Thermal behavior of benzobis(tetraethyldisilacyclobutene)

Akinobu Naka 1 , Kazunari Yoshizawa 2 ,  and Mitsuo Ishikawa 3
  • 1 Department of Life Science, Kurashiki University of Science and the Arts, 2640 Nishinoura, Tsurajima-cho, Kurashiki, Okayama 712-8505, Japan
  • 2 Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka 819-0395, Japan
  • 3 Faculty of Engineering, Department of Applied Chemistry, Hiroshima University, Higashi-Hiroshima 739-8527, Japan
Akinobu Naka, Kazunari Yoshizawa and Mitsuo Ishikawa

Abstract

The thermolysis of benzo[1,2:4,5]bis(1,1,2, 2-tetraethyl-1,2-disilacyclobut-3-ene) (1) in the presence of ethylene in an autoclave at 250 °C for 24 h afforded two products, compound 2, consisting of one molecule of 1 and two ethylene molecules, and compound 3, arising from two molecules of 1 and three molecules of ethylene in 60 and 20 % yields, respectively. The reaction of 1 with phenylacetylene at 150 °C for 24 h gave a mixture of regio-isomers 4a and 4b, arising from the insertion of the triple bond of phenylacetylene into two silicon–silicon bonds in 1 in 86 % combined yield. The reaction of 1 with 1-hexyne at 150 °C for 24 h again produced two regio-isomers 5a and 5b in 85 % combined yield.

1 Introduction

Small-ring compounds involving a silicon–silicon bond are extremely reactive, due to their high strain energy, and show interesting chemical behavior. Since our initial study on the chemistry of benzo-1,1,2,2-tetraethyl-1,2-disilacyclobutene published in 1991 [1], we have investigated the thermolysis, photolysis, and transition metal-catalyzed reactions of many benzo-1,2-disilacyclobutenes [2–6]. We have also found that the transition metal-catalyzed reactions of cis- and trans-benzo-1,2-di-tert-butyl-1,2-dimethyl- and benzo-1,2-diisopropyl-1,2-dimethyl-1,2-disilacyclobutenes with alkynes proceeded with high stereospecificity to give the respective adducts, arising from the insertion of the carbon-carbon triple bond into a silicon–silicon bond in the benzodisilacyclobutenyl ring [7, 8].

The thermolysis of cis- and trans-benzo-1,2-diisopropyl-1,2-dimethyl-1,2-disilacyclobutene in the presence of tert-butyl alcohol in a degassed sealed glass tube at 300 °C for 24 h proceeded with high stereospecificity to give the respective alcohol adducts in high yields [9]. The cis- and trans-benzodisilacyclobutenes also react stereospecifically with mono-substituted acetylenes to produce the respective insertion products. Interestingly, the thermal reactions of the benzodisilacyclobutenes with mono-substituted acetylenes take place more readily at lower temperature than that of tert-butyl alcohol.

To clarify the mechanism of the reactions of cis- and trans-benzodisilacyclobutenes with tert-butyl alcohol and mono-substituted acetylenes, we have carried out theoretical calculations, and found that the addition of tert-butyl alcohol to the benzodisilacyclobutenes occurs in the plane involving the benzodisilacyclobutenyl ring and the H–O bond of the tert-butyl alcohol, without a ring opening [9, 10]. In the reaction with mono-substituted acetylenes, the acetylenes also insert into a silicon–silicon bond in the benzodisilacyclobutenes, via a [2+1] concerted pathway, without the formation of biradical species or an o-quinodisilane [9, 10]. Yoshizawa and colleagues [11] carried out computational analyses for the reaction of benzobis(tetramethyldisilacyclobutene) with acetylene, and came to the conclusion that the ring-opening reactions via the o-quinodisilane require very high activation energies.

To get more information about the thermal behavior of the benzo(disilacyclobutene) derivatives, we investigated the thermolysis of benzobis(tetraethyldisilacyclobutene) [12–14] in the presence of alkenes and alkynes.

2 Results and discussion

First, we carried out the thermolysis of benzo[1,2:4,5]bis(1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene) (1) in the presence of ethylene [11, 15]. Treatment of 1 with ethylene in benzene in an autoclave at 150 °C for 24 h afforded no products. The starting compound 1 was recovered unchanged. However, when the same mixture was heated at 250 °C for 24 h, two products, benzo[1,2:4,5]bis(1,1,4,4-tetraethyl-1,4-disilacyclohex-5-ene) (2), consisting of one molecule of the starting compound 1 and two ethylene molecules, and bis(1,1,4,4-tetraethyl-2H,3H-1,4-disila[3, 4, 9, 10]naphtho)-1,1,2,2,5,5,8,8-octaethyl-1,2,5,8-tetrasilacyclodeca-3,9-diene (3), arising from two molecules of 1 and three ethylene molecules, were produced in 60 % and 20 % yields, respectively, as shown in Scheme 1. All spectral data for 2 and 3 were identical with those of the authentic samples obtained from the palladium-catalyzed reaction of 1 with ethylene [15].

