organometallics 1995,14, 2415-2421
2415
Dehydrohomopolymerization and Dehydrocopolymerization of New Alkylsilanes: Synthesis of Poly(3-aryl-l-silabutanes) Hee-Gweon Woo,**tSook-Yeon Kim,? Mi-Kyung Han,? Eun Jeong Cho,$ and I1 Nam Jung$ Department of Chemistry, Chonnam National University, Kwangju 500-757, Korea, and Organometallic Chemistry Laboratory, Korea Institute of Science & Technology, P.O. Box 131 Cheongryang, Seoul 130-650, Korea Received November 7, 1994@ 3-Aryl-l-silabutanes such as 3-phenyl-l-silabutane (11, 3-tolyl-l-silabutane (2), 3-(2,5dimethylphenyl)-l-silabutane(3),3-chlorophenyl-l-silabutane(4), 3-(chloro-p-tolyl)-l-silabutane (51, 3-(phenoxyphenyl)-l-silabutane(61, 3-naphthyl-l-silabutane (7), and bis(1-sila3-buty1)benzene (8)were prepared in 62-98% yields by reduction of the corresponding 3-aryl1,l-dichloro-l-silabutaneswith LiAlH4. The dehydrohomopolymerization and dehydrocopolymerization of the monomer silanes were carried out with the Cp2MCldRed-Al (M = Ti, Hf) combined catalyst system. The molecular weight of the polymers produced ranged from 600 to 1300 (vs polystyrene) with degree of polymerization (DP) equal to 3-16 and with polydispersity index (PDI) equal to 1.1-3.8. A set of the monomer silanes dehydrocoupled to produce a copolymer. The polymerization of bis(silabuty1)benzene ( 8 )seemed to initially produce a low molecular weight of polymer, which then underwent a n extensive cross-linking reaction of backbone Si-H bonds, leading to insoluble polymer.
Introduction
thermochemical results.6 A major disadvantage of the metallocene-catalyzed dehydrocoupling method is the production of low molecular weights of p ~ l y s i l a n e s . ~ , ~ Considerable efforts have been made t o increase the molecular weight of the poly~ilanes.~-l~ The 29SiNMR technique has been useful in analyzing polysilane chain microstructure.ll The structures of all polysilanes synthesized via the dehydrocoupling method are predominantly random atactic ones, although some diastereomeric selection was observed in certain cases.12 To date, silanes which have been employed in the literature have been mostly arylsilanes. There are few J~ reports on the dehydrocoupling of a l k y l ~ i l a n e s . ~To
Polysilanes with unusual optical and electronic properties due to a-conjugation along the silicon backbone have received a copious amount of attention as ceramic precursors, third-order NLO materials, deep-W photoresists, photoconductors, and phot~initiators.l-~ The conventional synthetic method to get high-molecularweight polysilanes to date has been the Wurtz coupling reaction of dichlorosilanes, which are intolerant of some functional groups and have other limitations for controlling stereochemistry and molecular weight. Harrod's recent discovery of group 4 metallocene catalyzed dehydropolymerization made great progress (5) (a) Woo, H.-G.; Tilley, T. D. J . A m . Chem. Soc. 1989,111, 3757. (b) Woo, H.-G.; Tilley, T. D. J . Am. Chem. SOC.1989,111, 8043. ( c ) Two mechanisms have in poly(organosilane)~ynthesis.~ Woo, H.-G.; Heyn, R. H.; Tilley, T. D. J . A m . Chem. SOC.1992,114, been suggested: (1)oxidative-additiodreductive-elimi5698. (d) Woo, H.-G.; Walzer, J. F.; Tilley, T. D. J . A m . Chem. Soc. 1992,114,7047. (e) Banovetz, J . P.; Suzuki, H.; Waymouth, R. M. nation sequences via the intermediacy of transitionOrganometallics 1993,12,4700. metal silylene complexes4 and (2) four-center a-bond (6)(a) Nolan, S. P.; Porchia, M.; Marks, T. J. Organometallics 1991, 10,1450.(b) Forsyth, C. M.; Nolan, S. P.; Marks, T. J. Organometallics metathesis processes among silicon, hydrogen, and a do 1991,10,2543. metal center via the intermediacy of transition-metal (7)(a) Woo, H.-G.; Walzer, J. F.; Tilley, T. D. Macromolecules 1991, silyl and hydride c~mplexes.~ While theoretical calcula24,6863. (b) Imori, T.; Woo, H.-G.; Walzer, J. F.; Tilley, T. D. Chem. Mater. 1993,5,1487. tion backs up the first the second mech(8)(a) Harrod, J. F. In Transformation of Organometallics into anism is supported by many model r e a ~ t i o n s ~ and ~ , ~ , ~ JCommon ~ ~ and Exotic Materials: Design and Activation; Laine, R. M., + Chonnam National University. Korea Institute of Science & Technology. @Abstractpublished in Advance ACS Abstracts, April 1, 1995. (1)Miller, R. D.; Michl, J . Chem. Rev. 1989,89,1359. (2)West, R.J . Organomet. Chem. 1986,300,327. (3)Ziegler, J. M.; Fearon, F. W. G. Silicon-Based Polymer Science; American Chemical Society: Washington, DC, 1990. (4)(a) Aitken, C.; Harrod, J. F.; Gill, U. S. Can. J . Chem. 1987,65, 1804. (b) Harrod, J. F.; Yun, S.S. Organometallics 1987,6, 1381.( c ) Aitken, C.; Barry, J.-P.; Gauvin, F.; Harrod, J. F.; Malek, A.; Rousseau, D. Organometallics 1989, 8, 1732. (d) Harrod, J . F.; Ziegler, T.; Tschinke, V.Organometallics 1990,9,897.(e) Woo, H.-G.; Harrod, J. F.; HBnique, J.; Samuel, E. Organometallics 1993,12,2883.(0 Britten, J.; Mu, Y.; Harrod, J. F.; Polowin, J.; Baird, M. C.; Samuel, E. Organometallics 1993,12,2672.
