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

• Published in: Chemistry : a European journal Vol. 23; no. 8; pp. 1910 - 1919
• Main Authors: Sidorkin, Valery F., Belogolova, Elena F., Wang, Yu, Jouikov, Viatcheslav, Doronina, Evgeniya P.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 03.02.2017; Wiley-VCH Verlag
• Subjects: Adiabatic flow; Cations; Chemical Sciences; Chemistry; Contact; cyclic voltammetry; density functional calculations; Electrochemical oxidation; Group 14 elements; hypervalent compounds; Ionization; Mathematical models; or physical chemistry; Other; Radicals; silatranes; Silicon compounds; Theoretical and; density functional calculations; Group 14 elements; cyclic voltammetry; silatranes; hypervalent compounds
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201604663

Using 18 silatranes XSi(OCH2CH2)3N (1) as examples, 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 (acetonitrile) 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<2.13 Å) 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 (dSiN>3.0 Å), the four‐coordinate 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), a reliable prediction of 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. Unexpected paths of ionization of silatranes were explained within the proposed vertical model of their adiabatic ionization. This provides the first theoretically justified grounds for the consideration of experimental peak potentials Ep versus theoretical standard oxidation potentials of hypervalent compounds of silicon.