7.9 Hz, 2H, py and py-Ph), 6.93 (t, J = 8.1 Hz, 1H, perimidine ring), 6.99 (t, J = 8.1 Hz, 1H, perimidine ring), 7.07-7.12 (m, 6H, 1H for Ph-py; 2H for perimidine ring; 3H for m, p-O2CPh), 7.30 (d, J = 8.2 Hz, 1H, py), 7.42 (d, J = 7.8 Hz, 1H, perimidine ring), 7.47 (d, J = 7.8 Hz, 1H, Ph-py), 7.64 (d, J = 8.1 Hz, 1H, N-Ph), 8.33-8.34 (m, 2H, o-O2CPh), 8.86 (d, J = 5.3 Hz, 1H, py). 13C NMR (C6D6, 100 MHz, 35 °C): δ 42.8 (NCH3), 107.0 (CH, perimidine ring), 110.7 (CH, perimidine ring), 112.9, 118.9 (py), 121.3 (CH, perimidine ring), 122.6 (py), 124.1 (N-Ph), 124.8, 125.2 (py-Ph), 127.6 (CH, perimidine ring), 127.7 (CH, perimidine ring), 127.8, 128.3, 128.4, 128.7, 129.9 (CH, O2CPh-o), 130.5 (pyPh), 132.6 (CH, O2CPh-p), 133.5, 134.0 (N-Ph), 135.2, 135.8, 138.1 (py), 138.8 (N-Ph), 144.6 (N-Ph), 147.8 (py), 153.0 (N-Ph), 165.9 (py), 193.9 (IrdC); some carbon resonances are overlapped with C6D6 signals. IR (KBr tablet, cm-1): ν~ 3448, 3050, 1633, 1603, 1586, 1516, 1477, 1421, 1385, 1319, 1265, 1064, 1030, 860, 817, 755, 719, 687. MS (FAB): m/z 725 (Mþ). Synthesis of N-Methyl-N-pentadeuteriophenylperimidinium Iodide ([MeNC6D5Ncarbene-H][ I], 1a-d5). 1H NMR (CDCl3, 400 MHz, 35 °C): δ 3.77 (s, 3H, CH3), 6.34 (d, J = 7.7 Hz, 1H, Ar), 6.85 (d, J = 7.5 Hz, 1H, Ar), 7.25 (t, J = 8.0 Hz, 1H, Ar), 7.44 (t, J = 7.3 Hz, 1H, Ar), 7.48 (d, J = 8.8 Hz, 1H, Ar), 7.54 (d, J = 8.5 Hz, 1H, Ar), 9.60 (s, 1H, NCHN). 13C NMR (CDCl3, 100 MHz, 35 °C): δ 39.9, 108.0, 109.3, 121.2, 124.4, 124.9, 128.0, 128.4, 133.0, 134.3, 134.9, 151.7. IR (KBr tablet, cm-1): ν~ 3448, 3030, 2270, 1661, 1605, 1589, 1555, 1496, 1424, 1384, 1349, 1258, 1228, 1144, 815, 762, 635. MS (FAB): m/z 264 ([MeNC6D5Ncarbene-H]þ). Synthesis of (C∧C:-d4)(C∧N)Ir(OC(O)Ph) (8-(C∧C:-d4)). 1H NMR (C6D6, 400 MHz, 35 °C): δ 3.91 (s, 3H, NCH3), 6.10 (d, J = 7.5 Hz, 1H, perimidine ring), 6.36 (t, J = 6.4 Hz, 1H, py), 6.74 (t, J = 7.5 Hz, 1H, py-Ph), 6.87 (t, J = 7.9 Hz, 2H, py and py-Ph), 6.93 (t, J = 8.1 Hz, 1H, perimidine ring), 6.99 (t, J = 8.1 Hz, 1H, perimidine ring), 7.07-7.12 (m, 6H, 1H for Ph-py; 2H for perimidine ring; 3H for m,p-O2CPh), 7.30 (d, J = 8.2 Hz, 1H, py), 7.42 (d, J = 7.8 Hz, 1H, perimidine ring), 7.47 (d, J = 7.8 Hz, 1H, Ph-py), 8.33-8.34 (m, 2H, o-O2CPh), 8.86 (d, J = 5.3 Hz, 1H, py). Synthesis of (C∧C:)(C∧N-d4)Ir(OC(O)Ph) (8-(C∧N-d4)). 1H NMR (C6D6, 400 MHz, 35 °C): δ 3.91 (s, 3H, NCH3), 6.10 (d, J = 7.5 Hz, 1H, perimidine ring), 6.36 (t, J = 6.4 Hz, 1H, py), 6.49 (d, J = 7.5 Hz, 1H, N-Ph), 6.62 (t, J = 7.5 Hz, 1H, N-Ph), 6.76 (t, J = 7.5 Hz, 1H, N-Ph), 6.87 (t, J = 7.9 Hz, 1H, py), 6.93 (t, J = 8.1 Hz, 1H, perimidine ring), 6.99 (t, J = 8.1 Hz, 1H, perimidine ring), 7.07-7.12 (m, 5H, 2H for perimidine ring; 3H for m,p-O2CPh), 7.30 (d, J = 8.2 Hz, 1H, py), 7.42 (d, J = 7.8 Hz, 1H, perimidine ring), 7.64 (d, J = 8.1 Hz, 1H, N-Ph), 8.33-8.34 (m, 2H, o-O2CPh), 8.86 (d, J = 5.3 Hz, 1H, py). Synthesis of (C∧C:)2Ir(acac) (11). Toluene (5 mL) was added to a Schlenk containing LiN(SiMe3)2 (58.0 mg, 3.50  10-1 mmol), [IrCl(cod)]2 (58.0 mg, 8.70  10-2 mmol), 1a (135.0 mg, 3.48  10-2 mmol), and AgOAc (297.0 mg, 1.78 mmol) at room temperature. The reaction mixture was stirred for 1 h at room temperature and then refluxed for 24 h. After evaporation of all the solvent, the iridium compound was extracted with CH2Cl2. The extract was concentrated, and hexane was added to form a yellow powder, which was dried in vacuo. The yellow powder was dissolved in toluene (5 mL), and Na2CO3 (95.0 mg, 8.90  10-1 mmol) and acetylacetone (0.18 mL, 1.70 mmol) were added. The reaction mixture was stirred for 1 h at room temperature and then refluxed for 6 h. After evaporation of all the solvent, the iridium compound was extracted with CH2Cl2. All the solvent was evaporated, and the resulting solid was washed with hexane to give a yellow powder of 11 in 33% yield

