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

摘要

Using 18 silatranes XSi(OCH_2CH_2)_3N (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···N (d_(SiN)<2.13 ?) along with the high five-coordinate character of Si are typical for the first isomer 1~(+·(s)), whereas the second one, 1~(+·(l)), has a longer (l) Si···N distance (d_(SiN)>3.0 ?), the four-coordinate Si and the SD localized on the silatrane nitrogen atom N_s. 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), 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.