Article pubs.acs.org/Organometallics
Synthesis and Characterization of [Ir(AcacBiMs)(COD)] and [cisIr(AcacBiMs)2(COE-OH)] Oracio Serrano,*,† Juan Nicasio-Collazo,*,† Guadalupe Morales,† J. Carlos Alvarado-Monzón,† Aarón Torres-Huerta,‡ Herbert Höpfl,‡ Jorge A. López,† and Ana C. Esqueda§ †
Departamento de Química, Sede Pueblito de Rocha, Universidad de Guanajuato, Cerro de la Velada s/n, Pueblito de Rocha, C.P. 36040, Guanajuato, México ‡ Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, C.P. 62209 Cuernavaca, México § Centro de Estudios Científicos y Tecnológicos No. 17, Instituto Politécnico Nacional, León, C.P. 37000, Guanajuato, México S Supporting Information *
ABSTRACT: The reaction of dinuclear complex [IrCl(COD)]2 (COD = 1,5cyclooctadiene) with 1 equiv of 1,3-dimesitylpropane-1,3-dione (H-AcacBiMs) and an excess of triethylamine in benzene or dichloromethane at room temperature results in the formation of β-diketonate complex [Ir(AcacBiMs)(COD)], 1. Further, compound 1 reacts with an equivalent of H-AcacBiMs in dichloromethane under atmospheric conditions to give the new complex with the formula [cis-Ir(AcacBiMs)2(COE-OH)], 2 (COE-OH = σ,π-hydroxyenediyl), through a formal insertion of a hydroxyl group into a COD ring. All compounds were characterized by melting point, analytical data, and IR and NMR spectroscopy. Additionally, an X-ray crystallographic study was undertaken to corroborate the structure of both complexes.
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INTRODUCTION The synthesis of aldehyde and epoxide compounds through alkene oxidation catalyzed by palladium/copper and titanium or manganese (Wacker process, and Sharples or Jacobsen− Katsuki epoxidation reactions) has been deeply studied theoretically and experimentally, for either academia or industrial interest.1−3 These oxidation reactions mostly are highly exothermic and often involve a cascade of concerted steps. In 1990, Klemperer and co-workers reported the first formal addition of a hydroxyl (OH) group into a CC bond in 1,5-cyclooctadiene (COD) through a molecular oxygen activation by 2 equiv of ionic iridium complex [Ir(COD)(P3O9)], to give a four-membered iridacycle, which finally evolves in concerted intramolecular C−H and Ir−O bond activations to give the final product (Chart 1).4 Furthermore, almost two decades ago, three elegant and independent reports by the Bergman, Gal, and Moya groups showed that the alkene oxidation can take place using catalytic precursor species supported by cyclopentadienyl, nitrile, or pyridyl ligands (Chart 1).5−7 Recently, Gade and co-workers reported neutral bisethylene and COD iridium complexes containing potential tridentate amido-pyridine ligands. These compounds can be used as catalytic precursors in the alkene epoxidation reaction using PPO (PPO = 3-phenyl-2-(phenylsulfonyl)-1,2-oxaziridine) as oxidizing agent; however, when the reactions were carried out using hydrogen peroxide, a deactivation of the catalyst was observed (Chart 1).8 © 2014 American Chemical Society
On the other hand, the family of neutral [trans-Ir(Acac)2(R)(L)] (R= alkyl; L = ethylene, pyridine) complexes reported by Periana et al. is one of the most versatile catalytic precursors in the C−H/C−D bond activation and C−C bond formation between ethylene and benzene (Chart 2).9 Encouraged by these results, herein, we report the reaction of [Ir(AcacBiMs)(COD)] (1) with an equivalent of bulky 1,3-dimesitylpropane1,3-dione (H-AcacBiMs) to give an unusual Ir(III) species with the formula [cis-Ir(AcacBiMs)2(COE-OH)] (COE-OH = σ,πhydroxyenediyl) (2). The new iridium complex shows a cisgeometry around the iridium atom, which has been proposed as a key intermediate in the Periana’s catalytic system. Most remarkably, compound 2 can be easily obtained under mild conditions, by selective oxidation on the COD fragment, involving