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

Cycloaddition reactions of the acyclic silylene Si(SAr i Pr4 ) 2 (Ar i Pr4 = C 6 H 3 -2,6(C 6 H 3 -2,6- i Pr 2 ) 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 (Ar i Pr4 S) 2 Si(CH═ CPh) ( 1 ), (Ar i Pr4 S) 2 Si(PhC═ CPh) ( 2 ), and (Ar i Pr4 S) 2 SiCH 2 CMeCMe CH 2 ( 3 ) at ambient temperature. The compounds were characterized by X-ray crystallography, 1 H, 13 C, and 29 Si 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(SAr Me6 ) 2 and stannylene Sn(SAr Me6 ) 2 (Ar Me6 = C 6 H 3 -2,6(C 6 H 2 -2,4,6-Me 3 ) 2 ) analogues of Si(SAr Me6 ) 2 displayed no reaction with ethylene. Quantum chemical calculations using model tetrylenes E(SPh) 2 (E = Si, Ge, Sn; Ph = C 6 H 5 ) show that cyclization reactions are endothermic in the case of germanium and tin derivatives but energetically favored for the silicon species.