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Organometallics 2010, 29, 2372–2376 DOI: 10.1021/om100243w
Ring Expansion versus exo-endo Isomerization in (2-Pyridyl)methylenecyclobutane Coordinated to Hydrido(trispyrazolyl)borate- and Cyclopentadienyl-Osmium Complexes Ruth Castro-Rodrigo,† Miguel A. Esteruelas,*,† Ana M. L opez,*,† Fernando L opez,§ ,‡ † † ‡ Jose L. Mascare~ nas,* Silvia Mozo, Enrique O~ nate, and Lucı´ a Saya †
Departamento de Quı´mica Inorg anica, Instituto de Ciencia de Materiales de Arag on, Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain, ‡Departamento de Quı´mica Org anica, Universidade de Santiago de Compostela, 15782, Santiago de Compostela, Spain, and §Instituto de Quı´mica Org anica General-CSIC, Juan de la Cierva 3, 28006, Madrid, Spain Received March 29, 2010
The reactions of (2-pyridyl)methylenecyclobutane with the metal fragments [OsTp(PiPr3)]þ and [OsCp(PiPr3)]þ (Tp = hydridotris(pyrazolyl)borate, Cp = cyclopentadienyl) are shown. Complex [OsTp(κ1-OCMe2)2(PiPr3)]BF4 (1) reacts with the organic substrate to give [OsTp{η2-C(CH2CH2CH2)dCH-C5H4N}(PiPr3)]BF4 (2), which evolves into the cyclopentylidene
j
j
derivative [OsTp(dCCH2CH2CH2CH-C5H4N)(PiPr3)]BF4 (3) as a result of the ring expansion of the j
j
methylenecyclobutane unit of the coordinated substrate. The reaction of (2-pyridyl)methylenecyclobutane with [OsCp(NCCH3)2(PiPr3)]PF6 (4) leads to [OsCp{η2-C(CH2CH2CH2)dCH-C5H4N}j
j
(PiPr3)]PF6 (5). In contrast to 2, complex 5 evolves by means of exo-endo isomerization of the C-C double bond of the coordinated substrate to afford [OsCp{η2-C(dCHCH2CH2)-CH2-C5H4N}(PiPr3)]PF6 (6). j
Introduction Alkylidenecyclopropanes are receiving much attention as building blocks in organic synthesis, due to the presence of an exocyclic C-C double bond and a strained threemembered carbocycle.1 Thus, a variety of metal-catalyzed processes involving this type of substrates have been developed.2 Although several pathways have been proposed for such reactions, isolated metal complexes are extremely scarce.3 In the search for insight into this chemistry, we have recently studied the behavior of [OsTp(PiPr3)]þ (Tp = hydridotris(pyrazolyl)borate) and [OsCp(P i Pr 3 )]þ (Cp = cyclopentadienyl) *Corresponding authors. E-mail:
[email protected]; amlopez@ unizar.es;
[email protected]. (1) Brandi, A.; Cicchi, S.; Cordero, F. M.; Goti, A. Chem. Rev. 2003, 103, 1213. (2) (a) Lautens, M.; Klute, W.; Tam, W. Chem. Rev. 1996, 96, 49. (b) Nakamura, I.; Yamamoto, Y. Adv. Synth. Catal. 2002, 344, 111. (c) Gulías, M.; García, R.; Delgado, A.; Castedo, L.; Mascare~nas, J. L. J. Am. Chem. Soc. 2006, 128, 384. (d) Rubin, M.; Rubina, M.; Gevorgyan, V. Chem. Rev. 2007, 107, 3117. (e) Aïssa, C.; F€urstner, A. J. Am. Chem. Soc. 2007, 129, 14836. (f ) García-Fandi~no, R.; Gulías, M.; Castedo, L.; Granja, J. R.; Mascare~ nas, J. L.; Cardenas, D. J. Chem.;Eur. J. 2008, 14, 272. (g) Masarwa, A.; F€urstner, A.; Marek, I. Chem. Commun. 2009, 5760. (h) Villarino, L.; L opez, F.; Castedo, L.; Mascare~nas, J. L. Chem.;Eur. J. 2009, 15, 13308. (3) (a) Tantillo, D. J.; Carpenter, B. K.; Hoffmann, R. Organometallics 2001, 20, 4562. (b) Binger, P.; M€uller, P.; Podubrin, S.; Albus, S.; Kr€uger, C. J. Organomet. Chem. 2002, 656, 288. (c) Nishihara, Y.; Yoda, C.; Itazaki, M.; Osakada, K. Bull. Chem. Soc. Jpn. 2005, 78, 1469. (d) Kozhushkov, S. I.; Foerstner, J.; Kakoschke, A.; Stellfeldt, D.; Yong, L.; Wartchow, R.; de Meijere, A.; Butensch€ on, H. Chem.;Eur. J. 2006, 12, 5642. pubs.acs.org/Organometallics
Published on Web 04/22/2010