a formal OH group addition into the COD (Scheme 1). The reaction of dinuclear complex [IrCl(COD)]2 with 1 equiv of 1,3-dimesitylpropane-1,3-dione (H-AcacBiMs) and an excess of triethylamine (TEA) in benzene or dicholomethane (CH2Cl2) at room temperature afforded the air- and moisturestable yellow crystals of [Ir(AcacBiMs)(COD)], 1 (Scheme 1). Compound 1 is kinetically and thermally robust and has been characterized by NMR and IR spectroscopy, elemental analysis, and X-ray single-crystal analysis. The 1H NMR spectrum of compound 1 shows characteristic signals at 6.66 (m, 4H); 5.62 Received: March 7, 2014 Published: May 7, 2014 2561
dx.doi.org/10.1021/om500230k | Organometallics 2014, 33, 2561−2564
Organometallics
Article
Chart 1
are in the range reported for analogous compounds.10 There is only a handful of structurally characterized [Ir(Acac)(alkene)] complexes, which have been shown to react with common solvents, such as acetone, toluene, alcohols, and [HgCN2].10b,c Unexpectedly, compound 1 is kinetically and thermodynamically stable to air and moisture either in the solid state (for a year) or in solution (toluene, CH2Cl2, or benzene-d6 solution for weeks). Compound 1 reacts with an equivalent of H-AcacBiMs ligand under atmospheric conditions in CH2Cl2 to give the new Ir(III)-σ-π complex with the formula [cis-Ir(AcacBiMs)2(COEOH)] (2) by a formal insertion of a OH group into the CC bond on the COD ring, resembling the Klemperer’s complex. Also, compound 2 is obtained as yellow crystals after a chromatographic column, in moderate yield, showing kinetic and thermal stability either in solution or in the solid state. Compound 2 has been fully characterized by NMR and IR spectroscopy and elemental analysis, and its structure was corroborated by X-ray single-crystal analysis. The IR spectrum of 2 shows a sharp band at 3450 cm−1 assigned to the HO group. In the NMR proton spectrum, a series of broad multiple signals from 5.8 to 0.59 ppm are assigned to the nonequivalent protons from the COE-OH entity. In good agreement, in the 13 C{1H} NMR spectrum, four signals from 187 to 181 ppm are
Chart 2
(s, 1H, CH); 2.32 (s, 12H); and 2.26 (s, 6H) ppm, which were assigned to the aromatic, methine, and methyl protons of the AcacBiMs fragment, respectively. Furthermore, the signals observed at 4.41 (bs, 4H) and 2.08 (bs, 8H) ppm, were attributed to the methine and methylene protons from the COD entity. 13C{1H} NMR spectra also show characteristic partner signals for the AcacBiMs and COD fragments and will not be discussed in detail (see the Supporting Information). The molecular structure of 1 was corroborated by X-ray diffraction (Figure 1). Its structure has a planar square geometry around the iridium atom, and the bonds and angles 2562
dx.doi.org/10.1021/om500230k | Organometallics 2014, 33, 2561−2564
Organometallics
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Scheme 1. Synthesis of Complexes 1 and 2
Figure 1. Perspective view of the molecular structure of [Ir(AcacBiMs)(COD)] 1. Ellipsoids are drawn at the 30% probability level. Hydrogen atoms have been omitted for clarity. Selected bond lengths [Å] and angles [deg]: Ir1−O1 = 2.035(4), Ir1−O2 = 2.050(3), Ir1− C2 = 2.037 (2), Ir1−C2 = 2.038(3); O1−Ir1−O2 = 91.17(10), O1− Ir1−C23= 89.67(8).
Figure 2. Perspective view of the molecular structure of [cisIr(AcacBiMs)2(COE-OH)] 2. Ellipsoids are drawn at the 30% probability level. Hydrogen atoms and methyl groups have been omitted for clarity. Selected bond lengths [Å] and angles [deg]: Ir1− O1 = 2.175(4), Ir1−O2 = 2.023(3), Ir1−O3 = 2.060(3), Ir1−O4 = 2.049(3), Ir1−C48 = 2.061 (2), Ir1−C43 = 2.152(3), Ir1−C44 = 2.158(3); O1−Ir1−O2 = 91.02(10), O3−Ir1−O4 = 90.22(10), O1− Ir1−O4 = 91.87(10), O1−Ir1−O3 = 88.57(10), O2−Ir1−C48 = 95.38(10), O3−Ir1−C48 = 89.64(10), C43−Ir1−C48 = 87.27(10), C44−Ir1−C48 = 81.07 (10).
