3970
Organometallics 2009, 28, 3970–3972 DOI: 10.1021/om9004127
C-H and Si-N Bond Oxygenations of a Divalent Ytterbium Amide of the Pyrrolyl-Cyclopentadienyl Ligand Jingjun Hao, Haibin Song, and Chunming Cui* State Key Laboratory of Elemento-organic Chemistry, Nankai University, Tianjin 300071, People’s Republic of China Received May 19, 2009 Summary: Reaction of Me4C5H-SiMe2-NC4H4 with Yb[N(SiMe3)2]2(THF)2 yielded a new type of ansa-sandwich divalent lanthanide amide (Me4C5-SiMe2-NC4H4)YbN(SiMe3)2 (2), in which the Yb atom is η5-coordinated to both the C5 and C4N rings. 2 rapidly reacted with dioxygen to give a dinuclear trivalent ytterbium species via intramolecular C-H and Si-N bond oxygenation reactions. Divalent lanthanide complexes bearing two cyclopentadienyl (Cp) families of ligands have been intensively investigated in the past two decades since they display an exceptionally high and unique reactivity.1 In contrast, lanthanide (II) complexes featuring one Cp type of ligand and a reactive group (amide, phenoxide, and alkyl) have been less studied, although they are expected to display more diverse reaction patterns. Evans, Schumann, and Hou have reported the preparation and structures of several C5Me5 and other substituted Cp-ligated divalent lanthanide halides and phenoxides, but these complexes are normally either solvated or dimeric.2 Recently, several types of neutral σ-donor-functionalized (amino and alkoxyl) cyclopendienyl ligands have been employed for the synthesis of this type of divalent lanthanide complexes.3 However, very little has been known about pendant neutral π-donor-functionalized cyclopentadienyl ligands in both transition metal and lanthanide chemistry. Recently, it has been demonstrated that cationic titanium and zinc alkyls supported by linked phenyl or *Corresponding author. E-mail:
[email protected]. (1) For reviews, see: (a) Evans, W. J. Polyhedron 1987, 6, 803. (b) Evans, W. J. Coord. Chem. Rev. 2000, 206, 263. (c) Evans, W. J. J. Organomet. Chem. 2002, 647, 2. (d) Evans, W. J.; Davis, B. L. Chem. Rev. 2002, 102, 2119. (e) Evans, W. J.; Allen, N. T.; Ziller, J. W. Angew. Chem., Int. Ed. 2002, 41, 359. (f) Meyer, G. Angew. Chem., Int. Ed. 2008, 47, 4962. (2) (a) Amdt, S.; Okuda, J. Chem. Rev. 2002, 102, 1953. (b) Hou, Z.; Wakatsuki, Y. J. Organomet. Chem. 2002, 647, 61. (c) Evans, W. J.; Grate, J. W.; Choi, H. W.; Bloom, I.; Hunter, W. E.; Atwood, J. L. J. Am. Chem. Soc. 1985, 107, 941. (d) Hou, Z.; Zhang, Y.; Yoshimura, T.; Wakatsuki, Y. Organometallics 1997, 16, 2963. (e) Evans, W. J.; Johnston, M. A.; Fujimoto, C. H.; Greaves, J. Organometallics 2000, 19, 4258. (f) Xie, Z.; Wang, S.; Yang, Q.; Mak, T. C. W. Organometallics 1999, 18, 2420. (g) Fedushkin, I. L.; Dechert, S.; Schumann, H. Organometallics 2000, 19, 4066. (h) Nishiura, M.; Hou, Z.; Wakatsuki, Y. Organometallics 2004, 23, 1359. (3) (a) Molander, G.; Schumann, H.; Rosenthal, E. C. E.; Demtschuk, J. Organometallics 1996, 15, 3817. (b) Schumann, H.; Rosenthal, E. C. E.; Demtschuk, J. Organometallics 1998, 17, 5324. (c) Schumann, H.; Erbstein, F.; Fedushkin, I. L.; Demtschuk, J. Z. Anorg. Allg. Chem. 1999, 625, 781. (d) Giesbrecht, G. R.; Cui, C.; Shafir, A.; Schmidt, J. A. R.; Arnold, J. Organometallics 2002, 21, 3841. (4) (a) Walker, D. A.; Woodman, T. J.; Schormann, M.; Hughes, D. L.; Bochmann, M. Organometallics 2003, 22, 797. (b) Sassmannshausen, J.; Powell, A. K.; Anson, C. E.; Wocadlo, S.; Bochmann, M. J. Organomet. Chem. 1999, 592, 84–94. (c) Deckers, P. J. W.; Hessen, B.; Teuben, J. H. Angew. Chem., Int. Ed. 2001, 40, 2516–2519. pubs.acs.org/Organometallics
