Organometallics 2004, 23, 3267-3269
3267
Synthesis, Structure, and Polymerization Behavior of Bridged Zirconocenes Bearing Seven-Membered Rings Naoshi Iwama,*,† Hideshi Uchino,† Yasuko T. Osano,‡ and Toshihiko Sugano§ Polymerization Technical Center, Japan Polypropylene Corp., Yokkaichi, Mie, 510-0848, Japan, Center for Analytical Chemistry and Science, Mitsubishi Chemical Group Science and Technology Research Center, Inc., Aoba-ku, Yokohama, 227-8502, Japan, and Research & Development Division, Japan Polychem Corp., Yokkaichi, Mie, 510-0848, Japan Received January 27, 2004
Bridged zirconocenes bearing seven-membered rings dichlorodimethylsilylenebis(2-methyl4-phenyl-4-H-azulenyl)zirconium (3a) and dichlorodimethylsilylenebis(2-methyl-4-phenyl4-H-5,6,7,8-tetrahydroazulenyl)zirconium (4) were synthesized. A silylene-bridged ligand was obtained by the reaction of 2-methylazulene, phenyllithium, and dichlorodimethylsilane. After lithiation of the ligand by n-butyllithium, reaction with zirconium tetrachloride gave a rac and meso mixture of 3. The structure was confirmed by X-ray crystallographic analysis. It was found that both of the phenyl groups at the 4-position are oriented outside toward the metal center and the seven-membered ring is not planar. Furthermore, reaction with hydrogen in the presence of platinum oxide gave 4. When activated with methylaluminoxane, these complexes showed high catalytic activity for polymerization of propene to give isotactic polypropylene. Introduction Since the discovery of ansa-zirconocene/methylaluminoxane catalyst producing isotactic polypropylene,1 many efforts have been focused on the improvement of polymerization performance in terms of activity, melting point, and molecular weight of the polymer.2 In the course of development, a number of bridged type complexes have been synthesized. In particular, dimethylsilyl-bridged bis(indenyl) zirconocenes have received much interest in isospecific polymerization of propene and extensively investigated by Spaleck et al.3 and Brintzinger et al.4 They found that 2-methyl- and 4-arylsubstituted complexes gave high melting point and high molecular weight polypropylene when two indenyl groups are bridged at the 1-position. Recently we have reported the synthesis of a novel 4,4′-dimethylsilylbridged bis(indenyl) zirconocene that gave highly isotactic polypropylene.5 However, only a few complexes * To whom correspondence should be addressed. E-mail: Iwama.
[email protected]. † Japan Polypropylene Corp. ‡ Mitsubishi Chemical Group Science and Technology Research Center, Inc. § Japan Polychem Corp. (1) (a) Ewen, J. A. J. Am. Chem. Soc. 1984, 106, 6355. (b) Kaminsky, W.; Ku¨lper, K.; Brintzinger, H.-H.; Wild, F. Angew. Chem., Int. Ed. Engl. 1985, 24, 507. (2) (a) Mo¨hring, P. C.; Coville, N. J. J. Organomet. Chem. 1994, 479, 1. (b) Brintzinger, H.-H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (c) Resconi, L.; Cavallo, L.; Fait, A.; Piemontesi, F. Chem. Rev. 2000, 100, 1253. (3) (a) Spaleck, W.; Antberg, M.; Rohrmann, J.; Winter, A.; Bachmann, B.; Kiprof, P.; Behm, J.; Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1992, 31, 1347. (b) Spaleck, W.; Ku¨ber, F.; Winter, A.; Rohrmann, J.; Bachmann, B.; Antberg, M.; Dolle, V.; Paulus, E. F. Organometallics 1994, 13, 954. (4) (a) Stehling, U.; Diebold, J.; Kirsten, R.; Ro¨ll, W.; Brintzinger, H.-H.; Ju¨ngling, S.; Mu¨lhaupt, R.; Langhauser, F. Organometallics 1994, 13, 964. (b) Schneider, N.; Huttenloch, M. E.; Stehling, U.; Kirsten, R.; Schaper, F.; Brintzinger, H.-H. Organometallics 1997, 16, 6. 3413.
