NH-Tautomerization of Quinolines and 2 ... - ACS Publications

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Organometallics 2009, 28, 2276–2284

NH-Tautomerization of Quinolines and 2-Methylpyridine Promoted by a Hydride-Iridium(III) Complex: Importance of the Hydride Ligand Miguel A. Esteruelas,* Francisco J. Fernańdez-Alvarez, Montserrat Olivań, and Enrique Onãte Departamento de Quı´mica Inorgańica, Instituto de Ciencia de Materiales de Aragoń, UniVersidad de Zaragoza-CSIC, 50009 Zaragoza, Spain ReceiVed December 18, 2008

The reactions of the iridium complexes IrHCl2(PiPr3)2 (1) and IrCl(η2-C8H14)(PiPr3)2 (2) with quinoline, 8-methylquinoline, 2-methylpyridine and benzo[h]quinoline (Hbq) have been studied. Complex 1 promotes the NH-tautomerization of quinoline and 8-methylquinoline and stabilizes the resulting NH-tautomers to afford IrHCl2{κ-C-(HNC9H6)}(PiPr3)2 (3) and IrHCl2{κ-C-(HNC9H5CH3)}(PiPr3)2 (4), while the respective reactions of 2 lead to IrH{CH2CH(CH3)PiPr2}Cl{κ-N-(NC9H7)}(PiPr3) (5) and IrHC1(CH2C9H6N)(PiPr3)2 (6). Complex 1 also tautomerizes 2-methylpyridine and stabilizes the resulting tautomer to give IrHCl2{κC-(HNC5H3CH3)}(PiPr3)2 (7). However, in the presence of 2, the tautomerization does not occur. Treatment of 2 with 2-methylpyridine leads to a mixture of unidentified nontautomer derivatives. The products from the reactions of 1 with benzo[h]quinoline depend upon the metal/heterocycle ratios used. Treatment of 1 with 1.2 equiv of benzo[h]quinoline leads to the NH-tautomer derivative IrHCl2{κ-C-(HNbq)}(PiPr3)2 (8; 15%) and the metalated species IrHCl{κ-N,C-(bq)}(PiPr3)2 (9; 85%). However, when a 1:3 molar ratio is used, 9 (60%) and the salt [HNHbq][IrHCl3(PiPr3)2] (10, 40%; HNHbq ) benzo[h]quinolinium) are formed. Complexes 4, 5, 6, 7, 9, and 10 have been characterized by X-ray diffraction analysis. The mechanism of the NH-tautomeration is also reported. Introduction

Scheme 1

Quinolines and pyridines have an ubiquitous presence in transition-metal chemistry.1 Their more classical mode of coordination is κ-N via the lone pair of the nitrogen atom. Several alternative metal ligand interactions, including η2-C,N-, η2-C,C-, and η6-bound heterocycle complexes have also been documented.2 We have recently observed that, in addition to these coordination modes, some osmium- and ruthenium-hydride complexes promote a 1,2-hydrogen shift from carbon to nitrogen in quinolines and 2-substituted pyridines. The rearrangement * To whom correspondence should be addressed. E-mail: maester@ unizar.es. (1) Sadimenko, A. P. AdV. Heterocycl. Chem. 2005, 88, 111. (2) (a) Cordone, R.; Taube, H. J. Am. Chem. Soc. 1987, 109, 8101. (b) Wucherer, E. J.; Muetterties, E. L. Organometallics 1987, 6, 1696. (c) Fish, R. H.; Kim, H.-S.; Fong, R. H. Organometallics 1989, 8, 1375. (d) Cordone, R.; Harman, W. D.; Taube, H. J. Am. Chem. Soc. 1989, 111, 2896. (e) Davies, S. G.; Shipton, M. R. J. Chem. Soc., Chem. Commun. 1989, 995. (f) Strickler, J. R.; Bruck, M. A.; Wigley, D. E. J. Am. Chem. Soc. 1990, 112, 2814. (g) Covert, K. J.; Neithamer, D. R.; Zonnevylle, M. C.; LaPointe, R. E.; Schaller, C. P.; Wolczanski, P. T. Inorg. Chem. 1991, 30, 2494. (h) Smith, D. P.; Strickler, J. R.; Gray, S. D.; Bruck, M. A.; Holmes, R. S.; Wigley, D. E. Organometallics 1992, 11, 1275. (i) Harman, W. D. Chem. ReV. 1997, 97, 1953. (j) Kleckley, T. S.; Bennett, J. L.; Wolczanski, P. T.; Lobkovsky, E. B. J. Am. Chem. Soc. 1997, 119, 247. (k) Meiere, S. H.; Brooks, B. C.; Gunnoe, T. B.; Sabat, M.; Harman, W. D. Organometallics 2001, 20, 1038. (l) Meiere, S. H.; Brooks, B. C.; Gunnoe, T. B.; Carrig, E. H.; Sabat, M.; Harman, W. D. Organometallics 2001, 20, 3661. (m) Bonanno, J. B.; Veige, A. S.; Wolczanski, P. T.; Lobkovsky, E. B. Inorg. Chim. Acta 2003, 345, 173. (n) Ozerov, O. V.; Pink, M.; Watson, L. A.; Caulton, K. G. J. Am. Chem. Soc. 2004, 126, 2105. (o) Graham, P. M.; Delafuente, D. A.; Liu, W.; Myers, W. H.; Sabat, M.; Harman, W. D. J. Am. Chem. Soc. 2005, 127, 10568. (p) Zhu, G.; Pang, K.; Parkin, G. J. Am. Chem. Soc. 2008, 130, 1564.

affords compounds with the heterocycle coordinated by the atom adjacent to nitrogen.3 Thus, we have reported that complex OsH2Cl2(PiPr3)2 reacts with quinoline, 8-methylquinoline, and 2-methylpyridine to give the corresponding NH-tautomer derivatives (Scheme 1).3a,e Carmona and co-workers have found the same behavior for pyridine, 2-substituted pyridines, 2,2′bipyridine, and 1,10-phenantroline in the presence of TpR-Ir(3) (a) Esteruelas, M. A.; Fernańdez-Alvarez, F. J.; Onãte, E. J. Am. Chem. Soc. 2006, 128, 13044. (b) Buil, M. L.; Esteruelas, M. A.; Garce´s, K.; Olivań, M.; Onãte, E. J. Am. Chem. Soc. 2007, 129, 10998. (c) Esteruelas, M. A.; Fernańdez-Alvarez, F. J.; Onãte, E. Organometallics 2007, 26, 5239. (d) Buil, M. L.; Esteruelas, M. A.; Garce´s, K.; Olivań, M.; Onãte, E. Organometallics 2008, 27, 4680. (e) Esteruelas, M. A.; FernańdezAlvarez, F. J.; Onãte, E. Organometallics 2008, 27, 6236. (4) (a) Alvarez, E.; Conejero, S.; Paneque, M.; Petronilho, A.; Poveda, M. L.; Serrano, O.; Carmona, E. J. Am. Chem. Soc. 2006, 128, 13060. (b) Alvarez, E.; Conejero, S.; Lara, P.; Lo´pez, J. A.; Paneque, M.; Petronilho, A.; Poveda, M. L.; del Rio, D.; Serrano, O.; Carmona, E. J. Am. Chem. Soc. 2007, 129, 14130. (c) Conejero, S.; Lara, P.; Paneque, M.; Petronilho, A.; Poveda, M. L.; Serrano, O.; Vattier, F.; Alvarez, E.; Maya, C.; Salazar, V.; Carmona, E. Angew. Chem., Int. Ed. 2008, 47, 4380.

10.1021/om8011954 CCC: $40.75  2009 American Chemical Society Publication on Web 02/26/2009

NH-Tautomerization by Hydride-Iridium(III) Complex

complexes (TpR ) substituted hydrotris(pyrazolyl)borate).4 During the last months, work has shown that other Nheterocycles can also undergo a metal-induced rearrangement to form related N-heterocyclic carbene complexes.5 DFT calculations on the reactions shown in Scheme 1 showed that the NH-tautomer derivatives are formed in three stages, including an intermolecular metal to nitrogen hydrogen migration, the subsequent CR-H bond activation of the protonated heterocycle, and finally the dihydride-dihydrogen tautomerization of the resulting dihydride.3e The nature of the metallic precursor appears to have a marked influence in the NH-tautomerization process of the heterocycles. Thus, in contrast to OsH2Cl2(PiPr3)2, the hexahydride complex OsH6(PiPr3)2 activates a C(sp3)-H bond of the methyl substituent of 8-methylquinoline to generate a five-membered heterometalacycle6 and the CR-H bond of 2-methylpyridine to afford an η2-(C,N)-pyridyl derivative.7 The rearrangement of the N-heterocycles is important in the preparation of new materials8 and, mainly, from the point of view of some relevant catalytic reactions.9 In these processes, the catalyst must tautomerize the heterocycle via the selective activation of a relatively inert C-H bond in the presence of other C-H bonds. Thus, knowing the reasons of this selectivity is of great interest. We have previously suggested that polar transition-metalhydride complexes should favor the NH-tautomerization of 2-substituted nitrogen containing heterocycles.3e To prove this, we have now carried out a comparative study between the reactions of the monohydride-iridium(III) complex IrHCl2(PiPr3)2 (1) and the iridium(I) compound IrCl(η2-C8H14)(PiPr3)2 (2) with quinoline, 8-methylquinoline, 2-methylpyridine, and benzo[h]quinoline. This paper shows different C-H bond activation reactions, as a function of the metallic precursor and the heterocycle, which illustrate the differences in behavior between the iridium compounds. Furthermore, it demonstrates that our mechanistic proposal for the reactions collected in Scheme 1 can be extended to the NH-tautomerizations promoted by the monohydride-iridium(III) complex.

