Probing M-O Bond Cleavage in Silicon and Titanium Bisenolate Radical Cations.

In this study, several novel sterically congested silicon and titanium bisenolates of exceptional hydrolytic stability have been synthesized and characterized. The structure of the titanium bisenolate T2 could be determined by X-ray structure analysis. Preparative one-electron oxidation of the sterically shielded metal bisenolates S1-S4 and T1-T2 led to formation of the benzofurans B1 and B2. As the benzofuran formation is strong evidence for an initial M-O bond cleavage process at the stage of the initial radical cation we were able to measure the kinetics of this scission process using cyclic voltammetry techniques (first-order rate constants range at k(f) = 0.1-90 s(-)(1)). These data indicate that both silicon and titanium bisenolates are interesting candidates for oxidative intramolecular carbon-carbon bond formation processes.