Electrochemical Oxidation and Radical Cations of Structurally Non-rigid Hypervalent Silatranes: Theoretical and Experimental Studies

Using 18 silatranes XSi(OCH2CH2)(3)N (1) as examples, the potentials of electrochemical oxidation E-0 of the hypervalent compounds of Si were calculated for the first time at the ab initio and DFT levels. The experimental peak potentials E-p (acetonitrile) show an excellent agreement (MAE = 0.03) with the MP2//B3PW91 calculated E-0 (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 center dot center dot center dot N (d(SiN)< 2.13 angstrom) along with the high five-coordinate character of Si are typical for the first isomer 1(+center dot(s)), whereas the second one, 1(+center dot(l)), has a longer (l) Si center dot center dot center dot N distance (d(SiN) > 3.0 angstrom), the four-coordinate Si and the SD localized on the silatrane nitrogen atom N-s. The vertical model of adiabatic ionization (1 -> 1(+center dot(s)) or 1 -> 1(+center dot(l))) was developed. It allows, in accordance with an original experimental test (electrooxidation of 1 in the presence of ferrocene), a reliable prediction of the most probable pathways of the silatrane oxidation. The reliable relationships of E-0(1) with the strength characteristics of the dative contact N -> Si were revealed.