*
Ed.; NATO AS1 Series E: Appl. Sci. No. 141; Martinus NijhoE Amsterdam, 1988;p 103. (b) Mu, Y.; Harrod, J. F. In Inorganic and Organometallic Polymers and Oligomers; Harrod, J. F., Laine, R. M., Eds.; Kluwer Academic: Dordrecht, The Netherlands, 1991;p 23. (9)Woo, H.-G.; Harrod, J . F. Manuscript in preparation. (10)Tilley, T. D. Acc. Chem. Res. 1993,26,22. (11)(a) Wolff, A. R.; Nozue, I.; Maxka, J.; West, R. J . Polym. Sci., Part A: Polym. Chem. 1988,26, 701. (b) Maxka, J.; Mitter, F. K; Powell, D. R.; West, R. Organometallics 1991,10,660. (12)(a) Banovetz, J . P.; Stein, K. M.; Waymouth, R. M. Organometallics 1991,10, 3430. (b) Corey, J. Y.; Huhmann, J. L.; Zhu, X.-H. Organometallics 1993, 12, 1121. ( c ) Woo, H.-G.; Harrod, J. F. Manuscript in preparation. (13)(a) Campbell, W. H.; Hilty, T. K Organometallics 1989,8,2615. (b) Hengge, E.; Weinberger, M.; Jammegg, C. J . Organomet. Chem. 1991,410, C1. ( c ) Hengge, E.; Weinberger, M. J . Organomet. Chem. 1992,433, 21.
0276-733319512314-2415$09.00/0 0 1995 American Chemical Society
2416 Organometallics, Vol. 14,No. 5, 1995
Woo et al.
ing! In the absence of diethyl ether solvent, A1C13 can catalyze silane redistribution reactions to produce SiH4, which is a n explosive gas upon contact with air. Therefore, the LiAlH4 reduction of the silicon chlorides should be performed in ether and quenched properly with a n isopropyl alcohol solution o f aqueous HCl and then with water.) All the silanes obtained here are stereoisomeric mixtures. Synthesis of 3-Phenyl-1-silabutane (1). To a diethyl ether suspension of lithium aluminum hydride (3.07 g, 0.08 mol) in 70 mL of diethyl ether in a 250 mL three-necked, round-bottomed flask equipped with a reflux condenser topped with an inletloutlet tube was slowly added 3-phenyl-1,ldichloro-1-silabutane (10.1 g, 0.04 mol) in 70 mL of diethyl ether in a pressure-equalizing addition funnel. After addition was completed, the mixture was stirred at room temperature Experimental Section for 3 h. The reaction mixture was filtered, cooled t o 0 "C, slowly quenched with an HCl/isopropyl alcohol solution (20 General Considerations. All reactions and manipulations mu150 mL), and then poured into ice-water. The resulting were performed under prepurified nitrogen using Schlenk slurry was extracted with diethyl ether. The combined ether techniques. Dry, oxygen-free solvents were employed throughphases were washed twice with water, dried over anhydrous out. Glassware was flame-dried or oven-dried before use. MgS04,and concentrated on a rotary vacuum evaporator. The Elemental analyses were performed by the Advanced Analysis solution was then fractionally distilled at 74-76 "C/20 mmHg Center of the Korea Institute of Science and Technology, Seoul, to yield 1 (3.70 g, 62%). Anal. Calcd for SiC9H14: C, 71.92; Korea. Infrared spectra were obtained using a Perkin-Elmer H, 9.31. Found: C, 71.72; H, 9.42. IR (neat, KBr, cm-'1: 2155 1600 Series FT-IR or a Nicolet 520P FT-IR spectrometer. s ( Y S ~ H ) ,910 s ( d s , ~ ) . 'H NMR (6, CDC13, 300 MHz): 1.14Electronic spectra were acquired using an IBM 9420 UV-vis 1.20 (m, 2 H, CHz), 1.36 (d, J = 3.5 Hz, 3 H, CH3),2.92 (sextet, spectrophotometer. Proton NMR spectra were recorded on a J = 3.6 Hz, 1 H, CH), 3.43 (t, J = 3.9 Hz, 3 H, SiH), 7.19Varian Gemini 300 spectrometer using CDC13/CHC13 as a 7.35 (m, 5 H, ArH). l3C(lH}NMR (6, CDC13,75.5 MHz): 16.16 reference at 7.24 ppm downfield from TMS. Carbon-13 NMR (SiCHZ), 24.54 (CH3), 37.77 (CHI, 126.13, 126.55, 128.43, spectra were obtained using a Varian Gemini 300 (operating 148.26 (Arc).GCMS ( m l e (relative intensity)): 150 (23) (M+), at 75.5 MHz) spectrometer with CDC13 as a reference at 77.0 135 (18), 119 (51, 109 (4), 108 (171,107 (661,105 (100),91(16), ppm. Gas chromatography (GC) analyses were performed 79 (12), 77 (181, 72 (13), 65 (41, 51 (8). using a Varian 3300 chromatograph equipped with a packed Synthesis of 3-tolyl-1-silabutane (2): 98% yield; bp 36column (10% OV-101 on Chromosorb, W/AW-DMCS 1.5 m x 38 "U0.6 mmHg. Anal. Calcd for SiCIOH16: C, 73.09; H, 9.81. in. 0.d.) in conjunction with a flame ionization detector. GC/ Found: C, 73.22; H, 9.99. IR (neat, KBr, cm-'): 2150 s ( Y S ~ H ) , MS data were obtained using a Hewlett-Packard 589011 910 s (Bs,H). 'H NMR (6, CDC13, 300 MHz): 1.00-1.19 (m, 2 chromatograph (HP-5,5% phenylmethylsiloxane, 0.25 mm i.d. H, CHz), 1.32, 1.31,1.32 (d, J = 7.0 Hz, 3 H, CH3), 2.33, 2.34, x 30.0 m, film thickness 0.25 pm) connected to a Hewlett2.35 (s, 3 H, Ar-CH31, 3.17, 2.86, 2.87 (sextet, J = 7.0 Hz, 1 Packard 5972A mass selective detector. Gel permeation H, CH), 3.44, 3.40, 3.41 (t, J = 4.0 Hz, 3 H, SiH), 7.00-7.27 chromatography (GPC) was carried out on a Waters Millipore (m, 4 H, ArH) (isomer ratio 0rtho:meta:para = 23:35:42). 