3 CHAPTER THREE
3.5 EXPERIMENTAL SECTION
General Procedure
All air and/or moisture sensitive materials were handled using high-vacuum line, swivel frit assembly, glovebox, Schlenk and cannula techniques under a nitrogen or argon atmosphere.11 Argon was purified by passage through MnO on vermiculite and activated 4 Å molecular sieves. All glassware was oven dried before use. Solvents were dried and degassed over sodium benzophenone ketyl or over titanocene12.
Unless otherwise mentioned, all starting materials were purchased from Aldrich and used as received. Trifluoroacetyl imidazole and heptafluoropentyl imidazole were purchased from Alltech in 0.5 mL ampules. (S)-2 was synthesized by the route previously reported for the racemic counterpart,13,14 except that (S)-LiMNCp15 was used in place of the racemate. Methylaluminoxane (MAO) was purchased from Albemarle.
All volatiles were removed in vacuo to give a white powder. The white MAO solid was dried at 150 ºC for 12 h at high vacuum. Tetradecane was stirred over pieces of Na metal for 24 h at room temperature. Tetradecane was vacuum distilled using a Vigoreaux column into a dry Schlenk flask and stored in the drybox. Toluene used for polymerization was vacuum transferred into a small Schlenk flask from sodium benzophenone ketyl and stored over sieves in the drybox. The trialkyl silyl protected olefins were dried over LAH for 2 d, filtered in the drybox, and stored over sieves in the drybox.
Instrumentation. NMR spectra were recorded on the Varian Mercury VX300 (1H, 300 MHz, 13C, 75.5 MHz) spectrometer. Gas chromatographs were obtained on an Agilent 6890 Series gas chromatography using a 30 m x 0.25 mm, γ-cyclodextrin trifluoroacetyl “Chiraldex-TA” column from Advanced Separations Technology.
[2-(3-Buten)](triethyl silyl) ether, “3BOTES” 50. In a 100-mL round bottom flask, 3-buten-2-ol (5.0 g, 69.3 mmol) and imidazole (10.4 g, 152.5 mmol) were weighed and dissolved with 50 mL of methylene chloride. The flask was sealed with a septum.
While cooling in an ice bath, chlorotriethyl silane (12.5 g, 83.2 mmol) was syringe added to the solution. The reaction was slightly exothermic. The thick white slurry was vigorously stirred at room temperature overnight. The slurry was transferred to a separatory funnel and washed with saturated aqueous solution of NH4Cl (50 mL), NaHCO3 (50 mL), and brine (50 mL). The organic layer was dried over MgSO4 and filtered. About half of the solvent was removed by rotary evaporator. The solution distilled at ambient pressure to remove methylene chloride and low boiling impurities.
The product was vacuum distilled (20 mmHg, 54 ºC). 1H NMR (300 MHz, toluene-d8, δ): 0.05 (s, 6H, SiCH3), 0.97 (s, 9H, t-Bu), 1.15 (d, J = 6.0 Hz, 3H, CH3), 4.14 (quint, J = 6.0 Hz, 1H, CH), 4.92 (dd, J = 10.2, 1.2 Hz, 1H, trans (H)(H)C=), 5.16 (dd, J = 17.1, 1.2, 1H, cis (H)(H)C=), 5.76 (m, 1H, =C(H)(C)).
[2-(3-Buten)](tert-butyl dimethyl silyl) ether, “3BOTBS” 51. The product was prepared in the same manner as 50 with 3-buten-2-ol (5.0 g, 69.3 mmol), imidazole (10.4 g, 152.5 mmol), 50 mL of methylene chloride, and tert-butyl chlorodimethyl silane (12.5
g, 83.2 mmol). The product was distilled under vacuum (20 mm Hg, 66-68ºC) to collect 22.82 g (82%) of clear and colorless liquid. 1H NMR (300 MHz, toluene-d8, δ): 0.575 (q, J = 8.1 Hz, 6H, CH2), 1.00 (t, J = 8.1 Hz, 9H, SiCH2CH3), 1.175 (d, J = 6.3 Hz, 3H, CH3), 4.164 (quint, J = 6.0 Hz, 1H, CH), 4.915 (dd, J = 10.2, 1.2 Hz, 1H, trans (H)(H)C=), 5.222 (dd, J = 17.1, 1.2, 1H, cis (H)(H)C=), 5.801 (m, 1H, =C(H)(C)).
[2-(4-Penten)](tert-butyl dimethyl silyl) ether, “4POTBS” 52. The product was prepared in the same manner as 50 with 4-pentene-2-ol (5.0 g, 58.1 mmol), imidazole (8.7 g, 127.8 mmol), 50 mL of methylene chloride, and chlorodimethyl tert-butyl silane (9.6 g, 63.9 mmol). The product was distilled under vacuum (20 mm Hg, 63ºC) to collect clear and colorless liquid. 1H NMR (300 MHz, toluene-d8, δ): 0.04 (s, 6H, SiCH3), 0.96 (s, 9H, t-Bu), 1.06 (d, J = 6.0 Hz, 3H, CH3), 2.09 (m, 1H, CH2), 2.15 (m, 1H, CH2), 3.70 (sextet, J = 6.3 Hz, 1H, CH), 4.99 (m, 1H, trans (H)(H)C=), 5.04 (m, 1H, cis (H)(H)C=), 5.80 (m, 1H, =C(H)(C)).
