Cp*MCl2 - American Chemical Society

Organometallics 2011, 30, 905–911 DOI: 10.1021/om101064v

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Alkyne Insertion Induced Regiospecific C-H Activation with [Cp*MCl2]2 (M = Ir, Rh) Ying-Feng Han, Hao Li, Ping Hu, 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 November 11, 2010

Regiospecific ortho-C2pyrene-H bond activation of a pyrene-based imine ligand was first promoted by sodium acetate with [Cp*IrCl2]2 to form a half-sandwich cycloiridation complex. Internal and terminal alkynes were then found to insert into the Ir-C2pyrene bond of a cycloiridation complex, which induced another regiospecific peri-C80 naphthyl-H bond activation: different coordination modes of the alkynes group were captured. Unlike the iridium-based insertion complex, which is very stable, the rhodium-catalyzed oxidative coupling of an aromatic imine with an internal alkyne effectively proceeds via regioselective C-H bond activation to produce an indenone imine product. All the intermediate compounds following C-H activation, alkyne insertion and reduction, as well as indenone imine product were fully characterized, including the determination of X-ray structures.

Introduction In the past half century, aromatic C-H activation mediated by transition metals has been investigated because of their potential use in many organic reactions and applications in industry.1 The formation of cyclometalated complexes is a key step for the development of synthetic applications. In particular, metalation of an ortho C-H bond of a substituted phenyl to form a five-membered metallacycle with nitrogen-containing ligands is common.2 Recently, a new, efficient route to the formation of nitrogen-containing half-sandwich cyclometalated complexes with [Cp*MCl2]2 (M = Rh, Ir) in the presence of sodium acetate was reported by the Davies group.3 Density functional calculations on the *Corresponding author. Tel: þ86-21-65643776. Fax: þ 86-2165641740. E-mail: [email protected]. (1) (a) Cope, A. C.; Friedrich, E. C. J. Am. Chem. Soc. 1968, 90, 909. (b) Ryabov, A. D. Chem. Rev. 1990, 90, 403. (c) Pfeffer, M. Pure Appl. Chem. 1992, 64, 335. (d) Arndtsen, B. A.; Bergman, R. G.; Mobely, T. A.; Peterson, T. H. Acc. Chem. Res. 1995, 28, 154. (e) Shilov, A. E.; Shulpin, G. B. Chem. Rev. 1997, 97, 2879. (f) Ritleng, V.; Sirlin, C.; Preffer, M. Chem. Rev. 2002, 102, 1731. (g) Zeni, G.; Larock, R. C. Chem. Rev. 2004, 104, 3341. (h) Chiou, W. H.; Lee, S. Y.; Ojima, I. Can. J. Chem. 2005, 83, 681. (i) Zeni, G.; Larock, R. C. Chem. Rev. 2006, 106, 4644. (j) Djukic, J. P.; Sortais, J. B.; Barloy, L.; Pfeffer, M. Eur. J. Inorg. Chem. 2009, 817. (2) (a) Newkome, G. R.; Puckett, W. E.; Gupta, V. K.; Kiefer, G. E. Chem. Rev. 1986, 86, 451. (b) Wang, C.-C.; Lin, P.-S.; Cheng, C.-H. J. Am. Chem. Soc. 2002, 124, 9696. (c) Chen, Y.; Sun, H.; Fl€orke, U.; Li, X. Organometallics 2008, 27, 270. (d) Nakao, Y.; Kanyiva, K. S.; Hiyama, T. J. Am. Chem. Soc. 2008, 130, 2448. (3) (a) Davies, D. L.; Al-Duaij, O.; Fawcett, J.; Giardiello, M.; Hilton, S. T.; Russell, D. R. Dalton Trans. 2003, 4132. (b) Davies, D. L.; Donald, S. M. A.; Al-Duaij, O.; Fawcett, J.; Little, C.; Macgregor, S. A. Organometallics 2006, 25, 5976. (c) Davenport, A. J.; Davies, D. L.; Fawcett, J.; Russell, D. R. J. Organomet. Chem. 2006, 691, 2221. (d) Boutadla, Y.; Al-Duaij, O.; Davies, D. L.; Griffith, G. A.; Singh, K. Organometallics 2009, 28, 433. (e) Davies, D. L.; Al-Duaij, O.; Fawcett, J.; Singh, K. Organometallics 2010, 24, 1413. (f) Boutadla, Y.; Davies, D. L.; Al-Duaij, O.; Fawcett, J.; Jones, R. C.; Singh, K. Dalton Trans. 2010, 39, 10447. r 2011 American Chemical Society

