Article pubs.acs.org/Organometallics
Studies on the Detailed Structure of Poly(dimethylsilylene) Soichiro Kyushin,*,† Keisuke Ichikawa,† Yu Koyama,† Hiroyuki Shiraiwa,† Hiroshi Ichikawa,‡ Kiyohito Okamura,‡ and Kenji Suzuki‡ †
Division of Molecular Science, Faculty of Science and Technology, Gunma University, Kiryu, Gunma 376-8515, Japan Advanced Institute of Materials Science, Taihaku-ku, Sendai 982-0252, Japan
‡
S Supporting Information *
ABSTRACT: The detailed structure of poly(dimethylsilylene) was analyzed by 29 Si and 13C CP/MAS NMR spectra and theoretical calculations. The end groups were assigned to methoxy and hydroxy groups. This assignment was also supported by the NMR measurement of model compounds. Branched structures are not present. A trace amount of siloxane bonds is contained. The degree of polymerization was estimated to be ca. 580−750 by the 29Si CP/ MAS NMR spectra.
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at −2.0 ppm in the 13C CP/MAS NMR spectra (Figure 1). When the number of scans was set large enough and the NMR spectra were enlarged, several small signals could be observed. The enlargements of the 29Si and 13C CP/MAS NMR spectra are shown in Figures 2 and 3, respectively. The 29Si CP/MAS NMR spectra in Figure 2 have several features. Two signals at ca. −43.5 and 18.5 ppm were observed in all spectra, and their relative intensity ratio is almost constant. Two signals at ca. −22.5 and 6.6 ppm were observed in some spectra. They are very small, but in the case of sample F, these signals were clearly observed. These features indicate that the signals at ca. −43.5 and 18.5 ppm are due to the same substructure, probably the end groups of poly(dimethylsilylene). The signals at ca. −22.5 and 6.6 ppm seem to be due to an irregularly formed substructure. The 13C CP/MAS NMR spectra in Figure 3 also have several features. The signal at ca. 51.5 ppm was observed in all spectra. In addition, shoulders were observed just on the left side of the main signal at −2.0 ppm. In some cases, the shoulders were observed as two kinds of signals. Assignment of the NMR Signals by Theoretical Calculations. In order to assign the signals in the 29Si and 13 C CP/MAS spectra, we calculated chemical shifts by the gauge-independent atomic orbital (GIAO) method at the B3LYP/6-311+G(2d,p) level. Quite recently, we assigned the signals of the 29Si CP/MAS and solution NMR spectra of organosilicon clusters with GIAO calculations.5 The GIAO calculations reproduced the signal pattern of the 29Si NMR spectra, although there is some difference between the observed and calculated chemical shifts. An important point of this methodology is the rigid structures of the organosilicon clusters. The rigid structures correspond to the fixed structures used in the GIAO calculations. As poly(dimethylsilylene) has been reported to be fixed at an all-anti conformation6 in the
INTRODUCTION Polysilane polymers show unique electronic and optical properties which are not observed in polymers with carbon skeletons. Polysilane polymers with various substituents have been synthesized so far, and their structures and properties have been studied extensively.1 Structural studies on polysilane polymers with alkyl and aryl groups on silicon atoms have been carried out by wide-angle X-ray diffraction (WAXD), temperature-dependent UV spectra, IR spectra, Raman spectra, etc. These studies showed that the silicon main chain can take 7/3 helical, all-anti, or TGTG′ conformations, depending on the temperature and the alkyl and aryl groups on silicon atoms.1 Among polysilane polymers, poly(dimethylsilylene) can be regarded as a prototype. However, poly(dimethylsilylene) has not been studied extensively since its first synthesis in 19492 because this polymer is not soluble in most organic solvents. In 1975, Yajima and co-workers reported that poly(dimethylsilylene) can be used as a starting material of silicon carbide fibers.3 Since then, silicon carbide fibers have been used as a thermally stable material with high tensile strength, and today this material has become more and more important. However, the fundamental structure of poly(dimethylsilylene) still remains unknown. We report herein the detailed structure of poly(dimethylsilylene). We found that 29Si and 13C crosspolarization magic angle spinning (CP/MAS) NMR spectroscopy is an effective method of analyzing poly(dimethylsilylene). A combination of this NMR measurement and theoretical calculations has revealed the detailed structure of poly(dimethylsilylene).