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(48.0 mg, 5.8  10-2 mmol), mp >270 °C. 1H NMR (CDCl3, 300 MHz, 35 °C): δ 1.62 (s, 6H, OCCH3), 3.88 (s, 6H, NCH3), 5.01 (s, 1H, OCCH), 6.56 (t, J = 7.5 Hz, 2H, Ar), 6.74 (dd, J = 8.1 and 8.2 Hz, 2H), 6.82 (dd, J = 2.4 and 6.3 Hz, 2H, Ar), 6.87 (dd, J = 1.5 and 7.5 Hz, 2H, Ar), 7.39-7.49 (m, 8H, Ar), 7.69 (d, J = 8.1 Hz, 2H, Ar), 7.79 (d, J = 7.2 Hz, 2H, Ar). 13C NMR (CDCl3, 75.5 MHz, 35 °C): δ 28.0 (OCCH), 40.4 (NCH3), 100.8, 106.0, 110.0, 111.6, 120.1, 120.4, 121.3, 121.9, 124.0, 127.26, 127.34, 129.5, 133.1, 134.5, 135.0, 139.5, 152.6, 185.9 (CdO), 206.5 (IrdC). IR (KBr tablet, cm-1): ν~ 3057, 2959, 2907, 1633, 1585, 1516, 1480, 1455, 1420, 1380, 1349, 1318, 1260, 1223, 1108, 1078, 1030, 816, 744. MS (FAB): m/z 707 ([M - acac]þ). X-ray Crystallographic Analysis. All crystals were handled similarly. The crystals were mounted on the CryoLoop (Hampton Research Corp.) with a layer of light mineral oil and placed in a nitrogen stream at 120(1) K. Measurements were made on a Rigaku RAXIS-RAPID imaging plate diffractometer or Rigaku Mercury CCD area detector with graphitemonochromated Mo KR radiation (λ = 0.71075). Crystal data and structure refinement parameters are summarized in Table S5. The structures were solved by direct methods (SIR 92,19 SIR2004,20 or SHELXS9721) and refined on F2 by full-matrix least-squares methods, using SHELXL-97.21 Non-hydrogen atoms were anisotropically refined. H-atoms were included in the refinement on calculated positionsPriding on their carrier atoms. The function minimized was [ w(Fo2 - Fc2)2] (w = 1/[σ2(Fo2) þ (aP)2 þ bP]), where P = (Max(Fo2,0) þ 2Fc2)/3 with 2 σP (Fo2) from counting 1 and wR2 were P statistics. P The functions R P ( ||Fo| - |Fc||)/ |Fo| and [ w(Fo2 - Fc2)2/ (wFo4)]1/2, respectively. The ORTEP-3 program22 was used to draw the molecules. Emission Lifetime Measurement. The light source for the picosecond time-resolved measurement was the second harmonic (355 nm) of a Ti:sapphire laser (Spectra Physics, Tsunami) generated in a type I BBO crystal, and the repetition rate was reduced to 500 kHz with a power of 1-2 μW by an EO modulator (Conoptics). The emission band at 550-560 nm of the iridium complexes was detected at the magic angle configuration utilizing a polarizer and a half-wave plate. A photomultiplier tube (Hamamatsu Photonics, R3809U-50) with an amplifier (Hamamatsu Photonics, C5594) and a TCSPC module (PicoQuant, PicoHarp 300) were used for the signal detection. A monochromator (Newport, Oriel 77250) was placed in front of the photomultiplier tube for the wavelength selection. The system response time was determined to be 32 ps full-width at half-maximum (fwhm) by scattered light from a colloidal solution.

Acknowledgment. H.T. acknowledges financial support from a Grant-in-Aid for Young Scientists (B). This work was supported by the Core Research for Evolutional Science and Technology (CREST) program of the Japan Science and Technology Agency (JST), Japan. Supporting Information Available: Molecular structures of 4a, 4b, and 8c, excitation spectra, and emission decay of 11, crystallographic data for 3a, 3b, 3c, 4a, 4b, 5, 7, 8c, 8d, and 11, and their CIF files. These materials are available free of charge via the Internet at http://pubs.acs.org. (19) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo, C.; Guagliardi, A.; Polidori, G. J. Appl. Crystallogr. 1994, 27, 435. (20) Burla, M. C.; Caliandro, R.; Camalli, M.; Carrozzini, B.; Cascarano, G. L.; De Caro, L.; Giacovazzo, C.; Polidoria, G.; Spagna, R. J. Appl. Crystallogr. 2005, 38, 381. (21) Sheldrick, G. M. Programs for Crystal Structure Analysis (Release 97-2); University of G€ottingen: Germany, 1997. (22) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.