SHARAD HAJELA, WILLIAM P. SCHAEFER AND JOHN E. BERCAW 1773 labeled drawing of the dimer; crystal packing is ScCH3 (144.7°) suggesting that formal replacement shown in Fig. 2. of a methyl ligand with a bulkier (77 5,77 1)-Cp* group as the alkyl does not significantly perturb the Discussion. The dimer is joined across an inversion Sc-Cp* bonding. center by an (77 5,77 1)-Cp* group which bridges the two symmetry-related Sc atoms. The 77 1-methylene This work was supported by the USDOE Office of (C6) has been formed as the result of C-H acti­ Basic Energy Sciences (Grant No. DE-FG03- vation of a Cp* methyl group. A somewhat surpris­ 85ER113431). ing result is that, in all other regards, the bonding is References very similar to that determined for Cp!ScCH3 (Thompson et al., 1987). The (77 5,77 1)-ring remains BURGER, B. J., THOMPSON, M. E., CoTIER, W. D. & BERCAW, J.E. planar with a maximum deviation of only 0.22 A (1990). J. Am. Chem. Soc. 112, 1566-1577. from the least-squares plane calculated for Cl CROMER, D. T. (1974). International Tables for X-ray Crystallog­ raphy, Vol. IV, pp. 149-151. Birmingham: Kynoch Press. through ClO. The geometry about C6 is essentially (Present distributor Kluwer Academic Publishers, Dordrecht.) tetrahedral; the angles Cl-C6-Sc', Cl-C6-H6A, CROMER, D. T. & WABER, J. T. (1974). International Tables for Cl-C6-H6B and H6A-C6-H6B are 118.9, X-ray Crystallography, Vol. IV, pp. 99-101. Birmingham: 107.3, 104.8 and 98.1°, respectively, giving an aver­ Kynoch Press. (Present distributor Kluwer Academic 0 Publishers, Dordrecht.) age value of 107.3 (8.6) • The H6A-C6-H6B angle DUCHAMP, D. J. (1964). CRYM crystallographic computing is slightly compressed (98.1°) while the Cl-C6-Sc' system. Am. Crystallogr. Assoc. Meet., Bozeman, Montana. angle is somewhat opened (118.9°). The Sc'···H6A Paper Bl4, p. 29. and Sc' .. ·H6B distances are 2.76 (3) and 2.79 (3) A JOHNSON, C. K. (1976). ORTEPII. Report ORNL-3794, third revision. Oak Ridge National Laboratory, Tennessee, USA. indicating that there is no agostic interaction for the THOMPSON, M. E., BAXTER, S. M., BULLS, A. R., BURGER, B. J., a-H atoms with the Sc center. The Cp*-Sc-Cp* NOLAN, M. C., SANTARSIERO, B. D., SCHAEFER, W. P. & angle (141.8°) is approximately the same as for Cp! BERCAW, J. E. (1987). J. Am. Chem. Soc. 109, 203-219. Acta Cryst. (1992). C48, 1773-1776 A Silicon-Bridged Bis(substituted Cp) Yttrium Complex BY RICHARD E. MARSH, WILLIAM P. SCHAEFER, E. BRYAN COUGHLIN AND JOHN E. BERCAW Division of Chemistry and Chemical Engineering* and The Beckman Institute, Mail Code 139-74, California Institute of Technology, Pasadena, California 91125, USA (Received 9 December 1991; accepted 11 February 