ansa-Cyclopentadienyl-Phenoxy Titanium(IV) Complexes (PHENICS

May 20, 2009 - †Petrochemicals Research Laboratory, Sumitomo Chemical Co., Ltd., 2-1 Kitasode ... fields of organometallic chemistry and polymer che...
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Organometallics 2009, 28, 3785–3792 DOI: 10.1021/om900019q

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ansa-Cyclopentadienyl-Phenoxy Titanium(IV) Complexes (PHENICS): Synthesis, Characterization, and Catalytic Behavior in Olefin Polymerization Masaaki Nabika,† Hiroaki Katayama,† Tsuyoshi Watanabe,† Hiroshi Kawamura-Kuribayashi,† Kazunori Yanagi,‡ and Akio Imai*,† †

Petrochemicals Research Laboratory, Sumitomo Chemical Co., Ltd., 2-1 Kitasode, Sodegaura, Chiba 299-0295, Japan, and ‡Genomic Science Laboratories, Dainippon Sumitomo Pharma Co., Ltd., 3-1-98, Kasugadenaka, Konohana-ku, Osaka 554-0022, Japan Received January 9, 2009

A series of ansa-cyclopentadienyl-phenoxy titanium complexes (PHENICS: phenoxy-induced complex of Sumitomo) (1a-e), [{Me2CCp(OC6H2-3-R-5-R0 )}TiCl2] (1a, R = R0 = H; 1b, R = tBu, R0 = Me) and [{Me2Si(C5Me4)(OC6H2-3-R00 -5-Me)}TiCl2] (1c, R00 = iPr; 1d, R00 = tBu; 1e, R00 = Adm), have been synthesized and characterized. It is noteworthy that the dihedral angles of the cyclopentadienyl and phenoxy moieties of the complexes 1b and 1d, revealed by X-ray crystal structure analysis, are 63.0 (1b) and 68.2 (1d), indicating a distortion from a mutual perpendicular arrangement, whereas the symmetrical patterns of the 1H NMR spectra indicate a dynamic behavior in solution. The PHENICS-type complexes exhibit good to excellent catalytic activities for copolymerization of ethylene and 1-hexene upon activation with AliBu3/[Ph3C][B(C6F5)4] cocatalyst. Particularly, the complexes with a bulky substituent at the ortho position of the phenoxy moiety showed excellent catalytic features (1d, 27 200 kg mol-1 h-1 at 80 C, 6000 kg mol-1 h-1 at 180 C). These data show that the catalytic activity of the PHENICS-type catalysts is higher than that reported for the so-called constrained geometry catalyst (CGC) precursors. This becomes even more evident in light of the results for polymerization at 180 C. Whereas the PHENICS catalyst system acts as a single-site catalyst at 180 C, the CGC-type catalysts proved to be inactive under analogous conditions. Moreover, the copolymers obtained with PHENICS incorporate much higher content of 1-hexene than those obtained with CGC.

Introduction Olefin polymerization catalyzed by homogeneous transition metal complexes has attracted particular attention in the fields of organometallic chemistry and polymer chemistry. Especially, since the discovery of group 4 metallocene singlesite catalysts,1 numerous studies have been reported involving early transition metal complex catalysts.2 Among them, halfsandwich catalysts are of particular interest and importance from the industrial point of view. After the discovery of ansa-Cp-amide titanium complexes (CGC), which upon activation with suitable cocatalysts show excellent activities *Corresponding author. E-mail: [email protected]. (1) Kaminsky, W.; Sinn, H. Transition Metals and Organometallics for Catalysts for Olefin Polymerization; Springer: New York, 1988. (2) (a) Thematic Issue on “Frontiers in Polymer Chemistry”, Chem. Rev. 2001, 101, 3581-4188. (b) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 428. (3) (a) Stevens, J. C.; Timmers, F. J.; Wilson, D. R.; Schmit, G. F.; Nickas, P. N.; Rosen, R. K.; Knight, G. W.; Lai, S. Y. (Dow) Eur. Pat. Appl. EP 416815, 1991. (b) Canich, J. A. M.; Hlatky, G. G.; Turner, H. W. (Exxon) PCT Appl. WO 92/00333, 1992, .(c) Hughes, A. K.; Meetsma, A.; Teuben, J. H. Organometallics 1993, 12, 1936. (d) du Plooy, K. E.; Moll, U.; Wocadol, S.; Massa, W.; Okuda, J. Organometallics 1995, 14, 3129. (e) Park, J. T.; Yoon, S. C.; Bae, B.-J.; Seo, W. S.; Suh, I.-H.; Han, T. K.; Park, J. R. Organometallics 2000, 19, 1269. (f ) Cho, D. J.; Wu, C. J.; S, S.; Han, W.-S.; Kang, S. O.; Lee, B. Y. Organometallics 2006, 25, 2133. r 2009 American Chemical Society

for copolymerization of ethylene and R-olefins to give novel copolymers, and the industrial application of these catalytic systems,3a,3b a variety of half-metallocene complexes with nitrogen,3 oxygen,4 and phosphorus5 donors employed as coordinating heteroatoms have been reported. Non-metallocene catalysts have been also intensively and widely studied since Kakugo et al. (Sumitomo Chemical) reported in 1985 the complex {2,20 -thiobis(6-tert-butyl-4-methylphenoxy)}titanium dichloride ((TBP)TiCl2).6 Syndiotactic (4) (a) Trouve, G.; Laske, D. A.; Meetsma, A.; Teuben, J. H. J. Organomet. Chem. 1996, 511, 255. (b) Gielens, E. E. C. G.; Tiesnitsch, J. Y.; Hessen, B.; Teuben, J. H. Organometallics 1998, 17, 1652. (c) Christie, S. D. R.; Man, K. W.; Whitby, R. J.; Slawin, A. M. Z. Organometallics 1999, 18, 348. :: (5) (a) Bredeau, S.; Altenhoff, G.; Kunz, K.; Doring, S.; Grimme, S.; Kehr, G.; Erker, G. Organometallics 2004, 23, 1836. (b) Kunz, K.; Erker, :: :: G.; Doring, S.; Frohlich, R.; Kehr, G. J. Am. Chem. Soc. 2001, 123, 6181. (6) (a) Kakugo, M.; Miyatake, T.; Kawai, Y.; Shiga, A.; Mizunuma, K. (Sumitomo) PCT Appl. WO 87/02370, 1987. (b) Kakugo, M.; Miyatake, T.; Mizunuma, K. Chem. Exp. 1987, 2, 445. (c) Miyatake, T.; Mizunuma, K.; Seki, Y.; Kakugo, M. Makromol. Chem., Rapid Commun. 1989, 10, 349. (d) Kakugo, M.; Miyatake, T.; Mizunuma, K. Stud. Surf. Sci. Catal. 1990, 56, 517. (e) Miyatake, T.; Mizunuma, K.; Kakugo, M. Makromol. Chem., Macromol. Symp. 1993, 66, 215. (f ) Takaoki, K.; Miyatake, T. Macromol. Symp. 2000, 157, 251. (g) Kawamura-Kuribayashi, H.; Miyatake, T. J. Organomet. Chem. 2003, 674, 73. (h) Fujita, M.; Seki, Y.; Miyatake, T. J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 1107. (i) Fujita, M.; Seki, Y.; Miyatake, T. Macromol. Chem. Phys. 2004, 205, 884.