Published on Web 06/24/2009
pyrrolyl-cyclopentadienyl ligands may be stabilized by an intramolecular M-arene interaction based on their spectroscopic data, but only the substituted Cp ligand was found to be coordinated to these ions in their neutral precursors.4 Electron-unsaturated ansa-sandwich complexes of early transition metals supported by two linked cyclopentadienyl ligands are of great interest owing to their unique geometric features as well as high performances in catalysis.5 In principal, this type of geometry could also be realized via the combination of a cyclopentadienyl ligand as a strong anionic π-donor and a neutral hemilabile π-donor ligand through a proper linker. This set of hybrid ligands might display a hemilabile property in suitable divalent metal complexes with a desired reactive group. It is well-known that lanthanide ions can form stable complexes with a π-bonded phenyl family of aromatic ligands.6 It is anticipated that heteroaromatic pyrroles could also interact with lanthanide ions as π-donors. Although the coordination properties of anionic pyrrolide ligands in various frameworks have been investigated,7 the information about neutral N-substituted pyrroles is very limited.8 Herein we report on the synthesis of the monoanionic silylene-bridged ligand (Me4C5-SiMe2-NC4H4)- (1) (Scheme 1) and its application for the synthesis of the novel ansa-sandwich ytterbium amide 2. Despite the interesting structure of 2, the reaction of 2 with dioxygen unexpectedly resulted in the clean formation of the novel dinuclear ytterbium complex 3 via the intramolecular oxygenations of one C-H and one Si-N bond. The new ligand 1 with a pendent neutral pyrrolyl group (Scheme 1) was prepared in good yield by the reaction of Me4HC5Li with N-(chlorodimethylsilyl)pyrrole.4a,9 The synthesis of a divalent ytterbium complex was accomplished via a silylamine elimination reaction. Thus, treatment of 1 with Yb[N(SiMe3)2]2(THF)210 yielded the expected monosubstituted amide 2 in good yield as dark green crystals after crystallization from toluene. Compound 2 has been fully (5) For leading reviews on ansa-metallocenes, see: (a) Alt, H. G.; K€ oppl, A. Chem. Rev. 2000, 100, 1205. (b) Hong, S.; Marks, T. J. Acc. Chem. Res. 2004, 37, 673. (c) M€uller, T. E.; Hutzsch, K. C.; Yus, M.; Foubelo, F.; Tada, M. Chem. Rev. 2008, 108, 3796. (6) Bochkarev, M. N. Chem. Rev. 2002, 102, 2089. (7) For examples, see: (a) Ganesan, M.; Gambarotta, S.; Yap, G. P. A. Angew. Chem., Int. Ed. 2001, 40, 766. (b) Christian, D.; Yazdanbakhsh, M.; Gambarotta, S.; Yap, G. P. A. Organometallic 2003, 22, 3742. (c) Evans, W. J.; Lee, D.; Rego, D. B.; Perotti, J. M.; Kozimor, S. A.; Moore, E. K.; Ziller, J. W. J. Am. Chem. Soc. 2004, 126, 14574. (d) Edelmann, F. T.; Freckmann, D. M. M.; Swchumann, H. Chem. Rev. 2002, 102, 1851. (8) Wang, J.; Gardiner, M. G.; Skelton, B. W.; White, A. H. Organometallics 2005, 24, 815. (9) Ganesan, M.; Berabe, C. D.; Gambarotta, S.; Yap, G. P. A. Organometallics 2002, 21, 1707. (10) Boncella, J. M.; Anderson, R. A. Organometallics 1985, 4, 205. r 2009 American Chemical Society