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RESULTS AND DISCUSSION Si and 13 C CP/MAS NMR Spectra of Poly(dimethylsilylene). Seven samples of poly(dimethylsilylene) (A−G) supplied by Nippon Soda Co., Ltd. were used for NMR measurements. These samples show a signal of the backbone silicon atoms at −34.4 ppm in their 29Si CP/MAS NMR spectra4 and a signal of the methyl groups on the silicon atoms 29
© XXXX American Chemical Society
Received: March 12, 2014
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Figure 1. 29Si (left) and 13C (right) CP/MAS NMR spectra of poly(dimethylsilylene) (sample B).
solid state,4,7 we carried out the GIAO calculations by using the all-anti conformation. Icosamethyldecasilanes bearing methoxy (1) and hydroxy groups (2) at the 1,10-positions were used as model compounds (Scheme 1),8 because after Wurtz-type
Among the data in Table 1, the chemical shifts of the 29Si nuclei of 1 and 2 reproduce well the 29Si CP/MAS NMR spectra. The calculated chemical shifts of the terminal 29Si nuclei are 17.9 and 17.2 ppm, and those of the 29Si nuclei at the 2- and 3-positions (−31.4 to −30.0 ppm) are slightly upfield from the main signal (−24.8 to −24.5 ppm), although there is a difference between the experimental and calculated values. The data of 4 and 5 do not fit the NMR spectra. The data of 1 and 2 in Table 2 also fit the 13C CP/MAS NMR spectra. The signal of the methyl groups on the terminal silicon atoms (1, 0.1 ppm; 2, 5.3 ppm) is present slightly downfield from the main signal (−0.5 to −0.4 ppm). Moreover, the 13C signal of the methoxy group of 1 is at 51.7 ppm, which is very close to the observed signal at ca. 51.5 ppm. Although the calculated 13C chemical shifts of 4 and 5 also fit the 13C CP/MAS NMR spectra, their calculated 29Si chemical shifts are quite different from those in the measured 29Si CP/MAS NMR spectra. In the case of 3, the calculated 29Si chemical shifts of the 1- to 3-positions (−31.0 to −27.3 ppm) and the calculated 13C chemical shifts of the methyl groups on the terminal and adjacent silicon atoms (−2.9 to −1.7 ppm) are so close to the broad and intense main signal that the signals could be hidden. However, the IR spectrum of poly(dimethylsilylene), which was prepared by Wurtz-type coupling of dichlorodimethylsilane with sodium similarly to our poly(dimethylsilylene), has been reported to show no Si−H vibration at all at 2250−2100 cm−1.9 Therefore, the possibility of hydrogen end groups is low. From these considerations, the end groups of poly(dimethylsilylene) can be assigned to methoxy and hydroxy groups. The presence of two kinds of shoulders just downfield from the main signal in the 13C CP/ MAS NMR spectra shows that both methoxy and hydroxy groups are present as the end groups. Assignment of the NMR Signals by NMR Measurement of Model Compounds. The above discussion based on the theoretical calculations was checked by NMR measurements of model compounds 6 and 7 (Scheme 2). Compound 6 shows signals at −45.7, −40.2, and 20.6 ppm in the 29Si NMR spectrum in CDCl3 and at −5.2, −4.5, 0.0, and 51.1 ppm in the 13 C NMR spectrum in CDCl3. Compound 7 shows signals at −46.6, −41.8, and 8.8 ppm in the 29Si NMR spectrum in CDCl3 and at −5.7, −4.5, and 2.6 ppm in the 13C NMR spectrum in CDCl3. These data correspond to the 29Si and 13C CP/MAS NMR spectra of poly(dimethylsilylene), showing that the above assignment is correct. Formation of the End Groups of Poly(dimethylsilylene). The methoxy and hydroxy end groups are considered to be formed as shown in Scheme 3.