cyclometalation of dimethylbenzylamine with [Cp*IrCl2]2 showed the metal acetate provides electrophilic activation of the C-H bond and acts as an intramolecular base for the deprotonation in the process.4 Jones’ group5 has employed a similar methodology to prepare cyclometalated compounds with phenylimines and 2-phenylpyridines. Dimethylacetylenedicarboxylate (DMAD) was then found to insert into the metal-carbon bonds of the cyclometalated compounds, and then the isoquinoline salts were obtained through oxidative coupling reactions. Compared to alkyne insertion into palladium-aryl and nickel-aryl, which often gives multipleinsertion adducts,6 clean monoinsertion products could be obtained in high yields when cyclometalated Cp*Rh and Cp*Ir undergo alkyne insertion reactions.3,5,7 Using sodium acetate for certain substrates the C-H bonds were cleaved at room temperature, and the expected cyclometalated complexes were formed almost stoichiometrically (4) (a) Davies, D. L.; Donald, S. M. A.; Al-Duaij, O.; Macgregor, S. A.; Polleth, M. J. Am. Chem. Soc. 2006, 128, 4210. (b) Boutadla, Y.; Davies, D. L.; Macgregor, S. A.; Poblador-Bahamonde, A. I. Dalton Trans. 2009, 5887. (5) (a) Li, L.; Brennessel, W. W.; Jones, W. D. J. Am. Chem. Soc. 2008, 130, 12414. (b) Li, L.; Brennessel, W. W.; Jones, W. D. Organometallics 2009, 28, 3492. (c) Li, L.; Jiao, Y. Z.; Brennessel, W. W.; Jones, W. D. Organometallics 2010, 29, 4593. (6) (a) Huggins, J. M.; Bergman, R. G. J. Am. Chem. Soc. 1981, 103, 3002. (b) Maassarani, F.; Pfeffer, M.; Borgne, G. L. Organometallics 1987, 6, 2043. (c) Ferstl, W.; Sakodinskaya, I. K.; Beydoun-Sutter, N.; Borgne, G. L.; Pfeffer, M.; Ryabov, A. D. Organometallics 1997, 16, 411. (d) Reddy, K. R.; Surekha, K.; Lee, G.-H.; Peng, S.-M.; Liu, S.-T. Organometallics 2001, 20, 5557. (7) (a) Stuart, D. R.; Bertrand-Laperle, M.; Burgess, K. M. N.; Fagnou, K. J. Am. Chem. Soc. 2008, 130, 16474. (b) Guimond, N.; Fagnou, K. J. Am. Chem. Soc. 2009, 131, 12050. (c) Mochida, S.; Hirano, K.; Satoh, T.; Miura, M. J. Org. Chem. 2009, 74, 6295. (d) Umeda, N.; Tsurugi, H.; Satoh, T.; Miura, M. Angew. Chem., Int. Ed. 2008, 47, 4019. (e) Fukutani, T.; Umeda, N.; Hirano, K.; Satoh, T.; Miura, M. Chem. Commun. 2009, 5141. Published on Web 01/18/2011

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Organometallics, Vol. 30, No. 4, 2011

with [Cp*MCl2]2 (M = Rh, Ir).3-5 On the other hand, it was necessary to prepare these cyclometalated complexes separately so that the catalytic reactions and mechanisms could be fully investigated. When a ligand has two or more activated C-H bonds, the problem of cyclometalation regioselectivity and subsequent regioselective functionalization at the metalated carbon can be an issue. The regioselectivity of the cyclopalladation has two different levels, reviewed by Ryabov:1b the more trivial level, referred to as enforced regioselectivity, when electronic, steric, or other factors make only one route of cyclometalation possible, and the second level, referred to as regulated regioselectivity, in which any path of cyclometalation is available through changing the reaction conditions. Compared to C(phenyl)-H bond activation, which has been studied extensively,1-7 C(naphthyl)-H bond activation in peri-(C8naphthyl) position has received less attention. Two examples of regiospecific peri-C8naphthyl-H bond activation of 1-(20 -X-50 -methylphenylazo)naphthalene (X = OH, OMe) by disodium tetrachloropalladate and one example of regiospecific peri-C8naphthyl-H bond activation of N-(naphthyl)picolinamide with [Ir(PPh 3)3Cl] were reported.8a-d Bicyclometalation of aromatic substrates containing imine anchoring groups has been achieved with a dimethyliron complex at low temperature.8e Recently, we have developed an efficient one-pot method for synthesizing molecular macrocycles of half-sandwich iridium complexes via C-H activation directed muticomponent self-assembly under mild conditions. An approach for postsynthetic modification of organometallic macrocycles through DMAD insertion has been employed.9 Herein, we report (i) the first example to our knowledge of the controllable iridium-promoted double C-H activation in one molecule: the alkyne insertion induced a second C-H activation on the rarely activated peri-C80 naphthyl position; (ii) stabilized by the newly formed Ir-C bond, different coordination modes of the alkyne groups were captured when using internal and terminal alkynes, which may provide information about the mechanism of the alkyne insertion process, (iii) the rhodium-catalyzed oxidative coupling of an aromatic imine with internal alkyne effectively proceeds via regioselective C-H bond activation to produce an indenone imine product.