1992) Abstract. rac-Bis(tetrahydrofuran)lithium [bis(2- Introduction. The Ziegler-Natta polymerization of trimethylsilyl-4-tert-butyl-rJ5-cyclopentadienyl)di­ olefins has occupied the attention of chemists for methylsilane]dichloroyttrate, [Li(C4H 80)2][Y(C26H48- nearly four decades. Recently, the development of Si3)Cli], Mr= 755.87, triclinic, PI, a= 13.110 (8), b homogeneous transition-metal catalyst systems has = 17.163 (15), c = 20.623 (14) A, a= 104.02 (7), /3 = afforded the possibility of mechanistic investigations 0 3 99.38 (5), y = 100.24 (6) , v = 4326 (6) A , z = 4, into various key steps of polymer initiation, pro­ Dx = 1.16 g cm-3, A.{Mo Ka)= 0.71073 A, µ = pagation and chain termination. Brintzinger and co­ 1 15.86 cm - , F(OOO) = 1608, room temperature, R = workers have developed a series of ansa-zirconocene 2 2 0.056 for 6136 reflections with F'a > 3u(F0 ). There catalysts which possess a C2 symmetric ligand are two virtually identical molecules in the asym­ arrangement about the metal center (Roll, metric unit. In each, the Y atom is tetrahedrally Brintzinger, Rieger & Zolk, 1990; Wiesenfeldt, coordinated to a substituted Si-bridged bis(cyclo­ Reinmuth, Barsties, Evertz & Brintzinger, 1989). pentadienyl) ligand and to two Cl ions in the cleft. Moreover, activation of these ansa-zirconocene cata­ The Li atom is 2.35 A from each Cl ion, and two lysts with methylalumoxane results in production of molecules of tetrahydrofuran are connected to the highly isospecific polymers. Work in this laboratory Li, completing its tetrahedral coordination. has centered on the study of well defined single­ component Ziegler-Natta-type catalyst systems *Contribution No. 8539. (Piers, Shapiro, Bunel & Bercaw, 1990). We report 0108-2701/92/101773-04$06.00 © 1992 International Union of Crystallography 1774 4 Table 1. Final heavy-atom coordinates ( x 10 ) and Table 1 (cont.) equivalent isotropic displacement parameters 2 4 x y z Ucq (A x 10 ) C28b 6714 (13) 6188 (10) 2621 (10) 2485 (81) C29b 6127 (15) 5857 (11) 3055 (8) 2715 (90) C30b 5115 (7) 5376 (6) 2646 (5) 1452 (39) 02b 3806 (4) 5367 (3) 713 (3) 1018 (17) x y z Ucq C31b 3480 (7) 5239 (5) -5 (5) 1193 (31) Ya 1810 (.4) 7217 (.3) 4009 (.3) 432 (2) C32b 2784 (9) 5833 (8) -63 (7) 1821 (51) Ola 3262 (1) 6960 (1) 3292 (1) 719 (5) C33b 3178 (10) 6511 (7) 561 (8) 1849 (51) 02a 2931 (1) 8756 (1) 4442 (1) 708 (5) C34b 3759 (8) 6177 (7) 1041 (5) 1634 (42) Sil a -400 (I) 6062 (1) 4245 (1) 611 (5) Si2a 1161 (2) 8070 (I) 5831 (1) 813 (6) Si3a 372 (I) 5333 (1) 2407 (1) 632 (5) Table 2. Selected bond distances (A) and angles (°) Cla -1428 (5) 6446 (4) 4683 (3) 976 (23) C2a -793 (5) 4914 (4) 3970 (3) 903 (21) C3a 978 (4) 6434 (4) 4793 (3) 531 (16) Ya--Cpla 2.383 Yb-Cplb 