Published on Web 05/20/2009

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Figure 1. PHENICS complexes.

polystyrene,6b,6d ethylene-styrene alternating copolymer,6d ring-closing polymerization homopolymer via R,ω-diene,6e and ultrahigh molecular weight atactic poly(R-olefin)s6h,6i were produced by this system. However, the polymerization activities displayed by this class of catalysts were insufficient for largescale industrial application. Excellent catalytic features of (TBP)TiCl2 and half-metallocene complexes stimulated us to develop phenoxy-based metallocene complexes. Herein, we report the synthesis and characterization of novel ansa-Cp-phenoxy titanium complexes (1a-1e), so-called PHENICS complexes (phenoxyinduced complex of Sumitomo, Figure 1),7 and their application as catalyst precursors for copolymerization of ethylene and 1-hexene at various temperatures.

Results and Discussion Synthesis and Structure of PHENICS Complexes. Isopropylidene-bridged PHENICS titanium complexes [{Me2C(Cp)PhO}TiCl2] (1a) and [{Me2C(Cp)(OC6H2-6-tBu-4-Me) TiCl2] (1b) were prepared in two steps starting from the corresponding bromobenzenes with OMe protecting group (4a and 4b) (Scheme 1). Thus, treatment of 2-methoxy-3-tertbutyl-5-methylbromobenzene 4b with n-BuLi in diethyl ether at -70 C followed by addition of 6,6-dimethylfulvene yielded the functionalized cyclopentadienes 2a/2b as pale yellow oils in good yield (2a, 75%; 2b, 60%). The lithium salts of 2a/2b were prepared in a reaction with n-BuLi in n-hexane or diethyl ether. Reactions of the lithium salts of 2a/2b with TiCl4 gave, upon LiCl abstraction, the formation of a Cp-Ti bond, and cleavage of an O-Me bond, the titanium complexes 1a and 1b as orange and yellow powders, respectively, in moderate yield (34%).8 The silylene-bridged PHENICS titanium complexes [{Me2Si(C5Me4)(OC6H2-3-iPr-5-Me)}TiCl2] (1c), [{Me2Si(7) (a) Katayama, H.; Nabika, M.; Imai, A.; Miyashita, A.; Watanabe, T.; Johohji, H.; Oda, Y.; Hanaoka, H. (Sumitomo) PCT Appl. WO 97/03992, 1997. (b) Imai, A.; Ogawa, A.; Takei, A.; Nishiyama, T.; Johoji, H. MetCon2000, 2000. (c) Imai, A; Katayama, H.; Nabika, M.; Watanabe, T. MetCon2001, 2001. (d) Imai, A.; Johoji, H.; Hozumi, H.; Nishiyama, T. MetCon2002, 2002. (e) Miyatake, T. The 15th International Symposium on Olefin Metathesis and Related Chemistry, Kyoto, 2003. (f ) Hanaoka, H.; Hino, T.; Souda, H.; Yanagi, K.; Oda, Y.; Imai, A. J. Organomet. Chem. 2007, 692, 4059. (g) Hanaoka, H.; Hino, T.; Nabika, M.; Kohno, T.; Yanagi, K.; Oda, Y.; Imai, A.; Mashima, K. J. Organomet. Chem. 2007, 692, 4717. (h) Rau, A.; Schmitz, S.; Luft, G. J. Organomet. Chem. 2000, 608, 71. (i) Chen Y.-X.; Fu, P.-F.; Stern, C. L.; Marks, T. J. Organometallics 1997, 16, :: 5958. (j) Zhang, Y.; Wang, J.; Mu, Y.; Shi, Z.; Lu, C.; Zhang, Y.; Qiao, :: L.; Feng, S. Organometallics 2003, 22, 3877. (k) Zhang, Y.; Mu, Y.; Lu, C.; Li, G.; Xu, J.; Zhang, Y.; Zhu, D.; Feng, S. Organometallics 2004, 23, 540. (8) Qian, Y.; Huang, J.; Chen, Y.; Li, G.; Chen, W.; Li, B.; Jin, X.; Yang, Q. Polyhedron 1994, 13, 1105.

Nabika et al.