Communication
Organometallics, Vol. 28, No. 14, 2009
3971
Scheme 1
characterized by 1H and 13C NMR and IR spectroscopy.11 The proton resonances for the SiMe3 and the bridging SiMe2 groups fall at δ 0.19 and 0.48 ppm. Furthermore, its proton NMR spectrum displays two singlets (δ 6.09 and 6.48 ppm) for the pyrrole ring protons, which are high-field shifted compared to those of 1 (δ 6.33 and 6.81 ppm), indicating the possible Yb-pyrrolyl bonding. The ansa-sandwich structure of 2 is finally confirmed by an X-ray single-crystal analysis. Single crystals of 2 were obtained from toluene at -40 °C.12 The structure is shown in Figure 1 with selected bond parameters. The most notable structural feature is the silylene-bridged ansa-sandwich structure, in which the Yb atom is η5-coordinated to both the C5 and C4N rings. The two fivemembered rings are essentially planar with the interplane angle of 69.3(1)°. The distances of the Yb atom to the Cp and pyrrolyl ring centers are 2.412(2) and 2.589(2) A˚, (11) 1: Mp: 37-39 °C. 1H NMR (CDCl3): δ 0.29 (s, 6H, SiMe2), 1.65 (s, 6H, Cp-Me2), 1.81 (s, 6H, Cp-Me2), 3.12 (m, 1H, Cp-CH), 6.33 (s, 2H, pyrrole-H), 6.81 (s, 2H, pyrrole-H). 13C NMR (CDCl3): δ -3.78, 11.14, 13.00, 55.18, 110.68, 123.25, 131.63, 137.09. Anal. Calcd for C15H23NSi (245.44): C, 73.40; H, 9.45; N, 5.71. Found: C, 73.18; H, 9.25; N, 5.59. 2: A mixture of 1 (0.74 g, 3.00 mmol) and Yb[N(SiMe3)2]2(THF)2 (1.92 g, 3.00 mmol) in toluene (50 mL) was stirred at room temperature for 5 h and then at 60 °C for 2 d. The solution was concentrated (ca. 15 mL) and stored at 40 °C overnight to give dark green crystals of 2 (1.13 g, 65.2%). Mp: 235237 °C. 1H NMR (C6D6): δ 0.19 (s, 18H, SiMe3), 0.48 (s, 6H, SiMe2), 2.08 (d, J=5.8 Hz, 12H, Cp-Me4), 6.09 (s, 2H, pyrrole-H), 6.48 (s, 2H, pyrroleH). 13C NMR (C6D6): δ -0.12, 2.60, 4.49, 11.53, 14.11, 114.02, 119.56, 120.84, 122.39. IR: 2953, 2912, 2859, 2733, 1664, 1457, 1324, 1256, 1190, 1082, 1045, 1025, 987, 939, 836, 812, 789, 733, 668, 630. EI-MS: m/z 578.2, 417.1 [M - N(SiMe3)2], 245.2. 3: Dry dioxygen (over activated molecular sieves) was injected into a solution of 2 (0.58 g, 1.00 mmol) in toluene (30 mL). The color of the solution turned from dark green to pink immediately. The solution was stirred for an additional 3 h, and solvent was concentrated (10 mL) and stored at -40 °C to give pink crystals of 3 (0.22 g, 43%). Mp: 224-226 °C. 1H NMR (C6D6): δ -128.51 (s, 3H), 90.59 (s, 3H), -63.80 (br, 3H), -52.30 (s, 3H), -45.38 (s, 3H), 0.074 (s, 3H), 5.12 (s, 3H), 6.34 (br, 2H), 9.58 (br, 3H), 10.86 (m, 18H), 34.45 (s, 1H), 39.30 (br, 3H), 49.50 (s, 3H), 60.35 (br, 1H), 65.89 (br, 1H), 84.22 (s, 3H). IR: 2951, 2907, 2861, 2728, 1633, 1493, 1440, 1375, 1326, 1286, 1250, 1178, 1149, 1097, 1075, 975, 932, 886, 836, 777, 674. Anal. Calcd for C36H61N3O2Si4Yb2 (1027.26): C, 42.13; H, 5.99; N, 4.09. Found: C, 41.64; H, 6.18; N, 3.75. (12) Crystallographic data for 2: C21H40N2Si3Yb, M=577.85, monoclinic, space group P2(1)/n, a=9.0936(18) A˚, b=28.185(6) A˚, c=10.081 (2) A˚, R=90.00°, β=97.94(3)°, γ=90.00°, V=2559.0(9) A˚3, Z=4, Dc= 1.497 g 3 cm-3, F(000)=1164, 20 616 reflections measured (6050 unique). R1 [I > 2σ(I)]=0.0280, wR2 (all