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fragments toward alkylidenecyclopropanes containing a chelation assistant at the terminal carbon atom of the olefinic moiety. Both metal fragments promote the ring expansion of the methylenecyclopropane unit of (2-pyridyl)methylenecyclopropane to give cyclobutylidene derivatives (eq 1).4 In the absence of the coordination auxiliary, the Tp-metal fragment cleaves the ring into two pieces to form ethylenevinylidene derivatives.5
Alkylidenecyclobutanes are a class of moderately strained alkenes,6 which have an extremely limited transition metal chemistry7 and have received significantly less attention than (4) Castro-Rodrigo, R.; Esteruelas, M. A.; Fuertes, S.; L opez, A. M.; L opez, F.; Mascare~ nas, J. L.; Mozo, S.; O~ nate, E.; Saya, L.; Villarino, L. J. Am. Chem. Soc. 2009, 131, 15572. (5) Castro-Rodrigo, R.; Esteruelas, M. A.; L opez, A. M.; L opez, F.; Mascare~ nas, J. L.; Olivan, M.; O~ nate, E.; Saya, L.; Villarino, L. J. Am. Chem. Soc. 2010, 132, 454. (6) Vinogradov, M. G.; Zinenkov, A. V. Russ. Chem. Rev. 1996, 65, 131. (7) (a) Batsanov, A. S.; Andrianov, V. G.; Struchkov, Y. T.; Koridze, A. A.; Kizas, O. A.; Kolobova, N. E. J. Organomet. Chem. 1987, 329, 401. (b) Jun, C.-H. Bull. Korean Chem. Soc. 1989, 10, 404. (c) Sugiyama, H.; Lin, Y.-S.; Hossain, Md. M.; Matsumoto, K. Inorg. Chem. 2001, 40, 5547. (d) Matsumoto, K.; Sugiyama, H. J. Organomet. Chem. 2004, 689, 4564. r 2010 American Chemical Society
Article
Organometallics, Vol. 29, No. 10, 2010
2373
Scheme 1
[OsTp{η2-C(CH2CH2CH2)dCH-C5H4 N}(PiPr3)]BF4 (2), as a result of the displacement of the acetone molecules by the organic substrate. The geometry around the metal center of 2 can be described as a distorted octahedron with the Tp ligand occupying fac positions. The metal coordination sphere is completed by the triisopropylphosphine ligand and the chelate (2-pyridyl)methylenecyclobutane molecule. The osmium-olefin coordination exhibits Os-C distances of 2.205(4) A˚ (Os-C(6)) and 2.217(4) A˚ (OsC(7)), which compare well with those found in other osmiumj
j
(8) (a) Liang, Y.; Jiao, L.; Wang, Y.; Chen, Y.; Ma, L.; Xu, J.; Zhang, S.; Yu, Z.-X. Org. Lett. 2006, 8, 5877. (b) Jiang, M.; Liu, L.-P.; Shi, M. Tetrahedron 2007, 63, 9599. (c) Jiang, M.; Shi, M. Org. Lett. 2008, 10, 2239. (d) Clark, D. A.; Basile, B. S.; Karnofel, W. S.; Diver, S. T. Org. Lett. 2008, 10, 4927. (e) Jiang, M.; Shi, M. Tetrahedron 2008, 64, 10140. (f ) Jiang, M.; Shi, M. J. Org. Chem. 2009, 74, 2516. (g) Crepin, D.; Dawick, J.; Aïssa, C. Angew. Chem., Int. Ed. 2010, 49, 620. (9) (a) Johnson, T. J.; Albinati, A.; Koetzle, T. F.; Ricci, J.; Eisenstein, O.; Huffman, J. C.; Caulton, K. G. Inorg. Chem. 1994, 33, 4966. (b) Edwards, A. J.; Elipe, S.; Esteruelas, M. A.; Lahoz, F. J.; Oro, L. A.; Valero, C. Organometallics 1997, 16, 3828. (c) Buil, M. L.; Esteruelas, M. A.; García-Yebra, C.; Gutierrez-Puebla, E.; Olivan, M. Organometallics 2000, 19, 2184. (d) Esteruelas, M. A.; Gonzalez, A. I.; Lopez, A. M.; O~nate, E. Organometallics 2003, 22, 414. (e) Baya, M.; Buil, M. L.; Esteruelas, M. A.; O~ nate, E. Organometallics 2004, 23, 1416. (f ) Barrio, P.; Esteruelas, M. A.; O~ nate, E. Organometallics 2004, 23, 3627. (g) Baya, M.; Buil, M. L.; Esteruelas, M. A.; O~ nate, E. Organometallics 2005, 24, 2030. (h) Esteruelas, M. A.; Fernandez-Alvarez, F. J.; Olivan, M.; O~nate, E. J. Am. Chem. Soc. 2006, 128, 4596. (i) Esteruelas, M. A.; Hernandez, Y. A.; Lopez, A. M.; Olivan, M.; Rubio, L. Organometallics 2008, 27, 799.
