Reactions of Alkenes and Alkynes with an Acyclic Silylene and Heavier Tetrylenes under Ambient Conditions

Cycloaddition
reactions of the acyclic silylene Si­(SAriPr4)2 (AriPr4 = C6H3-2,6­(C6H3-2,6-iPr2)2) with a variety of alkenes and alkynes
were investigated. Its reactions with the alkynes phenylacetylene
and diphenylacetylene and the diene 2,3-dimethyl-1,3-butadiene yielded
silacycles (AriPr4S)2Si­(CHCPh) (1), (AriPr4S)2Si­(PhCCPh) (2), and
(AriPr4S)2SiCH2CMeCMeCH2 (3) at ambient temperature.
The compounds were characterized by X-ray crystallography, 1H, 13C, and 29Si NMR spectroscopy, and IR spectroscopy.
No reaction was observed with more substituted alkenes such as propene,
(Z)-2-butene, tert-butylethylene,
cyclopentene, 1-hexene, or the alkyne bis­(trimethylsilyl)­acetylene
under the same reaction conditions. The germylene Ge­(SArMe6)2 and stannylene Sn­(SArMe6)2 (ArMe6 = C6H3-2,6­(C6H2-2,4,6-Me3)2) analogues of Si­(SArMe6)2 displayed no reaction with ethylene. Quantum
chemical calculations using model tetrylenes E­(SPh)2 (E
= Si, Ge, Sn; Ph = C6H5) show that cyclization
reactions are endothermic in the case of germanium and tin derivatives
but energetically favored for the silicon species.