Organometallics 1996, 14, 714-720
714
Polymeric Organosilicon Systems. 21. Synthesis and Photochemical, Conducting, and Thermal Properties of (2,6-and 2,5-Diethynylenepyridylene)disilanylene Polymers Atsutaka Kunai, Eiji Toyoda, Katsuhiro Horata, and Mitsuo Ishikawa" Department of Applied Chemistry, Faculty of Engineering, Hiroshima University, Kagamiyama, Higashi-Hiroshima 724,Japan Received June 3, 1994@ The reactions of 1,2-diethyl-1,2-dimethyl-, 1,1,2,24etraethyl-, 1,2-dibutyl-1,2-dimethyl-, and 1,2-dihexyl-1,2-dimethyl-1,2-diethynyldisilane (la-d) with 2,6-dibromopyridine were carried out in the presence of a Pd(PPh&-CuI catalyst in refluxing triethylamine to give poly[(2,6-diethynylenepyridylene)disilanylenesl (2a-d) with molecular weights of 15 00028 000. Similar treatments of la-d with 2,5-dibromopyridine under the same conditions afforded poly[(2,5-diethynylenepyridylene)disilanylenesl(3a-d) with molecular weights of 19 000-39 000. Irradiation of 2a-d and 3a-d with a low-pressure mercury lamp resulted in cleavage of the silicon-silicon bonds. When 3a-d were doped with iodine or ferric chloride vapor, polymers with conductivities of lo-' S9cm-l level were obtained. Thermal properties of these polymers were also examined.
Introduction There has been a considerable interest in the chemistry of silicon-containing polymers that can be used as functional materials. To date, many types of siliconcontaining polymers have been synthesized by alkali metal condensation of dichlorosilyl derivatives1 or bis(chlorosily1)-substituted compounds.2 The polymers obtained by this method always involve some siloxy units in the polymer backbone, which interrupt electron delocalization. Recently, we have found two types of synthetic methods that involve no alkali metal condensation. One involves the thermal and catalytic ring-opening polymand the erization of 1,2,5,6-tetrasilacycloocta-3,7-diynes3 other comprises the rhodium(1)-catalyzedreaction of 1,2diethynyldi~ilanes.~ The polymers obtained by these methods show no siloxy unit in the polymer backbone. As a part of our investigation concerning the synthesis of the polymers that have a regular alternating arAbstract published in Advance ACS Abstracts, December 1,1994. (1) (a) West, R.; Maxka, J. Inorganic and Organometallic Polymers; ACS Symposium Series 360;American Chemical Society: Washington, DC, 1988; Chapter 2. (b) Matyjaszewsky, K.; Chen, L.; Kim, H. Inorganic and OrganometallicPolymers; ACS Symposium Series 360; American Chemical Society: Washington, DC, 1988; Chapter 6. (2) (a) Ishikawa, M.; Ni, H.; Matsuzaki, K.; Nate, K.; Inoue, T.; Yokono, H. J . Polymer Sei., Polymer Lett. Ed. 1984,22, 669. (b) Nate, K.; Ishikawa, M.; Ni, H.; Watanabe, H.; Saheki, Y. Organometallics 1987, 6, 1673. ( c ) Ishikawa, M.; Nate, K. Inorganic and Organometallic Polymers; ACS Symposium Series 360; American Chemical Society: Washington, DC, 1988; p 209. (d) Ohshita, J.; Kanaya, D.; Ishikawa, M.; Yamanaka, T. J . Organomet. Chem. 1989,369, C18. (e) Hong, H. H.; Weber, W. P. Polymer Bull. 1989,22,363. (0 Hu, S.; Weber, W. P. Polymer Bull. 1989, 21, 133. (g) Ohshita, J.; Kanaya, D.; Ishikawa, M.; Koike, T.; Yamanaka, T. Macromolecules 1991, 24, 2106. (3) (a) Ishikawa, M.; Hasegawa, Y.; Hatano, T.; Kunai, A,; Yamanaka, T. Organometallics 1989,8, 2741. (b) Ishikawa, M.; Hatano, T.; Horio, T.; Kunai, A. J. Organomet. Chem. 1991, 412, C31. (c) Ishikawa, M.; Hatano, T.; Hasegawa, Y.; Horio, T.; Kunai, A.; Miyai, A.; Ishida, T.; Tsukihara, T.; Yamanaka, T.; Koike, T.; Shioya, J. Organometallics 1992, 11, 1604. (4) (a) Ohshita, J.; Furumori, K.; Ishikawa, M.; Yamanaka, T. Organometallics 1989, 8, 2084. (b) Ohshita, J.; Matsuguchi, A,; Furumori, K.; Hong, R.-F.; Ishikawa, M.; Yamanaka, T.; Koike, T.; Shioya, J . Macromolecules 1992, 25, 2134. @
0276-7333/95/2314-0714$09.00/0
rangement of a disilanylene unit and n-electron system in the polymer backbone, we carried out the preparation of the polymers containing a diethynylenepyridylene unit as the n-electron system and examined their photolytic, conducting, and thermal properties. To our knowledge, this type of polymer is the first example for the alternating polymers involving a diethynylenepyridylene unit and silicon-silicon bond in the polymer backbone.
Results and Discussion In 1975, Sonogashira et aL6reported that the reaction of monosubstituted acetylenes with aromatic and heteroaromatic halides in the presence of a catalytic amount of a palladium complex and copper(1)iodide in diethylamine or triethylamine affords ethynyl-substituted aromatic compounds. Recently, Corriu and coworkers7 have reported the preparation of (diethynyleneary1ene)silylene polymers by this method. We are interested in the synthesis and application t o the functionality materials of alternating polymers that involve the nitrogen-containing heteroaromatic ring in the polymer backbone and investigated the coupling reaction of 1,2-diethynyldisilanes and 2,5- and 2,6dibromopyridine in the presence of a catalytic amount of tetrakis(triphenylphosphine)palladium(O)and copper(I) iodide. 1,2-Diethynyldisilanes used as starting compounds were prepared by the method reported previo~sly.~~ When a mixture of 1 equiv of 1,2-diethyl-1,2-diethynyldimethyldisilane (la)and 2,6-dibromopyridinein the (5) Alternating polymers involving a diethynylenepyridylene group and silylene unit have been reported by Corriu et al.; see ref 7a-d. (6) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975, 4467. (7) (a) Corriu, R. J.-P.; Douglas, W. E.; Yang, Z.-X. J . Polymer Sci. C, Polymer Lett. 1990, 28, 431. (b) Corriu, R. J.-P.; Douglas, W. E.; Yang, Z.-X. Eur. Polym. J . 1993,29,1563. (c) Corriu, R. J.-P.; Douglas, W. E.; Yang, Z.-X. Karakus, Y.; Cross, G. H.; Bloor, D. J . Organomet. Chem. 1993, 455, 69. (d) Corriu, R. J.-P.; Douglas, W. E.; Yang, Z.-X. J . Organomet. Chem. 1993,456, 35.