[OsTp(dCCH2CH2CH2CH-C5H4 N)(PiPr3)]BF4 (3), as a result of the ring expansion of the coordinated methylenecyclobutane moiety of 2. Complex 3 is isolated as a green solid in 62% yield. As expected from the lower ring strain of a four-membered ring with regard to a three-membered ring, the expansion is significantly slower than that of the methylenecyclopropane counterpart.4 Thus, the quantitative rearrangement occurs only after 12 days. The geometry around the osmium atom of 3 can be described like that for 2, i.e., a distorted octahedron with the Tp ligand occupying fac positions. The metal coordination sphere is completed by the triisopropylphosphine ligand and the C,N-chelate group (N(1)-Os-C(1) of 79.9(2)°). The OsC(1) bond length of 1.892(6) A˚ agrees well with that of j
j
Treatment at room temperature of dichloromethane solutions of the bis(solvento) complex [OsTp(κ1-OCMe2)2(PiPr3)]BF4 (1) with 1.3 equiv of (2-pyridyl)methylenecyclobutane for 1 h leads to the π-olefin complex
Results and Discussion
olefin complexes (between 2.13 and 2.28 A˚).9 Similarly, the olefinic bond distance C(6)-C(7) of 1.403(6) A˚ is within the range reported for transition metal olefin complexes (between 1.340 and 1.445 A˚).10 In accordance with the coordination of the C(6)-C(7) double bond to the osmium atom, in the 13C{1H} NMR spectrum, the resonances due to C(6) and C(7) are observed at 85.0 and 41.8 ppm, respectively. In the 1H NMR spectrum, the most noticeable signal is a doublet at 5.56 ppm, with a H-P coupling constant of 10.5 Hz, corresponding to the olefinic C(6)-H proton. A singlet at -22.0 ppm in the 31P{1H} NMR is also characteristic of 2. Complex 2 is moderately stable in solution. In acetone at 70 °C, it evolves into the cyclopentylidene derivative
their three-membered counterparts in organic synthesis.8 The results reached with alkylidenecyclopropanes prompted us to investigate the reactions of the [OsTp(PiPr3)]þ and [OsCp(PiPr3)]þ metal fragments with (2-pyridyl)methylenecyclobutane (Scheme 1). We have now discovered that while the Tp-containing complex promotes a ring expansion of the methylenecyclobutane moiety, the complex featuring the Cp ligand induces an exo-endo isomerization of the C-C double bond.
[OsTp(dCCH2CH2CH2CH-C5H4N)(PiPr3)]BF4 (1.847(9) A˚)4 and supports the Os-C double bond formulation.11 In agreement j
j
(10) Allen, F. H.; Davies, J. E.; Galloy, J. J.; Johnson, O.; Kennard., O.; Macrae, C. F.; Mitchell, E. M.; Mitchell, G. F.; Smith, J. M.; Watson, D. G. J. Chem. Inf. Comput. Sci. 1991, 31, 187. (11) See for example: (a) Bola~ no, T.; Castarlenas, R.; Esteruelas, M. A.; Modrego, F. J.; O~ nate, E. J. Am. Chem. Soc. 2005, 127, 11184. (b) Castarlenas, R.; Esteruelas, M. A.; O~nate, E. Organometallics 2005, 24, 4343. (c) Bola~no, T.; Castarlenas, R.; Esteruelas, M. A.; O~nate, E. Organometallics 2007, 26, 2037. (d) Esteruelas, M. A.; Lopez, A. M.; O~nate, E. Organometallics 2007, 26, 3260. (e) Bola~no, T.; Castarlenas, R.; Esteruelas, M. A.; O~nate, E. J. Am. Chem. Soc. 2007, 129, 8850. (f ) Bola~no, T.; Castarlenas, R.; Esteruelas, M. A.; O~nate, E. Organometallics 2008, 27, 6367. (g) Castro-Rodrigo, R.; Esteruelas, M. A.; Lopez, A. M.; O~nate, E. Organometallics 2008, 27, 3547. (h) Castro-Rodrigo, R.; Esteruelas, M. A.; Fuertes, S.; Lopez, A. M.; Mozo, S.; O~nate, E. Organometallics 2009, 28, 5941.