(C5Me4)(OC6H2-3-tBu-5-Me)}TiCl2] (1d), and [{Me2Si(C5Me4)(OC6H2-3-Adm-5-Me)}TiCl2] (1e) were also prepared. Complex 1d was prepared via the corresponding chlorosilane derivative 3d. Therefore, treatment of 2-methoxy-3-tert-butyl-5-methylbromobenzene 4b with n-BuLi in THF/n-hexane followed by addition of dichlorodimethylsilane resulted in the formation of compound 3d in very good yield (84%). The subsequent reaction of 3d with tetramethylcyclopentadienyllithium afforded 2d as a yellow oil with an excellent yield (97%). Treatment of 2d with n-BuLi followed by addition of TiCl4 gave, upon LiCl abstraction and in situ cleavage of the O-Me bond, 1d as orange crystals in a poor yield of 2%. Related complexes 1c and 1e were prepared in a similar manner as dark brown crystals (4% and 5% yield, respectively). Low C-H bond reactivity of the C5Me4 moiety accounts for the very poor yield of the titanium complexes in the aforementioned reactions. Therefore, we investigated various reaction conditions to improve the reactivity of 2d. As a result, triethylamine was found to be an appropriate additive for the reaction, improving the yield of 1d to 27% because of elevating the C-H bond reactivity. The molecular structures of [{Me2C(Cp)(OC6H2-6-tBu-4Me)TiCl2] (1b) and [{Me2Si(C5Me4)(OC6H2-3-tBu-5-Me)} TiCl2] (1d) were determined by X-ray diffraction study. The single crystals were grown from toluene/n-hexane solutions at room temperature. The ORTEP diagrams of 1b and 1d are presented in Figures 2 and 3, respectively. The crystallographic data for 1b and 1d are shown in Table 1.9 Selected bond lengths and bond angles are listed in Table 2. The titanium atom in both cases adopts a distorted tetrahedral geometry with both chloro atoms in a cis arrangement. It is noteworthy that the dihedral angles of cyclopentadienyl and phenyl moieties in the complexes are 63.0(1) (1b) and 68.2(2) (1d), indicating a distortion from their mutual perpendicular arrangement. The distances between cyclopentadienyl moieties and titanium (1.997(2) and 2.008(2) A˚) are almost identical with those reported for [Cp0 (OAr0 )TiCl2] (Cp0 = Cp, 1,3-tBu2C5H3, C5Me5, Ar0 = 2,6-Me2C6H3, 2,6-iPr2C6H3) complexes (1.99-2.03 A˚).10c On the other hand, the Ti-O bond length in 1b (1.795(2) A˚) is slightly longer than that observed for 1d (1.784(2) A˚) and [Cp0 (OAr0 )TiCl2] complexes (1.76-1.79 A˚).10c The Ti-O bond length in 1d, having a Cl leaving group, is much shorter than the bond distances found for the hydrocarbonbound titanium complexes, [(Me2Si(C5Me4)(OC6H2-3-tBu5-Me)TiBz2] (1.812(2) A˚) and [Me2Si(C5Me4)(OC6H2-3-tBu5-Me) Ti(Ph-CHdCH-CHdCH-Ph) (1.874(2) A˚).7g NMR analyses of 1b and 1d in CDCl3 revealed that ligand architectures of the complexes show dynamic behavior in (9) For more detailed crystallographic data, see the Supporting Information. (10) (a) Nomura, K; Naga, N (Sumitomo) Jpn Pat. Appl. JP 1999166010, 1999, .(b) Nomura, K.; Naga, N.; Miki, M.; Yanagi, K.; Imai, A. Organometallics 1998, 17, 2152. (c) Nomura, K.; Naga, N.; Miki, M.; Yanagi, K. Macromolecules 1998, 31, 7588. (d) Nomura, K.; Oya, K.; Komatsu, T.; Imanishi, Y. Macromolecules 2000, 33, 3187. (e) Nomura, K. Rec. Res. Dev. Polym. Sci. 2004, 8, 105. (f) Nomura, K.; Tanaka, A.; Katao, S. J. Mol. Catal. A: Chem. 2006, 254, 197. (g) Nomura, K.; Komatsu, T.; Imanishi, Y. Macromolecules 2000, 33, 8122. (h) Byun, D. J.; Fudo, A.; Tanaka, A.; Fujiki, M.; Nomura, K. Macromolecules 2004, 37, 5520. (i) Nomura, K.; Tanaka, A.; Katao, S. J. Mol. Catal. A: Chem. 2006, 254, 197. (j) Nomura, K.; Tsubota, M.; Fujiki, M. Macromolecules 2003, 36, 3797. (k) Wang, W.; Tanaka, T.; Tsubota, M.; Fujiki, M.; Yamanaka, S.; Nomura, K. Adv. Synth. Catal. 2005, 347, 433. (l) Nomura, K.; Liu, J.; Padmanabhan, S.; Kitiyanan, B. J. Mol. Catal. A: Chem. 2007, 267, 1.

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Scheme 1. Synthesis of ansa-(Cyclopentadienyl)(phenoxy) Titanium Complexes

solution (Figure 4). As a result H(Cp) resonances of 1b were observed as two triplets at δ 6.12 and 6.97 ppm, whereas for CH3 protons of the Cp ring in 1d two singlet resonances at δ 2.15 and 2.34 ppm were found. Moreover, both CH3 groups of the bridging CMe2 (1b) and SiMe2 (1d) moieties were found to be equivalent, displaying in both cases a singlet resonance at δ 1.50 (1b) and 0.55 ppm (1d) (Figure 5). The effect of stabilized energy of the flipping mechanism of 1d was calculated by ab initio molecular orbital theory and density functional theory,11 and the results are shown in Figure 6. It is revealed that C1 states are more stable than the Cs state by 18.5 kcal/mol. This value is similar to the activation energy of ethylene insertion into a Ti-C bond (16-17 kcal/mol) and of a β-hydrogen elimination reaction (11) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A. Jr.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A. GAUSSIAN 98, Revision A.9; Gaussian, Inc.: Pittsburgh, PA, 1998, . (12) Kawamura-Kuribayashi, H.; Miyatake, T. J. Organomet. Chem. 2003, 674, 73.

(17-18 kcal/mol).12 These results indicate that the phenoxy ring of the PHENICS system easily flips during polymerization. Ethylene/1-Hexene Copolymerization Catalyzed by Complexes 1a-1d. PHENICS complexes 1a-1d were applied as catalyst precursors for copolymerization of ethylene and 1-hexene upon activation with AliBu3 (TIBA) and [Ph3C][B(C6F5)4] (TB). The polymerization results are summarized in Table 3. Upon activation with TIBA/TB, the silylenebridged PHENICS complexes (1c and 1d) showed higher activities than the isopropylidene-bridged ones (1a and 1b). Moreover, the activities observed for 1a-1d were higher than those reported for the [{Me2Si(C5Me4)(NtBu)}TiCl2] (CGC)/TIBA/TB system. Molecular weights of copolymers obtained with 1c or 1d/TIBA/TB systems were not only found to be 4-7 times higher than the values for copolymers obtained with isopropylidene-bridged PHENICS complexes 1a and 1b used as catalyst precursors but also indicate a single-site catalytic process. Complexes 1b-1d gave copolymers having relatively narrow molecular weight distribution (Mw/Mn = 2.0-2.6), indicating that these complexes act as single-site polymerization catalysts. To investigate the polymerization behavior of the catalyst system at high temperature, copolymerization at 180 C was carried out. The PHENICS catalyst system showed excellent catalytic features with an activity of 6000 kg mol(cat)-1 h-1 within only 2 min, whereas the CGC-Ti/TIBA/AB (AB = [PhNHMe2][B(C6F5)4]) catalyst did not show polymerization activity under analogous conditions (Table 5). At 180 C the higher molecular weight polymers were

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Nabika et al. Table 2. Selected Bond Distances (A˚) and Angles (deg) for 1b and 1d [{Me2CCp(6-tBu-4-MeC6H2O)}TiCl2], 1b

Figure 2. Molecular structure of complex [{Me2CCp(6-tBu-4MeC6H2O)}TiCl2] (1b) (50% probability ellipsoids). The hydrogen atoms are omitted for clarity.

