Potential energy surface of the cation-neutral hydroamination reaction: a computational study on the role of an ion-molecule complex in the reaction pathway

Detailed reaction profiles of the cation-neutral direct hydroamination reaction between ethylene and ammonia are analyzed using B3LYP and Full-MP2 methodologies. By investigating the PES for the reactions thoroughly we found that due to the presence of a stable ion-molecule complex, the transition state (TS) is now a true TS and thus the reaction proceeds through an energetic barrier. This observation contradicts our earlier report (Tetrahedron 2010, 66, 3030) where have shown that cation-neutral direct hydroamination reaction is barrierless. A detailed analysis of the reaction profile, shows that not only the energetics of the stationary points but also the molecular dipole moments, the spin density distribution and the structural orientations of the reactant complex indicate a preference for the reaction of CH2CH2+ with NH3 over the reaction of NH3+ with CH2CH2. This observation is in strong agreement with the experimental findings of Hamann et al. (Angew. Chem., Int. Ed. 2009, 48, 4643).