A theoretical study on the reactivity of vinyl iodonium ions

Reactions of methyl(vinyl)iodonium ion and the beta-substituted derivatives as well as divinyliodonium ion with chloride ion were examined theoretically by ab initio MO (MP2) calculations at the double-zeta (DZ) + d level. Interaction of the iodonium ion 1 with Cl- leads to chloro-lambda(3)-iodane 2. Transition states for the S(N)2, ligand-coupling substitution (LC), and beta-elimination (beta E) are found for reactions at the vinyl group. The barrier to LC is usually the lowest in the gas phase, but relative barriers to SN2 and to beta E change with the substituents. Effects of solvent were evaluated by a dielectric continuum model and found to be large on SN2 but small on LC. The experimental observations in solution that the SN2 is the most facile for the beta-methyl-substituted 1 while it is retarded by the beta-tert-butyl and beta-chloro substitutions are reproduced by the calculations that take medium effects into account.