Results and Discussion Because of their intense fluorescence, excimeric formation, and fluorescence anisotropy, the synthesis of pyrene-based derivatives has been extensively studied by many groups.10 Bromopyrenes or their corresponding lithiated pyrenes at (8) (a) Hugentobler, M.; Klaus, A. J.; Mettler, H.; Rys, P.; Wehrle, G. Helv. Chim. Acta 1982, 65, 1202. (b) Neogi, D. N.; Das, P.; Biswas, A. N.; Bandyopadhyay, P. Polyhedron 2006, 25, 2149. (c) Neogi, D. N.; Biswas, A. N.; Das, P.; Bhawmick, R.; Bandyopadhyay, P. Inorg. Chim. Acta 2007, 360, 2181. (d) Dasgupta, M.; Tadesse, H.; Blake, A. J.; Bhattacharya, S. J. Organomet. Chem. 2008, 693, 3281. (e) Klein, H.-F.; Camadanli, S.; Becka, R.; Fl€ orke, U. Chem. Commun. 2005, 381. (9) Han, Y.-F.; Li, H.; Weng, L.-H.; Jin, G.-X. Chem. Commun. 2010, 3556. (10) (a) Birks, J. B. Photophysics of Aromatic Molecules; WileyInterscience: London, 1970. (b) Moon, S.-Y.; Youn, N. J.; Park, S. M.; Chang, S.-K. J. Org. Chem. 2005, 70, 2394. (c) Fujimoto, K.; Muto, Y.; Inouye, M. Chem. Commun. 2005, 4780. (d) Sharma, J.; Tleugabulova, D.; Czardybon, W.; Brennan, J. D. J. Am. Chem. Soc. 2006, 128, 5496. (e) Mcqueen, E. W.; Goldsmith, J. I. J. Am. Chem. Soc. 2009, 131, 17554. (f) Stylianou, K. C.; Heck, R.; Chong, S. Y.; Bacsa, J.; Jones, J. T. A.; Khimyak, Y. Z.; Bradshaw, D.; Rosseinsky, M. J. J. Am. Chem. Soc. 2010, 132, 4119.

Han et al. Scheme 1. Synthesis of 2a-d

the C1, C3, C6, and C8 positions were employed in the syntheses of the σ-bonded organometallic pyrene complexes.11 1-Diphenylphosphinopyrene and 1,6-bis(diphenylphosphino)pyrene can be metalated at C5 and C10 to give cycloplatination complexes.12 The pyridine-substituted pyrene ligand 4-methyl-2-pyren-1-ylpyridine is known to undergo cyclometalation reactions with IrCl3 in trimethyl phosphate.13 The cyclometalation occurred only at the 2-position with the formation of a five-membered cyclometalated ring, instead of at the 10-position of the pyrene moiety with formation of a six-membered cyclometalated ring. From the viewpoint of synthetic applications, development of C-H activation reactions for pyrene-based substrates would substantially improve the versatility and usefulness of this reaction. Therefore, we chose a series of pyrene-based imines as substrates to investigate the regioselectivity for C-H activation. Independent treatment of 1a-d with [Cp*IrCl2]2 in dichloromethane at room temperature in the presence of sodium acetate gave a series of mononuclear complexes in good yields, as shown in Scheme 1. While the electronwithdrawing substituent (p-Cl) inhibits C-H activation, the electron-donating substituent (p-OMe) benefits C-H activation, which is similar to the effects observed in aromatic C-H activation of substituted phenylimines promoted by sodium acetate with [Cp*MCl2]2 (M = Ir, Rh) to form monocyclometalated complexes.5b Crystals of 2b suitable for an X-ray diffraction study were obtained by slow diffusion of diethyl ether into a concentrated solution of the complexes in dichloromethane at low temperature. According to X-ray crystallographic analysis of 2b, the cycloiridation reaction takes place at the C2 position with the formation of a five-membered ring, the same as the expected piano-stool type geometry. A perspective drawing of 2b with selected atomic numbering scheme, bond lengths, and angles is given in Figure 1. The Ir(1)-N(1) bond length [2.087(4) A˚] and C(3)-Ir(1)-N(1) angle [77.62(17)°] are very similar to those [2.0881(15) A˚ and 77.76(6)°] in the related cycloiridation complex [Cp*Ir(L1)Cl] (L1H = N-(4-methoxybenzylidene)aniline).5b The pyrene-based imine ligand 3 is easily synthesized by the reaction of 1-pyrenecarboxaldehyde with naphthalene-1-amine. As shown in Scheme 2, the C-H activation in 3 can offer some different positions for cyclometalation: (11) (a) Weisemann, C.; Schmidtberg, G.; Brune, H.-A. J. Organomet. Chem. 1989, 365, 403. (b) Yam, V. W.-W.; Choi, S. W.-K.; Cheung, K.-K. Dalton Trans. 1996, 3411. (c) Heng, W. Y.; Hu, J.; Yip, J. H. K. Organometallics 2007, 26, 6760. (d) Partyka, D. V.; Esswein, A. J.; Zeller, M.; Hunter, A. D.; Gray, T. G. Organometallics 2007, 26, 3279. (12) Hu, J.; Yip, J. H. K.; Ma, D.-L.; Wong, K.-Y.; Chung, W.-H. Organometallics 2009, 28, 51. (13) Ionkin, A. S.; Marshall, W. J.; Fish, B. M. Organometallics 2006, 25, 1461.

