The solvent effect on two competing reaction mechanisms involving hypervalent iodine reagents (λ3‐iodanes): Facing the limit of the stationary quantum chemical approach

Trifluoromethylation of acetonitrile with 3,3‐dimethyl‐1‐(trifluoromethyl)−1λ3,2‐ benziodoxol is assumed to occur via reductive elimination (RE) of the electrophilic CF3‐ligand and MeCN bound to the hypervalent iodine. Computations in gas phase showed that the reaction might also occur via an SN2 mechanism. There is a substantial solvent effect present for both reaction mechanisms, and their energies of activation are very sensitive toward the solvent model used (implicit, microsolvation, and cluster‐continuum). With polarizable continuum model‐based methods, the SN2 mechanism becomes less favorable. Applying the cluster‐continuum model, using a shell of solvent molecules derived from ab initio molecular dynamics (AIMD) simulations, the gap between the two activation barriers ( ΔΔG‡ ) is lowered to a few kcal mol−1 and also shows that the activation entropies ( ΔS‡ ) and volumes ( ΔV‡ ) for the two mechanisms differ substantially. A quantitative assessment of ΔΔG‡ will therefore only be possible using AIMD. A natural bond orbital‐analysis gives further insight into the activation of the CF3‐reagent by protonation. © 2014 Wiley Periodicals, Inc.

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