Results and Discussion 1. Reactions with Quinoline and 8-Methylquinoline. The hydride-iridium(III) derivative 1 tautomerizes quinoline and 8-methylquinoline and stabilizes the corresponding NH-tautomers. Treatment of a toluene solution of this complex with 4.0 equiv of quinoline at 100 °C for 16 h leads to IrHCl2{κC-(HNC9H6)}(PiPr3)2 (3). Under the same conditions, the treatment of 1 with 8.0 equiv of 8-methylquinoline affords IrHCl2{κ-C-(HNC9H5CH3)}(PiPr3)2 (4). These compounds are (5) (a) Burling, S.; Mahon, M. F.; Powell, R. E.; Whittlesey, M. K.; Willians, J. M. J. J. Am. Chem. Soc. 2006, 128, 13702. (b) Ruiz, J.; Perandones, B. F. J. Am. Chem. Soc. 2007, 129, 9298. (c) Wang, X.; Chen, H.; Li, X. Organometallics 2007, 26, 4684. (d) Begum, R.; Komuro, T.; Tobita, H. Chem. Lett. 2007, 36, 650. (e) Gribble, M. W., Jr.; Ellman, J. A.; Bergman, R. G. Organometallics 2008, 27, 2152. (f) Araki, K.; Kuwata, S.; Ikariya, T. Organometallics 2008, 27, 2176. (g) Song, G.; Li, Y.; Chen, S.; Li, X. Chem. Commun. 2008, 3558. (h) Miranda-Soto, V.; Grotjahn, D. B.; DiPascuale, A. G.; Rheingold, A. L. J. Am. Chem. Soc. 2008, 130, 13200. (i) Huertos, M. A.; Pe´rez, J.; Riera, L.; Meneńdez-Vela´zquez, A. J. Am. Chem. Soc. 2008, 130, 13530. (6) Baya, M.; Eguillor, B.; Esteruelas, M. A.; Lledo´s, A.; Olivań, M.; Onãte, E. Organometallics 2007, 26, 5140. (7) Esteruelas, M. A.; Forceń, E.; Olivań, M.; Onãte, E. Organometallics 2008, 27, 6188. (8) See for example: Matena, M.; Riehm, T.; Sto¨hr, M.; Jung, T. A.; Gade, L. H. Angew. Chem., Int. Ed. 2008, 47, 2414.

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Figure 1. Molecular diagram of complex 4. Selected bond lengths (Å) and angles (deg): Ir-C(1) ) 1.990(6), Ir-Cl(1) ) 2.5602(14), Ir-Cl(2) ) 2.4621(14), Ir-P ) 2.3574(11), C(1)-N ) 1.337(7), C(5)-N ) 1.385(8), C(1)-C(2) ) 1.428(8), C(2)-C(3) ) 1.360(8), C(3)-C(4) ) 1.413(7), C(4)-C(5) ) 1.400(8), Cl(1) · · · H(1)N ) 2.19(7); P-Ir-P ) 166.97(5), Cl(1)-Ir-Cl(2) ) 91.61(4), C(1)-Ir-Cl(1) ) 88.98(15), C(1)-Ir-Cl(2) ) 179.41(15), P-Ir-C(1) ) 91.94(3).

isolated as yellow solids in 70% (3) and 75% (4) yield, according to eq 1.

Complexes 3 and 4 were characterized by elemental analysis, IR, and 1H, 13C{1H}, and 31P{1H} NMR spectroscopy. Complex 4 was further characterized by an X-ray crystallographic study. A view of the molecular geometry of this compound is shown in Figure 1. The structure proves the stabilization of the NH-tautomer of the heterocycle, which coordinates to the metal center through the carbon atom at the 2-position (C(1)). The coordination geometry around the iridium atom can be rationalized as derived from a distorted octahedron with the phosphorus atoms of the triisopropylphosphine ligands occupying trans positions (P-Ir-P ) 166.97(5)°). The metal sphere is completed by the chloride ligands mutually cis disposed (Cl(1)-Ir-Cl(2) ) 91.61(4)°), the tautomerized 8-methylquinoline group trans disposed to Cl(2) (C(1)-Ir-Cl(2) ) 179.41(15)°), and the hydride ligand trans disposed to Cl(1). The Ir-C(1) bond length of 1.990(6)

(9) (a) Wiedemann, S. H.; Lewis, J. C.; Ellman, J. A.; Bergman, R. G. J. Am. Chem. Soc. 2006, 128, 2452. (b) Kunz, D. Angew. Chem., Int. Ed. 2007, 46, 3405. (c) Lewis, J. C.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc. 2007, 129, 5332. (d) Lariveé, A.; Mousseau, J. J.; Charette, A. B. J. Am. Chem. Soc. 2008, 130, 52. (e) Nakao, Y.; Kanyiva, K. S.; Hiyama, T. J. Am. Chem. Soc. 2008, 130, 2448. (f) Lewis, J. C.; Berman, A. M.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc. 2008, 130, 2493. (g) Berman, A. M.; Lewis, J. C.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc. 2008, 130, 14926. (h) Lewis, J. C.; Bergman, R. G.; Ellman, J. A. Acc. Chem. Res. 2008, 41, 1013.

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Å compares well with the Ir-C distances in Ir-NHC (NHC ) N-heterocyclic carbene) complexes.10 The heterocycle lies in the plane determined by the metal and the chloride ligands, with the NH-hydrogen toward Cl(1). The separation between them, 2.19(7) Å, is shorter than the sum of the van der Waals radii of hydrogen and chloride (rvdw(H) ) 1.20 Å, rvdw(Cl) ) 1.75 Å)11 suggesting that there is an intramolecular Cl · · · H-N hydrogen bond between these atoms,12 which contributes to the stabilization of the tautomer, as has been observed for the related ruthenium and osmium complexes.3 The hydrogen bond is a consequence of the electrostatic interaction between the electronegative halogen and the acidic NH-hydrogen.13 The Cl · · · H-N hydrogen bond is also supported by the 1H NMR spectra of these compounds in dichloromethane-d2, which show the NH resonance at unusually low field,14 14.90 (3) and 14.94 (4) ppm. The hydride ligand gives rise to triplets, at -24.04 (3) and -23.94 (4) ppm, with H-P coupling constants of about 15 Hz. In the 13C{1H} spectra, the resonances corresponding to the metalated carbon atoms of the heterocycles appear at 173.9 (3) and 173.6 (4) ppm, as triplets with C-P coupling constants of about 7 Hz. These chemical shifts, which agree well with those of the related resonances of the Ir-NHC complexes, are an additional evidence supporting the similarity between the NH-tautomers and the NHC ligands.15 The 31P{1H} NMR spectra are consistent with the structure shown in Figure 1. As expected for two equivalent phosphines, a singlet at 3.8 ppm is observed for both compounds. The iridium(I) complex 2, in contrast to 1, does not promote the NH-tautomerization of quinoline and 8-methylquinoline. The nature of the products of the reactions of 2 with these substrates depends upon the presence of the methyl substitutent in the heterocycle (Scheme 2). Treatment of a toluene solution of 2 with 4.0 equiv of quinoline at 100 °C for 16 h leads to a complex mixture of unidentified compounds. However, at room temperature the addition of 2.0 equiv of quinoline to a dichloromethane solution (10) See for example: (a) Gru¨ndemann, S.; Kovacevic, A.; Albrecht, M.; Faller, J. W.; Crabtree, R. H. J. Am. Chem. Soc. 2002, 124, 10473. (b) Chianese, A. R.; Kovacevic, A.; Zeglis, B. M.; Faller, J. W.; Crabtree, R. H. Organometallics 2004, 23, 2461. (c) Vogt, M.; Pons, V.; Heinekey, D. M. Organometallics 2005, 24, 1832. (d) Corberań, R.; Sanau´, M.; Peris, E. Organometallics 2006, 25, 4002. (e) Burling, S.; Mahon, M. F.; Reade, S. P.; Whittlesey, M. K. Organometallics 2006, 25, 3761. (f) Viciano, M.; Mas-Marza´, E.; Sanau´, M.; Peris, E. Organometallics 2006, 25, 3063. (g) Viciano, M.; Feliz, M.; Corberań, R.; Mata, J. A.; Clot, E.; Peris, E. Organometallics 2007, 26, 5304. (h) Tanabe, Y.; Hanasaka, F.; Fujita, K.; Yamaguchi, R. Organometallics 2007, 26, 4618. (i) Corberań, R.; Lillo, V.; Mata, J. A.; Fernańdez, E.; Peris, E. Organometallics 2007, 26, 4350. (j) Pontes da Costa, A.; Viciano, M.; Sanau´, M.; Merino, S.; Tejeda, J.; Peris, E.; Royo, B. Organometallics 2008, 27, 1305. (11) Barrio, P.; Esteruelas, M. A.; Lledo´s, A.; Onãte, E.; Toma´s, J. Organometallics 2004, 23, 3008. (12) See for example: (a) Castarlenas, R.; Esteruelas, M. A.; Onãte, E. Organometallics 2000, 19, 5454. (b) Castarlenas, R.; Esteruelas, M. A.; Gutie´rrez-Puebla, E.; Onãte, E. Organometallics 2001, 20, 1545. (c) Buil, M. L.; Esteruelas, M. A.; Goni, E.; Olivań, M.; Onãte, E. Organometallics 2006, 25, 3076. (13) (a) Stevens, R. C.; Bau, R.; Milstein, D.; Blum, O.; Koetzle, T. F. J. Chem. Soc., Dalton Trans. 1990, 1429. (b) Buil, M. L.; Esteruelas, M. A.; Onãte, E.; Ruiz, N. Organometallics 1998, 17, 3346. (c) Gusev, D. G.; Lough, A. J.; Morris, R. H. J. Am. Chem. Soc. 1998, 120, 13138. (d) Crabtree, R. H. J. Organomet. Chem. 1998, 557, 111. (e) Esteruelas, M. A.; Olivań, M.; Onãte, E.; Ruiz, N.; Tajada, M. A. Organometallics 1999, 18, 2953. (f) Lee, D.-H.; Kwon, H. J.; Patel, B. P.; Liable-Sands, L. M.; Rheingold, A. L.; Crabtree, R. H. Organometallics 1999, 18, 1615. (g) Esteruelas, M. A.; Gutie´rrez-Puebla, E.; Lo´pez, A. M.; Onãte, E.; Tolosa, J. I. Organometallics 2000, 19, 275. (h) Barrio, P.; Esteruelas, M. A.; Onãte, E. Organometallics 2002, 21, 2491. (14) Esteruelas, M. A.; Lahoz, F. J.; Lo´pez, A. M.; Onãte, E.; Oro, L. A.; Ruiz, N.; Sola, E.; Tolosa, J. I. Inorg. Chem. 1996, 35, 7811.

