Reactivity of a disilyne RSiSiR (R = SiiPr[CH(SiMe3)2]2) toward π-bonds:: Stereospecific addition and a new route to an isolable 1,2-disilabenzene

The reaction of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne 1 with cis- and trans-butenes produced cis- and trans-3,4-dimethyl-1,2-disilacyclobutenes 2a and 2b, respectively. The reactions proceeded in a stereospecific manner. Theoretical calculations on the reaction between 1 and 2-butenes show that the reaction proceeds via the interaction between the LUMO (pi(in)*) of 1 and the HOMO of 2-butene, resulting in a formal [1 + 2] cycloaddition to give the silacyclopropyl-silylene intermediate, followed by its ring expansion to produce the final product. The reaction of 1 with phenylacetylene produced 1,2-disilabenzene derivative as a mixture of the two regioisomers, one of them being characterized by X-ray crystallography. The six-membered ring of 1,2-disilabenzene of 3a is almost planar with an Si-Si bond length of 2.2018(18)angstrom and Si-C bond lengths of 1.804(4) and 1.799(5) angstrom.