Trifluoromethylation of acetonitrile with 3,3-dimethyl-1-(trifluoromethyl)-1 lambda(3),2- benziodoxol is assumed to occur via reductive elimnation (RE) of the electrophilic CF3-ligand and MeCN bond to the hypervalent lodine. Computations in gas phase showed that the reaction might also occur via an S(N)2 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, micro-solvation, and cluster-continuum). With polarizable continuum model-based methods, the S(N)2 mechanism becomes less favorable. Applying the cluster-continuum model, using a shell of solvent molecules derived form ab initio molecular dynamics (AIMD) simulations, the gap between the two activation barriers (Delta Delta G(+/-)) is lowered to a few kcal mol(-1) and also shows that the activation entropies (Delta S-+/-) and volumes (Delta V-+/-) for the two mechanisms differ substantialy. A quantitative assessmenet of Delta Delta G(+/-) will therefore only be possible using AIMD. A natutal bond orbital-analysis gives further insights into the activation of the CF3-reagnet by protonation. (c) 2014 Wiley Periodicals, Inc.
['Oliver Sala', 'Hans Peter Lüthi', 'Antonio Togni']
The solvent effect on two competing reaction mechanisms involving hypervalent iodine reagents (λ3‐iodanes): Facing the limit of the stationary quantum chemical approach