Esteruelas et al. Scheme 2

of 2 selectively affords IrH{CH2CH(CH3)PiPr2}C1{κ-N(NC9H7)}(PiPr3) (5), as a result of the release of the olefin, the intermolecular C(sp3)-H bond activation of the methyl group of an isopropyl substituent of one of the phosphine ligands, and the coordination of the lone pair of the nitrogen atom of the heterocycle to the metal center. Complex 5 is isolated as a yellow solid in 80%. Figure 2 shows a view of the X-ray structure of 5. The geometry around the iridium atom can be described as a distorted octahedron with the phosphorus atoms of the phosphine ligands occupying trans positions (P(1)-Ir-P(2) ) 161.16(4)°). The perpendicular plane is formed by the heterocycle, the chloride, the metalated carbon atom of the activated isopropyl group trans disposed to the heterocycle (C(10)-Ir-N ) 171.56(15)°), and the hydride trans disposed to the chloride. The distortion of the ideal octahedron is mainly due to the C(10)-Ir-P(1) bite angle of 69.14(11)° of the metalated phosphine, which agrees well with the angles reported for the scarce complexes with this group characterized by X-ray diffraction analysis.16The Ir-C(10) bond length of 2.090(4) Å also agrees well with those found in the few reported iridium complexes containing a metalated triisopropylphosphine group.16a The trans disposition of the heterocycle and the metalated carbon atom in 5 is in contrast with the cis disposition proposed for the γ-picoline compound IrH{CH2CH(CH3)PiPr2}Cl{γpicoline}(PiPr3) on the basis of the IR and 1H NMR spectrum.17 The presence of a metalated triisopropylphosphine ligand in 5 is also supported by its 1H, 13C{1H}, and 31P{1H} NMR spectra in benzene-d6. In the 1H NMR spectrum, the most noticeable resonances are those due to the CH2-protons of the metalated carbon atom, which appear at 2.40 and 1.45 ppm. The hydride ligand displays at -21.64 ppm a double doublet with H-P coupling constants of 24.4 and 14.6 Hz. In the 13C{1H} NMR spectrum, the Ir-CH2 and CH signals of the metalated isopropyl group are observed at -25.9 and 45.2 ppm, respectively. These chemical shifts are similar to those reported for other transition metal complexes containing a metalated triisopropylphosphine (15) (a) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290. (b) Nair, V.; Bindu, S.; Sreekumar, V. Angew. Chem., Int. Ed. 2004, 43, 5130. (c) Crudden, C. M.; Allen, D. P. Coord. Chem. ReV. 2004, 248, 2247. (d) Scott, C. M.; Nolan, S. P. Eur. J. Inorg. Chem. 2005, 1815. (e) Lappert, M. F. J. Organomet. Chem. 2005, 690, 5467. (f) Cavallo, L.; Correa, A.; Costabile, C.; Jacobsen, H. J. Organomet. Chem. 2005, 690, 5407. (g) Crabtree, R. H. J. Organomet. Chem. 2005, 690, 5451. (16) (a) Perego, G.; Del Piero, G.; Cesari, M.; Clerici, M. G.; Perrotti, E. J. Organomet. Chem. 1973, 54, C51. (b) Campion, B. K.; Heyn, R. H.; Tilley, T. D.; Rheingold, A. L. J. Am. Chem. Soc. 1993, 115, 5527. (c) Esteruelas, M. A.; Lo´pez, A. M.; Onãte, E.; Royo, E. Organometallics 2005, 24, 5780. (17) Hietkamp, S.; Stufkens, D. J.; Vrieze, K. J. Organomet. Chem. 1977, 139, 189.


Figure 2. Molecular diagram of complex 5. Selected bond lengths (Å) and angles (deg): Ir-C(10) ) 2.090(4), Ir-Cl ) 2.5194(12), Ir-P(1) ) 2.3127(12), Ir-P(2) ) 2.3092(12), Ir-N ) 2.231(3), C(10)-C(11) ) 1.541(6), C(11)-C(12) ) 1.519(5); P(1)-Ir-P(2) ) 161.16(4), C(10)-Ir-Cl ) 87.31(13), C(10)-Ir-N ) 171.56(15), C(10)-Ir-P(1))69.14(11),C(10)-Ir-P(2))92.68(12),P(1)-Ir-N ) 102.94(9), P(2)-Ir-N ) 95.45(9). 18

ligand. The 31P{1H} NMR spectrum shows two doublets, at 13.2 and 25.8 ppm, with a P-P coupling constant of 358 Hz. The intermolecular C-H bond activation of the methyl substituent of 8-methylquinoline is favored with regard to the intramolecular C-H bond activation of an isopropyl group of one of the phosphine ligands. Thus, the treatment of a toluene solution of 2 with 8.0 equiv of 8-methylquinoline at 100 °C for 16 h affords IrHCl(CH2C9H6N)(PiPr3)2 (6) in 67% yield, along with other decomposition products. In dichloromethane at room temperature, the formation of 6 takes place in almost quantitative yield. By crystallization in diethylether at 0 °C, it is isolated as yellow crystals in 85% yield. Figure 3 shows a view of the structure of 6. The geometry around the iridium atom can be described as a distorted octahedron with the phosphine ligands occupying trans positions (P(1)-Ir-P(2) ) 165.14(3)°). The perpendicular plane is formed by the metalated heterocyle, which acts with a bite angle C(7)-Ir-N of 80.94(11)°, the chloride ligand trans disposed to C(7) (Cl-Ir-C(7) ) 171.83(8)°) and the hydride trans disposed to the nitrogen atom. The Ir-C(7) bond length of 2.087(3) Å is statistically identical with the Ir-C(1) distance in 5 and supports the Ir-C single bond formation. The 1H, 13C{1H} and 31P{1H} NMR spectra of 6 are consistent with the structure shown in Figure 3 and agree well with those reported for the complex [IrH(CH2C9H6N)(CO)(PiPr3)2].19 In the 1 H NMR spectrum in dichloromethane-d2, the methylenic protons display at 2.90 ppm a triplet with a H-P coupling constant of 6.6 Hz, whereas the hydride resonance is observed at -21.23 ppm also as a triplet but with a H-P coupling constant of 18.0 Hz. In the 13C{1H} NMR spectrum, the metalated carbon atom gives rise at -9.3 ppm to a triplet with a C-P coupling constant of 6 Hz. In agreement with the (18) See for example: (a) Esteruelas, M. A.; Lo´pez, A. M.; Ruiz, N.; Tolosa, J. I. Organometallics 1997, 16, 4657. (b) Wen, T. B.; Cheung, Y. K.; Yao, J.; Wong, W.-T.; Zhou, Z. Y.; Jia, G. Organometallics 2000, 19, 3803. (c) Bolanõ, T.; Castarlenas, R.; Esteruelas, M. A.; Onãte, E. J. Am. Chem. Soc. 2007, 129, 8850. (19) Neve, F.; Ghedini, M.; De Munno, G.; Crispini, A. Organometallics 1991, 10, 1143.