2.396 C4a 1549 (4) 7246 (3) 5231 (3) 525 (17) Ya---Cp2a 2.385 Yb-Cp2b 2.389 C5a 2638 (5) 7228 (4) 5301 (3) 587 (18) Ya---Clla 2.628 (2) Yb--Cllb 2.614 (I) C6a 2789 (5) 6479 (4) 4926 (3) 563 (17) Ya---Cl2a 2.642 (2) Yb-Cl2b 2.623 (2) C7a 1748 (5) 5989 (3) 4610 (3) 571 (18) Lia---Clla 2.366 (11) Lib--Cllb 2.377 (11) C8a 567 (6) 7615 (5) 6447 (3) 1259 (29) Lia---C12a 2.340 (11) Lib--Cl2b 2.401 (11) C9a 245 (6) 8639 (4) 5464 (4) 1368 (30) Lia-Ola 1.917 (12) Lib-Olb 1.950 (12) ClOa 2392 (6) 8882 (4) 6303 (3) 1038 (26) Lia-02a 1.925 (12) Lib-02b 1.893 (12) Clla 3807 (5) 6180 (4) 4988 (4) 696 (21) Sila---Cla 1.869 (7) Silb-Clb 1.872 (6) Cl2a 4745 (5) 6882 (4) 5048 (4) 1049 (26) Sila---C2a 1.863 (6) Silb--C2b 1.858 (6) Cl3a 3780 (5) 5484 (5) 4385 (4) 1252 (29) Sila---C3a 1.878 (6) Silb--C3b 1.862 (5) Cl4a 3948 (5) 5889 (4) 5634 (4) 1177 (26) Sila---Cl5a 1.858 (6) Silb--C15b 1.887 (6) C15a -204 (4) 6555 (3) 3552 (3) 475 (17) Si2a---C4a 1.845 (6) Si2b--C4b 1.843 (6) Cl6a 280 (4) 6335 (3) 2977 (3) 450 (15) Si2a-C8a 1.850 (8) Si2b----C8b 1.869 (7) C17a 585 (4) 7071 (4) 2782 (3) 508 (16) Si2a---C9a 1.856 (8) Si2l>---C9b 1.868 (7) C18a 295 (4) 7738 (3) 3200 (3) 523 (18) Si2a---C10a 1.878 (7) Si2b--CIOb 1.859 (7) C19a -156 (4) 7421 (4) 3682 (3) 529 (17) C20a 1199 (5) 4727 (3) 2801 (3) 954 (23) Cp la--Ya---Cp2a 122.1 Cplb--Yb--Cp2b 122.5 C21a -985 (5) 4682 (4) 2047 (4) 1240 (29) Cplo-Ya--Clla 114.2 Cplb--Yb----Cllb 112.4 C22a 965 (5) 5552 (3) 1698 (3) 902 (23) Cpla--Ya---Cl2a 107.0 Cplb--Yb--Cl2b 108.6 C23a 317 (5) 8576 (4) 3081 (3) 679 (20) Cp2a--Ya---Clla 108.6 Cp2b-Yb--Cllb 108.1 C24a 1242 (6) 8841 (4) 2763 (3) 960 (23) Cp2a--Ya---Cl2a 114.2 Cp2b-Yb--C12b 114.3 C25a 372 (6) 9235 (4) 3732 (4) 1043 (26) Ola--Ya---Cl2a 84.6 (0) Cllb--Yb--Cl2b 84.6 (0) C26a -726 (6) 8500 (4) 2585 (4) 1278 (27) o 1a--Lia---CI2a 97.8 (4) Cllb--Lib--Cl2b 95.1 (4) Ola-Lia-Ola 113.7 (5) Cllb--Lib-Olb 107.9 (5) Yb 3053 (.4) 2441 (.3) 867 (.3) 450 (2) Ola--Lia-02a 115.5 (5) Cllb--Lib-02b 117.9 (5) alb 2749 (I) 3843 (I) 1553 (1) 642 (4) 02a--Lia-Ola 114.3 (5) Cl2b-Lib-Olb 120.3 (5) Q2b 4415 (I) 3364 (1) 406 (1) 751 (5) 02a--Lia-02a 113.9 (5) Cl2b-Lib-02b 113.3 (5) Silb 1996 (1) 449 (I) 726 (1) 536 (5) Olo-Lia-02a 102.4 (6) Olb--Lib-02b 103.0 (6) Si2b 2974 (1) 900 (I) -942 (1) 725 (6) 05a--Sil a--C3a 99.I (3) Cl5b--Silb--C3b 99.5 (2) Si3b 2180 (1) 2113 (1) 2530 (1) 632 (5) Clb 2456 (5) -477 (3) 297 (3) 765 (19) C2b 829 (4) 83 (3) 1066 (3) 627 (18) C3b 1682 (4) 1105 (3) 156 (3) 441 (16) herein the crystal structure of the C2 symmetric C4b 2233 (4) 1382 (3) -330 (3) 535 (18) complex rac-( CH3) 2Si[2-Si( CH3 )r4-C(CH 3) 3CsH2h­ C5b 1854 (4) 2088 (4) -425 (3) 578 (18) C6b 1106 (4) 2267 (3) -28 (3) 496 (17) YCl2Li(OCH2CH2CH2CH2)2.