0 1995 American Chemical Society
Polymeric Organosilicon Systems
Scheme 1
Organometallics, Vol. 14, No. 2, 1995 715
isomers for a disilanylene unit in the polymer chain (see below). As a typical example, the 'H and 13C NMR spectra of 2a are shown in Figures 1 and 2. In contrast to the 2,6-pyridylene isomer 2b, the 13C NMR spectrum of a 2,5- isomer 3b shows two resola. R'=Me. Rz=Et 2..R1=Me,RZ=Ei 39% nances a t 6 4.62 and 4.66 ppm, due to methylene lb, R1=EI, R*=Et Zb, R'=Et, RZ=Et 70% le. R'=Me. R2=Bu Ze, R'=Me.R2=& 61% carbons in a diethylsilyl group, and multiple resonances Id, R'=Me, RZ=Hexyl 2d, R'=Me. R2=Hexyl 81% around 6 93.9 (three peaks), 97.0 (three peaks), 104.8, and 107.0 ppm, assigned to ethynyl carbons. The 29Si Scheme 2 NMR spectrum of 3b also reveals two resonances at 6 -28.49 and -28.38 ppm. These multiple signals may be caused by micro structures of 2,5-pyridylenedisilanylene units in the polymer backbone, as discussed 38, R'=Me, R ~ = E I 53% la. R'=Me. R2=Et below. For polymers 3a,c,d which bear two chiral lb, R'=EI, R2=Et 3b. R'=Et, RZ=Et 90% centers in a disilanylene unit, 13C NMR spectra show le. R'=Me, R~=B" 3e, R'=Me.RZ=Bu 9G% three resonances due to a methylsilyl carbon, while 29Id, R'=Me. R2=Hexyl 3d, R1=Me.R2=Hexyl 83% Si NMR spectra reveal multiple resonances in a region of 6 -34.5 to -32.1 ppm. presence of a Pd(PPh&-CuI catalyst was heated to In order t o learn more about the chemical shifts of reflux in triethylamine, poly[(2,6-diethynylenepyridylene)meso and dl isomers for disilanylene compounds, we (1,2-diethyl-1,2-dimethyldisilanylene)l (2a) with a moexamined NMR spectra of 1,2-bis(2-pyridylethynyl)-and lecular weight of 15 000 was obtained after twice 1,2-bis(3-pyridylethynyl)-1,2-dihexyl-l ,a-dimethyldisireprecipitation from methanol (Scheme 1). Similar (4 and 5) as model compounds. These compounds lane reactions of 1,1,2,24etraethyl-, 1,2-dibutyl-1,2-dimethof Id with 2-bromowere synthesized by the reaction yl-, and 1,2-dihexyl-1,2-dimethyl-1,2-diethynyldisilane or 3-bromopyridine under similar conditions as de(lb-d) with 2,6-dibromopyridine under the same condiscribed for the synthesis of the polymers (Scheme 3). tions afforded corresponding poly[(2,6-diethynylenepyrAs expected, 2-pyridyl compound 4 reveals two resoidylene)disilanylenes] (2b-d) with molecular weights nances due to a methylsilyl group in 13C (6 -4.62 and of 19 000-28 000 in high yields. Polymers 2a-d are -4.53), lH (6 0.35 and 0.36), and 29Si (6 -34.11 and dark brown greaselike liquids and are soluble in com-34.05) NMR spectra (see Table 1). For 3-pyridyl mon organic solvents such as aromatic solvents, ethers, isomer 5, two signals due to the methylsilyl group are and halocarbons. also observed in the I3C (6 -4.53 and -4.45) and lH (6 2,5-Dibromopyridinealso reacted with 1,2-diethynyl0.34 and 0.35) NMR spectra, whereas, in its 29SiNMR disilanes in the presence of the palladium catalyst to spectrum, a single resonance was observed at 6 34.39 give poly[(2,5-diethynylenepyridylene)disilanylenesl(3appm. On the other hand, signals due to ethynyl carbons d). Thus, the reaction of 1,2-diethynyldisilanes la-d in 13C NMR spectrum appear as a singlet a t 6 92.5 with 1equiv of 2,5-dibromopyridine in the presence of (Sic=)and 106.7 (PyC=) ppm for 4 and a t 6 95.9 (Sic..) a catalytic amount of Pd(PPh&-CuI in a refluxing and 104.4 (PyC=) ppm for 5, respectively. triethylamine solution produced polymers 3a-d with These results clearly indicate that the double signals molecular weights of 19 000-39 000 in high yields due to the methylsilyl group in the lH, 13C, and 29Si (Scheme 2). Like polymers 2a-d, polymers 3a-d are NMR spectra of 2,g-pyridylene isomer 2d, as well as 2a dark brown greaselike liquids and are soluble in comand 2c, arise from dl and meso isomers. In the case of mon organic solvents. Some of the properties of polythe 2,5-pyridylene isomers, the existence of three kinds mers 2a-d and 3a-d are shown in Table 1. of micro structures A-C (Chart 1) in the polymer On the other hand, the similar reactions of 1,1,2,2tetramethyl- and 1,2-dimethyl-l,2-diphenyl-l,2-diethy- backbone would be possible. If the resonances due to ethynyl carbons in polymer 3d are compared with those nyldisilane with 2,5- and 2,6-dibromopyridine mainly in the model compounds, the resonances attributed to afforded insoluble polymers, together with small amounts silyl-substituted ethynyl carbons appear as a multiplet of oligomers (M, = ca. 2500) which are soluble in in a slightly lower field (ca. 2 ppm) than that in 4 and methanol. 5, while two signals due to pyridylene-substituted The structures of 2a-d and 3a-d were verified by carbons show the same chemical shift as that in 4 and spectroscopic analysis. IR spectra of these polymers 5, respectively. These results indicate that accumulashow strong absorption bands at 2152-2156 cm-l, due tion of the isomeric micro structures in the polymer to stretching frequencies of a carbon-carbon triple bond. affects the chemical shifts of silyl-substituted ethynyl For 2b, the 13C NMR spectrum shows two resonances carbons and, therefore, results in the multiple signals at 6 92.3 and 106.9 ppm, assigned t o ethynyl carbons, for those carbons. Polymers 3a-c also reveal multiplet and resonances a t 6 4.6 and 8.3 ppm, attributed to resonances for these carbons in their 13CNMR spectra methylene and methyl carbons in a diethylsilyl group, by the same reason. The multiple lines due to a together with resonances due to pyridyl carbons (6 methylsilyl group in the lH and 29SiNMR spectra for 127.0, 136.1, and 143.3), while the 29SiNMR spectrum the 2,5-pyridylene polymers can be explained by the reveals a single resonance at 6 -28.2 ppm, as expected existence of dl and meso isomers and the effect of the for the symmetric and regular alternating structure of micro structures. the polymer. In contrast to 2b, polymers 2a,c,d exhibit The polymers obtained by reprecipitation from bentwo signals due t o a methylsilyl carbon in the 13CNMR zene-methanol are still deeply colored, even after spectra and two signals due t o the methylsilyl protons treatment with chromatography on alumina or silica or in the lH NMR spectra, arising from meso and dl
716 Organometallics, Vol. 14, No. 2, 1995 ~ _ _ _ _ _
~~
Kunai et al.
