From ferrocenyl selenoesters to diferrocenyl methanols

Abstract The reaction of FcSeSiMe 3 (Fc = Fe(η 5 -C 5 H 5 )(η 5 -C 5 H 4 )) ( 1 ) with equimolar amounts of the acid chlorides Cl(O)C-2- c C 4 H 3 X ( 2a , X = O; 2b , X = NMe) gave the ferrocenyl selenoesters FcSe(C(O)-2- c C 4 H 3 X) ( 3a , X = O; 3b , X = NMe). Upon exposure to silica gel compounds both 3a and 3b underwent an intermolecular conversion followed by transesterification with the silica surface to afford diferrocenyl methanols Fc 2 C(OH)(2- c C 4 H 3 X) ( 4a , X = O; 4b , X = NMe). Compounds 3a, 3b, 4a and 4b have been characterized by elemental analysis, IR and NMR ( 1 H, 13 C{ 1 H}, 77 Se{ 1 H}) spectroscopy and ESI-TOF mass spectrometry ( 4a and 4b ). The molecular structures of 3a , 4a and 4b in the solid state were determined by single crystal X-ray diffraction studies. The electrochemical studies exhibit for 3a and 3b reversible one-electron Fc/Fc + redox processes. During the electrochemical investigations of 4a and 4b two well-separated one-electron redox events could be determined ( 4a , ΔE 0’  = 330 mV; 4b , 367 mV). UV-Vis/NIR spectroelectrochemical studies on 4a and 4b reveal a weak electronic coupling between the iron centers in the corresponding mixed-valent species of [ 4a ] + and [ 4b ] + according to Robin and Day classification.