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ortho-(C2pyrene), peri-(C80 naphthyl), and C10pyrene. Cyclometalation at the ortho-(C2pyrene) or peri-(C80 naphthyl) position would lead to the formation of a five-membered metallacycle, while cyclometalation at C10pyrene would give a sixmembered metallacycle. In addition, the C-H bond cleavage of the imine group can also occur under the right conditions.7e Actually, when ligand 3 was treated with [Cp*IrCl2]2 in dichloromethane at room temperature in the presence of sodium acetate, only the ortho-(C2pyrene) C-H activation happened, affording complex 4 in high yield. No peri(C80 naphthyl) or C10pyrene C-H activation product was found even on increasing the temperature, using polar solvents, or

Figure 1. Molecular structure of 2b with 30% displacement ellipsoids. All H atoms are omitted for clarity. Selected bond distances (A˚) and angles (deg): Ir(1)-C(2) 2.035(5), Ir(1)-N(1) 2.087(4), Ir(1)-Cl(1) 2.3992(14), N(1)-C(17) 1.284(5), N(1)-C(18) 1.447(6), C(1)-C(17) 1.413(6), C(1)-C(2) 1.418(7); C(2)-Ir(1)-N(1) 77.62(17), C(2)-Ir(1)-Cl(1) 86.12(13), N(1)-Ir(1)-Cl(1) 85.53(11), C(17)-N(1)-Ir(1) 116.1(3), C(18)-N(1)-Ir(1) 125.1(3), C(17)-C(1)-C(2) 113.5(4).

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using excess [Cp*IrCl2]2. The 1H NMR spectrum of complex 4 showed three singlet resonances at δ 9.28, 8.58, and 1.57 ppm due to HCdN, H3, and the Cp* ring, respectively. As expected, two aromatic regions were observed in the ranges δ 7.92-8.43 and 7.24-7.74 ppm due to the other protons of the pyrene and naphthalene rings. Crystals of complex 4 suitable for an X-ray diffraction study were obtained by slow diffusion of diethyl ether into a concentrated solution of the complex in dichloromethane at low temperature. According to X-ray crystallographic analysis of complex 4, the cycloiridation reaction takes place at the C2 position of the pyrene group with the formation of a five-membered metallacycle, the same as that found in complex 2b. A perspective drawing of complex 4 with selected atomic numbering scheme, bond lengths, and angles is given in Figure 2. The Ir(1)-N(1) bond length [2.056(7) A˚] and C(2)-Ir(1)-N(1) angle [77.8(3)°] are very similar to those [2.0881(15) A˚ and 77.76(6)°] in the related cycloiridation complexes. Reaction of DMAD with complex 4 at 40 °C in dichloromethane, as shown in Scheme 2, gave complex 5 in good yield. Complex 5 is an air and thermally stable red solid that has been fully characterized by NMR spectroscopy, elemental analysis, and X-ray crystallography. To our surprise, besides a single alkyne insertion into Ir-C2pyrene, another new C-H activation at peri-C80 naphthyl-H was also observed. Compared with C(phenyl)-H bond activation, which has been studied extensively, only a few examples of the C(naphthyl)-H bond activation in peri-(C80 naphthyl) position have been reported. As evident by 1H NMR spectroscopy in CDCl3, the appearance of two sharp singlets at δ 3.58 and 3.25 ppm were due to the COOMe protons. The resonances of the HCdN and Cp* protons were shifted from δ 9.28 and 1.57 to δ 10.05 and 1.13, respectively. As shown in Figure 3, the molecular structure of complex 5 shows a distorted seven-membered metallacycle, and a newly formed five-membered iridacycle through the peri-(C80 naphthyl) C-H activation. Such a structure is very similar to the heteroatomsubstituted cyclohept(a)acenaphthylene ring system.14 It is

Scheme 2. Synthesis of 4-8

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Figure 2. Molecular structure of 4 with thermal ellipsoids drawn at the 30% level. Hydrogen atoms are omitted for clarity. Selected distances (A˚) and angles (deg): Ir(1)-C(2) 2.029(8), Ir(1)-N(1) 2.056(7), N(1)-C(17) 1.312(10); C(2)-Ir(1)-N(1) 77.8(3), C(17)-N(1)-Ir(1) 118.8(5), C(2)-C(1)-C(17) 113.3(7), C(1)-C(2)-Ir(1) 115.4(6), N(1)-C(17)-C(1) 114.6(7). Symmetry transformations used to generate equivalent atoms: 1-x, 1-y, 2-z.

Figure 3. Molecular structure of 5 with thermal ellipsoids drawn at the 30% level. Hydrogen atoms are omitted for clarity. Selected distances (A˚) and angles (deg): Ir(1)-N(1) 2.085(4), Ir(1)-C(20) 2.044(5), Ir(1)-C(29) 2.046(5), N(1)-C(17) 1.278(6), C(28)-C(29) 1.350(7); C(20)-Ir(1)-C(29) 92.9(2), C(20)-Ir(1)-N(1) 78.8(2), C(29)-Ir(1)-N(1) 84.19(18).

also interesting to note that the newly formed Ir-C80 naphthyl bond was stable and free from further insertion even when an excess amount of DMAD was used. The sequential reaction of C-H activation and alkyne insertion in one pot was also examined, and the expected complex 5 was formed in 76% yield. In order to explore the reactivity, we treated complex 5 with an excess of sodium borohydride in methanol/dichloromethane (v/v = 1:1). A rapid color change from dark red to pale yellow was observed, affording complex 6 in 95% yield (Scheme 2). The detailed structure of complex 6 was confirmed by the single-crystal X-ray analysis, as shown in Figure 4, with selected bond distances and angles. The N(1)-C(17) bond length [1.487(7) A˚] is longer than that in complex 5 [1.278(6) A˚], implying the imine group was reduced to a single bond. The 1H NMR spectrum of complex (14) White, C.; Yates, A.; Maitles, P. M. Inorg. Synth. 1992, 29, 228.

