Bulky Alkyl Substituted 1,1’-Bis(trifluorovinyl)ferrocenes - Redox Autocatalytic Formation of Fluorinated Ferrocenophanes

Diastereomerically pure 1,1′-diiodoferrocenes with bulky alkyl groups in 3,3′ positions are obtained by a dilithiation strategy of 1,1′-di-tert-butylferrocene (1a) and 1,1′-bis(1-ethyl-1- methylpropyl)ferrocene (1b). The 3,3′-dilithiated species are converted to tri-n-butyltin derivatives (3a and 3b), which smoothly undergo a tin-iodine exchange reaction, yielding 1,1′-diiodo-3,3′-di-tert-butylferrocene (4a) and 1,1′-diiodo-3,3′-bis(1-ethyl-1-methylpropyl)ferrocene (4b). Negishi-type coupling reactions with trifluorovinylzinc chloride afforded the highly reactive 1,1′-bis(trifluorovinyl)ferrocenes with tert-butyl groups (5a) or 1-ethyl-1-methylpropyl groups (5b) in 3,3′-positions in excellent yields. 5a and 5b undergo under redox-conditions cyclizations to ferrocenophanes by a redox-autocatalytic mechanism. The main product four-carbon handle ferrocenophanes consist of CF 2 moieties in β-positions and one carbonyl function and one C(F)(H) unit (6a and 6c) or two carbonyl functions (6b and 6d) in α-positions. A ferrocenophane with a highly fluorinated handle bearing seven fluorine atoms (6e) was isolated as a byproduct. Formation of cyclic ether derivatives by unusual intramolecular substitution of fluorine is demonstrated for the case of 6a. Several new fluorinated ferrocenes were isolated and analyzed, including 1H, 13C, and 19F nuclear magnetic resonance spectroscopies. Molecular structures of five fluorinated ferrocenophanes by tert-butyl groups were elucidated with X-ray single-crystal diffraction. Influences of the electron-withdrawing fluorous substituents and the electron-donating alkyl groups on the redox behavior of the iron center were investigated by cyclic voltammetry. © 2012 American Chemical Society.