13CGPC liquid chromatograph. The calibrant (monodisperse {'HI NMR ( 6 ,CDC13, 75.5 MHz): 15.31, 16.11, 16.12 (SiCHZ), polystyrene) and the sample were dissolved in toluene and 19.46, 21.48, 20.98 (CH31, 23.71, 24.45, 24.63 (CH31, 32.31, separately eluted from an Ultrastyragel GPC column series 37.28, 37.61 (CH), 123.46, 124.96, 125.68, 126.25, 126.36, (sequence 500, lo3, lo4 A columns). Molecular weights were 126.80, 127.29, 128.25, 129.03, 130.23,135.51 ( A r c ) . GCMS extrapolated from the calibration curve derived from the ( m l e (relative intensity)): 164 (16) (M+), 122 (431, 121 (661, polystyrene standard. Data analyses were carried out using 120 (16), 119 (loo), 117 (301, 115 (261, 105 (281, 103 (111, 93 a Waters Data Module 570. An approximate estimate for the (141, 91 (69), 77 (25), 72 (121, 65 (191, 51 (12). average degree of polymerization (DP) for the polysilane chains Synthesis of 3-(2,S-dimethylphenyl)-l-silabutane (3): was made by simply calculating the differences in molecular 96% yield; bp 62-65 "C/0.6 mmHg. Anal. Calcd for weight between styrene and silylene monomer units. TherSiC11Hle: C, 74.08; H, 10.17. Found: C, 74.21; H, 10.22. IR mogravimetric analysis (TGA) of the polymer sample was (neat, KBr, cm-l): 2150 s (YS~H),905 s ( B S ~ H ) . 'H NMR (6, performed on a Perkin-Elmer 7 Series thermal analysis system CDC13, 300 MHz): 1.11- 1.16 (m, 2 H, CHz), 1.29 (d, J = 7.0 under an argon flow. The polymer sample was heated from Hz, 3 H, CH3), 2.29, 2.32 (s, 3 H, CH3), 3.13 (sextet, J = 7.0 25 to 800 "C at a rate of 20 "C/min. Ceramic residue yield is Hz, 1H, CH), 3.44 (t, J = 3.5 Hz, 3 H, SiH), 6.89-7.04 (m, 3 reported as the percentage of the sample remaining after H, ArH) (isomer ratio 3:2). I3C{lH} NMR (6, CDC13, 75.5 completion of the heating cycle. Differential scanning caloMHz): 15.35 (SiCHZ), 19.35, 21.26, 23.77 (CH3), 32.44 (CH), rimetry (DSC) of the polymer sample was performed on a 125.72, 126.50, 130.13, 131.92, 135.96, 146.15(ArC). GC/MS Perkin-Elmer 7 Series thermal analysis system under an argon ( m l e (relative intensity)): 178 (22) (M+),163 (lo), 136 (31), flow. Polymer sample was heated at 20 "C/min. Melting 135 (55), 133 (loo), 131 (201, 119 (151, 117 (181, 115 (22), 105 points were determined on a Thomas-Hoover Unimelt ap(381, 91 (271, 77 (14). paratus and are uncorrected. CpzTiClz, CpzHfClz, Red-Al(3.4 M in toluene), and L N H 4 were purchased from Aldrich Synthesis of 3-(chlorophenyl)-l-silabutane(4): 68% Chemical Co. and were used without further purification. yield; bp 64-67 "(30.6 mmHg. Anal. Calcd for SiCgH13Cl: C, Monomer Synthesis.14a 3-Aryl-l,l-dichloro-l-silabutanes14b 58.51; H, 7.09. Found: C, 58.50; H, 7.38. IR (neat, KBr, cm-I): and bis(l,l-dichloro-l-sila-3-butyl)benzene14c were prepared 2160 s ( Y S ~ H ) 910 , s (Bs,H). 'H NMR ( 6 , CDC13, 300 MHz): according to the literature procedure. The following reduction 1.09-1.27 (m, 2 H, CHz), 1.32 (1.31)(d, J = 7.0 Hz, 3 H, CH3), procedure is representative of the other monomers. (Warn3.43 (2.88) (sextet, J = 7.0 Hz, 1H, CHI, 3.46 (3.41) (t, J = 4.0 Hz, 3 H, SiH), 7.10-7.36 (m, 4 H, Ar H) (isomer ratio ortho: meta:para = 15:1:34). l3C{'H) NMR (6, CDC13, 75.5 MHz): (14)(a) There is a previous report; a series of analogous arylsubstituted alkylsilanes Ph(CH&SiHS, (p-chloromethy1)phenethylsi14.86, 15.95, 16.03 (SiCHZ), 22.77, 24.18, 24.40 (CH31, 33.22, lane, etc. were reported: Chang, V. S. C. Ph.D. Thesis, University of 37.24, 37.58 (CH), 124.76, 126.30, 126.91, 126.99, 127.09, Akron, 1981; Chem. Abstr. 1982,95, 220380a. (b) Lee, B. W.; Yoo, B. 127.88, 128.53, 129.66, 131.76, 146.67,150.40 (Ar C). GCMS R.; Kim, S.-I.; Jung, I. N. Organometallics 1994, 13, 1312. ( c ) Park, ( m l e (relative intensity)): 184 (19) (M+), 169 (121, 143 (32), S. K., Master's Thesis, Chosun University, 1995.
our knowledge, the dehydrocopolymerization of arylsubstituted alkylsilanes has not been reported to date. The transition-metal-mediated dehydrocoupling route of 34substituted aryl)-1-silabutanes may provide the possibility of controlling the molecular weight distribution and stereochemistry of polymer due to the presence of 3-methyl and 3-aryl groups as well as the introduction of functionality into the polymer. Here we report the dehydrohomopolymerization and dehydrocopolymerization of 3-aryl-1-silabutanes to give poly(3-aryl-1-silabutanes) catalyzed by metallocene complexes generated in situ from CpzMC1-2 (M = Ti, Homed-Al.