Table 1. Properties of Polymers 2a-d and 3a-d and Model Compounds 4 and 5 NMR chem shift, 6 (no. of peaks)
compd
Mw ( M J M n )
W: ,I,, nm , , , (dC=CSiSiC=CF'y)
2a
15 000 (2.5) 19 000 (1.9) 28 000 (2.3) 20 000 (2.4) 19 000 (2.8) 19 000 (2.6) 24 000 (2.4) 39 000 (2.6) 460.3 460.3
304.4 (11 100) 304.2 (1 1 900) 312.2 (28 100) 306.2 (23 800) 3 11.6 (45 800) 318.0 (32 900) 3 14.0 (34 800) 313.4 (38 200) 282.2 (22 400) 280.0 (14 300)
2b 2c 2d 3a 3b 3c
3d 4 5
92.8 92.3 93.3 93.1 94.5 (3) 93.9 (3) 94.8 (4) 94.9 (3) 92.5
97.5 (3) 97.0 (3) 97.9 (3) 97.9 (3)
106.3 106.9 106.4 106.3 106.5 107.0 106.4 106.5 106.7
95.9
104.3 104.8 104.3 104.3 104.4
-5.1 (2) 4.6' -4.6 (2) -4.7 (2) -5.1 (3) 4.6 (2)' -4.6 (3) -4.6 (3) -4.6 (2) -4.5 (2)
0.38 (2) 0.36 (2) 0.33 (2) 0.42 (2) 0.36 (2) 0.35 0.36 (2) 0.34 (2)
-32.1 -28.2 -33.8 -33.8 -32.4 -28.5 -34.2 -34.2 -34.1 -34.4
(2)
(2) (2) (3) (2)
-32.1 (3) -28.4 -33.8 (3) -33.9 (3)
In 2-PyCFCSi. In 3-PyCFCSi. Resonance due to SiCH2-
m
..
?
1
lk------
I -
0.7
0.6
0.5
I-
0.4
0.3
Figure 1. lH NMR spectrum for 2a. treatment with activated carbon. However, we have found that the dark brown color can be removed by treating the polymers with zinc powder and aqueous acetic acid in a short time under an inert atmosphere. For example, when a dark brown solution of polymer 3c in benzene was stirred with zinc powder and 40% aqueous acetic acid under a nitrogen atmosphere for 5 min, a rapid decolorization of the solution was observed.8 After immediate separation of the organic layer and neutralization with aqueous sodium bicarbonate, polymer 3c was recovered in more than 90% yield as a light brown oil. No changes were observed for the molecular weight of the recovered 3c. Another point to be stressed is that the silicon-silicon bonds in the polymer backbone are not cleaved under the conditions used for the synthesis of the present polymers. Tanaka and his co-workers reported that some acetylenic compounds insert into the siliconsilicon bonds of octamethyltrisilane and the related polymers in the presence of a Pd complex catalyst in benzene at 120 0C.9 If such insertion reaction of the (8) Similar treatment of 3c with zinc-acetic acid under aerobic conditions for 1 h resulted in decrease of the molecular weight and also contamination of some siloxy bonds in the polymer backbone.
acetylenic bonds of the polymers into the silicon-silicon bonds in the polymer backbone took place, branched or cross-linked structure would be formed. In order to check this possibility, we synthesized 1,2-bis(2-pyridylethyny1)tetramethyldisilane (6) as a model compound and examined the behavior toward the Pd catalyst. Thus, when a mixture of 1 equiv of 1,2-diethynyltetramethyldisilane and 2 equiv of 2-bromopyridine in the presence of the Pd(PPh&-CuI catalyst in triethylamine was heated to reflux for 8 h, compound 6 was obtained in 92% yield (GLC), as the sole product. No products arising from insertion of an ethynyl group into a silicon-silicon bond in the starting disilane were detected in the reaction mixture by GC-mass spectrometric analysis. Even in the prolonged reaction for 30 h under the same conditions, no change was observed for the yield of product 6. A similar result was obtained in the synthesis of disilane 4, indicating that insertion of the (9) They have reported that the Pd(dba)2--2P(OCH&CEt catalyst system is highly effective for the insertion of acetylenes to the Si-Si bonds, but PdC12(PPh& and Pd(PPh3)d show only low catalytic activity for this reaction: Yamashita, H.; Catellani, M.; Tanaka, M. Chem. Lett. 1991,241.See also: Horn, K. A.; Grossman, R. B.; Whitenack. A. A. J. Organomet. Chem. 1987,332,271.