bearing a larger ring than a six-membered ring have been reported so far.6 Recently, we have synthesized bridged zirconocenes bearing a seven-membered ring structure, i.e., an azulenyl structure. We have been interested in the structural difference between a planar rigid indenyl ring and a nonplanar azulenyl ring and in the difference in the polymerization behavior between them. Results and Discussion 2-Methylazulene was synthesized by the method reported previously.7 Tropolone was used as a starting compound, and a four-step synthesis gave 2-methylazulene in a good yield. Treatment of 2-methylazulene with 1 equiv of phenyllithium gave a lithium salt of 2methyl-4-phenyldihydroazulene (1) quantitatively. When quenched with H2O, 2-methyl-4-phenyldihydroazulene was obtained as a mixture of double-bond isomers. The reaction of 1 with chloranyl gave 2-methyl-4-phneylazulene by dehydrogenation, which confirmed exclusive addition of a phenyl group at the 4-posotion. It was reported that the reaction of azulene and alkyl- or aryllithium gave the corresponding lithium salt of dihydroazulene by addition at the 4-position.8 The lithium salt (1) was treated with 0.5 equiv of dichlorodimethylsilane. From the reaction mixture, bis(2-methyl-4phenyldihydroazulenyl)dimethylsilane (2) was separa(5) Kato, T.; Uchino, H.; Iwama, N.; Imaeda, K.; Kashimoto, M.; Osano, Y.; Sugano, T. In Metalorganic Catalysts for Synthesis and Polymerization; Kaminsky, W., Ed.; Springer-Verlag: Berlin, 1999; p 192. (6) (a) Herrmann, W. A.; Anwander, R.; Riepl, H.; Scherer, W.; Whitaker, C. R. Organometallics 1993, 12, 4342. (b) Polo, E.; Bellabarba, R. M.; Prini, G.; Traverso, O.; Green, M. L. H. J. Organomet. Chem. 1999, 577, 211. (c) Burger, P.; Hung, H.; Evertz, K.; Brintzinger, H.-H. J. Organomet. Chem. 1989, 378, 153. (7) (a) Yasunami M.; Takase, K. JP Patent, 62-207232, 1987. (b) Doering W. E.; Hiskey, C. F. J. Am. Chem. Soc. 1952, 74, 5688. (8) (a) Hafner K.; Weldes, H. Angew. Chem. 1955, 67, 302. (b) Hafner K.; Weldes, H. Ann. 1957, 606, 90.
10.1021/om040012j CCC: $27.50 © 2004 American Chemical Society Publication on Web 05/19/2004
3268
Organometallics, Vol. 23, No. 13, 2004
Iwama et al. Scheme 1
Table 1. Selected Bond Lengths (Å) and Angles (deg) 5 (indenyl)3b
3a (azulenyl) Zr-Cl Zr-Cp Cl-Zr-Cl Cp-Zr-Cp
2.422(1) 2.239(2) 100.43(5) 128.4 (2)
2.419(1) 2.243(4) 96.8(1) 128.5
Scheme 2
Figure 1. ORTEP drawing of 3a. Thermal ellipsoids are shown at the 50% probability level. The hydrogen atoms and a toluene molecule of crystallization are omitted for clarity.