Scheme 1:
Scheme 1:

Thermal reaction of 1 with ethylene.

Citation: Zeitschrift für Naturforschung B 71, 3; 10.1515/znb-2015-0155

According to our theoretical calculations for the thermal ring-opened products of benzotetramethyldisilacyclobutene [9], a singlet biradical is more stable than an o-quinodisilane. Therefore, in the present case, the formation of the products 2 and 3 would be understood by the reaction involving biradical species formed by the homolytic scission of a silicon–silicon bond in 1. The biradical species (A), generated by the homolytic scission of one of the silicon–silicon bonds in 1, reacts with ethylene to give adduct (B). Radical scission of a silicon–silicon bond in B also produces a biradical (C). The reaction of C with ethylene affords a biradical species (D). Finally, intramolecular ring closure of D gives the product 2. The product 3 would be produced by the intermolecular radical coupling between C and D.

In marked contrast to ethylene, the reactions of 1 with terminal olefins, such as propene and 1-hexene at 250 °C afforded no volatile products. Complicated reaction mixtures involving nonvolatile substances were always obtained.

Like benzodisilacyclobutenes, benzobis(disilacyclobutene) 1 readily reacts with mono-substituted acetylenes at lower temperature than with ethylene, to give two regio-isomers of a 1:2 adduct in high yields. Thus, the reaction of 1 with phenylacetylene in a sealed glass tube at 150 °C for 24 h produced two isomers (4a and 4b) of the 1:2 adduct, in a ratio of 1:1, in 86 % combined yield (Scheme 2). GLC analysis of the reaction mixture showed a homogeneous peak, and no other volatile products were detected. All attempts to separate 4a from 4b were unsuccessful. The mixture consisting of the same ratio of 4a and 4b was always obtained.

Scheme 2:
Scheme 2:

Thermal reactions of 1 with phenylacetylene and 1-hexyne.

Citation: Zeitschrift für Naturforschung B 71, 3; 10.1515/znb-2015-0155

The structures of 4a and 4b were confirmed by spectrometric analysis of the 1:1 mixture of 4a and 4b. The 1H NMR spectrum for the mixture of 4a and 4b revealed a single resonance at 7.71 ppm due to the phenylene ring proton of 4a and two resonances at 7.70 and 7.73 ppm attributed to the phenylene ring protons of 4b, with an integral ratio of 2:1:1.

Similar reaction of 1 with 1-hexyne at 150 °C for 24 h afforded 1:2 adducts 5a and 5b in the ratio of 1:1 in 85 % combined yield. Again, all attempts to isolate two regio-isomers 5a and 5b in a pure state were unsuccessful. The structures of 5a and 5b were verified by spectrometric analysis of the mixture.

As reported recently in a theoretical study of the reaction of benzotetramethyldisilacyclobutene with acetylene [10], an acetylene molecule directly inserts into a silicon–silicon bond in benzodisilacyclobutene to give benzodisilacyclohexene, without the formation of biradical species or an o-quinodisilane as the intermediates. The reaction of 1 with mono-substituted acetylenes also seems to proceed with the same fashion as the reaction of benzodisilacyclobutene with the acetylenes.

However, the reaction of 1 with a di-substituted acetylene, such as 3-hexyne at 150 °C for 24 h gave no 1:2 adduct, and at higher temperature (250 °C for 24 h), a complicated reaction mixture involving polymeric substances was obtained.

In conclusion, the reaction of benzobis(disilacyclobutene) 1 with ethylene in an autoclave at 250 °C gave two products, the 1:2 adduct 2 and the 2:3 adduct 3. Compound 1 reacted readily with mono-substituted acetylenes at lower temperature than with ethylene, to give 1:2 adducts 4a,b and 5a,b, respectively. With di-substituted acetylenes, 1 gave no adduct.

3 Experimental section

3.1 General procedures

The thermolysis of benzobis(disilacyclobutene) 1 with ethylene was carried out in a 10-mL autoclave, whereas the reactions with phenylacetylene, 1-hexyne were performed in a degassed sealed glass tube (1.0 × 15 cm2). 1H, 13C, and 29Si NMR spectra were recorded on a JNM-LA500 spectrometer. Low-resolution mass spectra were measured on a JEOL Model JMS-700 instrument. High-resolution mass spectra were measured using LTQ Orbitrap XL at the Natural Science Center for Basic Research and Development (N-BARD), Hiroshima University. Melting point was measured with a Yanaco-MP-S3 apparatus. Column chromatography was performed by using Wakogel C-300 (WAKO).