Ti1-Cl1 Ti1-O1 Ti1-C15 Ti1-C17 C1-C19 C2-O1 Cp(plane)-Ti1

2.272(1) 1.795(2) 2.324(2) 2.343(3) 1.546(3) 1.384(2) 1.997(2)

Ti1-Cl2 Ti1-C14 Ti1-C16 Ti1-C18 C14-C19

2.263(1) 2.309(2) 2.359(3) 2.321(3) 1.522(3)

Cl1-Ti1-Cl2 Cl2-Ti1-O1 Cl2-Ti1-C16 C1-C19-C14 Cp(center)-Ti1-O1

104.46(4) 104.82(7) 86.00(9) 111.5(2) 109.1(calcd)

Cl1-Ti1-O1 Cl1-Ti1-C17 Ti1-O1-C2 C12-C19-C13 Cp—Ph a

103.51(7) 97.85(9) 145.1(2) 108.0(2) 63.0(1)

[{Me2SiCp*(6-tBu-4-MeC6H2O)}TiCl2], 1d Ti1-Cl1 Ti1-O1 Ti1-C15 Ti1-C17 C1-Si1 C2-O1 Cp(plane)-Ti1

2.261(2) 1.784(2) 2.292(3) 2.394(3) 1.877(3) 1.363(3) 2.008(2)

Ti1-Cl2 Ti1-C14 Ti1-C16 Ti1-C18 Si1-C14

2.255(2) 2.290(3) 2.387(4) 2.359(3) 1.881(3)

Cl1-Ti1-Cl2 103.15(7) Cl1-Ti1-O1 103.86(9) Cl2-Ti1-O1 102.46(9) Cl1-Ti1-C17 93.5(1) Cl2-Ti1-C16 83.7(1) Ti1-O1-C2 155.7(2) C1-Si1-C14 110.2(1) C12-Si1-C13 106.4(2) a 68.2(2) Cp(center)-Ti1-O1 117.0(calcd) Cp—Ph a Angles between a cyclopentadienyl plane and a phenoxy plane.

Figure 3. Molecular structure of complex [{Me2Si(C5Me4) (6-tBu-4-MeC6H2O)}TiCl2] (1d) (50% probability ellipsoids). The hydrogen atoms are omitted for clarity. Table 1. Summary of Crystallographic Data for 1b and 1d

empirical formula fw cryst size, mm3 cryst syst a/A˚ b/A˚ c/A˚ V/A˚3 space group Z Dcalc/g cm-3 F000 μ(Mo KR)/cm-1 temp/C 2θmax/deg no. of reflns no. of observns no. of variables refln/param ratio residuals: R1 (I > 2σ(I)) residuals: R Residuals: wR2 GOF max/min peak/e A˚-3

1b

1d

C19H24OCl2Ti 387.20 0.1  0.2  0.2 monoclinic 18.437(4) 10.675(2) 10.002(4) 1954.7(8) P21/a (#14) 4 1.316 808.00 7.123 23.0 54.9 4580 4444 233 19.07 0.0593 0.1070 0.1789 1.015 0.46/-1.01

C22H32OCl2SiTi 459.30 0.2  0.2  0.2 monoclinic 10.010(2) 22.969(3) 10.416(1) 2380.0(6) P21/n (#14) 4 1.282 968.00 6.437 23.0 54.9 5731 5445 253 21.52 0.0540 0.1250 0.1686 1.026 0.70/-0.52

obtained with the complexes possessing bulkier substituents in the ortho position, and these polymers had narrow molecular weight distribution (Mw/Mn = 2.0-2.4), indicating that the PHENICS complexes act as a single-site polymerization catalyst even at high temperature (Table 5 and Figure 7).

Figure 4. Possible flipping mechanism in solution for 1d accounting for the symmetrical NMR with a pattern for the corresponding CH3 resonances.

The stability of the active species and the relative reactivity of 1-hexene with PHENICS catalyst systems are affected by substituents on a cyclopentadienyl ring and the ortho position of a phenoxy ring. PHENICS complexes 1b-d, having a substituent at the ortho position of the phenoxy ring, are relatively stable, since copolymers obtained with 1b-d/ TIBA/TB showed narrow molecular weight distribution (Mw/Mn = 2.0-2.6). On the other hand, non-ortho-substituted complex 1a, thought to have the widest coordination gap aperture (CGA) angle,14 is less stable because a copolymer obtained with 1a/TIBA/TB showed a broad molecular weight distribution (Mw/Mn = 4.7). The DSC data on the left side of Figure 7 showed that the copolymer obtained from 1a/TIBA/TB is entirely different from other copolymers from 1b-d/TIBA/TB. The sharp endothermic peak of 120 C shown in the copolymer from 1a/TIBA/TB is caused by the formation of the copolymer with relatively low (13) Mirabella, F. M.; Bafna, A. J. Polym. Sci.: B: Polym. Phys. 2002, 40, 1637. (14) Togni, A; Halterman, R. L. Metallocenes: Synthesis Reactivity Applications; Wiley-VCH: Weinheim, 1998, .

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Figure 5. Stability differences for Cs and C1 symmetries of 1d at the RHF/LANL2DZ level calculated with Gaussian 98. Hydrogen atoms of ligands are not shown for clarity.

Figure 6. DSC data for the ethylene-1-hexene copolymers produced with 1a-d/TIBA/TB (Al/Ti = 2000; left) and 1a/TIBA/TB (Al/Ti = 50, 125, 500; right). Table 3. Polymerization of Ethylene and 1-Hexene Catalyzed by PHENICS-Titanium Complexes with TIBA/TBa

Table 4. Polymerization of Ethylene and 1-Hexene Catalyzed by 1a/TB with Various Ratios of TIBAa

entry catalyst activityb Mwc  10-3 Mw/Mnc 1-hexene contentd

entry

1 2 3 4 5

1a 1880 34 4.7 12.3 1b 7800 37 2.0 13.7 1c 13 000 156 2.6 12.6 1d 27 200 193 2.4 10.1 CGC 1040 234 2.7 7.9 a Conditions: toluene 195 mL, 1-hexene 5 mL, ethylene 0.60 MPa, polymerization time 60 min, temperature 80 C, catalyst 0.50 μmol, TIBA 1.0 mmol, TB 3.0 μmol. b In kg mol(cat)-1 h-1. c Determined by GPC with polystyrene standards. d Mol %, determined by 13C NMR spectroscopy.16

1-hexene content. By considering the 1-hexene content determined by means of 13C NMR spectroscopy of the copolymer from 1a/TIBA/TB, it is reasonable to think that the copolymer is a mixture of a low crystalline polymer with high 1-hexene content with a high melting point polymer. The proportion of high melting point polymer seemed to be changed by the amount of TIBA used in the polymerizations (Table 4 and the right side of Figure 7, suggesting that the active species made to high melting point polymer

Al/Ti

activityb

1-hexene contentc

6 7 8

50 2800 34.6 125 1800 28.1 500 2070 8.9 a Conditions: toluene; 195 mL, 1-hexene; 5 mL, ethylene; 0.60 MPa, polymerization time; 60 min, temperature; 80 C, catalyst; 2.0 μmol, TB; 6.0 μmol. b In kg mol(cat)-1h-1. c Mol%, determined by IR spectroscopy.17

is generated to act on 1a and TIBA. One plausible explanation of this result is the generation of (2-alkoxybenzylcyclopentadienyl)titanium active species (Scheme 2).15 The difference of CGA angle attributable to the difference of the substituents on a cyclopentadienyl ring and the ortho position of a phenoxy ring may influence the ease of the approach of 1-hexene to the Ti center, leading to the different relative reactivity of 1-hexene in the case of 1b, 1c, and 1d. (15) Nabika, M.; Miyatake, T. Kobunshi Ronbunshu 2002, 59, 382.

