Heterocyclic-based ferrocenyl carboselenolates: Synthesis, solid-state structure and electrochemical investigations

Abstract

Treatment of two equiv. of [Fe(η5-C5H5)(η5-C5H4SeSiMe3)] (1) with one equiv. of 2,5-(ClC(O))2-cC4H2X (2) produced the corresponding ferrocenyl carboselenolates 2,5-[(FcSeC(O))2-cC4H2X] (3) ([Fc = Fe(η5-C5H5)(η5-C5H4)]; a, X = O; b, X = NMe; c, X = Se). On the other hand, [Fe(η5-C5H4SiMe3)2] (4) reacted with 2-ClC(O)-cC4H3X (5) in a 1:2 M ratio to give [Fe(η5-C5H4SeC(O)-2-cC4H3X)2] (6) (a, X = O; b, X = NMe; c, X = Se). Compounds 3a–c and 6a–c have been characterized by elemental analysis, NMR (1H, 13C{1H}, 77Se{1H}) and IR spectroscopy. The structures of 3a–c and 6a in the solid state were determined by single crystal X-ray structure analysis. The cyclic voltammetry measurements for 3a–c and 6a–c show reversible electrochemical processes (Fc/Fc+) between 135 and 170 mV for 3a−c and between 135 and 220 mV for 6a−c using [NnBu4][B(C6F5)4] as the supporting electrolyte. It was found that the furyl- and selenophyl-functionalized systems resulted in a significantly higher Fc/Fc+ redox potential (E0′) as observed for the more electron-rich pyrrolyl derivatives. The Fc/Fc+ redox potential (E0′) for 6a−c is significantly higher than the one for 3a−c, due to the presence of two selenoester moieties attached to the ferrocene in 6a−c. Spectroelectrochemical UV–Vis/NIR studies of 3b reveal that the two Fc/Fc+ centers in the mixed-valent species are not electronically intercommunicating via the heterocyclic bridge.