Synthesis of Poly(3-aryl-1d a b u t a n e s )
Organometallics, Vol. 14, No. 5, 1995 2417
141 (1001,139 (841,125 (111,115 (21),105 (191,103 (601,102 The column was rinsed with 200 mL of toluene. The removal (13),91(20), 78 (121,77 (43),75 (ll), 65 (19),63(32),51 (17). of volatiles at reduced pressure yielded 1.00g (83% yield) of Synthesis of 3-(chloro-p-tolyl)-l-silabutane (5): 93% off-white tacky product: IR (neat, KBr, cm-l) 2150 s ( Y S ~ H ) 'H ; (6, CDC13, 300 MHz) 0.68-1.96 (m, 5 H, SiCH2, CH3), yield; bp 50-52 "U0.6 mmHg. Anal. Calcd for S ~ C I O H ~ ~ C ~NMR : C, 60.42 H, 7.61. Found: C, 60.70;H, 7.89. IR (neat, KBr, 2.56-3.10(m, 1 H, CHI, 3.10-3.85(m, SiH), 6.88-7.47(m, 5 H, ArH); GPC M , = 821,M , = 455 (approximate DP = 61, cm-I): 2160 s (Y&, 910 s ( ~ 3 s ~ ~'H ) . NMR (6, CDC13, 300 MHz): 1.10-1.17(m, 2 H, CH2), 1.33(1.31)(d, J = 7.0Hz, 3 M,/M, = 1.78. H, CH3), 2.34(2.31)(s, 3 H,CH3), 3.44(3.13)(sextet, J = 7.0 Polymerization of 2: 91% yield; IR (neat, KBr, cm-l) 2105 Hz, 1 H, CHI, 3.48(3.47)(t, J = 4.0Hz, 3 H, SiH), 6.93-7.27 s (Y&; 'H NMR (6, CDC13, 300 MHz) 1.00-1.30(m, 5 H, (m, 3 H, ArH) (isomer ratio 4:l).13C{'H} NMR (6,CDC13,75.5 SiCH2, CH3), 2.35-2.39 (m, 3 H, Ar-CHs), 2.80-2.96 (m, 1 MHz): 14.86(15.23)(SiCHz), 22.10(18.90)(CH3), 22.79(22.52) H, CH), 3.37-3.53(m, SiH), 7.02-7.27 (m, 4 H, ArH); GPC (CH3), 33.05 (32.56)(CH), 125.29,125.72,127.51,127.84, M , = 1088,M , = 564 (approximate DP = 81, M d M , = 1.93. 129.16,130.16,131.51,133.10,136.66,144.90,148.36(Ar C). Polymerization of 3: 79% yield; IR (neat, KBr, cm-') 2105 GC/MS ( m l e (relative intensity)): 198(26)(M+),157(271,156 s ( Y S ~ H ) ;'H NMR (6, CDC13, 300 MHz) 0.80-1.50 (m, 5 H, (16),155 (loo),154 (ll), 153 (93),145 (12),121 (la),119 (18), SiCH2, CH3), 2.10-2.40(m, 6 H, Ar-CH31, 2.92-3.26(m, 1 117 (34),116 (18),115 (641,105 (lo), 93 (lo), 92 (lo),91 (511, H, CH), 3.26-3.72(m, SiH), 6.77-7.40(m, 3 H, Ar H); GPC 89 (ll), 77 (141,65 (211,63 (29). M , = 1292,M , = 1162(approximate DP = 161,Mw/Mn= 1.11. Synthesis of 3-(phenoxyphenyl)-l-~ilabutane (6):85% Polymerization of 4: 99% yield; IR (neat, KBr, cm-'1 2100 yield; bp 90-100 "C/O5 mmHg. Anal. Calcd for SiC15H180: s (vsa); lH NMR (6, CDC13, 300 MHz) 0.82-1.58 (m, 5 H, C, 74.32;H, 7.43. Found: C, 74.10;H, 7.42. IR (neat, KBr, SiCH2, CH3), 2.75-2.97(m, 1 H, CH), 3.29-3.55(m, SiH), cm-I): 2147 s ( Y S ~ H ) , 918 s ( 6 ~ i ~ 'H ) . NMR (6, CDC13, 300 6.93-7.26(m, 4 H, Ar H); GPC M , = 1050,M , = 497 MHz): 1.18-1.37(m, 2 H, CH2), 1.42(1.43)(d, J = 3.3Hz, 3 (approximate DP = 71,M,/Mn = 2.11. H, CH3), 3.44(2.99)(sextet, J = 3.6Hz, 1 H, CHI, 3.52(3.50) Polymerization of 5: 81% yield; IR (neat, KBr, cm-') 2108 (t, J = 3.9Hz, 3 H, SiH), 6.96-7.44(m, 9 H, Ar H) (isomer s ( Y S ~ H ) ;'H NMR (6, CDC13, 300 MHz) 0.78-1.49 (m, 5 H, ratio 0rtho:meta:para = 71:2:27).13C{'H} NMR (6,CDC13,75.5 SiCH2, CH3), 2.09-2.49 (m, 3 H, Ar-CH31, 3.31-3.43(m, 1 (SiCHz),23.47(24.79)(CH3),30.61(37.23) MHz): 15.10(16.44) H, CH), 3.43-3.62(m, SiH), 6.78-7.38(m, 3 H, Ar H); GPC (CH), 117.98,118.68,119.14,119.69,122.69,123.05,124.15, M , = 851,M , = 715 (approximate DP = lo), M J M , = 1.19. 127.23,127.42,127.83,129.79,130.16,139.46,143.30, 153.86, Polymerization of 6 79% yield; IR (neat, KBr, cm-l) 2140 155.38,158.17(ArC). GC/MS ( m l e (relative intensity)): 242 s ( Y S ~ H ) ;'H NMR (6, CDC13, 300 MHz) 0.96-1.46(m, 5 H, (34)(M+), 227 (15),197 (loo), 181 (171,165 (5), 149 (91,120 SiCH2, CH3), 2.77-2.94 (m, 1 H, CH), 3.20-3.54 (m, SiH), (91,103 (101,91 (171,77 (231,65 (51, 51 (9). 6.85-7.36(m, 9 H, ArH); GPC M , = 887,M , = 490 (apSynthesis of 3-Naphthyl-1-silabutane (7):66% yield; bp proximate DP = 7),Mw/Mn= 1.81;UV-vis (hexane): ,IF@ 285 72-75 "C/0.6 mmHg. Anal. Calcd for SiC13H16: C, 77.93;H, nm ( E = 2500). 7.98.Found: C, 77.83;H, 7.99. IR (neat, KBr, cm-'1: 2145 s Polymerization of 7: 83% yield; IR (neat, KBr, cm-') 2106 ( Y S ~ H ) 918 , s (&HI. 