Organometallics, Vol. 14, No. 2, 1995 717
Polymeric Organosilicon Systems
I
1
Figure 2. 13C NMR spectrum for 2a.
-
Scheme 3 ld
t
2-PyBr (or 3-PyBr
)
5
4
Chart 1 R' R'
A
B
C
ethynyl group into the silicon-silicon bonds does not occur during the synthesis of the present polymers. Although all of the spectrometric analyses undoubtedly support the structure of the polymers (see Figures 1and 21, combustion analysis for some polymers shows lower carbon values than theoretical ones. For example, the carbon content for 3c was determined to be 63% (calcd 70.04%). In such cases, the color of the ash obtained after combustion analysis is always gray, suggesting that a small amount of silicon carbide is produced. In order to clarify this, we carried out an ignition experiment for 3c under the same conditions as those of elemental analysis, i.e., a t 830 "C in an oxygen stream for 5 min. Although an ESCA spectrum of the resulting ash revealed a peak corresponding to
carbon, no crystalline materials were detected by XRD analysis. However, after the ash was treated at 1500 "C under argon for 30 min, X-ray diffraction peaks due to /3-siliconcarbide were clearly observed. These results unambiguously show that the low carbon content observed for 3c in elemental analysis is caused by the formation of silicon carbide. We carried out the pyrolysis of the polymer 3c under an argon atmosphere. Heating 3c at 1500 "C for 30 min under argon afforded a hard black solid consisting of /?-Sic,which was verified by XRD analysis. Peaks due to silicon nitride were not detected. The thermal behavior of the polymers was also examined by thermogravimetry under a nitrogen atmosphere. The TGA curves for all polymers display that the weight percent decreases rapidly in a range of 400-700 "C and becomes almost constant over 800 "C. The weight remaining at 1200 "C was found to be 33% for 2a, 37% for 2b, 32% for 2c, and 31%for 2d, in accordance with the formation of silicon carbide. Similar results were obtained for 3ad. The (diethynylenepyridy1ene)disilanylenepolymers exhibit strong W absorption bands at 304-318 nm in a THF solution, which are lower in energy than 1,2bis(pyridylethyny1)disilanes (282 nm for 4 and 280 nm for 5). The absorption maxima and the extinction coefficients per (diethynylenepyridyleneldisilanylene unit are given in Table 1. In general, polymers containing a disilanylene unit and n-electron system in the polymer backbone are photoactive. As expected, on irradiation of thin films of polymers 2a-d and 3a-d with W light in air, absorption bands near 310 nm decrease rapidly (within 10 min), indicating that homolytic scission of silicon-silicon bonds in the polymer backbone readily occurs. Profiles of U V spectra obtained from irradiation of the film prepared from 3d are shown in Figure 3, as a typical example. IR spectra of all of the resulting films show strong absorptions due to Si-OH and Si-0-Si bonds. The formation of the Si-OH and Si-0-Si bonds can best be explained by
Kunai et al.
718 Organometallics, Vol. 14, No. 2, 1995
Table 2. Conductivities of Polymers 3a-d Doped with 1 2 and FeCl3 Vapors conductivity, Seem-' polymer with 12 (thicknessy (period) with FeC13 (thickness)b (period)
3a 3b 3c 3d
7.9 x lo-' (0.5 mm) (5 days) 3.7 x (0.3 mm) ( 5 days) 1.9 x (0.2 mm) ( 5 days) 2.0 x (0.1 mm) (5 days)
9.5 x (1.3 mm) 3.2 x IO-5 (1.0 mm) 1.4 x (1.3 mm) 1.9 x 10-5 (1.6 mm)
(30 min) (40 min) (30 min) (40 min)
Film. Pellet.
200
300
400
h / m
Figure 3. Changes in W spectra of a thin film of 3d on irradiation with UV light: (A) before irradiation; (B)after irradiation for 5 min; (C) after irradiation for 10 min; (D) after irradiation for 30 min. 40000
In general, polymers composed of an alternating disilanylene unit and n e l e c t r o n system a r e insulators. However, on treatment of t h e polymers with an oxidizing agent, they become conducting. Thus, cast films of 3a-d were exposed t o iodine vapor under atmospheric pressure for 5 days, and t h e n an excess of 12 vapor was evacuated under a reduced pressure ( 1 mmHg) for 30 min to give solid films (Table 2). The conductivity of the films was determined to be 7.9 x (3a),3.7 x (3b), 1.9 x (3c), a n d 2.0 x (3d) 5I.cm-l by the two-probe method under aerobic conditions. We also carried out doping of t h e polymers with ferric chloride. Thus, a film of the polymer was exposed to a FeC4 vapor supplied by heating t h e salt at 150 "C under reduced pressure ( 1 mmHg) for 30-40 min. The resulting black polymer was compressed into a pellet. The conductivity was found to be 9.5 x (3a),3.2 x (3b), 1.4 x lop4 (3~1, a n d 1.9 x (3d) S-cm-l.