Figure 3. Molecular diagram of complex 6. Selected bond lengths (Å) and angles (deg): Ir-C(7) ) 2.087(3), Ir-Cl ) 2.5052(8), Ir-P(1) ) 2.3529(8), Ir-P(2) ) 2.3433(8), Ir-N ) 2.156(3); P(1)-Ir-P(2) ) 165.14(3), C(7)-Ir-Cl ) 171.83(8), Cl-Ir-N ) 90.99(7), P(1)-Ir-N ) 100.67(7), P(2)-Ir-N ) 94.13(7).

mutually trans disposition of the phosphine ligands the 31P{1H} NMR spectrum contains a singlet at 9.6 ppm. 2. Reactions with 2-Methylpyridine. Complex 1 also tautomerizes 2-methylpyridine and stabilizes the resulting NHtautomer. The treatment of this compound with 8.0 equiv of the heterocycle in toluene at 120 °C for 16 h leads to IrHCl2{κC-(HNC5H3CH3)}(PiPr3)2 (7), which is isolated as a white solid in 85% yield (eq 2). Under the same conditions or in dichloromethane at room temperature, complex 2 gives mixtures of unidentified compounds, which do not contain a NH-tautomerized heterocycle.

Figure 4 shows a view of the X-ray structure of 7. The coordination geometry around the iridium atom can be rationalized as that of 4; i.e., a distorted octahedron with transphosphines (P-Ir-P ) 165.82(7)°) and cis-chlorides (Cl(1)-IrCl(2) ) 90.42(7)°). The heterocycle coordinates to the metal center through C(1). The Ir-C(1) distance of 1.999(8) Å is statistically identical with the Ir-C(1) bond length in 4. As in the latter a hydrogen bond involving the NH group appears to play an important role in the stabilization of the tautomeric form. In accordance with the hydrogen bond, the NH-hydrogen points toward the chloride Cl(1). The separation between them of 2.24(9) Å, which compares well with that of 4, is also shorter than the sum of the van der Waals radii of hydrogen and chloride. The 1H NMR spectrum of 7 in dichloromethane-d2, as expected for the hydrogen bond, shows the NH resonance at unusually low field, 14.62 ppm. The hydride ligand displays at -24.44 a triplet with a H-P coupling constant of 15.0 Hz. In the 13C{1H} NMR spectrum the most noticeable resonance is a triplet with a C-P coupling constant of 7 Hz, at 165.3 ppm, corresponding to C(1). In agreement with equivalent phosphines, the 31P{1H} NMR spectrum shows a singlet at 4.1 ppm.


Esteruelas et al. Scheme 3

Figure 4. Molecular diagram of complex 7. Selected bond lengths (Å) and angles(deg): Ir-C(1) )1.999(8), Ir-Cl(1) ) 2.578(2), Ir-Cl(2) ) 2.449(2), Ir-P ) 2.362(2), Cl · · · H-N ) 2.29(9)Å, C(1)-N(1) ) 1.353(10), C(5)-N(1) ) 1.347(10), C(1)-C(2) ) 1.411(10), C(2)-C(3) ) 1.363(11), C(3)-C(4) ) 1.401(12), C(4)-C(5) ) 1.379(11); P-Ir-P ) 165.82(7), C(1)-Ir-Cl(1) ) 89.2(2), C(1)-Ir-Cl(2) ) 179.6(2), Cl(1)-Ir-Cl(2) ) 90.42(7).

3. Reactions with Benzo[h]quinoline. Benzo[h]quinoline (Hbq) forms N,C-cyclometalated transition metal complexes20 with extreme ease due to the great stability21 of the fivemembered heterometalaring resulting from the C10-H bond rupture. Recently, we have shown that this heterocycle can also undergo a metal induced 1,2-hydrogen shift from the carbon atom at 2-position to the nitrogen. As for quinoline, 8-methylquinoline and 2-methylpyridine the former tautomer is stabilized by coordination of the undressed carbon atom to osmium and ruthenium. The conversion of the NH-tautomerized heterocycle into the usual cyclometalated group takes place when the tautomer-metal species are deprotonated with a Brønsted base.3e The iridium(III) complex 1 also tautomerizes benzo[h]quinoline and stabilizes the formed NH-tautomer. However, the conversion of the resulting tautomer-metal species into the cyclometalated compound is significantly easier than for osmium and ruthenium (Scheme 3). Treatment of a toluene solution of 1 with 1.2 equiv of the heterocycle at 100 °C for 16 h gives a mixture of the tautomer-iridium species IrHCl2{κ-C-(HNbq)}(PiPr3)2 (8, 15%) and the cyclometalated-iridium complex IrHCl{κ-N-C-(bq)}(PiPr3)2 (9, 85%). When the HCl formed during the cyclometalation is captured with triethylamine, the quantitative formation of the cyclometalated species takes place, and complex 9 is isolated as a yellow solid in 90% yield. Complex 8 was isolated as a pure yellow solid by crystallization of the mixture from toluene. Its 1H, 13C{1H}, and (20) See for example: (a) Clot, E.; Eisenstein, O.; Crabtree, R. H. New. J. Chem. 2001, 25, 66. (b) Zhang, Q.-F.; Cheung, K.-M.; Williams, I.-D.; Leung, W.-H. Eur. J. Inorg. Chem. 2005, 4780. (c) Li, E. Y.; Cheng, Y.M.; Hsu, C.-C.; Chou, P. T.; Lee, G.-H.; Lin, I. H.; Chi, Y.; Liu, C.-S. Inorg. Chem. 2006, 45, 8041. (d) Pugliese, T.; Godbert, N.; Aiello, I.; Ghedini, M.; La Deda, M. Inorg. Chem. Commun. 2006, 9, 93. (e) Lo, K. K.-W.; Lau, J. S.-Y.; Lo, D. K.-K.; Lo, L. T.-L. Eur. J. Inorg. Chem. 2006, 4054. (f) Dick, A. R.; Remy, M. S.; Kampf, J. W.; Sanford, M. S. Organometallics 2007, 26, 1365. (21) It has been shown that the five-membered metalacycle of aromaticmetallated species exhibits a certain degree of aromaticity. See: (a) Crispini, A.; Ghedini, M. J. Chem. Soc., Dalton Trans. 1997, 75. (b) Aiello, I.; Crispini, A.; Ghedini, M.; La Deda, M.; Barigelletti, F. Inorg. Chim. Acta 2000, 308, 121. (c) Esteruelas, M. A.; Masamunt, A. B.; Olivań, M.; Onãte, E.; Valencia, M. J. Am. Chem. Soc. 2008, 130, 11612, and references there in.

31

P{1H} NMR spectra in dichloromethane-d2 are consistent with those of 3, 4, and 7. In agreement with the presence of the intramolecular Cl · · · H-N hydrogen bond in the complex, the 1 H NMR spectrum shows the NH resonance at unusually low field, 15.90 ppm. The hydride resonance appears at -24.20 ppm, as a triplet with a H-P coupling constant of 15.0 Hz. In the 13 C{1H} NMR spectrum the Ir-C signal is observed at 169.9 ppm as a triplet with a C-P coupling constant of 8 Hz. The 31 P{1H} NMR spectrum contains a singlet at 4.2 ppm. Complex 9, like 4, 5, 6, and 7, has been characterized by elemental analysis, IR, 1H, 13C{1H}, and 31P{1H} NMR spectroscopy, and by an X-ray crystallographic study. A view of its molecular geometry is shown in Figure 5. The coordination geometry around the iridium atom can be rationalized as a distorted octahedron with the phosphorus atoms of the triisopropylphosphine ligands occupying mutually trans positions (P(1)-Ir-P(2) ) 161.21(5)°). The metal sphere is completed by the metalated group, which coordinates with a bite angle N-Ir-C(10) of 80.2(2)°, the chloride ligand trans disposed to C(10) (Cl-Ir-C(10) ) 174.08(16)°), and the hydride trans disposed to the nitrogen atom. The Ir-C(10) bond length of 2.014(5) Å and the Ir-N distance of 2.173(5) Å compare well with those found in the cation [IrH{κ-N,C-(bq)}(CO)(PiPr3)2]+ (2.054(10) and 2.169(9) Å, respectively).22 The 1H, 13C{1H}, and 31P{1H} NMR spectra of 9 in dichloromethane-d2 agree well with the structure shown in Figure 5. In the 1H NMR spectrum the hydride ligand displays at -18.50 ppm a triplet with a H-P coupling constant of 17.7 Hz. In the 13C{1H} NMR spectrum the resonance due to the metalated carbon atom of the heterocycle appears at 146.1 ppm, as a triplet with a C-P coupling constant of 7 Hz. The 31P{1H} NMR spectrum shows a singlet at 6.4 ppm. Benzo[h]quinoline itself acts as a Brønsted base for the transformation from the tautomer species 8 to the metalated compound 9. The formed benzo[h]quinolinium chloride ([HNHbq]Cl) reacts with amounts of 1 present in the reaction mixture to afford the salt [HNHbq][IrHCl3(PiPr3)2] (10), where the iridium(III) anion is the result of the coordination of a chloride ligand to the iridium atom of 1. In agreement with this, we have observed that the treatment of a toluene solution of 1 with 3.0 equiv of the heterocycle at 100 °C for 16 h gives rise to a mixture of the metalated complex 9 (60%) and the salt 10 (40%), and that the addition of 1.0 equiv of [HNHbq]Cl to an acetone (22) Neve, F.; Ghedini, M.; Tiripicchio, A.; Ugozzoli, F. Inorg. Chem. 1989, 28, 3084.


