Energetics of Iodine Ate Complexes, Intermediates in the Iodine/Magnesium Exchange on 1,1-Diiodoalkanes

On reaction of 1,1-diiodoalkanes with Grignard reagents at −78 °C, long-lived α-iodoalkyl iodine ate complexes were generated as observable intermediates. Their lifetime depends on the nature of the Grignard reagent and the nature of the 1,1-diiodoalkane. An α-bromoalkyl iodine ate complex was observable only when generated from a 1-bromo-1-iodoalkane with allyl−MgX. The energetic situations and factors that affect the lifetime of such ate complexes are discussed.