(S)-Mosher ester derivatives of 3-buten-2-ol. 1H NMR (300 MHz, C6D6, δ):
0.99 (d, J = 6.3 Hz, 3H, CHCH3), 1.03 (d, J = 6.3 Hz, 3H, CHCH3), 3.20 (s, 6H, OCH3), 4.82 (dd, 2H, vinyl H), 5.05 (dd, 2H, vinyl H), 5.42 (m, 2H, vinyl H), 5.50 (m, 2H, CHCH3), 7.10, 7.70 (m’s, 10 H, Ar H). 19F NMR (500 MHz, CDCl3, δ): -71.81 (s, 3F, CF3); –71.84 (s, 3F, CF3).
(S)-Mosher ester derivatives of 4-penten-2-ol. 1H NMR (300 MHz, C6D6, δ):
0.92 (d, J = 6.3 Hz, 3H, CHCH3), 0.97 (d, J = 6.3 Hz, 3H, CHCH3), 1.95 (m, 2H, CH2),
2.10 (m, 2H, CH2), 3.20 (s, 3H, OCH3), 3.22 (s, 3H, OCH3), 4.78, 4.85, 4.95, 5.05 (m’s, 6H, vinyl H), 5.50 (m’s, 2H, CHCH3), 7.10, 7.70 (m’s, 10 H, Ar H). 19F NMR (500 MHz, CDCl3, δ): –71.95 (s, 3F, CF3), –71.89 (s, 3F, CF3).
Polymerization procedure. The typical polymerization procedure was carried out as follows. In the drybox, MAO (~600 mg), tetradecane (~1 g, distilled from Na), and olefin were weighed into a 20-mL vial. The vial was capped, and the mixture was allowed to stir at room temperature for 1 h to ensure removal of all traces of moisture.
Prior to catalyst injection, an aliquot was transferred to a vial. The vial was capped, and out of the drybox, the aliquot was quenched with n-butanol. The catalyst solution was added via syringe (0.50 mL of a 30 x 10-3 M solution in toluene is typical). The solution usually changed from colorless to yellow upon catalyst addition. When the desired conversion was reached, a final aliquot was taken. The reaction vial was removed from the drybox and placed in a –10 ºC bath. While cooling in a cold bath, methanol (~18 mL) was added dropwise to the vial, to quench the reaction. The aliquots were used for the GC determination of conversion, with tetradecane acting as the internal standard for integration.
REFERENCES AND NOTES
1 Giannini, U.; Brückner, G.; Pellino, E.; Cassata, A. Polym. Lett. 1967, 5, 527.
2 Giannini, U.; Brückner, G.; Pellino, E.; Cassata, A. J. Polym. Sci., Part C 1968, 22, 157.
3 (a) Aaltonen, P.; Löfgren, B. Macromolecules 1995, 28, 5353. (b) Aaltonen, P.; Fink, G.; Löfgren, B.; Seppala, J. Macromolecules 1996, 29, 5255.
4 Hakala, K.; Helaja, T.; Löfgren, B. J. Polym. Sci., Part A: Polym. Chem. 2000, 38, 1966.
5 Marques, M. M.; Correia, S. G.; Asceso, J. R.; Ribeiro, A. F. G.; Gomes, P. T.; Dias, A.
R.; Foster, P.; Rausch, M. D.; Chien, J. C.W. J. Polym. Sci., Part A: Polym. Chem.
1999, 37, 2457.
6 (a) Arit, K. P.; Binsack, R.; Grogo, U.; Neuray, D. U. S. Patent 4423196, 1983; Chem.
Abstr. 1984, 100, 139804.
7 Imuta, J.; Kashiwa, N. J. Am. Chem. Soc. 2002, 124, 1176.
8 Hagihara, H.; Tsuchihara, K.; Sugiyama, J.; Takeuchi, K.; Shiono, T. Macromolecules 2004, 37, 5145.
9 Corey, E. J.; Venkateswarlu, A. J. Am. Chem. Soc. 1972, 94, 6190.
10 Almqvist, F.; Frejd, T. J. Org. Chem. 1996, 61, 6947.
11 Burger, B. J.; Bercaw, J. E. Experimental Organometallic Chemistry; ACS symposium Series No. 357; Wayda, A. L., Darensbourg, M. Y. eds.; American Chemical
Society: Washington, D.C. 1987; ch. 4.
12 Marvich, R. H.; Brintzinger, H. H. J. Am. Chem. Soc. 1971, 93, 203.
13 Veghini, D.; Henling, L. M.; Terry J. Burkhardt, T. J.; Bercaw, J. E. J. Am. Chem.
Soc., 1999, 121, 564.
14 Herzog, T. A.; Zubris, D. L.; Bercaw, J. E. J. Am. Chem. Soc. 1996, 118, 11988.
15 Baar, C. R.; Levy, C. J.; Min, E. Y.; Henling, L. M.; Day, M. W.; Bercaw, J. E. J. Am.
Chem. Soc. 2004, 126, 8216.