A series of Se-ferrocenyl thiophene carboselenoates – Synthesis, solid-state structure and electrochemistry

Silylated ferrocene-selenium compounds of type Fe(η5-C5H4SeSiMe3)2 (1) and Fe(η5-C5H4SeSiMe3)(η5-C5H5) (6) react under mild conditions with thiophene acid chlorides C(O)ClR (2a, R = 2-cC4H3S; 2b, R = 3-cC4H3S) and 2,5-(C(O)Cl)2-cC4H2S (4) to give the appropriate Se-ferrocenyl thiophene selenoesters Fe(η5-C5H4SeC(O)R)2 (3a, R = 2-cC4H3S; 3b, R = 3-cC4H3S), Fe(η5-C5H4-2-SeC(O)-5-C(O)Cl-cC4H2S)2 (5), 2-Fe(η5-C5H5)(η5-C5H4SeC(O)-5-C(O)Cl-cC4H2S) (7), and 2,5-(Fe(η5-C5H5)(η5-C5H4SeC(O))2-cC4H2S (8). These compounds have been characterized by elemental analysis, IR and NMR (1H, 13C{1H}, 77Se{1H}) spectroscopy and ESI-TOF mass spectrometry. The molecular structures of 3b and 8 in the solid state were determined by single X-ray diffraction studies. Both organometallic compounds can be regarded as supramolecular synthons, as they assemble to 1D bands (3b) or 2D layers (8), due to intermolecular Se…O interactions. The calculated electrostatic potentials of 3a and 8 rationalize the formation of Se···O contacts as well. Electrochemical studies showed that 3a, 3b, 5, 7 and 8 display electrochemically reversible Fc/Fc+ processes between 160 and 335 mV vs FcH/FcH+ using [NnBu4][B(C6F5)4] as the supporting electrolyte. The corresponding redox event for 3a is shifted more anodic than in 3b, similar as found for 2- and 3-ferrocenyl thiophene. Furthermore, the highest formal potential was observed for the Fc/Fc+ redox process of 5, due to the electron withdrawing effect of the acyl chloride groups. An analogical effect was also observed for 7 in comparison to 8. Spectroelectrochemical UV–Vis/NIR studies of 8 reveal no electronic interaction between the iron fragments.