Experimental Section
30000
E 20000
0
2
6
4
8
10
Time I h
Figure 4. Plot of molecular weights of products vs irradiation time for 3d: (0)irradiation in benzene; ( 0 ) irradiation in the presence of methanol in benzene. t h e reaction of silyl radicals generated by photolytic scission of t h e silicon-silicon bonds in the polymer backbone with oxygen in air, as observed for poly[@-
di~i1anylene)phenylenesl.~~ When benzene solutions of polymers 2a-d and 3a-d were photolyzed with a low-pressure mercury lamp bearing a Vycol filter, photodegradation products with low molecular weights were obtained in all cases. As can be seen in t h e photolysis of 3d shown in Figure 4 as a typical example, t h e molecular weight of t h e product decreased rapidly with increasing irradiation time and remained unchanged after 3 h irradiation. Similar photolysis of 3d in t h e presence of methanol afforded the product whose molecular weight was determined to be lower than that of the photoproduct obtained in t h e absence of methanol. The 'H NMR spectrum of t h e resulting photoproduct displays signals due to methoxy protons. T h e photochemical behavior of t h e other polymers was also found to be similar to that of 3d. These results clearly indicate that, upon irradiation, homolytic scission of a silicon-silicon bond takes place readily to generate silyl radicals, as reported previously.2b
General Methods. All reactions were carried out under an atmosphere of dry nitrogen. IH, 13C,and 29SiNMR spectra were recorded on a JEOL Model JNM-EX 270 and Bruker AMX-400 spectrometers. Mass spectra were measured with Shimadzu Model QP 1000 and Hitachi M-80-B spectrometers. LJV and IR spectra were recorded on Hitachi U-3210 and Perkin-Elmer 1600-FTIR spectrophotometers. ESCA spectra were measured with a Perkin-Elmer PHI 5400 instrument. XRD patterns were determined with a Rigaku RAD-1B instrument using a Ni-filtered Cu Ka radiation. Thermogravimetric analysis was performed using a Seiko TGDTA 320 equipment. Molecular weights of polymers were determined by gelpermeation chromatography using Shodex 806 and 804 as the column and using THF as the eluent, relative t o polystyrene standards. Materials. Triethylamine used as the solvent for polymerization was dried over KOH and distilled just before use. Diethynyldisilanes la-d were prepared by the method reported p r e v i o u ~ l y . ~2,5-Dibromopyridine, ~ 2,6-dibromopyridine, and the Pd catalyst were used as received. Polymerization of la with 2,6-Dibromopyridine. A mixture of 0.205 g (1.05 mmol) of la, 0.240 g (1.02 mmol) of 2,6-dibromopyridine, 26 mg (0.02 mmol) of tetrakidtriphenylphosphine)palladium, and 4 mg (0.02 mmol) of copper(1) iodide in 10 mL of triethylamine was stirred at 89 "C for 24 h. The solution was filtered, and after evaporation of the solvent, the residue was reprecipitated from benzene-methanol and dried under reduced pressure to give 0.103 g (39% yield) of 2a: dark brown viscous liquid; M , = 15 000, M , = 5800 (Md M,, = 2.5); IR 2153 (C=C) cm-l; LJV A,, (THF) 304.4 nm ( E 11 100); 'H NMR (6, in CDCl3) 0.37, 0.38 (two s, 6H, MeSi), 0.90 (m, 4H, SiCHZ), 1.14 (t, 6H, CH3, J = 7.8 Hz), 7.38 (d, 2H, pyridyl C(3)H and C(5)H, J = 7.8 Hz), 7.58 (t, lH, C(4)H, J = 7.8 Hz); 13C NMR (6, in CDC13) -5.14, -5.05 (MeSi), 6.06, 6.09 (SiCHZ), 8.12 (CH3), 92.83 (Sic=), 106.31 (C=), 126.95 (pyridyl C(3) and C(5)), 136.14 ((3411, 143.25 (C(2) and C(6)); 29SiNMR (6, in CDC13) -32.11, -32.16. Anal. Calcd for (C15HIgNSi&: C, 66.85; H, 7.10; N, 5.19. Found: C, 66.34; H, 7.01; N, 5.07.
Polymeric Organosilicon Systems Polymerization of lb with 2,B-Dibromopyridine. A mixture of 0.225 g (1.00 mmol) of lb, 0.236 g (1.00 mmol) of 2,6-dibromopyridine, 23 mg (0.02 mmol) of tetrakidtriphenylphosphine)palladium, and 6 mg (0.03 mmol) of copper(1) iodide in 10 mL of triethylamine was stirred at 89 "C for 60 h. The solution was filtered, and after evaporation of the solvent, the residue was reprecipitated from benzene-methanol and dried under reduced pressure to give 0.209 g (70% yield) of 2b: dark brown viscous liquid; M , = 19 000, M , = 9700 (Mw/ M,, = 1.9); IR 2152 (C=C) cm-l; UV I,,, (THF) 304.2 nm ( E 11900); lH NMR (6, in CDC13) 0.90 (4, 8H, SiCHz, J = 7.6 Hz), 1.13 (t, 12H, CH3, J = 7.6 Hz), 7.36 (d, 2H, pyridyl C(3)H and C(5)H, J = 7.8 Hz), 7.57 (t, l H , C(4)H, J = 7.8 Hz); 13C NMR (6, in CDC13) 4.62 (SiCHz), 8.32 (CH3), 92.33 (Sic=), 106.87 (C=), 127.03 (pyridyl C(3) and C(5)), 136.08 (C(4)), 143.34 (C(2) and C(6));29SiNMR (6, in CDC13) -28.22. Anal. Calcd for (C17Hz3NSi~)~: C, 68.62; H, 7.79; N, 4.71. Found: C, 67.65; H, 7.69; N, 3.95. Polymerization of IC with 2,B-Dibromopyridine. A mixture of 0.260 g (1.04 mmol) of IC,0.245 g (1.03 mmol) of 2,6-dibromopyridine, 23 mg (0.02 mmol) of tetrakidtriphenylphosphine)palladium, and 4 mg (0.02 mmol) of