ted by silica gel chromatography in 38% yield, and the unreacted 2-methyl-4-phenyl-dihydroazulene was recovered. The ligand 2 was obtained as a diastereomer mixture, and the 1H NMR spectrum of 2 showed a complicated pattern owing to the mixture of diastereomers. In particular, several peaks corresponding to the dimethylsilyl group were observed in the 1H NMR from 0 to -1 ppm, indicating the formation of several diastereomers. Without further purification, 2 was treated with 2 equiv of n-butyllithium in diethyl ether to give the dilithium salt of 2. By subsequent treatment with zirconium tetrachloride in a mixture of toluene and diethyl ether, dichlorodimethylsilylenebis(2-methyl-4-phenyl-4H-azulenyl)zirconium was obtained as a mixture of rac (3a) and meso (3b). Assignment of these two isomers in the 1H NMR spectrum was done by NOE measurement. The rac isomer (3a) showed one singlet corresponding to the dimethylsilyl proton at 0.51 ppm and one singlet corresponding to the 2-methyl proton at 1.92 ppm. These two peaks exhibited NOE correlations showing C2 symmetry. On the other hand, the meso isomer (3b) showed two singlets (0.44 and 0.59 ppm) and one singlet (1.84 ppm) and an NOE was observed between only one signal of the dimethylsilyl proton and that of the 2-methyl proton, indicating C1 symmetry. A single crystal of 3a suitable for X-ray crystallographic analysis was obtained from the mixture of rac and meso isomers. Toluene molecule used as a solvent was contained in the crystal; the ratio of toluene molecule to the complex was 1. An ORTEP drawing of 3a is shown in Figure 1. It was found that both phenyl groups at the 4-position of the azulenyl moiety are outside the azulenyl plane and the seven-membered ring of the azulenyl moiety is not planar, as we expected. In
Table 2. Polymerization of Propene (co-cat: MAO)a complex
activityb
Tm (°C)
Mw
Mw/Mn
mmmm (%)
3a 4 5c
166 000 680 000 1 200 000
151 156 157
350 000 370 000 729 000
2.7 2.1
96.8 96.0 95.2
a Conditions: liquid propene, 70 °C, 1 h, Al/Zr ) 10 000 (3a, 4), Al/Zr ) 15 000 (5). b g polymer/g complex. c Data from ref 3b.
comparison with the structure of the corresponding bisindenyl zirconocene, Me2Si(2-methyl-4-phenylindenyl)2ZrCl2 (5),3b the direction of the phenyl group at the 4-position in 3a is different from that of 5 by the conformational change of the ring to which the phenyl groups were attached, whereas the structures around the zirconium atom are similar in both, as shown in Table 1. The Cl-Zr-Cl angle of 3a (100.43(5)°) is slightly larger than that in 5 (96.8(1)°). In the course of the synthesis of 3, other isomers (3c, 3d), which could arise from different configurations of the phenyl group at the 4-position, were not observed. Only the two isomers (3a, 3b) were formed probably because of steric repulsion as shown in Scheme 2. In addition to 3, another bridged zirconocene (4) was obtained quantitatively by the reaction of 3a with hydrogen in the presence of platinum oxide. The propene polymerization of bis-azulenyl zirconocenes (3a, 4) and referenced bis-indenyl zirconocene (5) has been examined using methylaluminoxane as cocatalyst. When activated with MAO, these complexes (3a, 4) produced active catalysts for polymerization of propene to give isotactic polypropylene. The polymerization behavior is summarized in Table 2. Activities and molecular weights of the polypropylene obtained by bis-azulenyl zirconocenes (3a, 4) are lower than those of referenced zirconocene (5). On the other hand, all three zirconocenes gave highly isotactic polypropylene; that is,
Bridged Zirconocenes with Seven-Membered Rings
