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

Using 18 silatranes XSi(OCH CH ) N (1) as examples, the potentials of electrochemical oxidation E of the hypervalent compounds of Si were calculated for the first time at the ab initio and DFT levels. The experimental peak potentials E (acetonitrile) show an excellent agreement (MAE=0.03) with the MP2//B3PW91 calculated E (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 <2.13 Å) along with the high five-coordinate character of Si are typical for the first isomer 1 , whereas the second one, 1 , has a longer (l) Si⋅⋅⋅N distance (d >3.0 Å), the four-coordinate Si and the SD localized on the silatrane nitrogen atom N . The vertical model of adiabatic ionization (1→1 or 1→1 ) 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 (1) with the strength characteristics of the dative contact N→Si were revealed.