Aryl ferrocenylmethylesters: Synthesis, solid-state structure and electrochemical investigations

Abstract

The reaction of [Fe(η5-C5H4CH2OH)2] (1) with 2 equiv of ClC(O)R (2) (a, R = C6H5; b, R = 2-CH3-C6H4; c, R = 3-CH3-C6H4, d, R = 4-CH3-C6H4) produced the corresponding ferrocenyl carboxylates [Fe(η5-C5H4CH2OC(O)R)2] (3a–d). Treatment of [FcCH2OLi] (4-Li) (Fc = Fe(η5-C5H5)(η5-C5H4)) with (ClC(O))2C6H4 (5) (a, 1,2-((ClC(O))2-C6H4; b, 1,3-((ClC(O))2-C6H4; c, 1,4-((ClC(O))2-C6H4) in a 2:1 M ratio gave (FcCH2OC(O))2-C6H4 (6a–c), while with 1,3,5-(ClC(O))3-C6H3 (7) in a 3:1 M ratio produced 1,3,5-(FcCH2OC(O))3-C6H3 (8). All compounds were characterized by NMR (1H, 13C{1H}) and IR spectroscopy, ESI-TOF mass spectrometry and elemental analysis. The molecular structures of 3a–d and 6b in the solid state were determined by single crystal X-ray structure analysis, showing anti-periplanar orientations of the 1,1′-positioned substituents at ferrocene (3a–d). In the cyclic voltammograms of 3a–d, 6a–d and 8 reversible electrochemical redox processes (Fc/Fc+) were observed, ranging between 146 and 164 mV for 3a–d, ca. 100 mV for 6a–d and at 113 mV for 8 using [NnBu4][B(C6F5)4] as the supporting electrolyte. The molecular electronic structure of 3, 6 and 8 was calculated by DFT methods in order to obtain the HOMO and LUMO absolute and relative energies in addition to electron density and distribution within the molecular arrangements. It was found that different degrees of HOMO-LUMO energy gaps within the series, due to a lowering in the LUMO energy depending on the positions of the carboxylic ester substituents on the aryl rings, are in agreement with the electrochemical results obtained. Keywords: Ferrocenylmethyl, Mono-dicarboxy benzene, Trimesic acid, Solid state structure, Electrochemistry, DFT