Reversible Reactions of Ethylene with Distannynes Under Ambient Conditions

Ethylene's cycloadditions to unsaturated hydrocarbons occupy well-established ground in classical organic chemistry. In contrast, its reactivity toward alkene and alkyne analogs of carbon's heavier-element congeners silicon, germanium, tin, or lead has been little explored. We show here that treatment of the distannynes AriPr⁴SnSnAriPr⁴ [AriPr⁴ = C₆H₃-2,6(C₆H₃-2,6-iPr₂)₂, 1] or AriPr⁸SnSnAriPr⁸ [AriPr⁸ = C₆H-2,6(C₆H₂-2,4,6-iPr₃)₂-3,5-iPr₂, 2] with ethylene under ambient conditions affords the cycloadducts [Formula: see text] (3) or [Formula: see text] (4) that were structurally and spectroscopically characterized. Ethylene incorporation in 3 and 4 involves tin-carbon σ bonding and is shown to be fully reversible under ambient conditions; hydrocarbon solutions of 3 or 4 revert to the distannynes 1 or 2 with ethylene elimination under reduced pressure or upon standing at approximately 25°C. Variable-temperature proton nuclear magnetic resonance studies showed that the enthalpies of reaction were near -48 (3) and -27 (4) kilojoules per mole.