Silabenzene preparation

The propene split-off route to generate intermediates is well-established, cf. Brown, R.F.C. "Pyrolytic Methods in Organic Chemistry" Academic Press New York 1980. It has been applied by our group to prepare e.g. silatoluene (Bock, H. Bowling, R.A. Solouki, B. Barton, T.J. Burns, G.T. J. 7 m. Chem. Soc. 1980, 102, 429), silabenzene (Solouki, B. Rosmus, P. Bock, H. Maier, G. Angew. Chem. 1980, 2, 56 Angew. Chem. Int. Ed. 

Compounds containing the silicon-carbon double bond have been prepared (Scheme 85) and derivatives of silabenzene and germabenzene have been characterized (Section 1.20.13). Methyllithium and n -butyllithium will alkylate the silole (126) showing the ring silicon to be the site for nucleophilic attack. The reaction is quantitative and no silole anion (127) was detected (Scheme 205) (8lJOM(2l8)C2l). 

The acidity of the methylene protons of siIacycIohexa-2,4-dienes promotes dehydrochlori-nation of (155) to give silatoluene (Scheme 245) (77JA5199). It also results from thermolysis of the allyl or methoxy derivatives (156), and readily dimerizes and adds alkynes (Scheme 246) (78JA5246, 81JA6788). The hindered l,4-di-f-butyl-l-silabenzene (157) can be prepared by the dehydrochlorination route. It readily dimerizes but through a less hindered [2+2] cycloaddition and forms Diels-AIder adducts with dienes (Scheme 247) (79AG(E)789>. 

After the successful preparation of silabenzene 24 by hydrogen elimination from 27, it was tempting to try to generate 1,4-disilabenzene 31 by pyrolysis of the easily accessible disilacyclohexadiene 3041 (equation 9). 

Photochemical methods have been used in the past to prepare a variety of rather unstable silaaromatic compounds. The photolyses of cyclic unsaturated silyldiazo compounds, which yield silabenzenes and/or silafulvenes, are described in Section VI. 

By using a very bulky substituent, Tbt (2,4,6-tris[bis(trimethylsilyl)methyl] phenyl), 2-silanaphthalene, silabenzene and other related compounds are prepared (Figure 10). 

Silabenzene has been prepared by the gas-phase pyrolysis of the acetoxy- or allyl-substituted silacyclohexadiene. Silatoluene can be prepared similarly and shows a photoelectron spectrum typical of a hetero-substituted benzene. The... 

---