mmmm, meso pentad fraction, is more than 95%. In all polymers obtained by 3a, 4, and 5 regioinversion was observed. The direction of the phenyl group at the 4-position is changed due to the ring structure in the three zirconocenes. The indenyl ring (six-membered ring) is the most rigid in these three zirconocenes, and the sevenmembered ring is more flexible. The seven-membered ring in 4 is more flexible compared to 3a because of the saturated structure. Thus it is expected that stereo- and/ or regiospecificity can be varied between these complexes through the interaction of the phenyl group at the 4-position and the growing polymer chain. In the comparison of 3a and 4, the activity and melting point of polymer were improved by the use of hydrogenated bis-azulenyl complex (4). Experimental Section General Procedures. All manipulations were performed under a nitrogen atmosphere. THF and diethyl ether were distilled from sodium/benzophenone. Dehydrated hexane, toluene, and dichloromethane were purchased from Kanto Chemical Co. and used without further purification. Dichlorodimethylsilane was freshly distilled prior to use. 1H NMR spectra were recorded on a Varian Gemini-300 and a JEOL GSX-400 spectrometer at 300 and 400 MHz, respectively. Mass spectra of zirconocenes were measured on a Hitachi M-2500 using negative chemical ionization (CI) mode (isobutane). Synthesis of Me2Si(2-Me-4-Ph-4H-Azu)2ZrCl2 (3a). 2-Methylazulene was prepared by the reported method from tropolone.7 A solution of 2-methylazulene (2.22 g, 15.7 mmol) in hexane (30 mL) was treated with a solution of phenyllithium in cyclohexane/diethyl ether (15.6 mL, 15.7 mmol, 1.0 M) at 0 °C. After stirring for 1 h at room temperature, the violet color in solution disappeared and the lithium salt of 2-methyl-4phenyldihydroazulene precipitated. The reaction mixture was cooled to -78 °C, and THF (30 mL) and dichlorodimethylsilane (0.95 mL, 7.83 mmol) were added sequentially. The mixture was warmed to 50 °C and stirred at this temperature for 1.5 h and at room temperature overnight. After quenching with a solution of ammonium chloride, the organic phase was separated and dried over MgSO4, and the solvent was removed. The crude product was purified by column chromatography with silica gel (with hexane/dichloromethane (5:1) as eluent) to give bis(2-methyl-4-phenyldihydroazulenyl)dimethylsilane (2) (1.48 g, 38%) as a diastereomer mixture. 2: 1H NMR (300 MHz, CDCl3) δ -0.8 to -0.2 (6 H, Me2Si), 2.0-2.1 (6 H, 2-Me), 3.6-4.0 (4 H), 5.5-5.7 (4 H), 6.1-6.3 (4 H), 6.6-6.9 (2 H), 7.37.4 (10 H, arom). To a solution of 2 (768 mg, 1.55 mmol) in diethyl ether (15 mL) was added a solution of n-butyllithum in hexane (1.98 mL, 3.3 mmol, 1.64 M) at -78 °C. The mixture was stirred at this temperature for 12 h and warmed to room temperature. After removal of solvent, the crude solid of the dilithium salt of 2 was washed with hexane and dissolved in a mixture of toluene (20 mL) and diethyl ether (0.5 mL). The resulting mixture was cooled, and zirconium tetrachloride (325 mg, 1.37 mmol) was added at -60 °C. After warming gradually to room temperature over 15 h with stirring, the resulting suspension was decanted to remove insoluble LiCl, concentrated, and washed with hexane to give a rac/meso mixture of 3 (150 mg). Recrystallization from toluene allowed isolation of pure 3a. A rac/meso mixture of 3 (310 mg) was recrystallized repeatedly to give pure 3a as a pale yellow crystalline solid (38 mg, 12%). 3a: 1H NMR (300 MHz, C6D6) δ 0.51 (s, 6 H, SiMe2), 1.92 (s, 6 H, 2-Me), 5.30 (br d, 2 H), 5.75-5.95 (m, 6 H), 6.13 (s, 2 H), 6.68 (d, J ) 14 Hz, 2 H), 7.05-7.20 (m 2 H, arom), 7.56 (d, J ) 7 Hz, 8 H); negative CI-MS, parent ion at m/z 656 (92Zr35Cl, M-) with appropriate isotope ratios. Anal. Found: C, 68.47; H, 5.86. Calcd (C36H34Cl2SiZr‚C7H8): C, 68.95; H, 5.65. Synthesis of Me2Si(2-Me-4-Ph-4H-5,6,7,8-tetrahydroAzu)2ZrCl2 (4). A dry 0.1 L steel autoclave was charged with