Han et al.

Figure 4. Molecular structure of 6 with thermal ellipsoids drawn at the 30% level. Hydrogen atoms are omitted for clarity. Selected distances (A˚) and angles (deg) for 6: Ir(1)-C(20) 2.047(7), Ir(1)-C(29) 2.056(6), Ir(1)-N(1) 2.142(5), N(1)C(17) 1.487(7), C(2)-C(28) 1.479(8), C(28)-C(29) 1.352(8); C(20)-Ir(1)-C(29) 89.7(2), C(20)-Ir(1)-N(1) 79.3(2), C(29)Ir(1)-N(1) 90.8(2).

Figure 5. Molecular structures of 7 with thermal ellipsoids drawn at the 30% level. Cl and H atoms are omitted for clarity. Selected distances (A˚) and angles (deg): Ir(1)-N(1) 2.062(7), Ir(1)-C(20) 2.076(9), Ir(1)-C(28) 2.130(8), Ir(1)-C(29) 2.179(8), N(1)-C(17) 1.292(9), C(28)-C(29) 1.404(10); N(1)Ir(1)-C(20) 78.5(3), N(1)-Ir(1)-C(28) 87.0(3), C(20)-Ir(1)C(28) 120.1(3), N(1)-Ir(1)-C(29) 84.0(3), C(20)-Ir(1)C(29) 82.5(3), C(28)-Ir(1)-C(29) 38.0(3).

6 in CDCl3 showed two doublets at δ 5.40 and 5.71 ppm in a 1:1 integration ratio, which indicates the existence of a methylene group, and one multiplet at approximately δ 4.40 ppm belongs to an NH proton. In addition, the signal for Cp* was observed at δ 0.98 ppm, more than 0.14 ppm upfield from the corresponding signal in complex 5. We also investigated the reaction of a terminal alkyne with complex 4. When complex 4 was treated with PhCtCH in 1:1 ratio in dichloromethane after 12 h, a monoinsertioninduced C-H activation at peri-C80 naphthyl-H led to the formation of complex 7 in 71% yield. The 1H NMR spectrum of the product showed two resonances for olefinic protons at δ 4.28 and 6.08 ppm, indicating that the olefinic group is coordinating to the metal center. A singlet at δ 1.21 ppm assigned to Cp* protons is 0.38 ppm upfield compared with complex 4, suggesting the influence of a ring current. Fortunately, we were able to obtain suitable crystals of

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decrease of conjugation, due to the non-coplannar structure of the ligand, in complex 5 and reduction of the CdN group in complex 6. It turns out that the luminescence emission of the pyrene group is quenched by the direct bonding to the metal in complex 4 and reappeared after the insertion of alkyne to the M-C bond. The fact that the UV-vis and luminescence emission spectra are so different in spite of the similarity of the organic portion of the molecule suggests that the differences involve the iridium center.

Conclusion

Figure 6. Molecular structure of 8 with thermal ellipsoids drawn at the 30% level. Hydrogen atoms are omitted for clarity. Selected distances (A˚) and angles (deg): C(1)-C(2) 1.408(3), C(1)-C(17) 1.480(3), C(17)-N(1) 1.283(3), C(17)-C(28) 1.492(3), C(28)-C(29) 1.352(3), C(18)-N(1) 1.419(2); C(1)-C(2)-C(29) 107.84(16), N(1)-C(17)-C(1) 124.10(19), N(1)-C(17)-C(28) 130.03(18), C(1)-C(17)-C(28) 105.74(16), C(29)C(28)-C(17) 108.92(17), C(28)-C(29)-C(2) 109.60(18).

complex 7 and determined its structure by X-ray crystallographic analysis. As shown in Figure 5, the structure shows that C-H activation at peri-C80 naphthyl-H occurred, forming a new Ir-C80 naphthyl bond. However, unlike complex 5, the structure of 7 shows that the metal centers coordinated with the inserted alkyne through a π-bonding mode. The phenyl of the alkyne is on the carbon atom next to the metal center. The bond lengths of Ir(1)-C(28) [2.130(8) A˚] and Ir(1)-C(29) [2.179(8) A˚] are very close to each other, confirming the η2-interaction between the alkene carbon atoms and metal center. Complex 5 was also treated with excess CO, PPh3, or Cu(OAc)2 3 H2O, but no reaction was observed at high temperature in different solvents. However, the rhodiumcatalyzed oxidative coupling of aromatic imine 1 with DMAD effectively proceeds via regioselective C-H bond cleavage to produce indenone imine 8. Actually, when the reaction of C-H activation and alkyne insertion in one pot was catalyzed by [Cp*RhCl2]2, after 8 h, though 5b was not observed, the indenone imine 8 was obtained in good yield. In addition, the synthesis of indenone imine 8 can be easily realized via rhodium-catalyzed oxidative coupling of an aromatic imine with alkyne in the presence of excess Cu(OAc)2 3 H2O.7e Indenone imine 8 can be recognized and characterized by 1H NMR spectroscopy and its single-crystal X-ray structure (Figure 6). UV-vis absorbance behaviors of ligand 3 and complexes 4, 5, and 6 were investigated (Figure S1). In the UV-vis absorption spectrum of complex 4, an obvious metal-ligand charge transfer (MLCT) absorbance was observed due to the fact that the metal is connected directly to the carbon atom of ligand 3. Cutting the direct bonding of metal and pyrene group by the insertion of alkyne can decrease this kind of MLCT absorbance. When the imine group was reduced, the visible absorbance almost disappeared completely. Significant change can also be found in the luminescence emission spectra of 3, 5, and 6 (Figure S2). The blue shift in the emission spectra of 5 and 6 compared with 3 is caused by the