'H NMR (6, CDC13, 300 MHz): 1.26-1.45 s ( v s ~ H )'H; NMR (6, CDC13, 300 MHz) 0.79-1.73 (m, 5 H, (m, 2 H, CHz), 1.58(1.52)(d, J = 3.5Hz, 3 H, CH3), 3.61(3.56) SiCH2, CH3), 2.71-3.08(m, 1 H, CH), 3.08-3.80 (m, SiH), (t, J = 3.9Hz, 3 H, SiH), 3.91 (3.17)(sextet, J = 3.9Hz, 1 H, 7.00-8.24 (m, 7 H, Ar H); GPC M , = 831, M , = 699 CH), 7.41-8.18(m, 7 H, Ar H) (isomer ratio 3:l). I3C{'H} (approximate DP = 9),M J M , = 1.19;UV-vis (hexane) ,IFo* NMR (6,CDC13, 75.5 MHz): 15.64 (16.10)(SiCH2), 23.55 290 nm ( E = 2800). (24.63)(CH3), 31.75 (37.99)(CH), 122.57,123.21,124.67, Homopolymerization Catalyzed by Cpd-IfC12/Red-Al: 125.36,125.46,125.70,125.94,126.04,126.71,127.75, 128.23, Polymerization of 1. The following procedure is representa129.16,131.32,132.42,133.75,134.12,144.35,145.75(Ar C). tive of the polymerization reactions. 1 (0.14g, 0.92mmol) was GCMS ( m l e (relative intensity)): 200 (37)(M+),185 (7),183 slowly added to a Schlenk flask charged with CpzHfClz (24 (6),169 (51, 158 (301,157 (41),156 (161,155 (loo), 153 (271, mg, 0.06mmol) and Red-Al(18 pL, 0.06mmol). The reaction 152 (201,141 (81,129 (91,128 (la), 115 (71,63 (21,53 (1). mixture immediately turned light yellow, and the reaction Synthesis of bis(1-sila-3-buty1)benzene (8): 98% yield; medium became slowly viscous with moderate gas evolution. bp 65-66 "U0.6 mmHg. Anal. Calcd for Si2C12H22: C, 64.80; The mixture was stirred under a stream of nitrogen for 30 min H, 9.97. Found: C, 64.90;H, 10.20.Isomer ratio (by GLC): and then heated at 90"C until the mixture became rigid. The meta:para = 2:3. IR (neat, KBr, cm-'1: 2147 s (YS~H), 932 s catalyst was inactivated by exposure to the air for a few 'H NMR (6, CDC13, 300 MHz): 1.14-1.25 (m, 2 H, (&). minutes, and the solution was then passed rapidly through a SiCHz), 1.38(1.39)(d, J = 6.9Hz, 3 H, CH3), 2.63(sextet, J = silica gel column (70-230 mesh, 20 cm x 2 cm). The column 7.2Hz, 2 H, CH), 3.46(t, J = 3.6Hz, 6 H, SiH), 7.07-7.30(m, was rinsed with 200 mL of toluene. The removal of volatiles 4H,Ar H). 13C{1H}NMR (6, CDC13, 75.5MHz): 16.30(CH3), at reduced pressure yielded 0.043g (31% yield) of off-white 24.50 (SiCHz), 37.40 (37.90)(CH), 122.00,125.00,126.50, ; NMR (6, tacky product: IR (neat, KBr, cm-l) 2150 s ( Y S ~ H ) 'H 128.50,146.0,148.30 (Ar C). GC/MS ( m l e (relative intenCDC13,300 MHz) 1.01-1.48(m, 5 H, SiCH2, CH3), 2.70-2.90 sity)): meta isomer 222 (M+)(22),177 (471,163(51, 149 (loo), (m, 1 H, CH), 3.15-3.56 (m, SiH), 7.08-7.39(m, 5 H, Ar H); 147 (501, 135 (331,133 (61),131 (161,107 (541,105 (20),91 GPC M , = 807,M , = 410 (approximate DP = 51, Mw/Mn= (13),73 (17);para isomer 222 (M+)(191,207 (6),177 (loo), 1.97. 149 (21), 147 (24), 133 (411,131 (14), 107 (21),105 (121,91 Polymerization of 2: 32% yield; IR (neat, KBr, cm-') 2105 (lo), 73 (18). s ( V S ~ H ) ;'H NMR (6, CDC13, 300 MHz) 0.85-1.46 (m, 5 H, Homopolymerization Catalyzed by Cp,TiClz/Red-Ak SiCH2, CH30, 2.23-2.47(m, 3 H, Ar-CH3), 2.61-2.90(m, 1 Polymerization of 1. The following procedure is representaH,CH), 3.18-3.60(m, SiH), 6.82-7.37(m, 4 H,ArH); GPC tive of the polymerization reactions. To a Schlenk flask M , = 954,M , = 251 (approximate DP = 31,Mw/Mn= 3.80. charged with CpzTiClz (0.20g, 0.80 mmol) and Red-AI (24mL, Polymerization of 3:46% yield; IR (neat, KBr, cm-') 2105 0.80 mmol) was slowly added 1 (1.20g, 8.00mmol). The s (Y&; 'H NMR (6, CDC13, 300 MHz) 1.01-1.36 (m, 5 H, reaction mixture immediately turned dark green, and the SiCH2, CH3), 2.17-2.36(m, 6 H, Ar-CH3), 2.98-3.19(m, 1 reaction medium became rapidly viscous with strong gas H, CH), 3.32-3.54(m, SiH), 6.83-7.14(m, 3 H, ArH); GPC evolution. The mixture was stirred under a stream of nitrogen M , = 948,M , = 488 (approximate DP = 71,M,IM, = 1.94. for 24 h and then heated at 90 "C until the mixture became rigid. The catalyst was allowed t o oxidize by exposure t o the Polymerization of 4: 53% yield; IR (neat, KBr, cm-l) 2150 air for a few seconds, and the solution was then passed rapidly s ( Y S ~ H ) ;'H NMR (6, CDC13, 300 MHz) 0.63-1.02(m, 5 H, through a silica gel column (70-230 mesh, 20 cm x 2 cm). SiCH2, CH3), 2.47-2.98 (m, 1 H, CH), 3.06-3.75 (m, SiH),
Woo et al.