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Table 5. High-Temperature Polymerization of Ethylene and 1-Hexene Catalyzed by PHENICS-Titanium Complexes with TIBA/ABa 1-hexene entry catalyst activityb Mwc  10-3 Mw/Mnc Tm (C) contentd 9 10 11 12

1b 640 18.9 2.0 62.3 11.0 1c 2000 66.2 2.0 80.2 8.4 1d 6000 60.5 2.4 89.6 7.7 CGC a Conditions: cyclohexane 185 mL, 1-hexene 15 mL, ethylene 2.50 MPa, polymerization time 2 min, temperature 180 C, catalyst 0.50 μmol, TIBA 1.0 mmol, AB 3.0 μmol. b In kg mol(cat)-1 h-1. c Determined by GPC with polystyrene standards. d Mol %, determined by 13 C NMR spectroscopy.16

Figure 7. GPC data for the ethylene-1-hexene copolymers produced with 1b-d/TiBA/TB at 180 C (see entries 8-10, Table 5). Scheme 2. Possible Formation of Active Species from 1a/TiBA/ TB

Conclusion We have prepared a series of ansa-cyclopentadienyl-phenoxy titanium complexes (PHENICS) [{Me2CCp(OC6H2-3R-5-R0 )}TiCl2] (1a, R = R0 = H; 1b, R = tBu, R0 = Me) and [{Me2C(C5Me4)(OC6H2-3-R00 -5-Me)}TiCl2] (1c, R00 = iPr; 1d, R00 = tBu; 1e, R00 = Adm). The identities of the complexes were confirmed by 1H and 13C NMR spectra, elemental analyses, mass spectroscopy, and X-ray crystallography (1b and 1d). The X-ray structures reveal that the dihedral angles of cyclopentadienyl and phenoxy moieties in 1b and 1d are 63.0 (1b) and 68.2 (1d), indicating a distortion from their mutual perpendicular arrangement, whereas the symmetrical patterns of the 1H NMR spectra indicate a dynamic behavior in solution. These complexes exhibited good catalytic activities for copolymerization of ethylene and 1-hexene upon activation with TIBA/borate. Particularly, the PHENICS complexes with a bulky substituent at the ortho position of the phenoxy moiety showed excellent catalytic behavior (27 200 kg mol(cat)-1 h-1 at 80 C, 6000 kg mol(cat)-1 h-1 at 180 C).

Experimental Section General Comments. Materials. All manipulations of airand moisture-sensitive compounds were performed under an

Nabika et al. inert atmosphere of dry nitrogen using a VAC drybox or standard Schlenk-line techniques. Solvents were purchased from Kanto Chemicals Co., Ltd. (anhydrous grade). Toluene-d8 and CDCl3 were stored in a drybox over molecular sieves. 2-Bromophenol, 2-tert-butyl-4-methylphenol, and tert-butylamine were purchased from Tokyo Chemical Industry Co., Ltd. 2-Adamantyl-4-methylphenol and 6,60 -dimethylfulvene were purchased from Sigma-Aldrich Co. 1,2,3,4-Tetramethylcyclopentadiene, bromine, N-bromosuccinimide (NBS), potassium hydroxide, sodium hydroxide, and n-butyllithium (1.55 or 1.62 M solution in hexane) were purchased from Kanto Chemicals Co., Ltd. Titanium tetrachloride and Wakogel C-100 were purchased from Wako Pure Chemical Industries, Ltd. Triisobutylaluminum (TIBA) (1 M solution in toluene) was purchased from Tosoh Finechem. Co. Ltd. Triphenylcarbenium tetrakis (pentafluorophenyl)borate (TB) and dimethylanilinium tetrakis (pentafluorophenyl)borate (AB) were purchased from Asahi Glass Co. Ltd. and used as 0.0050 mol/L and 0.0010 mol/L toluene solutions. NMR spectra were recorded on a JEOL EX270 (1H, 270 MHz; 13 C, 68 MHz) or JEOL AL400 (1H, 400 MHz; 13C, 100 MHz) at 25 C unless otherwise stated. The structure of the copolymer was examined by means of 13C NMR spectroscopy at 135 C with an estimated error of (0.2 mol % using a Bruker ARX400 spectrometer (100 MHz). The copolymer sample was prepared in sample tubes 10 mm in diameter by dissolving 250 mg of the polymer in 3.0 mL of o-dichlorobenzene containing 0.3 mL of o-dichlorobenzene-d4.16 A part of the 1-hexene content of ethylene/1-hexene copolymers was measured using a JASCO IR-810 spectrometer with an estimated error of (0.5 mol %.17 Mass spectra were recorded using a Hewlett-Packard HP-5970B instrument. High-resolution mass spectra were recorded using a JEOL JMS-T100GC spectrometer, and elemental analyses were performed using an ELEMENTAR element analyzer at Sumika Chemical Analysis Service Ltd. Molecular weights (Mw and Mn) and molecular weight distributions (Mw/Mn) were determined by high-temperature GPC and calibrated using polystyrene standards. GPC analysis was performed with a HLC8121GPC/HT liquid chromatograph at 152 C in o-dichlorobenzene using a TSK-GEL GMHHR-H(20)HT column. Differential scanning calorimetry (DSC) melting curves were recorded at a rate of 5 C/min using a Seiko SSC-5200 instrument. The melting point (Tm) of copolymers was measured from the second heating. 1-Bromo-2-methoxybenzene (4a). In a 50 mL flask fitted with a stirrer 2-bromophenol 5a (1.03 g, 5.92 mmol) was dissolved in acetonitrile (20 mL), and KOH (0.51 g, 9.07 mmol) was then added. Subsequently CH3I (1.90 mL, 4.33 g, 30.5 mmol) was slowly added with a syringe, and the resulting reaction mixture was stirred for 12 h at room temperature. Thereafter, the solvent was removed under vacuum, and the resulting residue was extracted three times with n-hexane (3  20 mL). 4a was isolated as a pale yellow oil upon removal of n-hexane from the extracts (0.97 g, 89%). 1H NMR (CD2Cl2): δ 3.89 (s, 3H), 6.7-7.7 (m, 4H). 2-(Cyclopentadienyl)(lithium)-2-(2-methoxyphenyl)propane (2a-Li). In a 100 mL flask fitted with a stirrer 4a (4.50 g, 24.1 mmol) was dissolved in diethyl ether (20 mL), and the solution was cooled to -70 C. n-BuLi (24.0 mmol, 1.54 g) was then slowly added, and the resulting mixture was stirred at -70 C for 2 h. To the reaction mixture was further added 6,6-dimethylfulvene (2.64 g, 24.0 mmol) in diethyl ether (10 mL), and the resulting mixture was slowly brought up to room temperature, whereby a white solid deposited, which was then collected by filtration. It was washed three times with n-hexane (3  10 mL) (16) de Pooter, M.; Smith, P. B.; Dohrer, K. K.; Bennet, K. F.; Meadows, M. D.; Smith, C. G.; Schouwenaars, H. P.; Geerards, R. A. J. Appl. Polym. Sci. 1991, 42, 399. (17) Blitz, J. P.; McFaddin, D. C. J. Appl. Polym. Sci. 1994, 51, 13.