In conclusion, we have established that regiospecific periC80 naphthyl-H bond activation under very mild conditions was induced by the insertion of alkynes into the Ir-C bond of half-sandwich cycloiridation complexes. The efficient rhodium-catalyzed oxidative coupling of an aromatic imine with an alkyne accompanied by regioselective C-H bond cleavage also was described. These C-H bond activation reactions provide efficient routes to pyrene- or/and naphthylbased derivatives, which are useful intermediates for organic materials and medicines. Further studies of the scope and mechanism of alkyne insertion reaction induced regiospecific peri-C80 naphthyl-H bond activation are currenly under investigation.

Experimental Section General Comments. General Data. All reactions and manipulations were performed under a nitrogen atmosphere, using standard Schlenk techniques. However, once the reactions were completed, subsequent workups were done without precaution, as the compounds are air-stable. Solvents were purified by standard methods prior to use. [Cp*MCl2]2 (M = Ir, Rh) were prepared according to the reported procedures,14 while other chemicals were obtained commercially and used without further purification. IR spectra were recorded on a Nicolet AVATAR360 IR spectrometer; UV-vis absorption spectra were measured using an Agilent HP8453 spectrophotometer, and luminescence emission spectra were recorded on a Vavian Cary Eclipse fluorescence spectrometer at room temperature under nitrogen atmosphere. Elemental analyses were carried out with an Elementar III Vario EI analyzer; the samples were dried under vacuum for 10 h before analyses. 1H NMR (400 MHz) spectra were obtained on a Bruker DMX-400 spectrometer in CDCl3 (δ 7.26) or CD3OD (δ 3.31) solution. Procedure for the Reaction of [Cp*IrCl2]2 and Ligands 1a-d. A mixture of [Cp*IrCl2]2 (40 mg, 0.05 mmol), NaOAc (25 mg, 0.3 mmol), and ligand (0.1 mmol) was stirred at 50 °C in 20 mL of dichloromethane for 6 h. The mixture was filtered through Celite and evaporated to afford a red solid, which was further purified by silica gel column chromatography to afford the corresponding cyclometalated complex.

2a (61 mg, 92%). Anal. Calcd for C33H29ClIrN: C 59.40, H 4.38, N 2.10. Found: C 59.23, H 4.36, N 2.09. 1H NMR (400 MHz, CDCl3, ppm): δ 9.32 (s, 1H, Ha, HCdN); 8.59 (s, 1H, Hb); 8.45 (d, J = 9.3 Hz, 1H, Hc); 8.12 (d, J = 7.8 Hz, 2H, He and Hg);

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8.05 (m, 3H, Hd, Hh, and Hi); 7.92 (m, 1H, Hf); 7.75 (d, J = 8.3 Hz, 2H, Hj); 7.48 (m, 2H, Hk); 7.36 (m, 1H, Hl); 1.56 (s, 15H, C5Me5).

2b (65 mg, 93%). Anal. Calcd for C34H31ClIrNO: C 58.56, H 4.48, N 2.01. Found: C 58.66, H 4.24, N 2.12. 1H NMR (400 MHz, CDCl3, ppm): δ 9.27 (s, 1H, Ha, HCdN); 8.58 (s, 1H, Hb); 8.43 (d, J = 8.8 Hz, 1H, Hc); 8.11 (d, J = 7.8 Hz, 2H, He and Hg); 8.04 (m, 3H, Hd, Hh, and Hi); 7.91 (m, 1H, Hf); 7.71 (d, J = 8.8 Hz, 2H, Hj); 6.99 (d, J = 8.8 Hz, 2H, Hk); 3.90 (s, 3H, OMe); 1.57 (s, 15H, C5Me5).

Han et al. (d, J = 8.3 Hz, 1H); 7.57 (m, 3H); 7.24 (d, J = 7.8 Hz, 1H). 13C NMR (CDCl3, ppm): δ 159.23 (HCdN), 150.28, 134.14, 133.63, 131.38, 130.76, 130.71, 129.32, 129.21, 129.14, 128.65, 127.83, 127.61, 127.50, 126.61, 126.38, 126.33, 126.31, 126.09, 126.02, 125.98, 125.18, 125.08, 124.74, 124.32, 122.77, 112.95.