Organometallics, Vol. 29, No. 10, 2010
Castro-Rodrigo et al.
2
j
[OsCp{η2-C(CH2CH2CH2)dCH-C5H4 N}(PMe3)]þ j
i
[OsCp{η -C(dCHCH2CH2)-CH2-C5H4N}(P Pr3)]PF6 (6) in fluorobenzene at 80 °C. After 5 days the rearrangement is quantitative. Complex 6 is isolated as a brown solid in 80% yield. The exo-endo isomerization of methylenecyclobutanes is energetically the least favorable compared with the corresponding rearrangements of its homologues with larger rings.12 It has been previously observed in the presence of strong bases and on passing the organic substrates by various heterogeneous catalysts in the temperature range 50-500 °C.6 Complex 6 has been also characterized by X-ray diffraction analysis. Like in 5, the geometry around the osmium atom is close to octahedral with the cyclopentadienyl group occupying three sites of a face. The Os-olefin coordination exhibits Os-C(7), Os-C(8), and C(7)-C(8) bond lengths of 2.172(6), 2.180(5), and 1.431(8) A˚, respectively, which compare well with the Os-methylenecyclobutane coordination distances in 5. The 1H, 13C{1H}, and 31P{1H} NMR spectra of 6 agree well with its X-ray structure. In the 1H NMR spectrum, the j
(12) Wiberg, K. B.; Wasserman, D. J.; Martin, E. J.; Murcko, M. A. J. Am. Chem. Soc. 1985, 107, 6019.
j
j
j
(5t),
[OsCp{η2-C(CH2CH2CH2)dCH-C5H4N}(PiPr3)]PF6 (5), as a result of the replacement of the acetonitrile molecules of 4 by the organic substrate. Complex 5 is isolated as a yellow solid in 92% yield. The geometry around the metal center of 5 is close to octahedral, with the cyclopentadienyl group occupying three sites of a face. The Os-methylenecyclobutane coordination exhibits Os-C(6), Os-C(7), and C(6)-C(7) bond lengths of 2.229(4), 2.188(4), and 1.412(6) A˚, respectively, which compare well with those of 2. The 1H, 13C{1H}, and 31P{1H} NMR spectra of 5 are consistent with its X-ray structure. In the 1H NMR spectrum the olefinic C(6)-H resonance appears at 4.14 ppm as a doublet with a H-P coupling constant of 9.5 Hz. According to the coordination of the C(7) and C(6) carbon atoms of the methylenecyclobutane to the metal center, their resonances are observed in the 13C{1H} NMR spectrum at 82.0 and 51.4 ppm as doublets with C-P coupling constants of 4 and 7 Hz. The 31P{1H} spectrum contains a singlet at 13.1 ppm. Complex 5 is the Cp counterpart of 2. However, there is a marked difference in behavior between them. In contrast to 2, complex 5 is stable in acetone at 70 °C. Thus, it remains unchanged after 12 days. Under these conditions, the ring expansion of the coordinated methylenecyclobutane moiety of 5 is not observed. On the other hand, the coordinated (2-pyridyl)methylenecyclobutane ligand of 5 undergoes an exo-endo isomerization to afford
olefinic C(8)-H resonance appears at 4.40 ppm as a double doublet with H-H and H-P coupling constants of 4 and 16 Hz, respectively. In the 13C{1H} NMR spectrum, the resonances due to the coordinated C(7) and C(8) carbon atoms are observed at 46.7 and 41.6 ppm, respectively. The first of them is a singlet, whereas the second one appears as a doublet with a C-P coupling constant of 11 Hz. The 31P{1H} NMR spectrum contains a singlet at -2.3 ppm, shifted about 15 ppm toward higher field with respect to that of 5. The Tp ligand is frequently compared with the Cp group due to the same number of electrons donated and the facial geometry adopted.13 However, there are a number of examples that demonstrate that they can exhibit different behaviors. The Tp ligand enforces conformations allowing N-M-N angles close to 90°.14 These structures favor nonclassical interactions between the hydrogen atoms bonded to the metal center.15 This has a strong influence on the products of the