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Organometallics 2000, 19, 4666-4668
Fluxional Behavior of Indenyl-Derived Ytterbocene(II) Complexes. The SiHR2 Group as a NMR Spectroscopic Probe Michael G. Klimpel, Wolfgang A. Herrmann, and Reiner Anwander* Anorganisch-chemisches Institut, Technische Universita¨ t Mu¨ nchen, Lichtenbergstrasse 4, D-85747 Mu¨ nchen, Germany Received April 18, 2000 Summary: Indenyl-derived ytterbocene(II) complexes [1-(SiHR2)-2-R′-C9H5]2Yb(L)2 (R ) Me, C6H5; R′ ) H, Me; L ) donor ligand) have been synthesized via silylamine elimination from Yb[N(SiMe3)2]2(THF)2 and the indene derivatives in hexane at ambient temperature. The “SiH-decorated” silyl substituents assist in the examination of the fluxional behavior of the stereoisomers in solution, the ratio and interconversion of which are affected by the size and ring position of the substituents as well as the type of donor ligand, e.g., THF vs TMEDA. Ytterbocene(II) and samarocene(II) complexes gained considerable interest in the field of rare earth-mediated R-olefin and ring-opening polymerization.1 Various derivatives comprising ansa- and nonlinked cyclopentadienyl and indenyl systems as well as heteroleptic complexes2-7 were ascribed high catalytic efficiency occurring via a novel bisinitiator mechanism.8 It is known that the interconversion of stereoisomers, implied chemically and thermally through rotation and epimerization processes, significantly affects the stereospecifity of olefin transformations.9 To better examine such fluxional phenomena, our interest was drawn to the design of specially functionalized indenyl derivatives of the diamagnetic ytterbium(II) center.10 We report here the synthesis of ytterbocene(II) complexes via a silylamine elimination reaction.11 Moreover, the indenyl-bonded * Corresponding author. Fax: +49 89 289 13473. E-mail: reiner.
[email protected]. (1) For a recent review, see: Yasuda, H. Top. Organomet. Chem. 1999, 2, 255-283. (2) Evans, W. J.; Bloom, I.; Hunter, W. E.; Atwood, J. L. J. Am. Chem. Soc. 1981, 103, 6507-6508. (b) Evans, W. J.; Katsumata, H. Macromolecules 1994, 27, 2330-2332. (c) Evans, W. J.; Katsumata, H. Macromolecules 1994, 27, 4011-4013. (d) Evans, W. J.; DeCoster, D. M.; Greaves, J. Organometallics 1996, 15, 3210-3221. (3) (a) Yamamoto, H.; Yasuda, H.; Yokota, K.; Nakamura, A.; Kai, Y.; Kasai, N. Chem. Lett. 1988, 1963-1966. (b) Yasuda, H.; Yamamoto, H.; Yamashita, M.; Yokota, K.; Nakamura, A.; Miyake, S.; Kai, Y.; Kanehisa, N. Macromolecules 1993, 26, 7134-7143. (4) Jiang, T.; Shen, Q.; Lin, Y.; Jin, S. J. Organomet. Chem. 1993, 450, 121-124. (5) Ihara, E.; Noduno, M.; Katsura, K.; Adachi, Y.; Yasuda, H.; Yamagashira, M.; Hashimoto, H.; Kanehisa, N.; Kai, Y. Organometallics 1998, 17, 3945-3956. (6) (a) Knjazhanski, S. Ya.; Nomerotsky, I. Yu.; Bulychev, B. M.; Belsky, V. K.; Soloveichik, G. L. Organometallics 1994, 13, 2075-2078. (b) Knjazhanski, S. Ya.; Kalyuzhnaya, E. S.; Elizalde Herrera, L. E.; Bulychev, B. M.; Khvostov, A. V.; Sizov, A. I. J. Organomet. Chem. 1997, 531, 19-25. (c) Knjazhanski, S. Ya.; Elizalde Herrera, L. E.; Cadenas, G.; Bulychev, J. Organomet. Chem. 1998, 568, 33-40. (7) (a) Hou, Z.; Tezuka, H.; Zhang, Y.; Yamazaki, H.; Wakatsuki, Y. Macromolecules 1998, 31, 8650-8652. (b) Zhang, Y.; Hou, Z.; Wakatsuki, Y. Macromolecules 1999, 32, 939-941. (8) Boffa, l. S.; Novak, B. M. Macromolecules 1994, 27, 6993-6995. (9) For a recent review, see: Brintzinger, H.-H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth, R. M. Angew. Chem. 1995, 107, 1255-1283; Angew. Chem., Int. Ed. Engl. 1995, 34, 1143-1170.
SiHR2 group (R ) Me, Ph) is exploited as a sensitive probe for dynamic NMR investigations. New silyl-substituted indenes 1-(SiHMe2)C9H7 (1),12 1-[SiH(C6H5)2]C9H7 (2), and 1-(SiHMe2)-2-Me-C9H6 (3) were prepared according to common salt metathesis procedures from lithiated indene and the corresponding chlorosilanes in THF/ether. Yb[N(SiMe3)2]2(THF)2 (4)13 reacts with 1 and 2 in hexane to form the dark red compounds [1-(SiHMe2)C9H6]2Yb(THF)2 (5) and [1-{SiH(C6H5)2}C9H6]2Yb(THF)2 (6), respectively, in yields >90% (Scheme 1).14-16 (10) For structurally characterized Ln(II) indenyl complexes, see: (a) Jin, J.; Jin, Z.; Wie, G.; Chen, W. J. Struct. Chem. (Jiegou Huaxue) 1993, 12, 24. (b) Evans, W. J.; Gummersheimer, T. S.; Boyle, T. J.; Ziller, J. W. Organometallics 1994, 13, 1281-1284. (c) Khvostov, A. V.; Bulychev, B. M.; Belsky, V. K.; Sizov, A. I. J. Organomet. Chem. 1999, 584, 164-170. (d) Qian, C.; Li, H.; Sun, J.; Nie, W. J. Organomet. Chem. 1999, 585, 59-62. (11) Further nonsalt metathesis routes to lanthanidocene(II) complexes comprise: (a) Fischer, E. O.; Fischer, H. Angew. Chem. 1964, 76, 52. (b) Hammel, H.; Weidlein, J. J. Organomet. Chem. 1990, 388, 75-87. (c) Watson, P. L.; Whitney, J. F.; Harlow, R. L. Inorg. Chem. 1981, 20, 3271-3278. (d) Deacon, G. B.; Newnham, R. H. Aust. J. Chem. 1985, 38, 1757-1765. (e) Wang, S.; Yu, Y.; Ye, Z.; Qian, C.; Huang, X. J. Organomet. Chem. 1994, 464, 55-58. (f) Qian, C.; Zou, G.; Sun, J. J. Organomet. Chem. 1998, 566, 21-28. (12) Eppinger, J.; Spiegler, M.; Hieringer, W.; Herrmann, W. A.; Anwander, R. J. Am. Chem. Soc. 2000, 122, 3080-3096. (13) (a) Andersen, R. A.; Boncella, J. M. Organometallics 1985, 4, 205-207. (b) Boncella, J. M. Ph.D. Thesis, University of California, Berkeley, 1982. (14) Complexes 5-9 were synthesized analogously (see Supporting Information). Complex 5: in a glovebox, indene 1 (349 mg, 2.00 mmol) and complex 4 (638 mg; 1.00 mmol) were dissolved in hexane (20 mL) and stirred at ambient temperature. The initially orange solution turned dark red within 3 min. After 3 h the reaction mixture was centrifugated, leaving a small amount (