Article and then dried under reduced pressure to give a white powder (4.0 g, 75%). A small portion of the white powder was hydrolyzed with dilute hydrochloric acid and subjected to 1H NMR spectroscopy. 1H NMR (C6D6): δ 1.66 (s, 3H), 1.75 (s, 3H), 3.26 (s, 3H), 5.9-7.5 (m, 9H). GC-MS m/z: 216 (M+). On the basis of the 1H NMR and GC-MS data the organic substance obtained by hydrolysis was identified as 2-cyclopentadienyl-2-(2-methoxyphenyl)propane (2a), and consequently the white powder was identified as its lithium salt 2a-Li. Isopropylidene(cyclopentadienyl)(2-phenoxy)titanium dichloride (1a). In a 50 mL flask fitted with a stirrer 2a-Li (0.20 g, 0.92 mmol) was added to n-hexane (15 mL), and the mixture was cooled to -70 C. Subsequently a solution of TiCl4 (0.10 mL, 0.17 g, 0.91 mmol) in n-hexane (5 mL) was slowly added with a syringe. The resulting mixture was slowly brought up to room temperature. The mixture turned light brown, and a brown solid deposited. It was separated by filtration, and the solid was extracted three times with n-hexane (3  10 mL). Hexane solutions were combined and concentrated to a volume of 10 mL, and the concentrated solution was allowed to stand at -20 C for 12 h. The yellow needles, which deposited after that time, were collected by filtration and dried under reduced pressure to yield 1a (0.10 g, 34%). 1H NMR (CD2Cl2): δ 1.62 (s, 6H), 6.17 (t, 3JHH = 2.9 Hz, 2H), 6.80 (d, 3JHH = 8.6 Hz, 1H), 7.00 (t, 3 JHH = 2.9 Hz, 2H), 7.20 (t, 3JHH = 7.3 Hz, 1H), 7.21 (t, 3JHH = 7.3 Hz, 1H), 7.58 (d, 3JHH = 9.6 Hz, 1H). 13C NMR (CD2Cl2): δ 29.8, 37.3, 114.9, 119.8, 122.4, 125.6, 126.7, 127.8, 136.5, 143.8, 162.7. 2-Bromo-6-tert-butyl-4-methylphenol (5b). In a 500 mL flask fitted with a stirrer 2-tert-butyl-4-methylphenol (6b) (20.1 g, 123.0 mmol) was dissolved in toluene (150 mL), and tertbutylamine (25.9 mL, 18.0 g, 246.0 mmol) was then added. The resulting solution was cooled to -70 C, and Br2 (10.5 mL, 32.6 g, 204.0 mmol) was slowly added with a syringe. The resulting solution was stirred at -70 C for 2 h. Thereafter the solution was brought up to room temperature and washed three times with 10% hydrochloric acid (3  10 mL). The organic layer was dried over anhydrous Na2SO4. The solvent was then removed on a rotary evaporator to give an orange oil. The crude oil was purified by column chromatography (Wako Gel C-100, silica gel, n-hexane). Removal of the solvent afforded 5b as a colorless oil (18.4 g, 62%). 1H NMR (CD2Cl2): δ 1.32 (s, 9H), 2.19 (s, 3H), 6.98 (s, 1H), 7.11 (s, 1H). 3-tert-Butyl-2-methoxy-5-methylbromobenzene (4b). Compound 4b was prepared in a similar manner to 4a (94% yield). 1H NMR (CD2Cl2): δ 1.31 (s, 9H), 2.20 (s, 3H), 3.81 (s, 3H), 7.02 (s, 1H), 7.18 (s, 1H). GC-MS m/z: 256 (M+), 258 (M++2). 2-(Cyclopentadienyl)-2-(3-tert-butyl-2-methoxy-5-methylphenyl)propanelithium (2b). In a 100 mL flask fitted with a stirrer 4b (4.61 g,17.9 mmol) was dissolved in diethyl ether (10 mL), and the solution was cooled to -70 C. n-BuLi (18.0 mmol, 1.15 g) was slowly added, and the resulting solution was stirred at -70 C for 2 h. To this solution was added a solution of 6, 6-dimethylfulvene (1.91 g, 18.0 mmol) in diethyl ether (10 mL), and the resulting mixture was slowly brought up to room temperature. Subsequently, diluted hydrochloric acid (5 wt %, 25 mL) was added to the mixture. The solution was extracted three times with n-hexane (3  30 mL). The extracts were dried over anhydrous Na2SO4, and the volatiles were then removed on a rotary evaporator to give a yellow oil. The crude oil was purified by column chromatography (Wako Gel C-100, silica gel, n-hexane). Removal of the solvent afforded 2b as a pale yellow oil (3.0 g, 60%). 1H NMR (CD2Cl2): δ 1.48 (s, 9H), 1.71 (s, 6H), 2.26 (s, 3H), 3.26 (s, 3H), 6.07-6.62 (m, 5H), 7.22-7.28 (m, 2H). GC-MS m/z: 284 (M+). 2-(Cyclopentadienyl)-2-(3-tert-butyl-2-methoxy-5-methylphenyl)propanelithium (2b-Li). In a 50 mL flask fitted with a stirrer 2b (0.28 g, 0.99 mmol) was dissolved in n-hexane (20 mL), and the solution was cooled to -70 C. n-BuLi (1.09 mmol, 0.070 g) was slowly added, and the resulting mixture was slowly brought

