Assessing the effects of covalent, dative and halogen bonds on the electronic structure of selenoamides

Here, the interaction between N,N-dimethyl-selenobenzoamide PhC(=Se)NMe2 (1) and various Lewis acids of different strengths, namely IC6F13(I), B(C6F5)(3) (B) and Met, has been analysed by a combined experimental and theoretical approach. In all cases, an increase of the C-NMe2 rotational barrier has been evidenced and quantified by H-1-variable temperature-exchange NMR spectroscopy (VT-EXSY) in the cases of 1-I and 1-B. For B(C6F5)(3), the structure of the adduct has been elucidated by single crystal X-ray diffraction, allowing the lengthening of the Se-C bond (186 pm) and the consequent double characteristic of the C-NMe2 bond (131 pm) to be measured. Computational studies (mainly natural bond orbitals and natural orbital for chemical valence analyses) gave precious insight into the effect of various Lewis acids on the electronic structure of 1. The advantages and the limitations of this new method to characterize chemical interactions are discussed.