reactions between osmium compounds and terminal alkynes,16 which depend upon the difference in energy between the dihydrogen and dihydride tautomers. While Tp-dihydrogen compounds afford hydride-carbyne derivatives11g via dihydrogen-vinylidene intermediates,17 Cp-dihydride complexes give olefins18 as a result of the insertion of the alkyne into one of the Os-H bonds and subsequent reductive elimination on the resulting hydridealkenyl species. Furthermore, the Tp ligand imposes more geometrical restrictions than Cp. This has been shown to be crucial for the olefin-alkylidene tautomerization equilibrium. The [OsTp(PiPr3)]þ metal fragment promotes the tautomerization of 2-vinylpyridine to the alkylidene form, which is stabilized by coordination to the metal center. In contrast to [OsTp(PiPr3)]þ, the [OsCp(PiPr3)]þ metal fragment promotes the tautomerization of the alkylidene form to afford the olefin species, which is not stable and evolves by C-H bond activation of the olefinic terminal CH2 group into a hydride-osmaindolizine derivative.11h The difference in behavior between [OsTp(PiPr3)]þ and [OsCp(PiPr3)]þ shown in Scheme 1 is consistent with these precedents. DFT calculations on the model cations
with the sp2 hybridization at C(1) the angles Os-C(1)C(2) and Os-C(1)-C(5) are 133.4(5)° and 117.6(4)°, respectively. In accordance with the formation of the cyclopentylidene unit, the 13C{1H} NMR spectrum contains at 308.9 ppm a doublet, with a C-P coupling constant of 11 Hz, due to the C(1) carbon atom. The 31P{1H} NMR spectrum shows a singlet at 1.0 ppm, shifted 23 ppm toward lower field with regard to that of 2. Treatment of dichloromethane solutions of the bis(solvento) complex [OsCp(NCCH3)2(PiPr3)]PF6 (4) with 1.5 equiv of (2-pyridyl)methylenecyclobutane for 24 h at room temperature leads to the π-methylenecyclobutane derivative
2374
[OsCp{η2-C(dCHCH2CH2)-CH2-C5H4 N}(PMe3)]þ j
j
(6t),
(13) (a) Tellers, D. M.; Bergman, R. G. J. Am. Chem. Soc. 2000, 122, 954. (b) Tellers, D. M.; Skoog, S. J.; Bergman, R. G.; Gunnoe, T. B.; Harman, W. D. Organometallics 2000, 19, 2428. (c) R€uba, E.; Simanko, W.; Mereiter, K.; Schmid, R.; Kirchner, K. Inorg. Chem. 2000, 39, 382. (d) Tellers, D. M.; Bergman, R. G. Organometallics 2001, 20, 4819. (e) Bergman, R. G.; Cundari, T. R.; Gillespie, A. M.; Gunnoe, T. B.; Harman, W. D.; Klinckman, T. R.; Temple, M. D.; White, D. P. Organometallics 2003, 22, 2331. (14) Becker, E.; Pavlik, S.; Kirchner, K. Adv. Organomet. Chem. 2008, 56, 155. (15) (a) Bohanna, C.; Esteruelas, M. A.; G omez, A. V.; L opez, A. M.; Martı´ nez, M.-P. Organometallics 1997, 16, 4464. (b) Jia, G.; Lau, C.-P. Coord. Chem. Rev. 1999, 190-192, 83. (c) Castro-Rodrigo, R.; Esteruelas, M. A.; Lopez, A. M.; Olivan, M.; O~nate, E. Organometallics 2007, 26, 4498. (d) Baya, M.; Esteruelas, M. A.; Olivan, M.; O~nate, E. Inorg. Chem. 2009, 48, 2677. (16) (a) Esteruelas, M. A.; L opez, A. M.; Olivan, M. Coord. Chem. Rev. 2007, 251, 795. (b) Jia, G. Coord. Chem. Rev. 2007, 251, 2167. (17) (a) Espuelas, J.; Esteruelas, M. A.; Lahoz, F. J.; Oro, L. A.; Ruiz, N. J. Am. Chem. Soc. 1993, 115, 4683. (b) Bourgault, M.; Castillo, A.; Esteruelas, M. A.; O~nate, E.; Ruiz, N. Organometallics 1997, 16, 636. (c) Esteruelas, M. A.; Olivan, M.; O~nate, E.; Ruiz, N.; Tajada, M. A. Organometallics 1999, 18, 2953. (18) Esteruelas, M. A.; Hernandez, Y. A.; L opez, A. M.; Olivan, M.; O~ nate, E. Organometallics 2007, 26, 2193.
Article
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1
H NMR (300 MHz, CDCl3): 8.44, 7.50, 7.05, 6.94 (py), 6.18 (m, dCH), 3.04, 2.85, 2.05 (all m, CH2). 13C NMR (75 MHz, CDCl3): 153.4, 151.3, 149.7, 136.3, 122.2, 121.9, 120.7 (py þ CHdC), 33.6, 33.1, 18.6 (CH2).