Preparation of 4. A mixture of [Cp*IrCl2]2 (40 mg, 0.05 mmol), NaOAc (25 mg, 0.3 mmol), and 3 (36 mg, 0.1 mmol) was stirred at 50 °C in 20 mL of dichloromethane for 6 h. The mixture was filtered through Celite and evaporated to afford red solid, which was further purified by silica gel column chromatography to afford red cyclometalated compound 4 (65 mg, 91%). Anal. Calcd for C37H31ClIrN: C 61.95, H 4.36, N 1.95. Found: C 61.77, H 4.21, N1.98. 1H NMR (400 MHz, CDCl3, ppm): δ 9.28 (s, 1H, Ha, HCdN); 8.58 (s, 1H, Hb); 8.43 (d, J = 8.8 Hz, 1H, Hc); 8.14 (d, J = 7.8 Hz, 2H, He and Hg); 8.05 (m, 3H, Hd, Hh, and Hi); 7.92 (m, 1H, Hf); 7.24-7.74 (m, 7H, Hj-p); 1.57 (s, 15H, C5Me5). IR(KBr): ν 3039, 2920, 2854, 1584, 1551, 1384, 1025 cm-1.

2c (62 mg, 89%). Anal. Calcd for C33H28Cl2IrN: C 56.48, H 4.02, N 2.00. Found: C 56.58, H 4.12, N 2.09. 1H NMR (400 MHz, CDCl3, ppm): δ 9.23 (s, 1H, Ha, HCdN); 8.57 (s, 1H, Hb); 8.42 (d, J = 9.3 Hz, 1H, Hc); 8.10 (d, J = 7.8 Hz, 2H, He and Hg); 8.03 (m, 3H, Hd, Hh, and Hi); 7.90 (m, 1H, Hf); 7.56 (d, J = 8.8 Hz, 2H, Hj); 6.74 (d, J = 8.8 Hz, 2H, Hk); 1.57 (s, 15H, C5Me5).

2d (62 mg, 92%). Anal. Calcd for C34H31ClIrN: C 59.94, H 4.59, N 2.06. Found: C 59.69, H 4.32, N 2.11. 1H NMR (400 MHz, CDCl3, ppm): δ 9.29 (s, 1H, Ha, HCdN); 8.58 (s, 1H, Hb); 8.38 (d, J = 8.8 Hz, 1H, Hc); 8.12 (d, J = 7.8 Hz, 2H, He and Hg); 8.03 (m, 3H, Hd, Hh, and Hi); 7.92 (m, 1H, Hf); 7.21-7.37 (m, 4H, Hj, Hk, Hl, and Hm); 2.42 (s, 3H, Me); 1.57 (s, 15H, C5Me5).

Preparation of 3. Ligand 3 was prepared by the reaction of 1-pyrenecarboxaldehyde with one equivalent of naphthalen-1amine in methanol overnight at room temperature in 89% yield. Anal. Calcd for C27H17N: C 91.24, H 4.82, N 3.94. Found: C 91.21, H 4.69, N 3.98. 1H NMR (400 MHz, CDCl3, ppm): δ 9.55 (s, 1H, Ha, HCdN); 9.18 (d, J = 9.2 Hz, 1H); 8.87 (d, J = 8.3 Hz, 1H); 8.52 (m, 1H); 8.04-8.29 (m, 7H); 7.91 (m, 1H); 7.79

Preparation of 5. A mixture of 4 (36 mg, 0.05 mmol) and DMAD (28 mg, 0.2 mmol) was stirred at 40 °C in 20 mL of dichloromethane for 12 h. The solution was evaporated to dryness, and the solid was further purified by silica gel column chromatography to afford red solid 5 (35 mg, 86%). Anal. Calcd for C43H36IrNO4: C 62.76, H 4.41, N 1.70. Found: C 62.59, H 4.26, N 1.67. 1H NMR (400 MHz, CDCl3, ppm): δ 10.05 (s, 1H, Ha, HCdN); 8.05-8.30 (m, 8H, Hb-i); 7.84 (d, J = 7.4 Hz, 1H, Ho); 7.73 (d, J = 7.8 Hz, 1H, Hm); 7.49 (d, J = 6.4 Hz, 1H, Hl); 7.41 (m, 2H, Hk and Hj); 7.35 (m, 1H, Hn); 3.58 (s, 3H, COOMe); 3.25 (s, 3H, COOMe); 1.13 (s, 15H, C5Me5). 13C NMR (CDCl3, ppm): δ 175.26 (Ir-C), 171.59, 167.68, 163.54, 155.26, 153.09, 142.65, 139.40, 133.35, 132.50, 132.22, 131.34, 130.95, 130.70, 130.09, 129.41, 129.14, 129.09, 129.03, 128.90, 128.82, 127.55, 126.49, 126.24, 124.62, 124.45, 122.91, 121.72, 119.19, 110.00, 91.11 (C5Me5), 51.79 (MeOOC), 49.28 (MeOOC), 8.42 (C5Me5). IR (KBr): ν 3041, 2944, 2904, 1696, 1560, 1549, 1435, 1384, 1211, 1022 cm-1.

Preparation of 6. NaBH4 (15 mg, 0.4 mmol) was added to solution of 5 (41 mg, 0.05 mmol) in 20 mL of chloroform/

Article methanol (v/v = 1:1). The red solution was changed to yellow after 5 min, and the solid was further purified by silica gel column chromatography to afford yellow solid 6 (39 mg, 95%). Anal. Calcd for C43H38IrNO4: C 62.60, H 4.64, N 1.70. Found: C 62.42, H 4.71, N 1.63. 1H NMR (400 MHz, CDCl3, ppm): δ 8.05-8.65 (m, 8H, Hb-i); 7.75 (d, J = 7.6 Hz, 1H, Ho); 7.66 (d, J = 7.6 Hz, 1H, Hj); 7.36-7.41 (m, 4H, Hk-n); 5.71 (d, J = 11.9 Hz, 1H, Ha); 5.40 (d, J = 11.9 Hz, 1H, Ha); 4.40 (m, 1H, N-H); 3.63 (s, 3H, COOMe); 3.35 (s, 3H, COOMe); 0.98 (s, 15H, C5Me5). IR (KBr): ν 3040, 2942, 2921, 1692, 1556, 1428, 1380, 1242, 1204, 1023 cm-1.