Organometallics, Vol. 23, No. 13, 2004 3269 nitrogen. A solution of 3a (92 mg, 0.14 mmol) in dichloromethane (10 mL) and a suspension of platinum oxide (20 mg) in dichloromethane (3 mL) were introduced to the reactor. The mixture was steered under hydrogen pressure of 0.5 MPa for 20 min. Platinum oxide was removed by decantation, and the reactant solution was concentrated and washed with a mixture of hexane (6 mL) and dichloromethane (2 mL) to give pure 4 as a colorless crystalline solid (84 mg, 90%). 4: 1H NMR (300 MHz, CDCl3) δ 0.93 (s, 6 H, SiMe2), 1.102.30 (m, 14 H, CH2), 2.02 (s, 6 H, 2-Me), 2.80-2.90 (m, 2 H), 4.23 (d, J ) 11 Hz, 2 H), 5.78 (s, 2 H), 7.20-7.42 (m, 10 H, arom); negative CI-MS, parent ion at m/z 664 (92Zr35Cl, M-) with appropriate isotope ratios. Anal. Found: C, 67.81; H, 6.53. Calcd (C36H42Cl2SiZr‚C7H8): C, 68.22; H, 6.66. Crystallographic Studies. The X-ray crystallographic analysis was performed using the crystal with the size 0.2 × 0.2 × 0.1 mm, obtained by recrystallization from hexane/ toluene/dichloromethane at room temperature. The X-ray diffraction data were collected on a four-circle diffractometer (Enraf-NONIUS CAD4) with the ω/θ scan mode using Mo KR radiation (40 kV, 40 mA). The structure was solved by direct methods (SHELXS-86)10a and refined by full matrix leastsquares technique (SHELXL-93).10b A total of 3584 reflections were measured, of which 3444 unique reflections were used in the structure refinement. The final R factor was 0.040 for 3444 reflections. Crystal data: fw ) C21.5H21ClSi0.5Zr0.5, monoclinic system, space group A2/n, a ) 27.410(7) Å, b ) 9.751(5) Å, c ) 14.500(7) Å, β ) 106.97(3)°, V ) 3707(3) Å3, Z ) 4, Dcalc ) 1.342 g/cm3, R ) 0.0324, Rw ) 0.0352 for 3451 unique reflection (Fo > σ(Fo)). Propene Polymerization. A dry 2 L steel reactor was charged with nitrogen and liquid propene (1500 mL) at room temperature. Then a solution of methylaluminoxane in toluene (2.0 mL, 4.0 mmol, Al/Zr ) 10000, MMAO purchased from Tosoh Finechem Corp.) and a solution of metallocene in toluene (0.5 mL, 0.4 µmol) were added to the reactor at room temperature. The reactor was heated to 70 °C within 10 min and kept for 1 h. The reaction was stopped by venting the unreacted monomer and cooling. The yield of polymer was determined by weighing. Polymer Analysis Procedures. Molecular masses were determined on a Waters 150C at 135 °C in 1,2-dichlorobenzene. The melting point of the polymer (Tm) was determined on a Dupont TA2000 at a heating rate of 10 °C/min. The result of the second scan was reported. The 13C NMR analysis of the polymer was performed on a JEOL GSX-400 at 130 °C. The sample was obtained with polymer (250 mg) dissolved in 1,2dichlorobenzene (2.0 mL) and C6D6 (0.5 mL), and the stereoregularity of the polymer was evaluated as described previously.9
Acknowledgment. We thank Dr. T. Mori (Mitsubishi Chemical Corp.) for help with the NMR experiments. Note Added after ASAP. In the version of this paper posted on the Web May 19, 2004, the mmmm value for complex 5 in Table 2 mistakenly appeared in the wrong column. The version of the table that now appears is the correct one. Supporting Information Available: Crystal data for 3a. This material is available free of charge via the Internet at http://pubs.acs.org. OM040012J (9) Grassi, A.; Zambelli, A.; Resconi, L.; Albizzati, E.; Mazzochi, R. Macromolecules 1988, 21, 617. (10) (a) Sheldrick, G. M. SHELXS-86, Program for Structure Solution; University of Go¨ttingen: Go¨ttingen, Germany, 1986. (b) Sheldrick, G. M. SHELXS-93, Program for Structure Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1993.