Scheme 1. Model Compounds of Linear Oligosilanes with Various End Groups Used for Theoretical Calculations
coupling of dichlorodimethylsilane, the reaction mixture was hydrolyzed with methanol and water. If the hydrolysis is not successful because of the low solubility of poly(dimethylsilylene), the end groups might be chlorine atoms (compound 4). We also calculated other model compounds with hydrogen atoms (3) and methyl groups (5), although the possibility of these end groups is low. The results of the 29Si and 13C chemical shifts are summarized in Tables 1 and 2. Only half of the data are shown because of the symmetry of the allanti conformation. Table 1. Chemical Shifts of the 29Si Nuclei of 1−5 Calculated by the GIAO Method at the B3LYP/6-311+G(2d,p) Level δ/ppm compound
Si1
Si2
Si3
Si4
Si5
1 2 3 4 5
17.9 17.2 −31.0 37.8 −12.7
−31.4 −31.2 −29.4 −29.0 −32.0
−30.0 −30.7 −27.3 −29.2 −27.5
−24.8 −24.5 −24.5 −24.7 −24.5
−24.6 −24.7 −24.9 −24.3 −24.6
Table 2. Chemical Shifts of the 13C Nuclei of 1−5 Calculated by the GIAO Method at the B3LYP/6-311+G(2d,p) Level δ/ppm compound
E
Me1
Me2
Me3
Me4
Me5
1 2 3 4 5
51.7
0.1 5.3 −2.9 6.3 0.7
−3.4 −3.3 −1.7 −3.5 −2.5
−1.1 −1.2 −0.8 −1.1 −0.8
−0.5 −0.4 −0.4 −0.5 −0.4
−0.4 −0.4 −0.4 −0.4 −0.3
−1.3
B
dx.doi.org/10.1021/om500264u | Organometallics XXXX, XXX, XXX−XXX
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Figure 2. Enlargements of the 29Si CP/MAS NMR spectra of poly(dimethylsilylene) (samples A−G). The abbreviation “ssb” denotes a spinning sideband.
spectra in Figure 3 show that the shapes of the shoulders slightly downfield from the main signal at −2.0 ppm are different, depending on the samples. This means that the workup conditions (temperature and time) in the hydrolysis process are not necessarily the same in different reactions. As a
Polymerization of dichlorodimethylsilane with sodium gave poly(dimethylsilylene) with chlorine end groups. The reaction mixture was hydrolyzed with methanol and water. During this workup process, the terminal chlorine atoms were converted into methoxy and hydroxy groups. The 13C CP/MAS NMR C
dx.doi.org/10.1021/om500264u | Organometallics XXXX, XXX, XXX−XXX
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Figure 3. Enlargements of the 13C CP/MAS NMR spectra of poly(dimethylsilylene) (samples A−G). The abbreviation “ssb” denotes a spinning sideband.