Preparation of 7. A mixture of 4 (36 mg, 0.05 mmol) and PhCtCH (20 mg, 0.2 mmol) was stirred at 40 °C in 20 mL of dichloromethane for 12 h. The solution was evaporated to dryness, and the solid was further purified by silica gel column chromatography to afford red solid 7 (29 mg, 71%). Anal. Calcd for C45H37ClIrN: C 65.96, H 4.55, N 1.71. Found: C 65.83, H 4.26, N 1.65. 1H NMR (400 MHz, CD3OD, ppm): δ 9.18 (s, 1H, Ha, HCdN); 6.28-8.63 (m, 19H, Hb-o and Ph); 6.08 (d, J = 11.9 Hz, 1H, Hp); 4.28 (d, J = 11.9 Hz, 1H, Hq); 1.23 (s, 15H, C5Me5).

Preparation of 8. A mixture of [Cp*RhCl2]2 (32 mg, 0.05 mmol), NaOAc (25 mg, 0.3 mmol), 3 (36 mg, 0.1 mmol), and DMAD (14 mg, 0.1 mmol) was stirred at 80 °C in 20 mL of 1,2dichloroethane (DCE) for 8 h. The mixture was filtered through Celite and evaporated to afford a purple solid, which was washed by hexane three times and further purified by silica gel column chromatography to afford purple compound 8 (46 mg, 93%). Anal. Calcd for C33H21NO4: C 79.99, H 4.27, N 2.83. Found: C 79.92, H 4.28, N 2.46. 1H NMR (400 MHz, CDCl3, ppm): δ 9.63 (d, 1H); 8.55 (s, 1H); 8.12-8.24 (m, 6H); 8.00 (m,


911

1H); 7.90 (m, 1H); 7.72 (d, 1H); 7.56-7.60 (m, 2H); 7.43 (m, 1H); 6.83 (d, 1H); 3.97 (s, 3H, COOMe); 2.92 (s, 3H, COOMe). 13C NMR (500 MHz, CDCl3, ppm): δ 165.0, 163.4, 162.8, 147.0, 142.4, 136.7, 133.7, 133.3, 131.7, 131.2, 131.0, 130.5, 129.1, 129.0, 128.2, 127.6, 127.2, 126.8, 126.7, 126.5, 126.4, 126.2, 126.0, 125.6, 125.3, 124.7, 124.6, 123.9, 123.7,120.5, 115.5, 52.5 (COOMe), 51.5 (COOMe). X-ray Structure Determinations. Intensity data for complexes 2b, 4, 5, 6, and 7 were collected on a CCD-Bruker SMART APEX system. All the determinations of unit cell and intensity data were performed with graphite-monochromated Mo KR radiation (λ = 0.71073 A˚), and the data were collected at room temperature using the ω scan technique. Intensity data for 8 were collected using an Oxford Diffraction KM-4 CCD diffractometer having kappa geometry and using graphite-monochromated Mo KR radiation (λ = 0.71073 A˚) at room temperature. Data reduction was carried out with CrysAlis PRO. All structures were solved by direct methods, using Fourier techniques, and refined on F2 by a full-matrix least-squares method. All the calculations were carried out with the SHELXTL program.15,16 All non-hydrogen atoms of complexes 2b, 4, 5, 6, 7, and 8 were refined anisotropically. There exist disordered solvent molecules in complex 7, which cannot be refined properly. Therefore, the SQUEEZE algorithm17 had to be used before the structure was refined to convergence. In all complexes, hydrogen atoms that could be found were placed in the geometrically calculated positions with fixed isotropic thermal parameters. However, the dichloromethane molecule in the asymmetric unit of complex 4 is disordered so that hydrogen atoms could not be found or calculated.

Acknowledgment. Financial support from the National Science Foundation of China (20721063, 20771028, 21001029), the Shanghai Leading Academic Discipline Project (B108), the Shanghai Municipal Natural Science Foundation (10ZR1404000), the National Basic Research Program of China (2009CB825300), and the Shanghai Science and Technology Committee (08dj1400100) is gratefully acknowledged. Supporting Information Available: UV/vis absorbance spectra, luminescence emission spectra, and crystallographic data for 2b, 4, 5, 6, 7, and 8 are available free of charge via the Internet at http://pubs.acs.org. (15) Sheldrick, G. M. SHELXL-97, Program for the Refinement of Crystal Structures; Universit€at G€ottingen: Germany, 1997. (16) Sheldrick, G. M. SADABS (2.01), Bruker/Siemens Area Detector Absorption Correction Program; Bruker AXS: Madison, WI, USA, 1998. (17) van der Sluis, P.; Spek, A. L. Acta Crystallogr. 1990, A46, 194.

Cp*MCl2 - American Chemical Society

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