2418 Organometallics, Vol. 14, No. 5, 1995 6.87-7.48 (m, 4 H, Ar H); GPC M , = 1028, M,, = 445 (approximate DP = 6), M d M n = 2.31. Polymerization of 6 67% yield; IR (neat, KBr, cm-') 2108 s (YSIH); 'H NMR (6, CDCl3, 300 MHz) 0.84-1.64 (m, 5 H, SiCHz, CH3), 2.62-2.97 (m, 1 H, CH), 3.15-3.64 (m, SiH), 6.68-7.57 (m, 9 H, Ar H); GPC M , = 900, M,, = 428 (approximate DP = 6), MJM,, = 2.10. Polymerization of 7: 84% yield; IR (neat, KBr, cm-') 2106 s ( v s ~ H'H ) ; NMR (6, CDC13, 300 MHz) 0.97-1.59 (m, 5 H, SiCHz, CH3), 2.89-3.06 (m, 1 H, CHI, 3.27-3.79 (m, SiH), 7.16-8.21 (m, 7 H, Ar H); GPC M , = 738, M,, = 400 (approximate DP = 51, MJM,, = 1.85. Copolymerization Catalyzed by CpzTiClz/Red-AkCopolymerization of 2 and 4. The following procedure is representative of the polymerization reactions. To a Schlenk flask charged with CpzTiClz (20 mg, 0.085 mmol) and Red-Al (25 pL, 0.085 mmol) was slowly added 1 (0.28 g, 1.70 mmol) and 2 (0.31 g, 1.70 mmol). The reaction mixture immediately turned dark green, and the reaction medium became rapidly viscous with strong gas evolution. The mixture was stirred under a stream of nitrogen for 20 h and then heated at 90 "C until the mixture became rigid. The catalyst was allowed to oxidize by exposure to the air for a few seconds, and the solution was then passed rapidly through a silica gel column (70-230 mesh, 20 cm x 2 cm). The column was rinsed with 200 mL of toluene. The removal of volatiles at reduced pressure afforded 0.30 g (51% yield) of off-white tacky product: IR (neat, KBr, cm-l) 2110 s (vs~H);'H NMR (6, CDC13, 300 MHz) 0.91-1.68 (m, 10 H, SiCHz, CH3),2.33 (m, 3 H, ArCH3), 2.78-2.82 (m, 2 H, CHI, 3.36-3.43 (m, SiH), 7.00-7.27 (m, 8 H, Ar H); GPC M , = 813, M , = 407 (approximate DP = 51, M,IM,, = 2.00. Copolymerization of 2 and 6: 86% yield; Ir (neat, KBr, cm-l) 2110 s ( Y S , H ) ; lH NMR (6, CDC13, 300 MHz) 1.60-1.89 (m, 10 H, SiCHz, CH3), 2.32 (m, 3 H, Ar-CH3),2.73-2.76 (m, 2 H, CHI, 3.28-3.50 (m, SiH), 6.92-7.27 (m, 13 H, Ar H); GPC M , = 904, M,, = 538 (approximate DP = 7), M,IM,, = 1.68. Copolymerization of 4 and 6: 71% yield; IR (neat, KBr, cm-l) 2120 s (Y&; 'H NMR (6, CDC13, 300 MHz) 0.97-1.52 (m, 10 H, SiCHz, CH3), 2.75-2.82 (m, 2 H, CHI, 3.30-3.47 (m, SiH), 6.85-7.32 (m, 13 H, Ar H); GPC M , = 678, M,, = 405 (approximate DP = 51, MJM,, = 1.68. Polymerization of 8 Catalyzed by CpZTiCldRed-Al. To a Schlenk flask charged with CpzTiClz (16 mg, 0.04 mmol) and Red-Al (8.8 pL, 0.034 mmol) was slowly added 8 (0.33 g, 1.48 mmol). The reaction mixture immediately turned dark green, and the reaction medium became rapidly gelatinous with violent gas evolution. The mixture remained undisturbed under a stream of nitrogen for 2 days. The catalyst was destroyed by exposure t o the air for a few hours. The yellow gelatinous material was washed several times with toluene and diethyl ether and dried at reduced pressure to give 0.18 g (55% yield) of off-white solid (mp '300 "C; TGA ceramic residue yield 64% (black solid)) which was insoluble in most organic solvents. The combined washing solutions were concentrated on a rotary vacuum evaporator and then passed rapidly through a silica gel column (70-230 mesh, 15 cm x 2 cm) with 200 mL of toluene used as the eluent. The colorless effluent was evaporated t o dryness to yield 0.12 g (36% yield) of a very viscous clear oil which was soluble in most organic ) solid. For solvents. IR (KBr pellet, cm-'1: 2140 s ( Y S ~ H for the very viscous clear oil: IR (neat, KBr, cm-') 2148 s ( Y S ~ H ) ; 'H NMR (6, CDC13, 300 MHz) 1.08-1.23 (m, 4 H, SiCHZ), 1.24-1.38 (m, 6 H, CH31, 2.85-2.95 (m, 2 H, CHI, 3.37-3.48 (m, SiH), 6.98-7.32 (m, 4 H, Ar H); GPC M , = 1046, M,, = 819 (approximate DP = 111, M,IM,, = 1.28.
Results
Table 1. Spectroscopic Characterizationof Monomeric Silanes IRb 'H NMRn yield bp ("CY monomer (%I P (mmHg) (Si-H, ppm) (Si-H, cm-l) 62 98 96
68
93 85 66
98
74-76120 36-3810.6 62 -6510.6 64 -6710.6 50-52.0.6 90-10010.5 72-7510.6 65-6610.6
3.43 3.40, 3.41, 3.44 3.44 3.41, 3.46 3.48 3.50,3.52 3.61 3.46
2155 2150 2150 2160 2160 2147 2145 2147
a All measurements were carried out in CDCl3 solvent. * All measurements were performed neat in a KBr cell.
tions of allyldichlorosilane with substituted aryl compounds. The monomeric silanes, 3-aryl-1-silabutanes and bis(l-sila-3-butyl)benzene,were prepared in 6298% yields by reaction of the corresponding 3-aryl-1,ldichloro-1-silabutanes and bis(1,l-dichloro-1-sila-3butyUbenzene, respectively, with LiAlH4 (eq 1).The
A
SiH7
X
X = H (1); CH, (2): CH3,CH7 (3);CI (4);
CH,.CI (5); OPh(6); c-(CH), (7): CH(CH,)CH,SiH, (8)
monomeric silanes 3-phenyl-1-silabutane (l),3-tolyl-l(31, silabutane (2),3-(2,5-dimethylphenyl)-l-silabutane 3-(chlorophenyl)-l-silabutane(4), 3-(chloro-p-tolyl)-lsilabutane (51, 3-(phenoxyphenyl)-l-~ilabutane(6), 3-naphthyl-1-silabutane (7), and bis(1-sila-3-buty1)benzene (8) were purified by fractional distillation. All the silanes obtained here are stereoisomeric mixtures and were used without further attempts to separate them. The spectroscopic data for the monomeric silanes are summarized in Table 1. Homopolymerization of Monomer Silanes. Polymerization of the monomeric silanes 1-7 with the Cp2TiClfid-Al catalyst system was initiated immediately, as evidenced by the immediate release of hydrogen gas, and the reaction medium became rapidly viscous (eq 2). HZ
L\J X
1
CpzMClz/Red-Al (M= Ti, Hf)
+\y tn
SiH (*'
Monomer Synthesis.14a3-Aryl-l,l-dichloro-l-silaX butanes14band bis(l,l-dichloro-l-sila-3-butyl)benzene14C were prepared by AlCls-catalyzed Friedel-Crafts reacTo drive the reaction toward completion, the mixture
Synthesis of Poly(3-aryl-1dabutanes)
Organometallics, Vol. 14, No. 5, 1995 2419
Table 2. GPC Characterization of Homopolymerization of Monomeric Silanes with CpzTiCldRed-AI"
Table 4. GPC Characterization of Copolymerization of Monomeric Silanes with CpzTiCldRed-Ala mol wtc
mol w t b monomer
yield (%)
Mw
M,(DPY
PDI
monome+
1 2 3 4 5 6 7
83 91 79 99 81 79 83
821 1088 1292 1050 851 887 831
455 (6) 564(8) 1162(16) 497 (7) 715(10) 490(7) 699(9)
1.78 1.93 1.11 2.11 1.19 1.81 1.19
2 and 4 2 and 6 4 and 6
a [Tijl[Si] = 0.10. GPC vs polystyrene. Approximate estimate for DP made by simply calculating the differences in molecular weight between styrene and silylene monomer units.