3.2 Thermolysis of 1 with ethylene at 250 °C

In a 10-mL autoclave was placed 0.1670 g (0.399 mmol) of 1 in 0.5 mL of dry benzene. To this was introduced ethylene until the pressure reached 34 bar. The mixture in the autoclave was heated at 250 °C for 24 h. The resulting mixture was analyzed by GLC as being benzo[1,2:4,5]bis(1,1,4,4-tetraethyl-1,4-disilacyclohex-5-ene) (2) (60 % yield) and bis(1,1,4,4-tetraethyl-2H,3H-1,4-disila[3,4:9,10]naphto)-1,1,2,2,5,5,8,8-octaethyl-1,2,5,8-tetrasilacyclodeca-3,9-diene (3) (20 % yield). The products 2 and 3 were isolated by silica gel column chromatography. All spectral data for 2 and 3 were identical with those of the authentic samples [9].

3.3 Thermolysis of 1 with ethylene at 150 °C

In a 10-mL autoclave was placed 0.1317 g (0.314 mmol) of 1 in 0.5 mL of dry benzene. To this was introduced ethylene until the pressure reached 34 bar. The mixture was heated at 150 °C for 24 h. The starting compound 1 was recovered unchanged.

3.4 Thermolysis of 1 with phenylacetylene

A mixture of 0.1214 g (0.29 mmol) of 1 and 0.1819 g (1.78 mmol) of phenylacetylene was heated in a sealed glass tube at 150 °C for 24 h. The mixture was analyzed by GLC as being 4a and 4b (86 % combined yield). A mixture of the products 4a and 4b was isolated by column chromatography: M.p. 96 °C. – 1H NMR (500 MHz, CDCl3): δ = 0.77–0.98 (m, 80H, EtSi), 6.88 (s, 2H, olefinic protons), 6.89 (s, 2H, olefinic protons), 7.22–7.35 (m, 20H, phenyl ring protons), 7.70 (s, 1H, phenylene ring proton), 7.71 (s, 2H, phenylene ring protons), 7.73 (s, 1H, phenylene ring proton). – 13C NMR (125 MHz, CDCl3): δ = 6.2 (2C), 6.3 (2C), 7.5, 7.6, 7.68, 7.72 (EtSi), 126.3, 126.4, 128.2, 138.0, 138.1, 138.3, 141.41, 141.44, 141.5, 141.6, 145.65, 145.69, 148.0, 161.3, 161.4 (olefinic, phenyl, and phenylene ring carbons). – 29Si NMR (99 MHz, CDCl3): δ = –14.7, –14.6, –12.8, –12.7. – MS (EI, 70 eV): m/z = 622 [M]+. – HRMS (APCI): m/z = 623.33600 (calcd. 623.33753 for C38H55Si4 [M+H]+).

3.5 Thermolysis of 1 with phenylacetylene at 250 °C

A mixture of 0.0950 g (0.23 mmol) of 1 and 0.1402 g (1.37 mmol) of phenylacetylene was heated in a sealed glass tube at 250 °C for 24 h. The mixture was analyzed by GLC as being 4a and 4b (91 % combined yield). A mixture of 4a and 4b was isolated by column chromatography. All spectral data for the mixture of 4a and 4b were identical with those of authentic samples.

3.6 Thermolysis of 1 with 1-hexyne

A mixture of 0.1241 g (0.30 mmol) of 1 and 0.1460 g (1.78 mmol) of 1-hexyne was heated in a sealed tube at 150 °C for 24 h. The resulting mixture was analyzed by GLC as being 5a and 5b (85 % combined yield). A mixture of 5a and 5b was isolated by column chromatography: – 1H NMR (500 MHz, CDCl3): δ = 0.71–1.01 (m, 92H, EtSi,CH3), 1.37 (sext, 8H, CH2, J = 7.9 Hz), 1.50 (quint, 8H, CH2, J = 7.9 Hz), 2.27 (t, 8H, CH2, J = 7.9 Hz), 6.61 (s, 2H, olefinic protons), 6.62 (s, 2H, olefinic protons), 7.60 (s, 1H, phenylene ring proton), 7.61 (s, 2H, phenylene ring protons), 7.62 (s, 1H, phenylene ring proton). – 13C NMR (125 MHz, CDCl3): δ = 5.8 (2C), 6.3 (2C), 7.7 (4C) (EtSi), 14.1 (2C), 22.7 (2C), 30.7 (2C), 39.1 (2C) (n-Bu), 137.8, 137.9, 138.1, 139.5, 139.6, 141.30, 141.34, 141.77, 141.80, 161.3, 161.4 (olefinic and phenylene ring carbons). – 29Si NMR (99 MHz, CDCl3): δ = –15.3, –15.2, –13.64, –13.58. – MS (EI, 70 eV): m/z = 582 [M]+. – HRMS (APCI): m/z = 583.40054 (calcd. 583.40013 for C34H63Si4 [M+H]+).