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up to room temperature, whereby a white precipitate deposited. The solid was collected by filtration, washed three times with n-hexane (3  10 mL), and dried under reduced pressure to give 2b-Li as a white solid (0.28 g, 98%). Isopropylidene(cyclopentadienyl)(3-tert-butyl-5-methyl-2-phenoxy)titanium Dichloride (1b). Complex 1b was prepared in a similar manner to 1a (34% yield). 1H NMR (CDCl3): δ 1.42 (s, 6H), 1.50 (s, 9H), 2.38 (s, 3H), 6.12 (t, 3JHH = 2.7 Hz, 2H), 6.97 (t, 3JHH = 2.7 Hz, 2H), 7.05 (s, 1H), 7.22 (s, 1H). HR-MS m/z: calcd 386.068, found 386.068. Mp: 247 C (dec). Anal. Calcd for C19H24Cl2OTi (387.18): C, 58.9; H, 6.25. Found: C, 59.4; H, 6.21. 3-Isopropyl-5-methyl-2-methoxybromobenzene (4c). In a 100 mL flask fitted with a stirrer 2-isopropyl-4-methylphenol (6c) (5.20 g, 34.6 mmol) was dissolved in acetone (50 mL), and to this solution was then slowly added NBS (6.62 g, 37.2 mmol). The resulting solution was stirred for 3 h. Distilled water (2.4 g), CH3I (7.5 g, 52.9 mmol), and NaOH (3.3 g, 82.5 mmol) were added, and the reaction mixture was stirred for 12 h. The solution was extracted three times with distilled water (3  25 mL) and then once with n-hexane (12 mL). The organic layer was dried over anhydrous Na2SO4. The solvent was then removed on a rotary evaporator to give a yellow oil (7.55 g, 88%). GC-MS m/z: 242 (M+), 244 (M++2). (3-Isopropyl-2-methoxy-5-methylphenyl)chlorodimethylsilane (3c). In a 200 mL flask fitted with a stirrer 4c (6.9 g, 28.2 mmol) was dissolved in THF (10 mL) and n-hexane (50 mL), and the mixture was cooled to -40 C. n-BuLi (29.6 mmol, 1.90 g) was then slowly added over 10 min, and the resulting mixture was kept at -40 C for 1 h. This mixture was added dropwise at -60 C into a solution of dichlorodimethylsilane (144 mmol, 17.5 mL) in n-hexane (67 mL). The resulting mixture was brought up to room temperature over 4 h and further stirred for 12 h. The solvents and the excess of dichlorodimethylsilane were distilled off under reduced pressure, and the residue was extracted with n-hexane. Removal of the volatiles afforded 3c as a yellow oil (6.65 g, 84%, GC purity: 87%). GC-MS m/z: 256 (M+), 258 (M++2). Dimethyl(3-isopropyl-2-methoxy-5-methylphenyl)(2,3,4,5-tetramethylcyclopentadienyl)silane (2c). In a 100 mL flask fitted with a stirrer 3c (4.84 g, 18.9 mmol) was dissolved in THF (70 mL), and tetramethylcyclopentadienyllithium (C5Me4HLi) (2.54 g, 19.8 mmol) was then added. The resulting mixture was stirred at room temperature for 12 h. The solvent was removed under reduced pressure, and the residue was extracted with n-hexane. Removal of the volatiles afforded 2c as a yellow oil (7.10 g, 98%, GC purity: 90%). GC-MS m/z: 342 (M+). Dimethylsilyl(2,3,4,5-tetramethylcyclopentadienyl)(3-isopropyl-5-methyl-2-phenoxy)titanium Dichloride (1c). In a 200 mL flask fitted with a stirrer 2c (2.51 g, 7.32 mmol) was dissolved in n-hexane (30 mL), and n-BuLi (11.0 mmol, 0.70 g) was then dropwise added. The resulting mixture was stirred at room temperature for 12 h. To this mixture was added dropwise TiCl4 (1.47 g, 7.75 mmol) in toluene (60 mL). The resulting mixture was heated at 95 C for 9 h. It was then filtered, and the solvents were removed under vacuum. 1c was obtained as dark brown crystals by recrystallization from a toluene/n-hexane solution (0.12 g, 4%). 1H NMR (toluene-d8): δ 0.39 (s, 6H), 1.23 (d, 3JHH = 6.9 Hz, 6H), 1.88 (s, 6H), 2.02 (s, 6H), 2.22 (s, 3H), 3.58 (m, 1H), 7.04 (br, 1H), 7.08 (br, 1H). HR-MS m/z: calcd 444.092, found 444.088. (3-tert-Butyl-2-methoxy-5-methylphenyl)chlorodimethylsilane (3d). Compound 3d was prepared in a similar manner to 3c (84%). 1H NMR (CDCl3): δ 0.68 (s, 6H), 1.32 (s, 9H), 2.23 (s, 3H), 3.70 (s, 3H), 7.20 (s, 1H), 7.21 (s, 1H). Dimethyl(3-tert-butyl-2-methoxy-5-methylphenyl)(2,3,4,5-tetramethylcyclopentadienyl)silane (2d). In a 100 mL flask fitted with a stirrer 3d (5.24 g, 19.3 mmol) was dissolved in THF (50 mL), and C5Me4HLi (2.73 g, 21.3 mmol) was added at -35 C. The resulting mixture was brought up to room