Table 3. GPC Characterizationof Homopolymerization of Monomeric Silanes with CpzHfCldRed-Ala mol w t b monomer
yield (%)
Mw
1 2
31 32 46 53 79 84
807 954 948 1028 900 738
3 4 6 7
M,,(DPY
410 (5) 251 (3) 488 (7) 445 (6) 428 (6) 400 (5)
PDI
1.97 3.80 1.94 2.31 2.10 1.85
yield(%)
51 86 71
M,
M,(DPF
407 (5) 538 (7) 405 (5)
813 904 678
PDI
2.00 1.68 1.68
a [Tijl[Si] = 0.025. 1:l mole ratio. GPC vs polystyrene. Approximate estimate for DP made by simply calculating the differences in molecular weight between styrene and silylene monomer units.
To reach completion, the mixture was stirred at room temperature for 24 h and then heated a t 90 "C until the mixture became rigid. The polymers were acquired in 5 1 4 6 % yields after workup including column chromatography as off-white tacky materials which were soluble in most organic solvents. The polymerization results are shown in Table 4. Polymerizationof Bis(1-sila-3-buty1)benzene(8). Polymerization of 8 with the CpsTiCldRed-Al catalyst system began immediately, as monitored by the immediate release of hydrogen gas, and the reaction medium became rapidly gelatinous (eq 4). The polymer
[Hfl/[Si] = 0.065. GPC vs polystyrene. Approximate estimate for DP made by simply calculating the differences in molecular weight between styrene and silylene monomer units. [I
H,Si
was stirred at room temperature for 24 h and then heated at 90 "C until the mixture became rigid. The polymers were isolated in 79-99% yields after workup including column chromatography as off-white tacky materials which were soluble in most organic solvents. The polymerization results are shown in Table 2. Polymerization of the monomer silanes 1-7 with the CpzHfCldRed-Al catalyst system commenced slowly, as monitored by the moderate release of hydrogen gas, and the reaction medium became slowly viscous (eq 2). To bring the reaction toward completion, the mixture was stirred at room temperature for 30 min and then heated at 90 "C until the mixture became rigid. The polymers were obtained in 3 1 4 4 % yields after workup including column chromatography as off-white tacky materials which were soluble in most organic solvents. The polymerization results are given in Table 3. Copolymerization of Monomer Silanes. Copolymerization of the monomeric silanes with the Cp2TiClned-Al catalyst system started immediately, as monitored by the immediate release of hydrogen gas, and the reaction medium became rapidly viscous (eq 3).
iH,
i' .
L\J
X'
I H
&SiH
k I
H
was acquired in 290% total yield as two phases after workup including washing and column chromatography. The first part of the polymer was obtained in 55%yield as an off-white solid (mp '300 "C) which was insoluble in most organic solvents. Its TGA ceramic residue yield was 64%. The second part of the polymer was acquired in 36% yield as a very viscous clear oil which was soluble in most organic solvents. The weight-average molecular weight (M,) and number-average molecular weight (M,) of the oily polymer were 1046 and 819, respectively. The approximate estimate for the average degree of polymerization (DP) was 11.
Discussion n
I
+
v
8
H
Cp,TiCI ,/Red-Al
X
Cp2TiC12/Red-Al
L\J
H
X' (3)
The chemical shifts and coupling constants associated with the protons of the Si-H bonds in the 'H NMR spectra of the monomer silanes are in the ranges of 3.43.6 ppm and 3.5-4.0 Hz, respectively. The variation of chemical shifts of the Si-H bonds with change of substituents was minor, albeit the aryl substitution on the 3-phenyl group as in 6 and 7 resulted in a downfield shift. The Si-H stretching bands in the IR spectra of the silanes are in the 2140-2160 cm-l range. The spectral data appear to be little affected by the substituents on the aryl ring, due probably to the separation
2420 Organometallics, Vol. 14,No. 5, 1995
of the silicon center from the aryl ring by an ethylene spacer, and were in good agreement with those for other alkylsilanes reported in the literature. Thus, one may expect that the dehydrocoupling of 3-aryl-substituted alkylsilanes should closely resemble the dehydrocoupling of other alkylsilanes. While the molecular weights of polysilanes produced via the dehydrocoupling reaction are lower than those produced via Wurtz coupling of dichlorosilanes, the dehydrocoupling method is more tolerant of functional groups. The Wurtz coupling method cannot be used t o polymerize chlorine-substituted arylsilanes due to crosslinking.' Organ0 rare-earth-metal complexes have been used as catalysts to dehydrocouple silanes to give lowmolecular-weighto l i g ~ m e r s . ~Although J~ Cp2MMe2 (M = Ti, Zr),4 CpzZr[Si(SiMe3)~]Me,~ and CpzZrCldnBuLilzb are known to be the active catalysts for the dehydropolymerization of primary silanes and CpCp*Zr[Si(SiMe&lMe and (CpCp*ZrHz)awere the most active catalysts previously e ~ a m i n e dwe , ~ wanted to employ a new catalyst system, CpzMClfled-Al (M = Ti, HD,9 which was recently found to give predominantly linear, higher molecular weight polysilanes than for any other catalyst system, because the monomeric silanes 3-aryll-silabutanes are sterically hindered. Sterically hindered silanes were known to be very slow to polymerize and to give low-molecular-weight olig~silanes.