result, the ratio of the methoxy and hydroxy groups changes, depending on the samples. Possibility of Branched Structures. Dichlorodimethylsilane is contaminated with a trace amount of other chlorosilanes. The major contaminant is trichloromethylsilane, and the
second major contaminant is chlorotrimethylsilane. Other minor chlorosilanes are also contained, but they have not fully been analyzed. Trichloromethylsilane has the possibility of forming branched structures in poly(dimethylsilylene). If other chlorosilanes with three and four chlorine atoms are contained D
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Scheme 2. Model Compounds Used for NMR Measurements
Scheme 4. Model Compounds of Branched Oligosilanes Used for Theoretical Calculations
as minor contaminants, they might also form branched structures. In order to study the presence of the possible branched structures, we calculated the 29Si chemical shifts of model compounds 8−12 (Scheme 4). The results are summarized in Table 3. The calculated chemical shifts of the branched 29Si nuclei (Si1) of 8, 9, and 11 are in the range 31.8− 35.4 ppm. The signal of the branched 29Si nucleus of 10 is expected to appear at −87.4 to −86.5 ppm. The 29Si CP/MAS NMR spectra in Figure 2 do not show signals in these regions. In the case of 12, the calculated chemical shift of the Si1 nucleus (−43.2 to −43.1 ppm) is in accord with the observed signal at ca. −43.5 ppm. However, the calculated signal due to the Si2 nucleus (−24.2 to −22.4 ppm) was observed as a far smaller signal than that at ca. −43.5 ppm, except for sample F. From these considerations, it is reasonable to conclude that poly(dimethylsilylene) does not contain the branched structures, although the branched structures cannot be completely excluded in the case of sample F. The assignment of the signal at ca. −22.5 ppm is discussed below. Contamination of Siloxane Structures. The 29Si CP/ MAS NMR spectra in Figure 2 show very weak signals at ca. −22.5 and 6.6 ppm. In most cases, the intensity of these signals is much lower than those of the end groups at ca. −43.5 and 18.5 ppm. This means that these weak signals are due to irregular structures of poly(dimethylsilylene) and/or contaminants. We considered many possibilities and found that the chemical shifts of these two signals are in good accord with those of the M (6 to 8 ppm) and D (−23 to −18 ppm) structures of siloxane.10 We postulated the M and D structures in Scheme 5 and calculated the 29Si chemical shifts. The results are summarized in Table 4. The calculated chemical shifts of Si0 and Si1 reproduce the observed chemical shifts well. From these results, the weak signals at 6.6 and −22.5 ppm can be assigned to the M and D structures, respectively. The formation of the M and D structures is explained by hydrolysis and condensation of poly(dimethylsilylene) with chlorine end groups (Scheme 6). The condensation of two molecules of poly(dimethylsilylene) gives the M structure, and the condensation of poly(dimethylsilylene) and dichlorodimethylsilane gives the M and D structures. Two points are noted. Signals due to the T (−66 to −65 ppm) and Q (−110 to −105 ppm) structures10 of siloxane were not observed, as shown in Figure 2. This result is rationalized by the fact that the T and Q structures cannot be formed from dichlorodimethylsilane and poly(dimethylsilylene) with chlorine end groups. Another point is the much weaker intensity of the signals of the M and D structures in comparison to those of
Table 3. Chemical Shifts of the 29Si Nuclei of 8−12 Calculated by the GIAO Method at the B3LYP/6311+G(2d,p) Levela δ/ppm
a
1
compound
Si
8a 8b 9a 9b 10a 10b 11a 11b 12a 12b
34.4 34.3 35.4 35.4 −86.5 −87.4 32.5 31.8 −43.1 −43.2
Si
2
−28.5 −28.0 −21.4 −24.0 −22.9 −23.8 −22.7 −20.2 −24.2 −22.4
Si3
Si4
Si5
−31.2 −30.8 −26.8 −32.9 −30.1 −32.6 −30.9 −28.8 −31.0 −32.4
−37.2 −36.3 −35.5 −36.9 −36.3 −34.7 −35.7 −36.5 −33.8 −33.6
19.7 19.7 21.2 20.1 19.7 19.7 19.6 20.0 19.7 20.2
The chemical shifts of Si2−Si5 are averaged values of three 29Si nuclei.