copper(1) iodide in 10 mL of triethylamine was stirred at 89 "C for 44 h. The solution was filtered, and after evaporation of the solvent, the residue was reprecipitated from benzene-methanol and dried under reduced pressure t o give 0.198 g (61% yield) of 2c: dark brown viscous liquid; M , = 28 000, M , = 12 000 ( M J M , = 2.3); IR 2152 (C=C) cm-'; UV I,,, (THF) 312.2 nm ( E 28 100); lH NMR (6, in CDC13) 0.35, 0.36 (two s, 6H, MeSi), 0.88 (t, 10H, SiCHz and CH3), 1.31-1.51 (m, 8H, CH2), 7.35 (d, 2H, pyridyl C(3)H and C(5)H, J = 7.9 Hz), 7.55 (t, l H , C(4)H, J = 7.9 Hz); 13C NMR (6, in CDC13) -4.60, -4.51 (MeSi), 13.73 (SicHz and CH3), 26.36, 26.72 (CHz), 93.28 (Sic=), 106.36 (Cz), 126.97 (pyridyl C(3) and C(5)), 136.15 (C(4)), 143.41 (C(2) and C(6)); 29SiNMR (6, in CDC13) -33.82. Anal. Calcd for (C19Hz7NSi2)n: C, 70.09; H, 8.36; N, 4.30. Found: C, 69.45; H, 8.56; N, 3.52. Polymerization of Id with 2,B-Dibromopyridine. A mixture of 0.318 g (1.04 "01) of Id, 0.246 g (1.04 mmol) of 2,6-dibromopyridine, 26 mg (0.02 mmol) of tetrakidtriphenylphosphine)palladium, and 4 mg (0.02 mmol) of copper(1) iodide in 10 mL of triethylamine was stirred at 89 "C for 44 h. The solution was filtered, and after evaporation of the solvent, the residue was reprecipitated from benzene-methanol and dried under reduced pressure to give 0.307 g (81%yield) of 2 d dark brown viscous liquid; M , = 20 000, M , = 8300 (Mw/ M , = 2.4); IR 2154 (C=C) cm-'; UV I,,, (THF) 306.2 nm ( E 23 800); lH NMR (6, in CDC13) 0.326, 0.332 (two s, 6H, MeSi), 0.81 (m, 10H, SiCHz and CH3), 1.15-1.53 (m, 16H, CHz), 7.32 (d, 2H, pyridyl C(3)H and C(5)H, J = 7.9 Hz), 7.52 (t, lH, C(4)H, J = 7.9 Hz); 13C NMR (6, in CDC13) -4.71, -4.62 (MeSi), 13.88,13.91 (SiCHZ), 14.00 (CH3), 22.45,24.39,31.36, 32.92 (CHz), 93.14 (Sic=), 106.25 (C=), 126.83 (pyridyl C(3) and C(5)), 135.99 (C(4)), 143.27 (C(2) and C(6)); 29SiNMR (6, in CDC13) -33.82. Anal. Calcd for (C23H35NSi~)~: C, 72.37; H, 9.24; N, 3.67. Found: C, 70.41; H, 9.22; N, 2.96. Polymerization of l a with 2,5-Dibromopyridine. A mixture of 0.188 g (0.96 mmol) of la, 0.223 g (0.94 mmol) of 2,5-dibromopyridine, 25 mg (0.02 mmol) of tetrakidtriphenylphosphine)palladium, and 4 mg (0.02 mmol) of copper(1) iodide in 10 mL of triethylamine was stirred at 89 "C for 24 h. The solution was filtered, and after evaporation of the solvent, the residue was reprecipitated from benzene-methanol and dried under reduced pressure to give 0.142 g (53% yield) of 3a: dark brown viscous liquid; M , = 19 000, M , = 6700 (Mw/ M , = 2.8); IR 2155 (C=C) cm-l; UV I,, (THF) 311.6 nm ( E 45 800); lH NMR (6, in CDC13) 0.34, 0.35 (two s, 6H, SiMe), 0.85 (m, 4H, SiCHZ), 1.10 (t, 6H, CH3, J = 7.8 Hz), 7.33 (m, l H , pyridyl C(3)H), 7.61 (m, l H , C(4)H), 8.58 (s, lH, C(6)H); 13CNMR (6, in CDC13) -5.14, -5.07, -4.99 (SiMe), 6.07, 8.12 (SiEt), 94.39,94.47, 94.54,97.47, 97.52, 97.58 (Sic=), 104.30, 106.45 (CE), 119.41, 119.44 (pyridyl C(5)), 126.52, 126.60
Organometallics, Vol. 14,No. 2, 1995 719 (C(3)), 138.58, 138.63 (C(4)), 141.60(C(2)),152.54 ((36)); 29Si NMR (6, in CDC13) -32.45, -32.35, -32.18, -32.11, -32.09. Anal. Calcd for (C15HlgNSi2)~:C, 66.85; H, 7.10; N, 5.19. Found: C, 65.09; H, 7.15; N, 5.23. Polymerization of l b with 2,5-Dibromopyridine. A mixture of 0.239 g (1.08 mmol) of lb, 0.239 g (1.01 mmol) of 2,5-dibromopyridine, 24 mg (0.02 mmol) of tetrakis(triphenylphosphine)palladium, and 4 mg (0.02 mmol) of copper(1) iodide in 10 mL of triethylamine was stirred at 89 "C for 17 h. The solution was filtered, and after evaporation of the solvent, the residue was reprecipitated from benzene-methanol and dried under reduced pressure t o give 0.270 g (90% yield) of 3b: dark brown viscous liquid; M , = 19 000, M , = 7300 (MJ M , = 2.6); IR 2155 (C=C) cm-'; UV ,A (THF) 318.0 nm ( E 32 900); 'H NMR (6, in CDC13) 0.89 (m, 8H, SiCHZ), 1.13 (t, 12H, CH3, J = 7.6 Hz), 7.34, 7.63 (two m, 2H, pyridyl C(3)H and C(4)H), 8.59 (s, lH, C(6)H); 13CNMR (6, in CDC13) 4.62, 4.66 (SiCHz), 8.29 (CH3), 93.84, 93.91, 93.98, 96.89, 96.95, 97.00 (Sic=),104.80, 106.99 (C=), 119.48 (pyridyl C(5)), 126.56, 126.63 (C(3)), 138.49, 138.54 (C(4)), 141.65 (C(2)), 152.54 (C(6)); 29SiNMR (6, in CDC13) -28.38, -28.49. Anal. Calcd for (C17H~3NSiz)~: C, 68.62; H, 7.79; N, 4.71. Found: C, 67.22; H, 7.88; N, 4.18. Polymerization of IC with 2,5-Dibromopyridine. A mixture of 0.263 g (1.05 mmol) of IC,0.239 g (1.01 mmol) of 2,5-dibromopyridine, 25 mg (0.02 mmol) of tetrakis(triphenylphosphine)palladium, and 4 mg (0.02 mmol) of copper(1) iodide in 10 mL of triethylamine was stirred a t 89 "C for 17 h. The solution was filtered, and after evaporation of the solvent, the residue was reprecipitated from benzene-methanol and dried under reduced pressure to give 0.270 g (90% yield) of 3c: dark brown viscous liquid; M , = 24,000, M , = 10 000 ( M J M , = 2.4); IR 2155 (C=C) cm-'; UV I,,, (THF) 314 nm ( E 34 000); lH NMR (6, in CDC13) 0.35, 0.36 (two s, 6H, SiMe), 0.87 (m, 10H, SiCHz and CH3), 1.37 (m, 4H, CHZ),1.47 (m, 4H, CHz), 7.33, 7.63 (two m, 2H, pyridyl C(3)H and C(4)H), 8.58 (s, l H , C(6)H);13CNMR (6, in CDC13) -4.68, -4.61, -4.52 (SiMe), 13.69,26.24,26.27,26.66 (n-BuSi),94.76,94.82,94.84, 94.90,97.83,97.89,97.95 (Sic=), 104.26, 106.42 (CE), 119.43, 119.47, 119.51 (pyridyl C(5)), 126.50, 126.57 (C(3)), 138.55, 138.60 (C(4)),141.58,141.61,141.65 (C(2)),152.53 (C(6));29Si NMR (6, in CDC13) -34.25, -34.16, -33.93, -33.83, -33.73. Polymerization of Id with 2,5-Dibromopyridine. A mixture of 0.316 g (1.03 mmol) of Id, 0.244 g (1.03 mmol) of 2,5-dibromopyridine, 25 mg (0.02 mmol) of tetrakis(triphenylphosphine)palladium, and 5 mg (0.03 mmol) of copper(1) iodide in 10 mL of triethylamine was stirred at 89 "C for 20 h. The solution was filtered, and after evaporation of the solvent, the residue was reprecipitated from benzene-methanol twice and dried under reduced pressure to give 0.316 g (83% yield) of 3d: dark brown viscous liquid; M , = 39 000, M , = 15 000 ( M J M n = 2.6); IR 2156 (C=C) cm-l; UV I,,, (THF) 313.4 nm ( E 38 200); 'H NMR (6, in CDC13) 0.35 (s, 6H, MeSi), 0.83 (br s, 10H, SiCHz and CH3), 1.10-1.57 (m, 16H, CH2), 7.33, 7.62 (two m, 2H, pyridyl C(3)H and C(4)H), 8.58 (s, l H , C(6)H); 13C NMR (6, in CDC13) -4.65, -4.58, -4.51 (MeSi), 14.00, 22.48,24.44,31.39,32.87,32.94(n-HexSi), 94.77,97.86,94.93, 97.84,97.92,97.99 (Sic=), 104.30, 106.48 (CE), 119.43,126.48 (pyridyl C(5)), 126.45, 126.51 (C(3)), 138.47, 138.51 (C(4)), 141.67, 141.71 (C(2)), 152.52 (C(6));29SiNMR (6, in CDC13) -34.31, -34.25, -34.18, -34.00, -33.93, -33.88. Anal. Calcd for (C23H35NSiz),: C, 72.37; H, 9.24; N, 3.67. Found: C, 71.96; H, 9.29; N, 3.18. Synthesis of 4. A mixture of 0.318 g (1.03 mmol) of Id, 0.384 g (2.40 mmol) of 2-bromopyridine, 63 mg (0.05 mmol) of tetrakis(triphenylphosphine)palladium,and 10 mg (0.05 mmol) of copper(1)iodide in 10 mL of triethylamine was refluxed for 26 h. The solution was filtered, and the solvent was evaporated. Products were separated by preparative GPC eluting with chloroform to give 4 (78% yield by GLC) as a liquid: IR 2158 (C=C) cm-'; UV I,, (THF) 249.2 ( E 23,6001,282.2 nm ( E 22,400); lH NMR (6, in CDC13) 0.35, 0.36 (s, 6H, MeSi), 0.80
Kunai et al.
720 Organometallics, Vol. 14, No. 2, 1995 (mc, 10H, SiCHz and CH3), 1.23 (mc, 8H, CHd, 1.32 (mc, 4H, CHz), 1.48 (mc, 4H, CHz), 7.16 (dd, 2H, pyridyl C(5)H, J = 7.6 Hz, J = 5.0 Hz), 7.39 (d, 2H, pyridyl C(3)H,J = 7.9 Hz), 7.57 (td, 2H, pyridyl C(4)H, J = 7.9 Hz, J = 7.6 Hz), 8.52 (d, 2H, C(6)H, J = 5.0 Hz); I3C NMR (6, in CDC13) -4.62, -4.53 (MeSi), 13.95, 14.02, 22.48, 24.42, 31.41, 32.98 (CH2), 92.53 (Sic=), 106.72 (Cs), 122.82, 127.40 (pyridyl C(3) and C(5)), 135.89 (C(4)), 143.13 (C(2)), 149.79 (C(6)); 29SiNMR (6, in CDCl3) -34.11, -34.05; MS m l z 460 (M+). HRMS: calcd for CzsH40NzSiz, mlz 460.2728; found, mlz 460.2701. Anal. Calcd for CzeH40NzSiz: C, 72.98; H, 8.75, N, 6.08. Found: C, 72.82; H, 8.61; N, 6.06. Synthesis of 5. A mixture of 0.326 g (1.06 mmol) of Id, 0.369 g (2.34 mmol) of 3-bromopyridine, 59 mg (0.05mmol) of tetrakis(triphenylphosphine)palladium, and 11mg (0.06 mmol) of copper(1) iodide in 10 mL of triethylamine was refluxed for 23 h. The solution was filtered, and the solvent was evaporated. Products were separated by preparative GPC eluting with chloroform to give 5 (66% yield by GLC) as a liquid: IR (THF) 249.0 ( E 26 200), 280.0 nm ( E 2154 ( C W ) cm-'; W A,, 14 300); 'H NMR (6, in CDC13) 0.341,0.347 (s, 6H, MeSi), 0.83 (mc, 10H, SiCHz and CH3), 1.26 (mc, 8H, CHd, 1.36 (mc, 4H, CHz), 1.48 (mc, 4H, CHd, 7.19 (dd, 2H, pyridyl C(5)H, J = 7.9 Hz, J = 5.0 Hz), 7.67 (dt, 2H, pyridyl C(4)H, J = 7.9 Hz, J = 1.7 Hz), 8.48 (dd, 2H, pyridyl C(6)H, J = 5.0 Hz, J = 1.7 Hz), 8.63 (d, 2H, C(2)H,J = 1.7 Hz); I3C NMR (6, in CDC13) -4.53, -4.45 (MeSi), 14.04, 22.52, 24.49, 31.45, 32.94 (CHz), 95.90 (Sic=), 104.44 (Ce), 120.41 (pyridyl C(3)), 122.84 (c(5)), 138.67 (C(4)), 148.55 (C(6)), 152.45 ((32)); 29Si NMR (6, in CDC13) -34.39; MS m l z 460 (M+). HRMS: calcd for C28H40N2Siz, mlz 460.2728; found, mlz 460.2668. Anal. Calcd for (228H40N~Si2:C, 72.98; H, 8.75, N, 6.08. Found: C, 72.71; H, 8.54; N, 5.87. Synthesis of 6. A mixture of 0.171 g (1.03 mmol) of 1,2diethynyltetramethyldisilane, 0.330 g (2.09 mmol) of 2-bromopyridine, 23 mg (0.02 mmol) of tetrakis(tripheny1phosphine)palladium, and 4 mg (0.02 mmol) of copper(1) iodide in 10 mL of triethylamine was heated to reflux for 8 h. After workup as usual, compound 6 was obtained in 92% yield (GLC). NO products arising from Si-Si bond scission were detected in the reaction mixture by GC-mass spectrometric analysis. After the mixture was heated for 30 h under the same conditions, no