Figure 5. Molecular diagram of complex 9. Selected bond lengths (Å) and angles (deg): Ir-C(10) ) 2.014(5), Ir-Cl ) 2.4811(14), Ir-N ) 2.173(5), Ir-P(1) ) 2.3514(15), Ir-P(2) ) 2.3443(15); P(1)-Ir-P(2) ) 161.21(5), N-Ir-Cl ) 93.98(12), N-Ir-C(10) ) 80.2(2), Cl-Ir-C(10) ) 174.08(16), P(2)-Ir-N ) 99.58(12), P(2)-Ir-C(10) ) 92.34(15).

Figure 6. Molecular diagram of complex 10. Selected bond lengths (Å) and angles (deg): Ir-Cl(1) ) 2.5851(10), Ir-Cl(2) ) 2.3751(10), Ir-Cl(3) ) 2.3653(10), Ir-P(1) ) 2.3592(11), Ir-P(2) ) 2.3522(11), H(02) · · · Cl(2) ) 2.12(4); P(1)-Ir-P(2) ) 167.64(3), Cl(1)-Ir-Cl(2) ) 91.07(4), Cl(1)-Ir-Cl(3) ) 90.82(4), Cl(2)-Ir-Cl(3) ) 178.10(3), P(2)-Ir-Cl(2) ) 90.73(3), P(1)-Ir-Cl(2) ) 90.36(3), P(2)-Ir-Cl(1) ) 97.58(3), P(1)-Ir-Cl(1) ) 94.71(3).

solution of 1 leads to 10, which is isolated as an orange solid in 80% yield. Salt 10 has been also characterized by X-ray diffraction analysis. Figure 6 shows a view of the structures of both the anion and the cation, which are associated by means of a Cl(2) · · · H-N hydrogen bond (Cl(2) · · · H(02) ) 2.12(4) Å). The structural parameters of the anion agree well with those reported for the salt [PPN][IrHCl3(PiPr3)2]23 (PPN ) bis(triphenylphosphine)iminium). The iridium(I) complex 2 reacts with benzo[h]quinoline in dichloromethane at room temperature to give the metalated derivative 9, in agreement with its tendency to afford products resulting from direct C-H bond activation processes. Evidences for the NH-tautomerization of the heterocycle were not found. (23) Simpson, R. D.; Marshall, W. J.; Farischon, A. A.; Roe, D. C.; Grushin, V. V. Inorg. Chem. 1999, 38, 4171.


4. Mechanism of the Tautomerization. On the base of the results from DFT calculations on the mechanism of the NHtautomerization of quinoline and 2-methylpyridine promoted by the osmium complex OsH2Cl2(PiPr3)2, we had advanced that “transition-metal hydride complexes should favor the NHtautomerization of 2-substituted nitrogen containing heterocycles”,3e since the first step of the process involves an intermolecular metal to nitrogen hydrogen migration. The differences observed in behavior between the iridium(III)-hydride complex 1 and the iridium(I) compound 2 are totally consistent with this prediction. The results from the DFT calculations also show that once the metal to nitrogen hydrogen migration has occurred, the NC-H bond activation of the protonated heterocycle takes place. Thus, one should expect the formation of a deuteride complex from the reaction of 1 with a perdeuterated heterocycle. In order to confirm this we have performed the reaction of 1 with perdeuterated 2-methylpyridine in a NMR tube, using toluene-d8 as solvent. As expected the formation of IrDCl2{κC-(DNC5D3CD3)}(PiPr3)2 (7d, in eq 3) was observed. The presence of deuterium at the nitrogen atom of the tautomerized heterocycle is a consequence of the exchange between the original NH and the humidity of the reaction environment.24

The abstraction of the hydride ligand of 1 as a proton, by the nitrogen atom of the heterocycle, should involve the reduction of the metal center. So, the NC-H bond activation of the protonated heterocycle should be promoted by an iridium(I) intermediate. To prove this, we have also carried out the reaction of 2 with quinolinium chloride. As expected, the treatment of 2 with 2.0 equiv of this salt in toluene at 100 °C for 16 h gives 3, according to eq 4. Equations 3 and 4 indicate that, in an analogous manner to the NH-tautomerization of 2-substituted nitrogen containing heterocycles promoted by OsH2Cl2(PiPr3)2, the NH-tautomerization processes promoted by 1 take place by initial intermolecular metal to nitrogen hydrogen migration, followed by NC-H bond activation of the resulting protonated heterocycle on an iridium(I) intermediate.

In addition, complexes 3, 4, 7, and 8 show two common characteristic features: (i) the presence of an intramolecular Cl · · · H-N hydrogen bond, which increases the stability of the NH-tautomeric form, like in the osmium and ruthenium counterparts, and (ii) the cis disposition of the hydride ligand and the metalated carbon atom of the heterocycle, which is a consequence of the NC-H bond activation of the protonated heterocycle by an iridium(I) intermediate. (24) Under the same reaction conditions, in toluene-d8 and in the absence of the heterocycle, complex 1 does not exchange the hydride ligand with deuterium atoms of the enviroment.


Esteruelas et al.

Concluding Remarks

C), 143.9 (s, CH), 139.6 (s, Cipso), 133.6 (s, CH), 131.4 (s, CH), 128.1 (s, CH), 125.7 (s, CH), 123.8 (s, Cipso), 117.0 (s, CH), 25.4 (vt, N ) 27, CH-iPr), 19.6 (s, CH3-iPr), 18.9 (s, CH3-iPr). 31P{1H} NMR (121.42 MHz, CD2Cl2, 293 K): δ 3.8 (s). IR (KBr, cm-1): ν (Ir-H) 2266. Reaction of 1 with 8-Methylquinoline: Preparation of IrHCl2{KC-(HNC9H5CH3)}(PiPr3)2 (4). A Schlenk flask provided with a Teflon closure was charged with 8-methylquinoline (0.32 mL, 2.32 mmol), 1 (170 mg, 0.291 mmol) and toluene (15 mL). The mixture was heated during 16 h to give a red solution and a yellow precipitate. The solvent was removed in vacuo and the residue was extracted with CH2Cl2 and washed with cold toluene to afford a yellow solid which was recrystallized in a CH2Cl2/Et2O (1:1) mixture giving a yellow crystalline solid which was characterized as 4. Yield 160 mg (75%). Anal. Calcd for C28H52Cl2NIrP2: C, 46.21; H, 7.20; N, 1.92. Found: C, 46.08; H, 6.84; N, 2.11. 1H NMR (300 MHz, CD2Cl2, 293 K): δ 14.94 (br, 1H, NH), 7.79 (m, 1H, CH), 7.60 (m, 1H, CH), 7.57 (m, 1H, CH), 7.51 (m, 1H, CH), 7.40 (m, 1H, CH), 2.75 (s, 3H, CH3), 2.34 (m, 6H, CH-iPr), 1.27 (dvt, 36H, JH-H ) 6.6, N ) 13.2, CH3-iPr), -23.98 (t, 1H, JP-H ) 15.0, Ir-H). 13C{1H} NMR (75.43 MHz, CD2Cl2, 293 K, plus APT, HMQC and HMBC): δ 173.6 (t, JP-C ) 7, Ir-C), 143.6 (s, CH), 138.4 (s, Cipso), 133.8 (s, CH), 132.1 (s, CH), 126.8 (s, Cipso), 125.9 (s, CH), 125.0 (s, CH), 123.7 (s, Cipso), 25.2 (vt, N ) 27, CH-iPr), 19.4 (s, CH3-iPr), 18.8 (s, CH3-iPr), 16.9 (s, CH3). 31P{1H} NMR (121.42 MHz, CD2Cl2, 293 K): δ 3.8 (s). IR (KBr, cm-1): ν(Ir-H) 2260. Reaction of IrCl(η2-C8H14)(PiPr3)2 (2) with Quinoline: Prepa-

This study has revealed that, in agreement with its osmium and ruthenium counterparts MH2Cl2(PiPr3)2 (M ) Ru, Os), the iridium(III)-hydride complex IrHCl2(PiPr3)2 tautomerizes quinoline, 8-methylquinoline, 2-methylpyridine and benzo[h]quinoline and stabilizes the resulting NH-tautomers. The tautomerization process involves the abstraction of the hydride ligand from the metal center as a proton, by the nitrogen atom of the heterocycle, and the subsequent NC-H bond activation of the protonated heterocycle by the resulting iridium(I) intermediate. In accordance with the first step of the tautomerization processes, the iridium(I) compound IrCl(η2-C8H14)(PiPr3)2, which does not contain any hydride ligand, does not tautomerize the heterocycles but it promotes direct heterocyclic C-H bond activations or the intramolecular C-H bond activation of a coordinated phosphine. In conclusion, the NH-tautomerization reactions of 2-substituted pyridines and quinolines on hydride complexes of osmium and ruthenium, the determining factors for the tautomerizations, as well as the mechanism of the processes can be extended to the chemistry of iridium-hydride complexes.

