Electrochemical studies of ferrocene derivatives and their complexation by β-cyclodextrin

The voltammetric behaviour of (ferrocenylmethyl)trimethylammonium hexafluorophosphate, 2-ferrocenylacrylic acid, N-ferro-cenylmethyl-N-methyl-4.4'-bipyridium hexafluorophosphate and 9-ferrocenylmethyladenine was studied in aqueous and/or acetonitrile solutions by means of cyclic voltammetry and rotating-disc electrode voltammetry. The influence of beta-cyclodextrin on the voltammetric behaviour of the compounds was also studied in aqueous solutions. (Ferrocenylmethyl)trirmethylammonium hexafluomphosphate and 2-ferrocenylacrylic acid, studied in aqueous solutions at pH 9.2, exhibit typical reversible one electron transfer behaviour. whereas the redox reaction of 9-ferrocenylmethyladenine, studied in acetonitrile, is strongly affected by adsorption. N'-ferrocenylmethyl-N'-methyl-4,4'-bipyridinium hexafluorophosphate gives voltammetric responses for both ferrocene and viologen redox centres In acetonitrile. In aqueous solutions it is hydrolyzed to ferrocenylmethylalcohol and N-methylbipyridyl, a process facilitated by the neighbouring group participation of the iron atom. In all cases beta-cyclodextrin causes a decrease in the currents and shifts the potentials positively. The formation constants of the inclusion complexes of compounds with beta-cyclodextrin were determined by quantitative evaluation of E-1.2 values and possible explanations about their differentiation are discussed. In the case of N-ferrocenylmethyl-N'-methyl-4,4'-bipyridinium hexafluorophosphate it was found that beta-cyclodextrin decreases the rate of Its hydrolysis substantially. (C) 1999 Elsevier Science S.A. All rights reserved.