given to the carbonyl groups. Two signals observed at 106.7 and 106.1 ppm are attributed to methine carbons from AcacBiMs ligands. The signal at 89.8 ppm is assigned to the carbon of the Ir-CH(OH) fragment. Furthermore, four signals observed at 37.2, 31.8, 25.0, and 21.8 ppm are assigned to the methylene carbons of the COE-OH entity. The molecular structure of 2 is shown in Figure 2. Its structure has an octahedral geometry around the iridium atom, with the auxiliary coligands in a cisposition. The Ir(1)−C(1) and Ir(1)−(η2:C(2)C(3)) bonds are in the expected range found in similar complexes,9 showing a clear trans-effect on the Ir(1)−O(1) bond distance (2.175 Å) trans to the alkyl substituent.4 Finally, the OH group adopts an endo with regards to the iridium atom. According to Periana et al.’s reports, the isomerization reaction of the auxiliary ligands in the complex [transIr(Acac)2(R)(L)] to give the [cis-Ir(Acac)2(R)(L)] isomer can be driven under thermic treatment at 180 °C in benzene. However, this isomer cannot be isolated, and its structure was supported by variable-temperature NMR experiments. Additionally, his theoretical studies showed that the [cis-Ir(Acac)2(Alkene)(Alkyl)] species play a crucial role as a key intermediate in the catalytic cycle for the C−H bond activation reaction.9 To the best of our knowledge, this is the first Ir(III) complex structurally characterized having a formula of [cisIr(Acac)2(Alkene)(Alkyl)].11 In summary, we have demonstrated that air- and moisturestable complex [Ir(AcacBiMs)(COD)] 1 can be easily synthe-
sized by [IrCl(COD)]2 and 1 equiv of H-AcacBiMs. Furthermore, compound 1 reacts with an equivalent of H-AcacBiMs ligand to give complex 2 through a formal addition of a OH group into a double bond on the COD fragment, presumably by CC bond insertion into an Ir−OH bond. Compound 2 is the first iridium(III) complex with the structural arrangement [cis-R-Ir-L(AcacBiMs)2].
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EXPERIMENTAL SECTION
General Considerations. Unless otherwise noted, all manipulations were performed using standard Schlenk techniques under an inert atmosphere. All solvents were reagent grade and were dried and deoxygenated before use. CDCl3, CD2Cl2, and C6D6 were purchased from Aldrich and were also deoxygenated using the freeze−pump− thaw method. [IrCl(COD)]212 and H-AcacBiMs13 were prepared following literature procedures. Mesitylene, COD, ClC(O)CH2C(O)Cl, and AlCl3 were purchased from Aldrich. IrCl3·6H2O was purchased from Pressure Chemical Co. All other chemicals, filter aids, and chromatographic materials were reagent grade and were used as received. 1H and 13C{1H} NMR spectra were recorded at ambient temperature. Preparation of [Ir(AcacBiMs)(COD)] (1). A mixture of H-AcacBiMs (0.308 g, 1.00 mmol) and TEA (1.00 g, 10 mmol) was added to a 2563