Scheme 5. Model Compounds of Oligosilanes Containing Siloxane Structures Used for Theoretical Calculations
Table 4. Chemical Shifts of the 29Si Nuclei of 13 and 14 Calculated by the GIAO Method at the B3LYP/6311+G(2d,p) Level δ/ppm 0
compound
Si
13 14
−24.2
Si
1
12.8 9.2
Si
2
−38.4 −35.2
Si3
Si4
Si5
−32.4 −36.6
−35.7 −32.6
−10.5 −13.2
the end groups. This result is explained as follows. When poly(dimethylsilylene) with chlorine end groups is hydrolyzed with methanol and water, the resulting poly(dimethylsilylene) with methoxy and hydroxy end groups immediately precipitates. As a result, condensation of poly(dimethylsilylene) seldom occurs.
Scheme 3. Formation of Methoxy and Hydroxy End Groups of Poly(dimethylsilylene)
E
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These values are in the range of ca. 580−750, and the variation is not very large except for the data of sample C. Our result is in accord with the result of Wesson and Williams,9 but it is quite different from the results of Burkhard2 and Ohnaka.11 Perhaps the NMR and IR measurements are more direct methods of estimating the degree of polymerization in comparison to ebulliometry and high-temperature GPC. The degrees of polymerization are much smaller than those of other soluble polysilane polymers reported so far (103−104).1 The low degrees of polymerization might be explained by the fact that polymerization is complete when poly(dimethylsilylene) precipitates because of insolubility in the solvent.
Scheme 6. Formation of Poly(dimethylsilylene) Containing Siloxane Structures
The signals at 18.5 and −34.4 ppm are due to the terminal two silicon atoms and the remaining silicon atoms, respectively. Therefore, the ratio of “the integration of the signal at −34.4 ppm” to “the integration of the signal at 18.5 ppm/2” corresponds to the number of the silicon atoms except for the terminal two silicon atoms. This ratio plus 2 is the number of all silicon atoms: that is, the degree of polymerization. The correction term C (=1.02) was estimated from the integration ratio of the 29Si signal at 15.3 ppm and those at −44.3 and −40.6 ppm of the model compound 7 (Figure S7, Supporting Information). The correction term C is the relative sensitivity of both signals in the 29Si CP/MAS NMR spectra and was estimated by the 29Si NMR spectrum of 6. The results are summarized in Table 5. Table 5. Degree of Polymerization of Poly(dimethylsilylene) Estimated by 29Si CP/MAS NMR Spectra n
sample
n
A B C D
660 750 1150 720
E F G
700 750 580
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EXPERIMENTAL SECTION
Materials. Samples of poly(dimethylsilylene) (A−G) were supplied by Nippon Soda Co., Ltd. These samples were prepared by the Wurtz-type coupling of dichlorodimethylsilane with sodium in toluene, followed by hydrolysis with methanol and water. Samples A− E were prepared in the standard reaction time, while samples F and G were prepared at short and prolonged reaction times, respectively. 1,6Dichlorododecamethylhexasilane was prepared by a published procedure.13 Diethyl ether was distilled from sodium benzophenone ketyl. Hexane was distilled. Other reagents were purchased and used without further purification. Measurements. 1H (500 MHz), 13C (126 MHz), and 29Si (99 MHz) NMR spectra were measured with a JEOL JNM-LA500 spectrometer. 1H (300 MHz) NMR spectra were measured with a JEOL JNM-AL300 spectrometer. 