The main factor determining the low inversion barriers of N-sulfenylimines

Abstract

The energy and electronic parameters of the nitrogen atom inversion in isoelectronic N-alkylimines and N-sulfenylimines (H2C=NR, where R=Me, Et, SH, SMe) have been calculated using DFT method (B3LYP/6-311+G(d,p)) in terms of NBO. It has been established that substitution of methylene group by sulfur atom does not lead to the decrease in the inversion barriers due to the nN*S–H(С) interactions, since total energies of the nN*S–H(С), nNS–H(С) and nNnS interactions in the N-sulfenylimines and of the nN*С–H(С), nNС–H(С) interactions in the N-alkylimines are almost equal. The interactions of the nitrogen lone pair with the Rydberg orbitals of the sulfur atom (nNRY*S) promote the reduction of the inversion barriers of the N-sulfenylimines (by 28–33 kJ•mol–1) in comparison with the N-alkylimines. However, analysis of the total energies of all donor-acceptor and repulsive interactions between the nitrogen lone pair and the orbitals of neighboring atoms and bonds showed that they promote the increase in the inversion barriers of the N-sulfenylimines by 0.8–14.3 kJ•mol–1. The nS*C=N and nS*C=N interactions are the main factor that determines the decrease in the inversion barriers of the N-sulfenylimines relative to the N-alkylimines. These interactions, taking into account the corresponding interactions in the N-alkylimines, contribute to the barriers decrease of 64.5–71.7 kJ•mol–1.