A theoretical study on the reactivity of vinyl iodonium ions

Reactions of methyl(vinyl)iodonium ion and the β-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-λ3-iodane 2. Transition states for the SN2, ligand-coupling substitution (LC), and β-elimination (βE) 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 βE 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 β-methyl-substituted 1 while it is retarded by the β-tert-butyl and β-chloro substitutions are reproduced by the calculations that take medium effects into account.Key words: vinyliodonium salt, polyvalent iodine, vinylic SN2 reaction, ligand coupling, ab initio MO calculation.