13C (75 MHz) and 29Si (59 MHz) CP/MAS NMR spectra were measured with a Bruker Avance III spectrometer with a CP/MAS probe. Theoretical Calculations of NMR Chemical Shifts. All theoretical calculations were performed using Gaussian 0314 and Gaussian 09.15 The optimized structures were calculated at the B3LYP/6-31G(d) level. The structures of 1−5 were optimized by assuming the all-anti conformation. The magnetic shielding tensors of the 13C and 29Si nuclei were calculated by the GIAO method at the B3LYP/6-311+G(2d,p) level using the optimized structures. All calculations were carried out on an HPC Systems HPC-5000XW208T computer and the PRIMERGY system of the Research Center for Computational Science, Japan. For details, see the Supporting Information. Synthesis of 1,6-Dimethoxydodecamethylhexasilane (6). This compound was previously synthesized by heating a mixture of 1,2-dimethoxytetramethyldisilane and 1,4-dimethoxyoctamethyltetrasilane at 220 °C in a sealed ampule for 24 h.16 We synthesized this compound by the reaction of 1,6-dichlorododecamethylhexasilane with methanol. This reaction was carried out under an argon atmosphere. A mixture of methanol (0.429 g, 13.4 mmol) and triethylamine (1.32 g, 13.0 mmol) was added dropwise to a solution of 1,6-dichlorododecamethylhexasilane (1.78 g, 4.24 mmol) in hexane (20 mL) at room temperature. The mixture was stirred at room temperature for 3 h. The reaction mixture was filtered twice to remove salts. Evaporation of the filtrate gave 6 (1.62 g, 93%) as a colorless oil. Data for 6 are as follows. 1H NMR (300 MHz, CDCl3): δ 0.205 (s, 12H), 0.213 (s, 12H), 0.25 (s, 12H), 3.42 (s, 6H). 13C NMR (126
integration of the signal at −34.4 ppm × C +2 integration of the signal at 18.5 ppm
sample
CONCLUSION
In summary, after a long period from the first synthesis of poly(dimethylsilylene), its detailed structure has been revealed: (1) the end groups can be assigned to methoxy and hydroxy groups, (2) branched structures are not present, (3) a trace amount of siloxane bonds is present, and (4) the degree of polymerization is estimated to be ca. 580−750. The 29Si and 13 C CP/MAS NMR spectra were found to be effective for analyzing insoluble poly(dimethylsilylene). GIAO calculations support these structural details.
Degree of Polymerization. The degrees of polymerization of polysilane polymers have been measured by gel permeation chromatography (GPC) with polystyrene standards.1 This method cannot be easily applied to poly(dimethylsilylene) because this polysilane is not soluble in most organic solvents. In spite of this difficulty, there have been a few reports on the degree of polymerization of poly(dimethylsilylene). Burkhard measured the molecular weight of poly(dimethylsilylene) ebulliometrically and estimated that the average degree of polymerization is approximately 55.2 Ohnaka analyzed the molecular weight by high-temperature GPC in chloronaphthalene at ca. 210 °C. The degree of polymerization was found to be about 60.11 On the other hand, Wesson and Williams estimated an average degree of polymerization as 637 on the basis of the intensity of the Si−O stretching band in the IR spectrum.9 We analyzed the degree of polymerization of poly(dimethylsilylene) by the 29Si CP/MAS NMR spectra.12 The degree of polymerization n was calculated by using the equation n=2
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MHz, CDCl3): δ −5.2, −4.5, 0.0, 51.1. 29Si NMR (99 MHz, CDCl3): δ −45.7, −40.2, 20.6. Synthesis of 1,6-Dihydroxydodecamethylhexasilane (7).17 This reaction was carried out in a Schlenk flask equipped with a dropping funnel under a nitrogen atmosphere. A solution of 1,6dichlorododecamethylhexasilane (1.00 g, 2.38 mmol) in diethyl ether (4.2 mL) was added dropwise to a mixture of sodium hydrogencarbonate (0.40 g, 4.8 mmol), diethyl ether (1.6 mL), and water (3.4 mL) at room temperature. The mixture was stirred at room temperature for 90 min. Anhydrous sodium sulfate was added to remove the remaining water. This mixture was filtered, and the filtrate was evaporated. The residue was recrystallized from hexane to give 7 (0.644 g, 71%) as colorless crystals. Data for 7 are as follows. 1H NMR (500 MHz, CDCl3): δ 0.17 (s, 12H), 0.20 (s, 12H), 0.26 (s, 12H), 1.76 (s, 2H). 13C NMR (126 MHz, CDCl3): δ −5.7, −4.5, 2.6. 29Si NMR (99 MHz, CDCl3): δ −46.6, −41.8, 8.8. 29Si CP/MAS NMR (59 MHz): δ −44.3, −40.6, 15.3.
