Chemists Make Elusive Multifluorinated Ferrocene

Ferrocene, the iconic sandwich-shaped metal complex, is the compound that made researchers hungry to explore organometallic chemistry. Chemists have prepared countless derivatives by modifying ferrocene’s two cyclopentadiene rings. But fluorinated ferrocenes have proven elusive, a frustrating situation given the importance of fluorinated hydrocarbons in catalysis. Chemists in Germany have now made 1,2,3,4,5-pentafluoroferrocene, which is only the second fluorinated ferrocene reported, after monofluoroferrocene in 1971 (J. Am. Chem. Soc. 2014, DOI: 10.1021/ja511588p). Karlheinz Sünkel of Ludwig Maximilian University of Munich and coworkers performed five sequential lithiation-fluorination reactions to obtain pentafluoroferrocene in 6.7% yield from ferrocene. Chemists in the 1960s predicted that polyfluorinated ferrocenes would have high oxidative stability. Surprisingly, cyclic voltammetry data suggest the new compound is easy to oxdize, particularly when compared with pentachloroferrocene or with similar ruthenium complexes. The researchers corroborated their experimental results with density functional theory calculations and verified pentafluoroferrocene’s structure with NMR and IR spectroscopy and X-ray crystallography.