Chart 1
Preparation of [OsTp{η2-C(CH2CH2CH2)dCH-C5H4N}(PiPr3)]-
Experimental Section General Methods and Instrumentation. All reactions were carried out under argon with rigorous exclusion of air. Solvents were dried by the usual procedures and distilled prior to use. The starting materials 115c and 419 were prepared according to the published methods. 1H, 31P{1H}, and 13C{1H} NMR spectra were recorded at 293 K, chemical shifts (expressed in ppm) are referenced to residual solvent peaks (1H, 13C{1H}) or external H3PO4 (31P{1H}), and coupling constants, J, are given in hertz. Preparation of (2-Pyridyl)methylenecyclobutane. nBuLi (7.86 mL, 2.5 M in THF) was added to a THF solution (20 mL) of triphenyl(2-pyridylmethyl)phosphonium chloride hydrochloride (4.0 g, 9.36 mmol) at 0 °C. The mixture was heated at 62 °C. After 2 h, cyclobutanone (0.8 mL, 10.29 mmol) was added. After 12 h, the resulting mixture was cooled to 20 °C. The addition of pentane led to a solid, which was filtered. Purification by column chromatography (silica gel; 10% Et2O/hexane) afforded a colorless oil (880 mg, 65%). MS (EI) m/z: 145 (100).
(19) Esteruelas, M. A.; G onzalez, A. I.; L opez, A. M.; Olivan, M.; O~ nate, E. Organometallics 2006, 25, 693.
j
Preparation of [OsTp(dCCH2CH2CH2CH-C5H4 N)(PiPr3)]j
j
BF4 (3). A solution of 2 (158 mg, 0.20 mmol) in 10 mL of acetone was heated at 70 °C for 12 days. The solution was concentrated to ca. 0.5 mL, and diethyl ether was added, causing the appearance of a light green solid. Yield: 98 mg (62%). Anal. Calcd for C28H42B2F4N7OsP: C, 42.28; H, 5.32; N, 12.33. Found: C, 41.69; H, 5.23; N, 12.99. HRMS (electrospray): calcd for C28H42BN7OsP [M]þ 710.2947, found 710.2945. IR (ATR, cm-1): ν(BH) 2485 (w), ν(BF4) 1038 (vs). 1 H NMR (400 MHz, CD2Cl2): 8.54 (d, JH-H=6.0, H6 py), 8.30, 8.02 (both d, 1H each, Tp), 7.81 (m, 2H, H4 py þ Tp), 7.74 (m, 2H, H3 py þ Tp), 7.55 (d, 1H, Tp), 7.18 (dd, JH-H=6.4, JH-H= 6.0, H5 py), 6.65, 6.37, 5.88 all (t, 1H each, Tp), 5.25 (d, 1H, Tp), 2.93 (m, 1H, CHCH2), 2.51 (m, 1H, CH2CH2CH2), 2.35 (m, 4H, PCH þ 1H =CCH2), 2.09 (m, 1H, dCCH2), 1.55 (m, 1H, CHCH2), 1.10 (dd, JH-P = 12.2, JH-H = 7.0, 9H, PCHCH3), 0.62 (br, 9H, PCHCH3), 0.29 (m, 1H, CH), -0.55 (m, 1H, CH2CH2CH2); all coupling constants for the pyrazolyl proton resonances were about 2 Hz. 31P{1H} NMR (161.98 MHz, CD2Cl2): 1.0 (s). 13C{1H} NMR (100.63 MHz, CD2Cl2): 308.9 (d, JC-P =11, OsdC), 169.2 (s, C2 py), 153.8 (s, C6 py), 147.6, 146.0 (both s, Tp), 139.1 (s, C4 py), 138.7, 138.0, 137.1 (all s, Tp), 135.9 (d, JC-P =1, Tp), 123.9 (s, C5 py), 122.1 (s, C3 py), 108.4, 107.1 (both s, Tp), 106.8 (d, JC-P = 1, Tp), 89.3 (d, JC-P =1, CH), 59.6 (s, CH2CH2CH2), 29.4 (s, CHCH2), 27.3 (s, dCCH2), 25.5 (d, JC-P = 26, PCH), 19.1 (d, JC-P = 3, PCHCH3), 18.8 (br, PCHCH3).