~ Thus, in order t o accelerate the rate of polymerization, both higher catalyst concentration (Le., 10 mol % for Ti and 6.5 mol % for Hf in the homopolymerization; 2.5 mol % for Ti in the copolymerization) than the usual concentration range of 0.5-1.0 mol % and heating to 90 "C were employed in these polymerization reactions. The lH NMR spectra of all of the polysilanes prepared apparently show only one broad unresolved mountainlike resonance centered a t ca. 4.4 ppm, unlike poly(phenylsilane), which shows a set of broad resonances centered at 4.5 and 5.1 ppm corresponding to linear and cyclic polymers.4a The IR spectra of all of the polysilanes produced here exhibit an intense Y S ~ Hband at ca. 2100 cm-l and a weak or nearly absent dSiH band at ca. 910 cm-l. The weak intensity of the 6SiH IR band and lH NMR spectra imply that the polysilanes could be mostly cyclic.4a However, one should note that the decrease of polydispersity index in GPC is not always proportional to the increase of percent of cyclic We expect some degree of diastereomeric selection in the polymerization,especially at the Si-Si coupling step via a-bond m e t a t h e ~ i s due , ~ to the presence of asymmetric center by the 2-methyl group of the 3-aryl-lsilabutanes, although the monomeric silanes are used as a mixture of stereoisomers. An investigation of percentage of cyclic and linear oligomers in the polymers and the degree of diastereomeric selection in the polymerization in detail by using 29SiNMR and GC/mass/ FT-IR techniques is currently in progress and will be the subject of a future paper. The polymers reported here apparently show no sign of cross-linking due t o coupling of the substituted chlorine and of the backbone Si-H bonds of the polymer chains, evidenced by lH NMR, IR, and GPC. UV-vis spectra in hexane of poly(3-(phenoxyphenyl)-l-~ilabutane) and poly(3-naphthyl(15) (a)Watson, P. L.; Tebbe, F. N. US.Patent 4965386 Oct 23 1990; Chem. Abstr. 1991,114,123331~.(b) Sakakura, T.;Lautenschlager, H.-J.; Tanaka, M. J. Chem. SOC.,Chem. Commun. 1991,40.
Woo et al.
l-silabutane) showed A,,-@ 285 ( E = 2500) and 290 ( E = 2800), respectively, which are in the normal range for po1ysilanes.l The polysilanes did not exhibit a significant photobleaching behavior upon irradiation by room light under an atmosphere of nitrogen within several hours. Although the molecular weights determined by GPC (vs polystyrene standard) are not directly comparable for various substituted polysilanes,' it appears that the polymers of 3-aryl-l-silabutanes have a lower degree of polymerization than those obtained from phenylsilane but have an approximately similar degree of polymerization as those obtained from benzylsilane8or n-butyl~ i 1 a n e . lA ~ n~ approximate estimate for the average degree of polymerization (DP) for these polysilanes, made by simply calculating the differences in molecular weight between styrene and silylene monomer units, can be made. As shown in Tables 2-4, polymers with degrees of polymerization (DP) of 6-16 and with polydispersity indexes (PDI) of 1.1-2.1 were obtained by the CpzTiClfled-Al system, and polymers with DP values of 3-7 and with PDI values of 1.8-3.8 were obtained by the CpzHfClfled-Al system. For 'comparison, the dehydropolymerization of the monomeric silanes with the CpzMClz (M = Ti, HDh-BuLi catalyst system is currently underway. As seen in Table 4, copolymers with DP values of 5-7 and with PDI values of 1.6-2.0 were obtained. Although the homopolymers of each component monomer along with the copolymer may be formed, the possibility is slim due t o the similar reactivity of each monomeric silane. However, it is currently uncertain whether the copolymers are random or not. lH NMR, IR, and GPC for these copolymers are relatively uninformative. Differential scanning calorimetry (DSC) for these copolymers did not give us much information either: it did not show the existence of a glass transition temperature (T,)between 25 and 200 "C. Dehydropolymerization of 8 produced two phases of polymers. One is a very viscous oil (M,= 1046, M, = 819 (approximate DP = 11))which seems to be noncross-linked or slightly cross-linked and thus soluble in most organic solvents. The other is an off-white solid which appears to be extensively cross-linked and thus insoluble in most organic solvents. The solid polymer did not melt or decompose upon heating to 300 "C. Thermogravimetric analysis (TGA)shows that only 10% of the initial weight of the polymer is lost by 400 "C and the TGA ceramic residue yield is 64% a t 800 'C. Differential scanning calorimetry (DSC) for these polymers did not show the existence of a glass transition temperature (T,)between 25 and 350 "C. X-ray powder pattern analysis (28 = 5-80') of the solid polymer was featureless, which suggests that the polymer adopts an amorphous, glasslike structure. One might naturally think that the polymerization first produced a lowmolecular-weight polymer which then underwent an extensive cross-linking reaction of backbone Si-H bonds, leading to an insoluble polymer. The dehydropolymerizability of two isomers (meta:para = 2:3) of 8 seems t o be similar by judging from the lH NMR spectrum of the oily product. The monomer 8 can be used as a crosslinking agent in the dehydropolymerization of 3-aryll-silabutanes. Details on the dehydropolymerization of multi(silylalky1)-substituted arenes will be reported in
Synthesis of Poly(3-aryl-1dabutanes)
the near future. One of us reported the dehydropolymerization of m~ltisilanylenearylenes.~
Conclusion
This work describes the preparation, dehydrohomopolymerization, and dehydrocopolymerizationof new arylsubstituted alkylsilanes, 3-aryl-l-silabutanes, catalyzed by the CpzMClz (M = Ti, Homed-Al combined system. While polymers produced by the CpzTiCl&d-Al system with degrees of polymerization (DP) of 6-16 and with polydispersity indexes (PDI) of 1.1-2.1 were obtained, polymers produced by the CpzHfCldFted-Alsystem with DP values of 3-7 and with PDI values of 1.8-3.8 were obtained. The dehydrocopolymerization of the silanes
Organometallics, Vol. 14, No. 5, 1995 2421
gave copolymers with DP = 5-7 and with PDI = 1.62.0. Bis(silabuty1)benzene (8) dehydrocoupled to produce two phases of polymers: one is a highly crosslinked solid, and the other is a non-cross-linked or slightly cross-linked oil and could be a precursor for the solid. X-ray powder pattern analysis suggests the solid polymer adopts amorphous structure.
Acknowledgment. This research was supported in part by the Non-directed Research Fund, Korea Research Foundation (19941, in part by the Korea Science and Engineering Foundation (1994), and in part by the Ministry of Science and Technology of Korea. OM940844P