Experimental Section General Information. All manipulations were performed with rigorous exclusion of air at an argon/vacuum manifold using standard Schlenk-tube techniques or in a drybox (MB-UNILAB). Solvents were dried by the usual procedures and distilled under argon prior to use. Quinoline, 8-methylquinoline, 2-methylpyridine, 2-methylpyridine-d7, and benzo[h]quinoline (Aldrich) were used without further purification. The starting materials [IrCl(coe)2]2,25 IrHCl2(PiPr3)2 (1)26 and IrCl(η2-C8H14)(PiPr3)2 (2)27 were prepared according with methods reported in the literature. NMR spectra were recorded on either a Varian Gemini 2000, a Bruker ARX 300, a Bruker Avance 300 MHz or a Bruker Avance 400 MHz instrument. Chemical shifts (expressed in parts per million) are referenced to residual solvent peaks (1H, 13C{1H}) or external H3PO4 (31P{1H}). Coupling constants, J, and N are given in hertz. Infrared spectra were recorded on a Perkin-Elmer Spectrum One FT-IR Spectrometer. C, H, and N analyses were carried out in a Perkin-Elmer 2400 CHNS/O analyzer. Reaction of IrHCl2(PiPr3)2 (1) with Quinoline: Preparation of IrHCl2{K-C-(HNC9H6)}(PiPr3)2 (3). A Schlenk flask provided with a Teflon closure was charged with quinoline (0.10 mL, 0.84 mmol), 1 (120 mg, 0.205 mmol) and toluene (15 mL). The mixture was heated at 100 °C during 16 h to give a red solution. The solvent was removed in vacuo and the residue was extracted with CH2Cl2. The solution was concentrated to ca. 1.0 mL and precipitated by addition of Et2O (10 mL). The yellow precipitate was dried in vacuo and characterized as 3. Yield 100 mg (70%). Anal. Calcd for C27H50Cl2NIrP2: C, 45.43; H, 7.06; N, 1.96. Found: C, 45.45; H, 6.94; N, 1.99. 1H NMR (300 MHz, CD2Cl2, 293 K): δ 14.90 (br, 1H, NH), 7.76-7.74 (m, 2H, CH), 7.70 (m, 1H, CH), 7.65 (m, 1H, CH), 7.60 (m, 1H, CH), 7.50 (m, 1H, CH), 2.35 (m, 6H, CH-iPr), 1.26 (dvt, 36H, JH-H ) 6.9, N ) 13.2, CH3-iPr), -24.04 (t, 1H, JP-H ) 15.3, Ir-H). 13C{1H} NMR (75.43 MHz, CD2Cl2, 293 K, plus APT, HMQC and HMBC): δ 173.9 (t, JP-C ) 7, Ir(25) (a) Van der Ent, A.; Onderdelinden, A. L.; Shunn, R. A. Inorg. Synth. 1973, 14, 92. (b) Van der Ent, A.; Onderdelinden, A. L.; Shunn, R. A. Inorg. Synth 1990, 28, 90. (26) (a) Werner, H.; Wolf, J.; Ho¨hn, A. J. Organomet. Chem. 1985, 287, 395. (b) Simpson, R. D.; Marshall, W. J.; Farischon, A. A.; Roe, D. C.; Grushin, V. V. Inorg. Chem. 1999, 38, 4171. (27) (a) Werner, H.; Ho¨hn, A.; Dziallas, M. Angew. Chem., Int. Ed. 1986, 25, 1090. (b) Dirnberger, T.; Werner, H. Organometallics 2005, 24, 5127. (c) Werner, H.; Ho¨hn, A.; Dziallas, M.; Dirnberger, T. Dalton Trans. 2006, 2597.

ration of IrH{CH2CH(CH3)PiPr2}Cl{K-N-(NC9H7)}(PiPr3) (5). PiPr3 (0.17 mL, 0.90 mmol) was added to a CH2Cl2 (10 mL) solution of [IrCl(coe)2]2 (200 g, 0.224 mmol); the mixture was stirred at room temperature for 5 min and the formation of a yellow solution was observed. Quinoline (0.10 mL, 0.85 mmol) was then added. The mixture was further stirred for 12 h. The solvent was removed in vacuo and the residue was washed with cold pentane to afford a yellow solid which was dried in vacuo and characterized as 5. Yield 242 mg (80%). Anal. Calcd for C27H49ClNIrP2: C, 47.87, H, 7.29; N, 2.06. Found: C, 47.91; H, 7.35; N, 2.12. 1H NMR (300 MHz, C6D6, 293 K, plus HSQC, plus COSY): δ 11.30 (m, 1H, CH), 9.77 (m, 1H, CH), 7.44 (t, 1H, JH-H ) 8.4, CH), 7.40-7.36 (m, 1H, CH), 7.21-7.17 (m, 1H, CH), 7.07 (t, 1H, JH-H ) 7.8, CH), 6.70 (dd, 1H, JH-H ) 8.1, JH-H ) 5.1, CH), 3.88 (m, 1H, CH-Me), 3.24 (m, 1H, CH-iPr), 2.40 (dddd, 1H, JP-H ) 30.0, JP-H ) 5.2, JH-H ) 8.4, JH-H ) 9.5, CH2), 2.09-1.92 (m, 4H, CH-iPr), 1.44 (dd, 4H, JP-H ) 14.1, JH-H ) 6.9, CH3-iPr, masked 1H CH2), 1.32 (m, 9H, JP-H ) 12.3, JH-H ) 7.2, CH3-iPr), 1.18 - 1.09 (m, 12H, CH3-iPr), 1.02 (m, 3H, JP-H ) 13.2, JH-H ) 7.2, CH3-iPr), 0.85 (m, 3H, JP-H ) 11.7, JH-H ) 7.5, CH3-CHCH2), 0.62 (m, 3H, JP-H ) 14.7, JH-H ) 7.5, CH3-iPr), -21.64 (dd, 1H, JP-H ) 24.4, JP-H ) 14.6, Ir-H). 13C{1H} NMR (75.48 MHz, CD2Cl2, 243 K, plus APT, HSQC): δ 157.2 (s CH), 148.2 (s, Cipso), 136.4 (s, CH), 134.6 (s, CH), 128.6 (s, CH), 128.4 (s, Cipso), 127.8 (s, CH), 126.5 (s, CH), 121.4 (s, CH), 45.2 (d, JP-C ) 31, CHCH2), 24.4 (dd, JP-C ) 23; JP-C ) 2, CH-iPr), 24.1 (dd, JP-C ) 12; JP-C ) 7, CH-iPr), 23.8 (dd, JP-C ) 23; JP-C ) 2, CH-iPr), 20.7 (d, JP-C ) 5 CH3), 20.5 (br, CH3), 19.4 (m, CH3-CHCH2), 18.4 (s, CH3), 18.3 (s, CH3), 17.9 (m, CH3), 17.2 (m, CH3), -25.9 (dd, JP-C ) 23; JP-C ) 5, Ir-CH2). 31P{1H} NMR (121.42 MHz, CD2Cl2, 293 K): δ 13.2 (d, JP-P ) 358), 25.8 (d, JP-P ) 358). IR (KBr, cm-1): ν(Ir-H) 2223. Reaction of 2 with 8-Methylquinoline: Preparation of IrHCl(CH2C9H6N)(PiPr3)2 (6). PiPr3 (0.16 mL, 0.84 mmol) was added to a stirred CH2Cl2 (10 mL) suspension of [IrCl(coe)2]2 (190 mg, 0.212 mmol). The immediate formation of a yellow solution was observed. After 10 min 8-methylquinoline (0.12 mL, 0.87 mmol) was added to the above-mentioned solution and the mixture was further stirred for 12 h at room temperature. The solvent was