j
and [OsCp(dCCH2CH2CH2CH-C5H4 N)(PMe3)]þ (7t) indicate that both the exo-endo isomerization and the ring expansion rearrangement are possible from a thermodynamic point of view (Chart 1). On the other hand, the product from the exo-endo isomerization (6t) is 16.0 kcal 3 mol-1 less stable than that from the ring expansion (7t). This indicates that the exo-endo isomerization, the experimental finding, is kinetically favored with regard to the ring expansion; that is, complex 6 is a kinetic control product. The formation of the latter is probably related to the fewer geometrical restrictions imposed by the Cp group with regard to the Tp ligand. In a similar manner to that observed for 2-vinylpyridine,11h the [OsCp(PiPr3)]þ fragment seems to promote the activation of a C(10)-H bond of the coordinated (2-pyridyl)methylenecyclobutane of 5, which is necessary for the migration of the C-C double bond. In conclusion, the Tp metal fragment [OsTp(PiPr3)]þ promotes the ring expansion of the methylenecyclobutane moiety of (2-pyridyl)methylenecyclobutane to afford a cyclopentylidene derivative. Although DFT calculations suggest that the ring expansion is also possible from a thermodynamic point of view with the Cp-metal fragment [OsCp(PiPr3)]þ, there is a lower energy pathway that leads to a kinetic control product resulting from an exo-endo isomerization of the C-C double bond of the organic substrate.
j
j
BF4 (2). Dichloromethane (7 mL) was added to a mixture of 1 (250 mg, 0.33 mmol) and (2-pyridyl)methylenecyclobutane (62 mg, 0.42 mmol). This solution was stirred at room temperature for 1 h and then concentrated to ca. 1 mL. The addition of diethyl ether caused the appearance of yellow solid. Yield: 216 mg (83%). Anal. Calcd for C28H42B2F4N7OsP: C, 42.28; H, 5.32; N, 12.33. Found: C, 42.22; H, 5.12; N, 11.85. HRMS (electrospray, m/z): calcd for C28H42BN7OsP [M]þ 710.2947, found 710.2978. IR (ATR, cm-1): ν(BH) 2487 (w), ν(BF4) 1034 (vs). 1H NMR (300 MHz, CD2Cl2): 7.91 (m, 4H, H5 þ H6 py þ2Tp), 7.73 (m, 2H, 2Tp), 7.33 (dd, JH-H = 7.5, JH-H = 5.7, H4 py), 7.11 (m, 2H, H3 py þ Tp), 6.44, 6.33, 6.13 (all d, 1H each, Tp), 6.09 (s, 1H, Tp), 5.56 (d, JH-P = 10.5, dCH), 2.54 (m, 3H, PCH), 2.38 (m, 1H, CH2CH2CH2), 2.11 (m, 2H, CH2CH2CH2), 1.97 (m, 2H, CH2CH2CH2), 1.69 (m, 1H, CH2CH2CH2), 1.05 (dd, JH-P=11.6, JH-H=7.4, 9H, PCHCH3), 0.92 (br, 9H, PCHCH3); all coupling constants for the pyrazolyl proton resonances were about 2 Hz. 31 P{1H} NMR (121.49 MHz, CD2Cl2): -22.0 (s). 13C{1H} NMR (75.48 MHz, CD2Cl2): 170.7 (s, C2 py), 148.4 (s, Tp), 147.3 (s, C5 py), 144.0, 140.7, 138.1, 137.5 (all s, Tp), 136.9 (d, JC-P=2, Tp), 136.4 (s, C6 py), 124.8 (s, C3 þ C4 py), 108.0, 107.1, 106.6 (all s, Tp), 85.0 (s, CHdC), 41.8 (d, JC-P=5, dCH), 37.2 (s, CH2CH2CH2), 35.2 (s, CH2CH2CH2), 25.2 (d, JC-P = 24, PCH), 21.0 (s, CH2CH2CH2), 19.9 (br, PCHCH3), 19.6 (d, JC-P=2, PCHCH3).
