Electrochemical oxidation and radical cations of structurally non-rigid hypervalent silatranes. Theoretical and experimental studies

Using 18 silatranes XSi(OCH2CH2)3N (1) as an example, the potentials of electrochemical oxidation E0 of the hypervalent compounds of Si were calculated for the first time at the ab initio and DFT levels. The experimental peak potentials Ep show an excellent agreement (MAE = 0.03) with the MP2//B3PW91 calculated E0 (C-PCM). Radical cations of 1 reveal a "stretch isomerism" of the NSi dative bond. Localization of the spin density (SD) on the substituent X and the short (s) coordination contact Si…N (dSiN 3.0 A), the tetra-coordinated Si and the SD localized on the silatrane nitrogen atom Ns. The vertical model of adiabatic ionization (1→1+*(s) or 1→1+*(l)) was developed. It allows, in accordance with an original experimental test (electrooxidation of 1 in the presence of ferrocene), reliably predicting the most probable pathways of the silatrane oxidation. The reliable relationships of E0(1) with the strength characteristics of the dative contact NSi were revealed.