Consecutive disilanylsilylene to silyldisilene rearrangements

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Abstract

Thermolysis of 2,3-benzo-1,4-diphenyl-7-silanorbornadiene derivatives 1 in the presence of 2,3-dimethylbutadienes gave the trapping products of the corresponding bissilylene, disilenylsilylene, and a tetrasila-1,3-butadiene, via a consecutive disilanylsilylene to silyldisilene rearrangement.

Graphical abstract

Thermolysis of 2,3-benzo-1,4-diphenyl-7-silanorbornadiene derivatives 1 in the presence of 2,3-dimethylbutadienes gave the trapping products of the corresponding bissilylene, disilenylsilylene, and a tetrasila-1,3-butadiene, via a consecutive disilanylsilylene to silyldisilene rearrangement.

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Introduction

Silylenes are significant, highly reactive organosilicon compounds [1]. The chemistry of silylenes has enjoyed a few decades of explosive growth, and recently, stable silylenes have been reported [2]. The reactions of silylenes are: (a) insertion of O–H, N–H, Si–Si, Si–O, and Si–X (halogen) bonds, (b) addition to carbon–carbon π-bonds, (c) dimerization to disilenes, and (d) silylene to disilene rearrangements. Among these, the dimerization of silylenes and the rearrangement reactions are interesting, because these reactions provide disilenes, which are silicon–silicon double bonded compounds [3]. Indeed, West et al. obtained the first isolable disilene, tetramesityldisilene, in 1981, based on the dimerization of dimesitylsilylene [4]. The isomerization of disilanylsilylenes to silyldisilenes using thermal and photochemical pathways has been also discussed (Scheme 1). For example, the thermolysis of a 2,3-benzo-1,4-diphenyl-7-silanorbornadiene derivative in the presence of 2,3-dimethylbutadienes gives a silylene adduct and a disilene adduct [5]. However, a limited number of reactions utilizing this reaction have been available until now.

We have recently reported on the first example of the generation and consecutive intramolecular dimerization of two silylenes in a molecule to form a cyclic disilene [6], and we have extended this cumulative silylene system to oligosilanes. In this report, we describe the consecutive disilanylsilylene to silyldisilene rearrangement of two silylenes in tetrasilane-1,1,4,4-tetrayl. This reaction shows evidence for the transient existence of a tetrasila-1,3-butadiene. Recently, the chemistry of tetrasila-1,3-butadiene has attracted great interest. Kira and co-workers have reported on the dehalogenation reaction of 2,2,3,3-tetrabromotetrasilane and 2,2-dibromotetrasilane yielding a tetrasila[1.1.0]bicyclobutane, which undergoes interconversion with a tetrasilacyclobutene [7]. Weidenbruch et al. have reported on a kinetically stable hexaaryltetrasilabuta-1,3-diene [8]. In addition, Sekiguchi and co-workers have reported on a stable tetrasila-1,3-butadiene, based the reaction of 1,1-dilithiosilane with 1,1,2,2-tetrachlorodisilane derivatives [9].

Section snippets

Results and discussion

We reported some years ago on the isomerization of disilanylsilylenes to silyldisilenes (and vice versa) using thermal and photochemical pathways, which can be applied to generate oligosilenes [5]. Thus, we have adopted this strategy to form tetrasilane-1,1,4,4-tetrayl compounds, and expected the formation of tetrasila-1,3-butadiene based on a thermal disilanylsilylene to silyldisilene rearrangement.

To generate the required tetrasilane-1,1,4,4-tetrayl compound, 1,4-bissilylene, 1 was

Summary

We examined the consecutive disilanylsilylene to silyldisilene rearrangement of two silylenes in a tetrasilane-1,1,4,4-tetrayl compound. The thermal reaction of the 2,3-benzo-1,4-diphenyl-7-silanorbornadiene derivative 1 in the presence of 2,3-dimethylbutadiene gave the trapping products of the corresponding bissilylene, disilenylsilylene, and a tetrasila-1,3-butadiene. This reaction may open a new way to form cumulative silylenes, and silicon–silicon double-bonded compounds.

General procedures

1H (300 MHz), 13C (75 MHz), and 29Si (59 MHz) NMR spectra were measured using a Buruker DPX 300 spectrometer. CDCl3 or C6D6 was used as the solvent, with the residual chloroform (δ = 7.24 ppm; 13C = 77.0 ppm) benzene (δ = 7.15 ppm; 13C = 128.0 ppm), and Me4Si used as an internal standard. The GLC data were recorded on Shimadzu GC-8A and GC-17A chromatographs. The GPC data were obtained using a JEOL LC-908 chromatograph equipped with Shodex AC 80M and 804 columns using toluene as the eluent. The GC mass

Acknowledgements

We are grateful to the Ministry of Education, Culture, Sports, Science, and Technology of Japan for financial support.

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