change was observed in product distribution. Data for 6: Mp 88.5-89 "C; UV A,, (THF) 248.2 ( E 21 600), 281.6 nm ( E 19 100); IR 2156 (CzC) cm-'; 'H NMR (6, in CDC13) 0.44 (s, 12H, MeSi), 7.23 (dd, 2H, pyridyl C(5)H, J = 7.5 Hz, J = 5.0 Hz), 7.46 (d, 2H, pyridyl C(3)H,J = 7.5 Hz), 7.65 (t, 2H, pyridyl C(4)H,J = 7.5 Hz), 8.58 (d, 2H, C(6)H, J = 5.0 Hz); I3C NMR (6, in CDC13) -3.14 (MeSi), 92.80 (Sic=), 106.43 (Cz), 122.97, 127.44 (pyridyl C(3) and C(5)), 136.01 (C(4)), 143.12 (C(2)), 149.92 (C(6));29SiNMR (6, in CDC13) -36.0; MS m l z 320 (M'). Anal. Calcd for Cl8HzoN2Siz: C, 67.45; H, 6.29, N, 8.74. Found: C, 67.53; H, 6.18; N, 8.61. Decolorization of 3c. To a solution of 3c (0.113 g, M , = 14 200, M,IM,, = 3.0) in 20 mL of benzene were added zinc powder (2.0 g) and 20 mL of 40% aqueous acetic acid. The mixture was stirred for 5 min under a nitrogen atmosphere, and then excess of zinc was filtered off. The organic layer was separated, washed with 5%aqueous sodium bicarbonate three times, and dried over magnesium sulfate. After evaporation of the solvent, 3c was recovered in 90% yield as a light brown oil: M , = 14 800, M,/Mn = 2.7. IR and 'H and NMR spectra were identical with those of the starting polymer. Photolysis of Polymer Films. A polymer was dissolved in THF and cast onto a quartz or NaCl plate. The film was irradiated with a 6-W low-pressure mercury lamp in air for
30 min, and the progress of the reaction was monitored periodically by IR and UV spectroscopy. In all cases, absorption bands near 310 nm decreased rapidly within 10 min, and IR spectra of the resulting films showed strong absorptions a t 3100 (Si-OH) and 1060 (Si-0-Si) cm-l. As a typical example, changes in UV spectra for 3d during the photolysis are shown in Figure 3. Photolysis of Polymers in Solution. A solution of a polymer (15 mg) in benzene (25 mL) was irradiated with a 6-W low-pressure mercury lamp bearing a Vycol filter in the presence or absence of methanol (10 mL) under dry nitrogen. Changes in molecular weight were monitored by GPC. In all cases, the molecular weights of the product decreased rapidly with increasing irradiation time and remained unchanged after 3-h irradiation. As a typical example, changes in molecular weight for 3d ( M , = 31 000, M J M n = 1.7) in the presence or absence of methanol are shown in Figure 4.
ConductivityMeasurementfor Polymers Doped with 12. A benzene solution of a polymer was cast into a thin film on a glass plate by evaporating the solvent. The film was dried in vacuo overnight and then exposed to saturated I2 vapor for 5 days under atmospheric pressure. An excess of 1 2 vapor was removed under reduced pressure (1mmHg) for 30 min. The resulting solid film was cut into a small piece, and the conductivity was measured by the two-probe method. The results obtained for 3a-d are shown in Table 2.
ConductivityMeasurement for Polymers Doped with FeCk Vapor. A thin film of a polymer was prepared in the same manner as described above. The film was held over ferric chloride powder which was placed in a glass vessel. Doping was performed under reduced pressure (1mmHg) by heating the bottom of the glass vessel at 150 "C for 30-40 min. The resulting solid polymer was pressed into a pellet, and the conductivity was determined by the two-probe method. The results obtained for 3a-d are shown in Table 2. Pyrolysis of 3c. Polymer 3c was solidified by preheating for 30 s. The sample was powdered finely and taken in an alumina crucible. F'yrolysis was carried out at 1500 "C in a quartz tube under a n argon atmosphere for 30 min. The resulting material was examined by X-ray powder diffraction analysis. Diffraction peaks due to /?-silicon carbide were observed clearly a t 28 = 35.50, 58.86, and 71.60", corresponding to the distances of d = 2.53,1.54, and 1.32 A, respectively. Thermogravimetric Analysis for Polymers. Thermal behavior of the polymers was examined by thermogravimetry under nitrogen. In all cases, a rapid weight loss of the polymer was found in a range 400-800 "C and then the weight became almost constant over 800 "C. The weight remaining at 1200 "C was found t o be 33%, 37%, 32%, and 31% for 2a-d and 34%, 24%, 30%, and 22% for 3a-d, respectively.
Acknowledgment. This research was supported in part by a Grant-in-Aid for Developmental Scientific Research (No. 06555274) from the Ministry of Education, Science, and Culture, to which our thanks are due. We also express our appreciationto Shin-EtsuChemical Co. Ltd.,Nitto Electric Industrial Co. Ltd., Dow Corning Asia Ltd., Toshiba Silicone Co. Ltd., Sumitomo Electric Co. Ltd., Kaneka Corp., and the Japan High Polymer center for financial support. We are also indebted to Dr. Hitoshi Kawaji, Mr. Kazunari Ando, and Mr. Hiroomi Horie of our university for measurements of XRD and ESCA spectra. OM940429X
