Silacyclobutenes pyrolysis

Nowadays silenes are well-known intermediates. A number of studies have been carried out to obtain more complex molecules having Si=C double bonds. Thus, an attempt has been made to generate and stabilize in a matrix 1,1-dimethyl-l-silabuta-l,3-diene [125], which can be formed as a primary product of pyrolysis of diallyldimethylsilane [126] (Korolev et al., 1985). However, when thermolysis was carried out at 750-800°C the absorptions of only two stable molecules, propene and 1,1-dimethylsilacyclobut-2-ene [127], were observed in the matrix IR spectra of the reaction products. At temperatures above 800°C both silane [126] and silacyclobutene [127] gave low-molecular hydrocarbons, methane, acetylene, ethylene and methylacetylene. A comparison of relative intensities of the IR... 

Keywords silacyclobutanes, pyrolysis, silenes, rearrangement, 3,4-benzo-1-silacyclobutenes, 2-silaindanes, B3LYP/6-31G calculations... 

The pyrolysis of a precursor to cyclopropyl(trimethylsilyl)silylene is most easily interpreted by assuming that the silylene undergoes a rearrangement to l-(trimethylsilyl)-I-silacyclobutene which in turn undergoes a silene-to-silylene rearrangement (equation... 

An approach via 1-silacyclobut-l-ene224 was by pyrolysis of 1-methoxy-l-cyclo-propyltetramethyldisilane, which yields methylcyclopropylsilylene, as demonstrated by trapping with dimethylbutadiene. Methylcyclopropylsilylene then ring expands to 1-methyl-1-silacyclobutene (equation 105). 

The 1-silacyclobutene side of this type of equilibrium was also reached by ring expansion in phenylcyclopropylsilylene obtained by pyrolysis of a silabenzonorborna-diene precursor (equation 106)223. Photochemical or pyrolytic ring opening of a l-silacyclobut-2-ene derivative provides an entry to the 1-silabutadiene series151. 

Scheme 1. Formation of silacyclobutene diannelated [a,d] benzene upon very low pressure pyrolysis of 2,5-bis (1 -methyl-1 -silacyclobut-1 -yl)-o-xylene.

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