data)=0.0661. Crystallographic data for 3: C36H61N3O2Si4Yb2, M=1027.26, monoclinic, space group P2(1)/ n, a=12.099(2) A˚, b=26.325(5) A˚, c=13.147(3) A˚, R=90.00°, β=98.66 (3)°, γ=90.00°, V=4139.7(14) A˚3, Z=4, Dc =1.647 g 3 cm-3, F(000)= 2040, 28 176 reflections measured (7299 unique). R1 [I > 2σ(I)]=0.0470, wR2 (all data)=0.1055. The X-ray data were collected on a Siemens Smart-CCD diffractometer using graphite-monochromated Mo KR (λ= 0.710 73 A˚) at 113(2) K. The structure was solved by direct methods (SHELXS-97)19 and refined by full-matrix least-squares on F2. All nonhydrogen atoms were refined anisotropically and hydrogen atoms by a riding model (SHELXL-97).20
Figure 1. ORTEP diagram of 2. Selected bond lengths (A˚) and angles (deg): Yb(1)-N(2) 2.300(2), Yb(1)-C(7) 2.666(3), Yb(1)-C(8) 2.670(3), Yb(1)-C(9) 2.728(3), Yb(1)-C(10) 2.744(3), Yb(1)-C(11) 2.703(3), Yb(1)-N(1) 2.807(3), Yb(1)-C(1) 2.824(3), Yb(1)-C(2) 2.879(3), Yb(1)-C(3) 2.894(3), Yb(1)C(4) 2.835(3), Yb(1)-C(16) 2.906(3), N(1)-C(4) 1.382(4), N(1)-C(1) 1.389(4), C(1)-C(2) 1.382(4), C(2)-C(3) 1.413(4), C(3)-C(4) 1.376(4); C(7)-Si(1)-N(1) 148.19(9), N(2)-Si(3)C(16) 106.06(13), N(2)-Yb(1)-C(16) 65.66(9).
respectively. The latter is notably longer than those found in the divalent ytterbium pyrrolide [{(μ-η1:η5-Me2C4H2N)2Yb(μ-I)2[Li(THF)]2}2(C7H8)]n (2.440(7) and 2.450(7) A˚),13 indicating the labile nature of the π-coordinated pyrrolyl ring in 2. The Yb(1)-N(2) bond length (2.300(2) A˚) is slightly shorter than that found in NaYb(N(SiMe3)2)3 (Yb-Nterminal = 2.38(2) A˚).14 The close contact of the Yb(1)-C(16) (2.906(3) A˚) and the acute N(2)-Si(3)-C(16) angle (106.06(13)°) indicate the presence of the agostic interaction due to the electron deficiency of the ytterbium ion. Complex 2 represents a new class of ansa-sandwich lanthanide complexes that are stabilized by an anionic Cp family of ligand with a neutral hemilabile π arm. The monomeric and unsolvated structure of 2 combining the existence of the hemilabile arm may facilitate the attack of appropriate substrates to the metal center. Complex 2 reacts instantly with dioxygen in C6D6 to give a pink solution. The 1H NMR spectrum indicates the formation of a paramagnetic material alone with HN(SiMe3)2. Complex 3 was isolated as pink crystals in good yield from toluene on a preparative scale. An X-ray single-crystal analysis disclosed a dinuclear structure (Figure 2), in which the two ytterbium ions are linked by the μ-O(1), and the η1:η5 pyrrolide and the [Me4C5SiMe2O]2- ligands. The Yb(1)-O(1) and Yb(2)-O(1) bond lengths (2.298(4) and 2.274(4) A˚) are comparable to the typical range (2.23-2.26 A˚) for Yb-μOR bonds.15 The Yb(1)-O(2) distance (2.042(4) A˚) is very close to that in the siloxide [Na(12-crown-4)2]{[Yb(N(SiMe3)2]3(OSiMe3)} (2.085(4) A˚).16 The dioxygen reactions of divalent lanthanide complexes have been previously investigated by Takats and (13) Ganesan, M.; Berabe, C. D.; Gambarotta, S.; Yap, G. P. A. Organometallics 2002, 21, 1707. (14) Tilley, T. D.; Andersen, R. A.; Zalkin, A. Inorg. Chem. 1984, 23, 2271. (15) Boyle, T. J.; Ottley, L. A. M. Chem. Rev. 2008, 108, 1896. (16) Karl, M.; Seybert, G.; Massa, W.; Harms, K.; Agarwal, S.; Maleika, R.; Stelter, W.; Greiner, A.; Heitz, W.; Neumuller, B; Dehnicke, K. Z. Anorg. Allg. Chem. 1999, 625, 1301.