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temperature over 2 h and further stirred at room temperature for 10 h. The solvent was removed under reduced pressure, and the residue was extracted with n-hexane. Removal of the volatiles afforded 2d as a yellow oil (6.69 g, 97%). 1H NMR (C6D6): δ 0.31 (s, 6H), 1.49 (s, 9H), 1.81 (s, 6H), 1.89 (s, 6H), 2.22 (s, 3H), 3.60 (s, 3H), 5.23 (s, 3H), 7.23 (br, 2H). Dimethylsilyl(2,3,4,5-tetramethylcyclopentadienyl)(3-tert-butyl-5-methyl-2-phenoxy)titanium Dichloride (1d). Method A. In a 100 mL flask fitted with a stirrer 2d (1.28 g, 3.60 mmol) was dissolved in n-hexane (20 mL), and n-BuLi (5.4 mmol, 0.35 g) was added dropwise at 0 C. The resulting mixture was brought up to room temperature over 2 h and further stirred at room temperature for 12 h. After that time a white solid deposited. It was then filtered and washed three times with n-hexane. The white powder was cooled to -70 C in n-hexane (20 mL), and a solution of TiCl4 (0.68 g, 3.58 mmol) in n-hexane (10 mL) was then added dropwise. The resulting mixture was brought up to room temperature over 3 h and further stirred at room temperature for 12 h. It was then filtered, and the solvents were removed under vacuum. 1d was obtained as columnar orange crystals by recrystallization from n-hexane (0.03 g, 2%). 1 H NMR (CDCl3): δ 0.55 (s, 6H), 1.39 (s, 9H), 2.13 (s, 6H), 2.33 (s, 6H), 2.37 (s, 3H), 7.12 (s, 1H), 7.15 (s, 1H). 13C NMR (CDCl3): δ 1.2, 14.5, 16.3, 22.5, 31.2, 36.3, 120.2, 130.6, 131.5, 133.9, 135.5, 137.4, 140.8, 142.3, 167.7. HR-MS m/z: calcd 458.108, found 458.107. Mp: 241 C (dec). Anal. Calcd for C22H32Cl2OSiTi (459.37): C, 57.5; H, 7.02. Found: C, 57.8; H, 7.03. Method B. In a 200 mL flask fitted with a stirrer 2d (9.96 g, 27.9 mmol) was dissolved in toluene (100 mL), and triethylamine (6.30 g, 62.3 mmol) was added. The solution was cooled to -70 C, and n-BuLi (31.0 mmol, 1.99 g) was then dropwise added. The resulting mixture was brought up to room temperature over 2 h and further stirred at room temperature for 12 h. Upon cooling to 0 C, TiCl4 (4.82 g, 25.4 mmol) in toluene (50 mL) was dropwise added. The resulting mixture was brought up to room temperature over 1 h and then refluxed for 10 h. It was then filtered and the solvents were removed under vacuum. 1d was obtained as columnar orange crystals by recrystallization from toluene/n-hexane (3.46 g, 27%). 3-Adamantyl-5-methyl-2-methoxybromobenzene (4e). In a similar manner to that for 4c, the reaction of 6e with NBS gave 2e (97%). GC-MS m/z: 335 (M+), 337 (M++2). (3-Adamantyl-2-methoxy-5-methylphenyl)chlorodimethylsilane (3e). In a 200 mL flask fitted with a stirrer 4e (2.84 g, 8.48 mmol) was dissolved in THF/n-hexane (6.5/47 mL), and the solution was cooled to 0 C. n-BuLi (8.85 mmol, 0.57 g) was then slowly added over 5 min. The resulting mixture was kept at 0 C for 1 h and then added dropwise at -70 C to a solution of dichlorodimethylsilane (43 mmol, 5.2 mL) in n-hexane (28 mL). The resulting mixture was brought up to room temperature over 4 h and further stirred for 12 h. The solvents and the excess of dichlorodimethylsilane were distilled off under reduced pressure, and the residue was extracted with n-hexane. Removal of the volatiles afforded 3e as a yellow powder (2.93 g, 82%, GC purity: 83%). GC-MS m/z: 348 (M+), 350 (M++2). Dimethyl(3-adamantyl-2-methoxy-5-methylphenyl)(2,3,4,5-tetramethylcyclopentadienyl)silane (2e). In a 100 mL flask fitted with a stirrer 3e (2.44 g, 6.99 mmol) was dissolved in THF (60 mL), and C5Me4HLi (0.98 g, 7.65 mmol) was then added. The resulting mixture was stirred at room temperature for 12 h. THF was removed under reduced pressure, and the residue was extracted with n-hexane. Removal of the volatiles afforded 2e as a yellow oil (3.55 g, 99%, GC purity: 87%). GC-MS m/z: 434 (M+).

Nabika et al. Dimethylsilyl(2,3,4,5-tetramethylcyclopentadienyl)(3-adamantyl-5-methyl-2- phenoxy)titanium Dichloride (1e). In a 200 mL flask fitted with a stirrer 2e (3.07 g, 7.06 mmol) was dissolved in toluene (36 mL), and the solution was cooled to 0 C. n-BuLi (10.6 mmol, 0.68 g) was then dropwise added. The resulting mixture was brought up to room temperature over 30 min and further stirred at room temperature for 12 h. Subsequently it was dropwise added to TiCl4 (1.34 g, 7.06 mmol) in toluene (10 mL). The reaction mixture was heated at 100 C for 10 h. It was then filtered, and the solvents were removed under vacuum. 1e was obtained as dark brown crystals by recrystallization from n-hexane (0.09 g, 5%). 1H NMR (toluene-d8): δ 0.39 (s, 6H), 0.89 (m, 6H), 1.94 (s, 6H), 2.00 (s, 6H), 2.03 (m, 3H), 2.26 (d, 3JHH = 2.4 Hz, 6H), 2.30 (s, 3H), 7.02 (s, 1H), 7.14 (s, 1H). HR-MS m/z: calcd 536.155, found 536.151. Mp: 299 C (dec). Typical Ethylene/1-Hexene Copolymerization Experiment. An autoclave with an inner volume of 0.4 L was dried under vacuum and then purged with argon. After charging with 5 mL of 1-hexene and 195 mL of toluene, the autoclave was heated to 80 C. Subsequently ethylene was fed with the pressure adjusted at 0.60 MPa. After the system was stabilized 0.25 mmol of TIBA was added to the mixture. Subsequently 0.5 μmol of 1a and 3.0 μmol of TB were added. Polymerization was carried out for 60 min, while the temperature was kept at 80 C. The polymerization reaction mixture was quenched with methanol (5 mL). A few minutes later the gas was vented, and the reaction mixture was then poured into 400 mL of methanol with 5 mL of hydrochloric acid (1 mol/L). The copolymer obtained was collected by filtration, washed with fresh methanol, and dried under high vacuum at 80 C for 8 h. X-ray Crystal Structure Determination. Relevant crystallographic data are summarized in Table 1. The X-ray diffraction data of the complexes 1b and 1d were collected on an EnrafNonius CAD4 diffractometer with Mo KR radiation (graphite monochromator, λ = 0.71069 A˚). Preparation procedures for the crystals are given above. For more details see the Supporting Information. Computational Calculations. Geometries of 1d were obtained using a restricted Hartree-Fock (RHF) method. Energy values were also calculated by the standard LANL2DZ basis set. 18 All calculations were performed with the GAUSSIAN98 program.11

Acknowledgment. We dedicate this paper to the late Professor Akira Miyashita (Saitama University, deceased November 2003) in honor of his remarkable contribution to this research. The authors thank Mr. Seiki Kiuchi and Mr. Saburo Ohta for experimental assistance, Ms. Misao Miki for X-ray crystallography analysis, Mr. Hideji Sekine and Mr. Takashi Kohara for NMR analyses, and Mr. Yoshio Yagi and Mr. Mitsuharu Mitobe for GPC analyses. We express also our sincere gratitude to Mr. Tatsuya Miyatake, Dr. Hidenori Hanaoka, Dr. Kotohiro Nomura, and Dr. Masahiro Kakugo for their helpful discussions throughout this research project. Supporting Information Available: Text and tables giving X-ray crystal data for 1b and 1d. This material is available free of charge via the Internet at http://pubs.acs.org. (18) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.