Cyclic voltammetric characteristics of tri- and diarylcarbenium salts having some methoxyphenyl groups

Triarylcarbenium salts (Phi C-a(3)+, Phi (a)Phi C-b(2)+, Phi C-b(3)+, Phi (f)Phi C-b(2)+, Phi (e)Phi C-b(2)+, Ph Phi C-b(2)+, and FcC(+) Phi Ph-b [Phi (a), Phi (b), Phi (e), Phi (f), Ph, Fc = 2,4,6-(MeO)(3)C6H2, 2,6-(MeO)(2)C6H4, 2-(MeO)C6H4, 4-(MeO)C6H4, C6H5, Fe(eta (5)-C5H5)(eta (5)-C5H4)]) showed a reversible redox wave with one-electron transfer at a Pt electrode in 1,2-dichloroethane, while the reduction of diarylcarbenium salts (Phi (2C+H)-C-a, FcC(+) Phi H-a, FcC(+) Phi H-b, FcC(+) Phi (c)C(+)Phi H-e, and FcC(+)PhH [Phi (c) = 2,5-(MeO)(2)C6H3]) proceeded irreversibly. A wide range of cathodic shifts in the redox potentials (198- -377 mV for triarylcarbenium salts) and in the reduction peak potentials (-23- -311 mV for monoaryl(ferrocenyl)carbenium salts) could be observed as the number of o- and p-methoxy groups increased. Probably, the electron donation from the o- and p-methoxy substituents to the central carbon caused the wide negative shift in the redox potentials. These triarylcarbenium salts again showed reversible redox waves in their relatively low concentration region at an ITO electrode in an aqueous acidic medium In the higher concentration region, an anodic wave was varied to a sharp peak, indicating the adsorption of triarylmethyl radicals. It is very interesting that the reversible redox behavior of these triarylcarbenium salts was observable even in an aqueous medium.