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(2) (a) Katsuki, T.; Sharpless, K. B. J. Am. Chem. Soc. 1980, 102, 5974−5976. (b) Gao, Y.; Klunder, J. M.; Hanson, R. M.; Masamune, H.; Ko, S. Y.; Sharpless, K. B. J. Am. Chem. Soc. 1987, 109, 5765−5780. (c) Rudolph, J.; Reddy, K. L.; Chiang, J. P.; Sharpless, K. B. J. Am. Chem. Soc. 1997, 119, 6189−6190. (d) Kolb, H. C.; Van Nieuwenhze, M. S.; Sharpless, K. B. Chem. Rev. 1994, 94, 2483−2547. (3) (a) Zhang, W.; Loebach, J. L.; Wilson, S. R.; Jacobsen, E. N. J. Am. Chem. Soc. 1990, 112, 2801−2803. (b) Jacobsen, E. N.; Zhang, W.; Guler, M. L. J. Am. Chem. Soc. 1991, 113, 6703−6704. (c) Jacobsen, E. N. Acc. Chem. Res. 2000, 33, 421−431. (d) Martin, V. S.; Woodard, S. S.; Katsuki, T.; Yamada, Y.; Ikeda, M.; Sharpless, K. B. J. Am. Chem. Soc. 1981, 103, 6237−6240. (e) Tanaka, H.; Nishikawa, H.; Uchida, T.; Katsuki, T. J. Am. Chem. Soc. 2010, 132, 12034−12041. (4) Day, V. W.; Klemperer, W. G.; Lockledge, S. P.; Mainlb, D. J. J. Am. Chem. Soc. 1990, 112, 2031−2033. (5) (a) Woerpel, K. A.; Bergman, R. G. J. Am. Chem. Soc. 1993, 115, 7888−7889. (b) Ritter, J. M. C.; Bergman, R. G. J. Am. Chem. Soc. 1997, 119, 2580−2581. (6) (a) de Bruin, B.; Boerakker, M. J.; Donners, J. J. J. M.; Christiaans, B. E. C.; Schlebos, P. P. J.; de Gelder, R.; Smits, J. M. M.; Spek, A. L.; Gal, A. W. Angew. Chem., Int. Ed. Engl. 1997, 36, 2064− 2067. (b) Budzelaar, P. H. M.; Blok, A. N. J. Eur. J. Inorg. Chem. 2004, 2385−2391. (c) de Bruin, B.; Hetterscheid, D. G. H. Eur. J. Inorg. Chem. 2007, 211−230. (7) Quijije, L. A.; Mediavilla, M.; Pardey, A. J.; Longo de Pardey, C.; Baricelli, P.; Moya, S. A. React. Kinet. Catal. Lett. 1997, 62, 251−256. (8) Camerano, J. A.; Sämann, C.; Wadepohl, H.; Gade, L. H. Organometallics 2011, 30, 379−382. (9) (a) Matsumoto, T.; Taube, D. J.; Periana, R. A.; Taube, H.; Yoshida, H. J. Am. Chem. Soc. 2000, 122, 7414−7415. (b) Wong-Foy, A. G.; Bhalla, G.; Liu, X.-Y.; Periana, R. A. J. Am. Chem. Soc. 2003, 125, 14292−14293. (c) Tenn, W. J., III; Young, K. J. H.; Oxgaard, J.; Nielsen, R. J.; Goddard, W. A., III; Periana, R. A. Organometallics 2006, 25, 5173−5175. (d) Oxgaard, J.; Muller, R. P.; Goddard, W. A., III; Periana, R. A. J. Am. Chem. Soc. 2004, 126, 352−363. (e) Bischof, S. M.; Ess, D. H.; Meier, S. K.; Oxgaard, J.; Nielsen, R. J.; Bhalla, G.; Goddard, W. A., III; Periana, R. A. Organometallics 2010, 29, 742−756. (f) Bhalla, G.; Liu, X.-Y.; Oxgaard, J.; Goddard, W. A., III; Periana, R. A. J. Am. Chem. Soc. 2005, 127, 11372−11389. (g) Tenn, W. J., III; Young, K. J. H.; Bhalla, G.; Oxgaard, J.; Goddard, W. A., III; Periana, R. A. J. Am. Chem. Soc. 2005, 127, 14172−14173. (10) (a) Hart, I. J. Polyhedron 1992, 11, 729−734. (b) Leipoldt, J. G.; Basson, S. S.; van Zyl, G. J.; Steyn, G. J. J. J. Organomet. Chem. 1991, 418, 241−247. (c) Steyn, G. J. J.; Basson, S. S.; Leipoldt, J. G.; van Zyl, G. J. J. Organomet. Chem. 1991, 418, 113−118. (d) Böttcher, H.-G.; Graf, M.; Sünkel, K.; Mayer, P.; Krüger, H. Inorg. Chim. Acta 2011, 365, 103−107. (e) Oro, L. A.; Carmona, D.; Esteruelas, M. A.; FocesFoces, C.; Cano, F. H. J. Organomet. Chem. 1983, 258, 357−366. (f) Basson, S. S.; Leipoldt, J. G.; Purcell, W.; Schoeman, J. B. Inorg. Chim. Acta 1990, 173, 155−158. (11) (a) Caruso, F.; Chan, E. J.; Hanna, J. V.; Marchetti, F.; Pettinari, C.; Di Nicola; Pettinari, R.; Pizzabiocca, A.; Rees, G. J.; Quigley, D.; Rossi, M.; Skelton, B. W.; Sobolev, A. N.; White, A. H. Eur. J. Inorg. Chem. 2012, 9, 1369−1379. (b) Barreca, D.; Carraro, G.; Gasparotto, A.; Maccato, C.; Seraglia, R.; Tabacchi, G. Inorg. Chim. Acta 2012, 380, 161−166. (12) Wehman-Ooyevaar, I. C. M.; Drenth, W.; Grove, D. M.; van Koten, G. Inorg. Chem. 1993, 32, 3347−3356. (13) Zhang, C.; Yang, P.; Yang, Y.; Huang, X.; Yang, X.-J.; Wu, B. Synth. Commun. 2008, 38, 2349−2356.