NH-Tautomerization by Hydride-Iridium(III) Complex removed in vacuo and Et2O (10 mL) was added to the residue. The mixture was kept at 0 °C for 12 h to afford a yellow precipitate which was dried in vacuo and characterized as 6. Yield 249 mg (85%). Anal. Calcd for C28H51ClNIrP2: C, 48.65; H, 7.44; N, 2.02. Found: C 49.05, H 8.01, N 1.89. 1H NMR (300 MHz, CD2Cl2, 293 K, plus HSQC): δ 10.00 (m, 1H, CH), 8.10 (m, 1H, CH), 7.54 (m, 1H, CH), 7.46 (m, 1H, CH), 7.38 (m, 1H, CH), 7.36 (m, 1H, CH), 2.90 (t, JP-H ) 6.6, 2H, Ir-CH2), 2.64 (m, 6H, CH-iPr), 1.15 (dvt, 18H, JH-H ) 6.3, N ) 12.6, CH3-iPr), 0.76 (dvt, 18H, JH-H ) 6.3, N ) 12.6, CH3-iPr), -21.23 (t, 1H, JP-H ) 18.0, Ir-H). 13 C{1H} NMR (75.48 MHz, CD2Cl2, 243 K, plus APT, HSQC): δ 155.3 (s, Cipso), 154.9 (s, Cipso), 151.5 (s, CH), 135.5 (s, CH), 129.8 (s, CH), 129.2 (s, Cipso), 126.9 (s, CH), 123.4 (s, CH), 121.5 (s, CH), 23.1 (vt, N ) 25, CH-iPr), 19.3 (s, CH3-iPr), 18.6 (s, CH-iPr), -9.3 (t, JP-C ) 6, Ir-CH2). 31P{1H} NMR (121.42 MHz, CD2Cl2, 293 K): δ 9.6 (s). IR (KBr, cm-1): ν(Ir-H) 2177. Reaction of 1 with 2-Methylpyridine: Preparation of IrHCl2{K-C-(HNC5H3CH3)}(PiPr3)2 (7). A Schlenk flask provided with a Teflon closure was charged with 2-methylpyridine (0.19 mL, 1.92 mmol), 1 (140 mg, 0.240 mmol), and toluene (15 mL). The mixture was heated at 120 °C during 16 h to give an orange solution. The solution was filtered through Celite and the solvent was removed in vacuo. The residue was washed with pentane (15 mL) to give a white solid which was extracted with CH2Cl2 (10 mL) the CH2Cl2 solution was concentrated in vacuo to ca. 1.0 mL and precipitated with pentane (10 mL) to give a white solid of 7. Yield 140 mg (85%). Anal. Calcd for C24H50Cl2NIrP2: C, 42.53; H, 7.43, N, 2.07. Found: C, 42.54; H, 7.39; N, 2.15. 1H NMR (300 MHz, CD2Cl2, 293 K): δ 14.62 (br, 1H, NH), 7.53 (m, 1H, CH), 7.10 (m, 1H, CH), 6.63 (m, 1H, CH), 2.40 (s, 3H, 2-CH3-py), 2.33 (m, 6H, CH-iPr), 1.27 (dvt, 36H, JH-H ) 6.9, N ) 13.8, CH3-iPr), -24.44 (t, 1H, JP-H ) 15.0, Ir-H). 13C{1H} NMR (75.43 MHz, CD2Cl2, 293 K, plus APT): δ 165.3 (t, JP-C ) 7, Ir-C), 148.3 (s, Cipso), 143.4 (s, CH), 136.8 (s, CH), 115.4 (s, CH), 25.1 (vt, N ) 27, CH-iPr), 19.6 (s, CH3-iPr), 19.0 (s, CH3-iPr), 18.7 (s, 2-CH3py). 31P{1H} NMR (121.42 MHz, CD2Cl2, 293 K): δ 4.1 (s). IR (KBr, cm-1): ν(Ir-H) 2271. Reaction of 1 with Benzo[h]quinoline. A Schlenk flask provided with a Teflon closure was charged with benzo[h]quinoline (0.055 g, 0.306 mmol), 1 (150 mg, 0.256 mmol), and toluene (5 mL). The mixture was heated at 100 °C during 16 h to give a red solution. The solvent was removed and the yellow residue was washed with pentane and characterized by 1H NMR (300 MHz, CD2Cl2, 293 K) as a mixture of complexes IrHCl2{κ-C-(HNbq)}(PiPr3)2 (8; 15%) and IrHCl{κ-N,C-(bq)}(PiPr3)2 (9, 85%). Crystals of 8 suitable for elemental analysis were obtained from toluene solutions of these 8/9 mixtures. Data for 8: Anal. Calcd for C31H52Cl2NIrP2: C, 48.74; H, 6.86; N, 1.83. Found: C 49.03, H 7.05, N 1.89. 1H NMR (300 MHz, CD2Cl2, 293 K): δ15.90 (br, 1H, NH), 9.04 (d, 1H, JH-H ) 8.4, CH), 8.01 (m, 1H, CH), 7.90 (d, 1H, JH-H ) 8.7, CH), 7.87 (m, 1H, CH), 7.84 (d, 1H, JH-H ) 8.7, CH), 7.79 (m, 1H, CH), 7.69 (d, 1H, JH-H ) 8.7, CH), 7.65 (d, 1H, JH-H ) 8.7, CH), 2.37 (m, 6H, CH-iPr), 1.30 (dvt, 18H, JH-H ) 6.6, N ) 13.5, CH3-iPr), 1.24 (dvt, 18H, JH-H ) 6.6, N ) 13.2, CH3-iPr), -24.20 (t, 1H, JP-H ) 15.0, Ir-H). 13C{1H} NMR (75.48 MHz, CD2Cl2, 293 K, plus APT): δ 169.9 (t, JP-C ) 8 Hz, Ir-C), 143.9 (s, CH), 137.0 (s, Cipso), 134.6 (s, CH), 134.2 (s, Cipso), 129.2 (s, CH), 128.7 (s, CH), 128.4 (s, CH), 126.2 (s, CH), 124.4 (s, CH), 123.0 (s, Cipso), 121.7 (s, CH), 121.2 (s, Cipso), 25.0 (vt, N ) 27, CH-iPr), 19.4 (s, CH3-iPr), 18.71 (s, CH3-iPr). 31P{1H} NMR (121.42 MHz, CD2Cl2, 293 K): δ 4.2 (s). IR (KBr, cm-1): ν(Ir-H) 2262. Reaction of 1 with Benzo[h]quinoline in Presence of NEt3: Preparation of IrHCl{K-N,C-(bq)}(PiPr3)2 (9). A Schlenk flask provided with a Teflon closure was charged with benzo[h]quinoline (0.10 g, 0.558 mmol), 1 (150 mg, 0.256 mmol), NEt3 (0.20 mL, 1.44 mmol) and toluene (10 mL). The mixture was heated at 100 °C during 16 h. The solvent was removed in vacuo and the residue

Organometallics, Vol. 28, No. 7, 2009 2283 was washed with pentane (2 × 5 mL) and extracted with toluene. The toluene solution was filtered through Celite and the solution was concentrated in vacuo to ca. 1.0 mL and pentane (5 mL) was added to give a yellow precipitate which was dried in vacuo and characterized as 9. Yield 168 mg (90%). Anal. Calcd for C31H51ClNIrP2: C, 51.19; H, 7.06; N, 1.93. Found: C, 51.23; H, 7.16; N, 2.01. 1H NMR (300 MHz, CD2Cl2, 293 K): δ 10.10 (m, 1H, CH), 8.19 (m, 1H, CH), 7.80 (m, 1H, CH), 7.75 (m, 1H, CH), 7.60 (m, 1H, CH), 7.58 (m, 1H, CH), 7.42 (m, 1H, CH), 7.26 (m, 1H, CH), 2.27 (m, 6H, CH-iPr), 1.10 (dvt, 18H, JH-H ) 6.6, N ) 12.9, CH3-iPr), 0.60 (dvt, 18H, JH-H ) 6.6, N ) 13.2, CH3-iPr), -18.5 (t, 1H, JP-H ) 17.7, Ir-H). 13C{1H} NMR (75.48 MHz, CD2Cl2, 293 K, plus APT): δ 157.5 (s, Cipso), 151.1 (s, CH), 146.1 (t, JP-C ) 7, Ir-C), 137.7 (s, CH), 135.1 (s, CH), 133.7 (s, Cipso), 129.2 (s, CH), 129.1 (s, CH), 126.4 (s, Cipso), 123.3 (s, CH), 119.7 (s, CH), 117.9 (s, CH), 24.0 (vt, N ) 27, CH-iPr), 18.9 (s, CH3-iPr), 18.4 (s, CH3-iPr). 31P{1H} NMR (121.42 MHz, CD2Cl2, 293 K): δ 6.4 (s). IR (KBr, cm-1): ν(Ir-H) 2266. Reaction of 1 with Benzo[h]quinolinium Chloride: Preparation of [HNHbq][IrHCl3(PiPr3)2] (10). Acetone (20 mL) was added to a mixture of 1 (150 mg, 0.257 mmol) and benzo[h]quinolinium chloride (0.056 g, 0.260 mmol). The resulting mixture was stirred at room temperature for 2 h. Et2O (20 mL) was added affording an orange precipitate which was decanted and dried in vacuo to give an orange-yellowish solid which was characterized as 10. Yield 165 mg (80%). Anal. Calcd for C31H53Cl3NIrP2: C, 46.52; H, 6.67; N, 1.75. Found: C, 46.62; H, 6.73; N, 1.82. 1H NMR (300 MHz, CD2Cl2, 293 K): δ 18.17 (br, 1H, NH), 10.01 (m, 1H, CH), 9.47 (m, 1H, CH), 8.88 (m, 2H, CH), 8.04 (m, 1H, CH), 7.96 (m, 1H, CH), 7.93 (m, 1H, CH), 2.99 (m, 6H, CH-iPr), 1.35 (dvt, 36H, JH-H ) 6.6, N ) 12.9, CH3-iPr), -37.52 (br, 1H, Ir-H). 13C{1H} NMR (75.48 MHz, CD2Cl2, 293 K, plus APT): δ 144.7 (s, CH), 143.2 (s, CH), 138.9 (s, Cipso), 135.1 (s, Cipso), 131.7 (s, CH), 129.6 (s, CH), 129.1 (s, CH), 128.7 (s, Cipso), 126.0 (s, CH), 124.5 (s, Cipso), 124.1 (s, CH), 122.2 (s, CH), 22.1 (vt, N ) 26, CH-iPr), 19.2 (s, CH3-iPr). 31P{1H} NMR (121.42 MHz, CD2Cl2, 293 K): δ 22.4 (br). IR (KBr, cm-1): ν(Ir-H) 2294. Reaction of 1 with 3.0 equiv of Benzo[h]quinoline. A Schlenk flask provided with a Teflon closure was charged with benzo[h]quinoline (0.129 g, 0.720 mmol), 1 (140 mg, 0.240 mmol), and toluene (15 mL). The mixture was heated at 100 °C during 16 h to give a red solution. The solvent was removed and the residue was washed with pentane to give a yellow solid which was characterized by 1H NMR (300 MHz, CD2Cl2) as a mixture of complexes 9 (60%) and 10 (40%). Reaction of 2 with Benzo[h]quinoline. PiPr3 (0.14 mL, 0.73 mmol) was added to a CH2Cl2 (10 mL) solution of [IrCl(coe)2]2 (150 mg, 0.168 mmol). After 5 min a yellow solution was formed. Benzo[h]quinoline (0.060 g, 0.334 mmol) was then added and the mixture was further stirred for 12 h. The solvent was removed in vacuo and the residue was washed with cold pentane to afford a yellow solid characterized as 9. Yield 140 mg (80%). Reaction of 1 with 2-Methylpyridine-d7. A Young’s NMR tube was charged with 2-methylpyridine-d7 (28 µL, 0.286 mmol), 1 (0.021 g, 0.036 mmol) and toluene-d8 (0.50 mL). The mixture was heated at 120 °C for 24 h. After this time the solvent was removed in vacuo and CH2Cl2 (0.5 mL) was added. The NMR spectra of these solutions showed the resonances corresponding to the complex IrDCl2{κ-C-(DNC5D3CD3)}(PiPr3)2 (7d). 2H NMR (46.97 MHz, CH2Cl2, 293 K): δ 14.8 (br, N-D), 7.8 - 6.8 (3D, CD), 2.6 (s, CD3), -24.0 (Ir-D). 31P{1H} NMR (121.42 MHz, CD2Cl2, 293 K): δ 3.7 (br). Reaction of 2 with Quinolinium Chloride. In a Schlenk flask provided with a Teflon closure PiPr3 (0.085 mL, 0.445 mmol) was added to a suspension of [IrCl(coe)2]2 (100 mg, 0.112 mmol) in toluene (10 mL) getting a yellow solution. Quinolinium chloride (0.040 g, 0.241 mmol) was added to the above-mentioned solution