3972
Organometallics, Vol. 28, No. 14, 2009
Figure 2. ORTEP diagram of 3. Selected bond lengths (A˚) and angles (deg): Yb(1)-O(1) 2.298(4), Yb(1)-N(2) 2.582(6), Yb(2)O(1) 2.274(4), Yb(1)-O(2) 2.042(4), Yb(2)-N(2) 2.412(6), Yb(2)N(4) 2.189(5), Yb(2)-C(16) 2.623(6), Yb(2)-C(17) 2.754(6), Yb(2)-C(18) 2.756(7), Yb(2)-C(19) 2.644(7), O(1)-Yb(1)-O(2) 95.39(16), O(1)-Yb(2)-N(2) 75.27(17), N(2)-Yb(2)-N(4) 99.13(19), Yb(1)-O(1)-Yb(2) 105.19(18), Yb(1)-O(2)-Si(2) 152.2(3).
several other research groups. By employing bulky ligands, the lanthanide superoxo complex (TpMe2)2Sm(η2-O2) (TpMe2=HB(3,5-Me2pz)3)17 and several lanthanide peroxo complexes, such as [(THF)(C5H9C5H4)2Yb]2O2 and [(THF) [(Me3Si)2N]2Yb]O2,18 were isolated and structurally charac(17) Zhang, X. W.; Loppnow, G. R.; McDonald, R.; Takats, J. J. Am. Chem. Soc. 1995, 117, 7828–7829. (18) (a) Niemeyer, M. Z. Anorg. Allg. Chem. 2002, 628, 647. (b) Cui, D.; Tang, T.; Cheng, J.; Hu, N.; Chen, W.; Huang, B. J. Organomet. Chem. 2002, 650, 84. (19) Sheldrick, G. M. SHELXS-90/96, Program for Structure Solution. Acta Crystallogr., Sect. A 1990, 46, 467. (20) Sheldrick, G. M. SHELXL 97, Program for Crystal structure Refinement; University of Goettingen: Geottingen, Germany, 1997.
Hao et al.
terized. Thus, the formation of 3 may involve a dimeric ytterbium peroxo intermediate, which subsequently underwent O-O bond cleavage followed by the oxygen insertion into one of the C-H bonds in the pyrrolyl ring and one of the Si-N bonds. The resulting OH group then underwent the deprotonation reaction with the amide group, and the O-N bond cleavage also occurred to give HN(SiMe3)2 and 3. Addition of PPh3 to 2, prior to the dioxygen oxidation, gave the same products, indicating that the intramolecular oxidation is favorable. Although a number of transition metal superoxo and peroxo complexes have been known to undergo both intermolecular and intramolecular C-H bond activations, this process, to the best of our knowledge, has not been reported for lanthanide complexes. Moreover, the clean formation of the mixed lanthanide siloxide and heteroaryl oxide indicates the high selectivity of the dioxygen oxidation reaction. In summary, the first ansa-sandwich divalent lanthanide complex featuring both a strong anionic π-donor and a neutral hemilabile π-donor have been isolated and structurally characterized by employing a monoanionic hybrid pyrrolyl-cyclopentadienyl ligand. The complex rapidly and cleanly reacts with dioxygen to undergo intramolecular CH and Si-N bond oxygenation reactions. This reactivity is distinct from those previously observed for divalent lanthanide species. The synthesis and reactivity studies of other lanthanide derivatives with this ligand system are currently in progress.
Acknowledgment. We are grateful to the National Science Foundation of China (20572050 and 20725205), Tianjin Natural Science Foundation (05YFJMJC00500), and 111 plan for the support of this work. Supporting Information Available: Cif files for 2 and 3. This material is available free of charge via the Internet at http:// pubs.acs.org.