Preparation of [OsCp{η2-C(CH2CH2CH2)dCH-C5H4N}(PiPr3)]j
j
PF6 (5). A solution of 4 (135 mg, 0.21 mmol) in 8 mL of dichloromethane was treated with (2-pyridyl)methylenecyclobutane (46 mg, 0.31 mmol) at room temperature for 24 h. The yellow solution was filtered through Celite and concentrated to ca. 1 mL under reduced pressure. The addition of diethyl ether caused the formation of a yellow solid. Yield: 137 mg (92%). Anal. Calcd for C24H37NOsP2F6: C, 40.85; H, 5.28; N, 1.98. Found: C, 40.54; H, 4.92; N, 1.90. HRMS (electrospray, m/z): calcd for C24H37NOsP [M]þ 562.2274, found
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Castro-Rodrigo et al. 831 (s). 1H NMR (400 MHz, (CD3)2CO): 8.80 (d, JH-H=6.0, H6 py), 7.67 (dd, JH-H=JH-H=7.6, H4 py), 7.47 (d, JH-H=7.6, H3 py), 7.06 (dd, JH-H =7.6, JH-H =6.0, H5 py), 5.38 (s, 5H, Cp), 4.40 (dd, JH-P = 16, JH-H = 4, 1H, dCHCH2CH2), 3.75 (AB spin system, Δν = 70.9, JAB = 19.6, dCCH2-C5H4N), 3.06 (m, 1H, dCHCH2CH2), 2.97 (m, 1H, dCHCH2CH2), 2.79 (m, 3H, PCH), 2.22 (m, 1H, dCHCH2CH2), 1.80 (m, 1H, dCHCH2CH2), 1.33 (dd, JH-P = 12.4, JH-H = 7.2, 9H, PCHCH3), 1.14 (br, 9H, PCHCH3). 31P{1H} NMR (121.49 MHz, (CD3)2CO): -2.3 (s), -144.0 (sept, PF6). 13C{1H} NMR (100.63 MHz, (CD3)2CO): 171.6 (d, JC-P = 2, C2 py), 159.7 (d, JC-P = 2, C6 py), 139.6 (s, C4 py), 125.4 (s, C5 py), 124.6 (s, C3 py), 82.7 (s, Cp), 62.2 (d, JC-P =4, dCCH2-C5H4N), 47.6 (s, =CCH2-C5H4N), 41.6 (d, JC-P = 11, dCHCH2CH2), 36.5 (s, dCHCH2CH2), 35.3(d, JC-P = 2, dCHCH2CH2), 29.5 (d, JC-P=30, PCH), 21.3 (d, JC-P=3, PCHCH3), 21.2 (s, PCHCH3).
562.2309. IR (ATR, cm-1): ν(PF6) 819 (s). 1H NMR (500 MHz, (CD3)2CO): 8.56 (d, JH-H=6.0, H6 py), 7.82 (dd, JH-H=JH-H= 8.0, H4 py), 7.17 (dd, JH-H = 8.0, JH-H = 6.0, H5 py), 7.14 (d, JH-H =8.0, H3 py), 5.31 (s, 5H, Cp), 4.14 (d, JH-P =9.5, CHd), 2.99 (m, 1H, CH2CH2CH2), 2.84 (m, 1H, CH2CH2CH2), 2.80 (m, 3H, PCH), 2.64 (m, 1H, CH2CH2CH2), 2.48, 2.37 (both m, 1H each, CH2CH2CH2), 2.10 (m, 1H, CH2CH2CH2), 1.23 (dd, JH-P= 13.5, JH-H =7, 9H, PCHCH3), 0.83 (dd, JH-P =12.5, JH-H =7, 9H, PCHCH3). 31P{1H} NMR (161.98 MHz, (CD3)2CO): 13.1 (s), -143.4 (sept, PF6). 13C{1H} NMR (100.63 MHz, (CD3)2CO): 168.7 (d, JC-P=3, C2 py), 152.9 (s, C6 py), 136.8 (d, JC-P=1, C4 py), 128.1 (d, JC-P=2, C3 py), 125.3 (s, C5 py), 82.0 (d, JC-P=4, CHdC), 78.9 (s, Cp), 51.4 (d, JC-P = 7, CHd), 40.7 (s, CH2CH2CH2), 37.2 (s, CH2CH2CH2), 29.4 (d, JC-P=27, PCH), 23.2 (s, CH2CH2CH2), 22.2 (s, PCHCH3), 20.0 (d, JC-P = 2, PCHCH3). Preparation of [OsCp{η2-C(dCHCH2CH2)-CH2-C5H4N}(PiPr3)]j
j
PF6 (6). A solution of 5 (100 mg, 0.14 mmol) in 6 mL of fluorobenzene was stirred for 5 d at 80 °C. The resulting brown solution was evaporated, and the addition of acetone and diethyl ether afforded a light brown solid, which was washed with diethyl ether and dried in vacuo. Yield: 80 mg (80%). Anal. Calcd for C24H37NOsP2F6: C, 40.85; H, 5.28; N, 1.98. Found: C, 40.73; H, 5.37; N, 1.55. HRMS (electrospray, m/z): calcd for C24H37NOsP [M]þ 562.2274, found 562.2289. IR (ATR, cm-1): ν(PF6)
Acknowledgment. Financial support from the Spanish MICINN (Projects CTQ2008-00810 and Consolider Ingenio 2010 (CSD2007-00006)) and the Diputaci on General de Arag on (E35) is acknowledged. Supporting Information Available: Crystal structure determinations and CIF file giving crystal data for complexes 2, 3, 5, and 6 as well as computational details for 5t, 6t, and 7t. This material is available free of charge via the Internet at http://pubs.acs.org.