2284 Organometallics, Vol. 28, No. 7, 2009 and the mixture was stirred at 100 °C for 16 h. The solvent was removed in Vacuo and the residue was extracted with CH2Cl2. The solution was concentrated to ca. 1.0 mL and a yellow solid was precipitated by addition of Et2O (10 mL). The precipitate was washed with MeOH (2 × 5 mL) and with Et2O (2 × 5 mL) to give a yellow solid of 3. Yield 100 mg (65%). Structural Analysis of Complexes 4, 5, 6, 7, 9, and 10. X-ray data were collected for all complexes on a Bruker Smart APEX CCD diffractometer equipped with a normal focus, 2.4 kW sealed tube source (Mo radiation, λ ) 0.71073 Å) operating at 50 kV and 30 (4, 6, 10) or 40 mA (5, 7, 9). Data were collected over the complete sphere by a combination of four sets. Each frame exposure time was 10 s (4, 6, 9, 10), 20 s (5), or 30 s (7) covering 0.3° in ω. Data were corrected for absorption by using a multiscan method applied with the SADABS program.28 The structures of all compounds were solved by the Patterson or direct methods. Refinement, by full-matrix least-squares on F2 with SHELXL97,29 was similar for all complexes, including isotropic and subsequently anisotropic displacement parameters. The hydrogen atoms were observed or calculated and refined freely or using a restricted riding model. Hydride ligands were observed in the difference Fourier maps and refined with restrained Ir-H bond length (1.59(1) Å, CSD). In 4 two molecules of disordered diethyl ether were observed in the same site of the asymmetric unit, and were refined with restrained geometry, isotropic atoms, without hydrogen atoms and with occupancy 0.5 each. In all complexes, all the highest electronic residuals were observed in close proximity of the Ir centers and make no chemical sense. Crystal data for 4: C28H52Cl2IrNP2xOC4H10, MW 801.87, yellow, irregular block (0.10 × 0.08 × 0.08), orthorhombic, space group Pnma, a: 20.892(5) Å, b: 21.270(5) Å, c: 8.648(2) Å, V ) 3842.7(17) Å3, Z ) 4, Dcalc: 1.386 g cm-3, F(000): 1690, T ) 100(2) K, µ 3.720 mm-1. 46011 measured reflections (2θ: 4-58°, ω scans 0.3°), 4986 unique (Rint ) 0.0538); min/max transm. factors 0.644/ 0.847. Final agreement factors were R1 ) 0.0346 (4532 observed reflections, I > 2σ(I)) and wR2 ) 0.0892; data/restraints/parameters 4986/29/230; GoF ) 1.084. Largest peak and hole 1.742 and -1.007 e/Å3. Crystal data for 5: C27H49ClIrNP2, MW 677.26, yellow, irregular block (0.08 × 0.04 × 0.02), triclinic, space group P1j, a: 10.435(3) Å, b: 11.908(3) Å, c: 12.635(4) Å, R: 73.086(4)°, β: 88.357(5)°, γ: 76.943(5)°, V ) 1462.1(7) Å3, Z ) 2, Dcalc: 1.538 g cm-3, F(000): 684, T ) 100(2) K, µ 4.782 mm-1. 18002 measured reflections (2θ: 4-58°, ω scans 0.3°), 6955 unique (Rint ) 0.0520); min/max transm. factors 0.640/0.848. Final agreement factors were R1 ) 0.0363 (5838 observed reflections, I > 2σ(I)) and wR2 ) 0.0522; data/restraints/parameters 6955/1/304; GoF ) 0.888. Largest peak and hole 0.964 and -1.529 e/Å3. (28) (a) Blessing, R. H. Acta Crystallogr. 1995, A51, 33. (b) SADABS: Area-detector absorption correction; Bruker-AXS: Madison, WI, 1996. (29) (a) SHELXTL Package V. 6.10; Bruker-AXS: Madison, WI, 2000. (b) Sheldrick, G. Acta Crystallogr. 2008, A64, 112.

Esteruelas et al. Crystal data for 6: C28H51ClIrNP2, MW 691.29, colorless, irregular block (0.10 × 0.08 × 0.08), monoclinic, space group P21/c, a: 15.497(3) Å, b: 10.194(2) Å, c: 18.662(4) Å, β: 101.219(4)°, V ) 2891.9(11) Å3, Z ) 4, Dcalc: 1.588 g cm-3, F(000): 1400, T ) 100(2) K, µ 4.837 mm-1. 33072 measured reflections (2θ: 4-58°, ω scans 0.3°), 7154 unique (Rint ) 0.0368); min/max transm. factors 0.586/ 0.698. Final agreement factors were R1 ) 0.0251 (6434 observed reflections, I > 2σ(I)) and wR2 ) 0.0553; data/restraints/parameters 7154/0/314; GoF ) 1.083. Largest peak and hole 1.159 and -0.836 e/Å3. Crystal data for 7: C24H50Cl2IrNP2xCH2Cl2, MW 762.62, colorless, irregular block (0.10 × 0.06 × 0.02), orthorhombic, space group Pnma, a: 23.365(9) Å, b: 12.868(5) Å, c: 10.606(4) Å, V ) 3189(2) Å3, Z ) 4, Dcalc: 1.589 g cm-3, F(000): 1536, T ) 100(2) K, µ 4.638 mm-1. 20281 measured reflections (2θ: 4-58°, ω scans 0.3°), 4026 unique (Rint ) 0.0496); min./max. transm. factors 0.639/ 0.913. Final agreement factors were R1 ) 0.0523 (3409 observed reflections, I > 2σ(I)) and wR2 ) 0.1060; data/restraints/parameters 4026/ 1/177; GoF ) 1.150. Largest peak and hole 2.161 and -1.963 e/Å3. Crystal data for 9: C31H51ClIrNP2, MW 727.32, yellow, irregular block (0.08 × 0.04 × 0.02), triclinic, space group P1j, a: 10.764(3) Å, b: 10.934(3) Å, c: 15.860(4) Å, R: 100.251(5) °, β: 98.123(5)°, γ: 119.351(4)°, V ) 1543.1(7) Å3, Z ) 2, Dcalc: 1.565 g cm-3, F(000): 736, T ) 100(2) K, µ 4.537 mm-1. 19415 measured reflections (2θ: 4-58°, ω scans 0.3°), 7384 unique (Rint ) 0.0587); min/max transm. factors 0.680/0.915. Final agreement factors were R1 ) 0.0431 (6225 observed reflections, I > 2σ(I)) and wR2 ) 0.0906; data/restraints/parameters 7384/1/341; GoF ) 1.032. Largest peak and hole 2.502 and -1.922 e/Å3. Crystal data for 10: C31H53Cl3IrNP2, MW 800.23, yellow, irregular block (0.12 × 0.06 × 0.06), monoclinic, space group P21/n, a: 16.352(4) Å, b: 12.250(3) Å, c: 16.848(4) Å, β: 90.314(4)°, V ) 3374.8(13) Å3, Z ) 4, Dcalc: 1.575 g cm-3, F(000): 1616, T ) 100(2) K, µ 4.310 mm-1. 38701 measured reflections (2θ: 4-58°, ω scans 0.3°), 8367 unique (Rint ) 0.0575); min/max transm. factors 0.610/ 0.782. Final agreement factors were R1 ) 0.0362 (6991 observed reflections, I > 2σ(I)) and wR2 ) 0.0681; data/restraints/parameters 8367/1/ 363; GoF ) 1.043. Largest peak and hole 1.047 and -1.118 e/Å3.

Acknowledgment. Financial support from the MICINN of Spain (project number CTQ2008-00810 and Consolider Ingenio 2010 CSD2007-00006) and the Diputacioń General de Aragoń (E35) is acknowledged. Supporting Information Available: Detailed X-ray crystallographic data (bond distances, bond angles, and anisotropic parameters) for 4, 5, 6, 7, 9, and 10 as CIF files. This material is available free of charge via the Internet at http://pubs.acs.org. OM8011954

NH-Tautomerization of Quinolines and 2 ... - ACS Publications

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