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 (ArSnSnAriPr4)-Sn-iPr4 [Ar-iPr4 = C6H3-2,6(C6H3-2,6-Pr-i(2))(2), 1] or (ArSnSnAriPr8)-Sn-iPr8 [Ar-iPr8 = C6H-2,6(C6H2-2,4,6-Pr-i(3))(2)-3,5-Pr-i(2), 2] with ethylene under ambient conditions affords the cycloadducts (ArSn)-Sn-iPr4(mu(2):eta(1):eta(1)-C2H4)(2)SnAriPr4 (3) or (ArSn)-Sn-iPr8(mu(2):eta(1):eta(1)-C2H4)(2)SnAriPr8 (4) that were structurally and spectroscopically characterized. Ethylene incorporation in 3 and 4 involves tin-carbon sigma 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 similar to 25 degrees C. Variable-temperature proton nuclear magnetic resonance studies showed that the enthalpies of reaction were near -48 (3) and -27 (4) kilojoules per mole.