3.7 Thermolysis of 1 with 1-hexyne at 250 °C

A mixture of 0.1001 g (0.24 mmol) of 1 and 0.1178 g (1.43 mmol) of 1-hexyne was heated in a sealed tube at 250 °C for 24 h. The resulting mixture was analyzed by GLC as being 5a and 5b (87 % combined yield). A mixture of 5a and 5b was isolated by column chromatography. All spectral data for the mixture of 5a and 5b were identical with those of authentic samples.

Acknowledgments

This work was supported by JSPS KAKENHI grant numbers 26410061, 24109014, and 15K13710.

References

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    • Crossref
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    A. Naka, J. Ikadai, I. Miyahara, K. Hirotsu, M. Ishikawa, Organometallics 2004, 23, 2397.

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    A. Naka, J. Ohshita, E. Miyazaki, T. Miura, H. Kobayashi, M. Ishikawa, Organometallics 2012, 31, 3492.

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    A. Naka, J. Ikadai, J. Sakata, M. Ishikawa, Y. Hayashi, L. Antonoy, S. Kawauchi, T. Yamabe, Organometallics 2013, 32, 6476.

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    Y. Hayashi, T. Natsumeda, S. Otsu, A. Naka, M. Ishikawa, T. Yamabe, S. Kawauchi, Organometallics 2014, 33, 763.

    • Crossref
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    A. Naka, K. Yoshizawa, S. Kang, T. Yamabe, M. Ishikawa, Organometallics 1998, 17, 5830.

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    M. Ishikawa, S. Okazaki, A. Naka, H. Sakamoto, Organometallics 1992, 11, 4135.

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    S. Kyushin, T. Kitahara, R. Tanaka, M. Takeda, T. Matsumoto, M. Matsumoto, Chem. Commun. 2001, 2714.

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    A. Naka, K.-K. Lee, K. Yoshizawa, T. Yamabe, M. Ishikawa, J. Organomet. Chem. 1999, 587, 1.

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  • [1]

    M. Ishikawa, H. Sakamoto, T. Tabuchi, Organometallics 1991, 10, 3173.

  • [2]

    A. Naka, M. Ishikawa, Synlett 1995, 794.

  • [3]

    A. Naka, M. Hayashi, S. Okazaki, M. Ishikawa, Organometallics 1994, 13, 4994.

  • [4]

    T. Kusukawa, Y. Kabe, B. Nestler, W. Ando, Organometallics 1995, 14, 256.

    • Crossref
    • Export Citation
  • [5]

    Y. Uchimaru, M. Tanaka, J. Organomet. Chem. 1996, 521, 335.

  • [6]

    M. Ishikawa, J. Ikadai, A. Naka, J. Ohshita, A. Kunai, K. Yoshizawa, S.-Y. Kang, T. Yamabe, Organometallics 2001, 20, 1059.

  • [7]

    A. Naka, J. Ikadai, I. Miyahara, K. Hirotsu, M. Ishikawa, Organometallics 2004, 23, 2397.

  • [8]

    A. Naka, J. Ohshita, E. Miyazaki, T. Miura, H. Kobayashi, M. Ishikawa, Organometallics 2012, 31, 3492.

  • [9]

    A. Naka, J. Ikadai, J. Sakata, M. Ishikawa, Y. Hayashi, L. Antonoy, S. Kawauchi, T. Yamabe, Organometallics 2013, 32, 6476.

  • [10]

    Y. Hayashi, T. Natsumeda, S. Otsu, A. Naka, M. Ishikawa, T. Yamabe, S. Kawauchi, Organometallics 2014, 33, 763.

    • Crossref
    • Export Citation
  • [11]

    A. Naka, K. Yoshizawa, S. Kang, T. Yamabe, M. Ishikawa, Organometallics 1998, 17, 5830.

  • [12]

    M. Ishikawa, S. Okazaki, A. Naka, H. Sakamoto, Organometallics 1992, 11, 4135.

  • [13]

    A. Naka, K.-K. Lee, K. Yoshizawa, T. Yamabe, M. Ishikawa, Organometallics 1999, 18, 4524.

  • [14]

    S. Kyushin, T. Kitahara, R. Tanaka, M. Takeda, T. Matsumoto, M. Matsumoto, Chem. Commun. 2001, 2714.

  • [15]

    A. Naka, K.-K. Lee, K. Yoshizawa, T. Yamabe, M. Ishikawa, J. Organomet. Chem. 1999, 587, 1.

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