solution of [Ir(Cl)(COD)]2 (0.37 g, 0.50 mmol) in CH2Cl2 (30 mL) at room temperature. The suspension was stirred for 24 h. During this period, a change of color from orange to pale yellow was observed. The volatiles were removed under reduced pressure, and the residue was dissolved in 30 mL of Et2O. The yellow solution was filtered, concentrated under reduced pressure, and cooled overnight to approximately −15 °C to give yellow microcrystals. Yield: 0.335 g (55%), mp = 193−195 °C, r.f. = 0.77 (THF/hexanes, 1:5). Anal. Calcd. for C29H35O2Ir: C, 57.35; H, 5.80. Found: C, 57.34; H, 5.76. 1H NMR (CDCl3, 20 °C): 6.74 (s, 4H, CHAr), 5.63 (s, 1H, CHAcac), 3.99 (s, 4H, CHCOD), 2.21 (bm, 4H, CH2COD), 2.18 (s, 18H, CH3), 1.56 (bd, 4H, CH2COD). 13C{1H} NMR (CDCl3, 20 °C): 185.1 (2C, C OAcac), 137.3 (4C, o-CHAr), 136.9 (2, p-CHAr), 133.1 (2C, CHqAr), 127.2 (2C, m-CHAr), 104.9 (1C, CHAcac), 58.3 (4C, CHCOD), 30.0 (4C, CH2COD), 20.0 (2C, p-CH3), 18.8 (4C, o-CH3). Preparation of [cis-Ir(AcacBiMs)2(COE-OH)] (2). A solution of HAcacBiMs (0.153 g, 5.00 mmol) was added dropwise to a solution of compound 1 (0.304 g, 0.50 mmol) in CH2Cl2 (30 mL) at room temperature. The yellow solution was stirred for 48 h. The volatiles were removed under reduced pressure, and the yellow solid was dissolved in 30 mL of CH2Cl2 and absorbed on silica. Compound 2 was purified by a chromatographic column using an Et2O/hexanes mixture (1:20). Yield: 0.240 g (%), mp = 245−247 °C, r.f. = 0.34 (THF/hexanes, 1:5). Anal. Calcd. for C50H59O5Ir: C, 64.42; H, 6.38. Found: C, 64.39; H, 6.35. 1H NMR (CDCl3, 20 °C): 6.78−6.56 (m, 8H, CHAr), 5.69 (bs, 1H, CHCOD), 5.60 (s, 1H, CHAcac), 5.47 (s, 1H, CHAcac), 5.43 (bs, 1H, CHCOD), 4.39 (bd, 1H, 2JH−H = 10.67 Hz, CH2COD), 3.47 (bs, 1H, CH2COD), 3.08 (bd, 1H, CH2COD), 2.48 (bd, 1H, CH2COD), 2.38−1.94 (m, CH3 and CH2COD), 1.84 (bm, 1H, CH2COD), 0.59 (bm, 1H, CH2COD). 13C{1H} NMR (CDCl3, 20 °C): 187.5, 182.8, 181.9, 181.8, (4 C, COAcac), 138.9, 138.8, 137.7, 137.7, 137.6, 137.5, 137.2, 136.8, 136.5, 135.9, 135.0, 134.8, 134.4, 133.7, 133.2, 132.8 (16C, CqAr), 128.7, 128.5, 128.4, 128.1(4C, m-CHAr), 106.7, 106.3 (2C, CHAcac), 89.8 (Ir-CHOH), 81.6, 78.8 (C, Ir-CH CH) 37.2, 31.8, 25.0, 21.8 (4C, CH2COE‑OH), 21.1, 21.0, 21.0, 20.0, 20.0, 19.8, 19.5, 18.5 (12C, CH3).
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ASSOCIATED CONTENT
S Supporting Information *
NMR spectra and additional crystallographic data for compounds 1 and 2; and CCDC 905119 and 984287. This material is available free of charge via the Internet at http:// pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS O.S. thanks the Universidad de Guanajuato and the Secretaria de Educación Pública for the support of this work (Grant UGTO-PTC 270). J.A.N.-C. is grateful to CONACYT (México) for a Doctoral Fellowship (No. 229119).
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REFERENCES
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