C-OH bond cleavage initiated by electron transfer: electroreduction of 9-fluorenol

Highlights: • The electroreduction of 9-Fluorenol in aprotic media was studied. • The process proceeds via C–O bond cleavage in the radical anion. • The substrate is deprotonated by anionic products giving rise 9-fluorenone dianion. - Abstract: Cyclic voltammetry, chronoamperometry, coulometry, electrolysis, digital simulation, quantum chemical calculations of 9-fluorenol as an example, were used to show that the electroreduction of aryl derivatives of methanol in 0.1 M Bu₄NClO₄/DMF proceeds via the ECE mechanism (including the stages of radical anion formation and the C−OH bond cleavage in the radical anion) complicated by the reactions of the depolarizer with the anionic products. Among these reactions are the deprotonation of 9-fluorenol and its monoanions by hydroxide anion and fluorenyl anion. The thermodynamic parameters of the reactions have been estimated both theoretically and experimentally. It was found that the equilibrium constants of the fluorenyl anions deprotonation are close (C-anion) or higher (O-anion) than that of fluorenol. As a result the total equilibrium is shifted towards the side of the dianion of 9-fluorenone. The unusual ratio of the equilibrium constants was explained by lower basicity of π*-dianion compare with other anions.