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ASSOCIATED CONTENT
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AUTHOR INFORMATION
A.; Koganezono, M.; Otsuka, K.; Ishida, S.; Kyushin, S. Chem. Eur. J. 2014, 20, 9263−9266. (6) Michl, J.; West, R. Acc. Chem. Res. 2000, 33, 821−823. (7) Furukawa, S.; Takeuchi, K. Solid State Commun. 1993, 87, 931− 934. (8) For reviews of the 29Si NMR of alkoxysilanes and silanols, see: (a) Liepiņs,̌ E.; Zicmane, I.; Lukevics, E. J. Organomet. Chem. 1986, 306, 167−182. (b) Brook, M. A. Silicon in Organic, Organometallic, and Polymer Chemistry; Wiley: New York, 2000; Chapter 1. (9) Wesson, J. P.; Williams, T. C. J. Polym. Sci., Polym. Chem. Ed. 1979, 17, 2833−2843. (10) The M, D, T, and Q structures denote the R3SiO0.5, R2Si(O0.5)2, RSi(O0.5)3, and Si(O0.5)4 structures of siloxane, respectively. See: Williams, E. A. In The Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: Chichester, U.K., 1989; Chapter 8. (11) Ohnaka, T. In Development of Organosilicon Polymers; Sakurai, H., Ed.; CMC: Tokyo, Japan, 1989; pp 99−114. (12) For studies estimating the degrees of polymerization of carbon polymers with 13C CP/MAS NMR spectra, see: (a) VanderHart, D. L.; Pérez, E. Macromolecules 1986, 19, 1902−1909. (b) Akiyama, S.; Komoto, T.; Ando, I.; Sato, H. J. Polym. Sci., Part B: Polym. Phys. 1990, 28, 587−594. (c) Princi, E.; Vicini, S.; Proietti, N.; Capitani, D. Eur. Polym. J. 2005, 41, 1196−1203. (13) (a) Gilman, H.; Inoue, S. J. Org. Chem. 1964, 29, 3418−3419. (b) Chernyavskii, A. I.; Zavin, B. G. Russ. Chem. Bull. 1997, 46, 1449− 1453. (14) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision D.02; Gaussian, Inc., Wallingford, CT, 2004. (15) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Keith, T.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision C.01; Gaussian, Inc., Wallingford, CT, 2010. (16) Atwell, W. H.; Mahone, L. G.; Hayes, S. F.; Uhlmann, J. G. J. Organomet. Chem. 1969, 18, 69−75. (17) Stüger, H.; Eibl, M.; Hengge, E.; Kovacs, I. J. Organomet. Chem. 1992, 431, 1−15.
* Supporting Information S
Figures, tables, and xyz files giving spectral data, details of theoretical calculations, and all computed molecule Cartesian coordinates in a format for convenient visualization. This material is available free of charge via the Internet at http:// pubs.acs.org. Corresponding Author
*E-mail for S.K.:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the PD-SiC’s Project of the Advanced Institute of Materials Science, Japan in collaboration with Ube Industries, Ltd., Nippon Soda Co., Ltd., Gunze Ltd., the Japan Wool Textile Co., Ltd., and Shikibo Ltd. We thank Prof. Takeshi Yamanobe, Gunma University, Japan, for the measurement of the 29Si and 13C CP/MAS NMR spectra. We also thank Dr. Takafumi Imai, Momentive Performance Materials Japan LLC, for helpful discussions. Theoretical calculations were performed at the Research Center for Computational Science, Japan.
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dx.doi.org/10.1021/om500264u | Organometallics XXXX, XXX, XXX−XXX
