Multi-functionalized ferrocenes: –Synthesis and characterization –

•High yield of multi-functionalized ferrocenes via ortho-lithiation was achieved.•π Interactions leading to a columnar arrangement of the ferrocenes were found.•Reversibility of the redox properties improved using weakly coordinating electrolyes.•A linear correlation between redox potential and number of formyl groups exists.

Ferrocenes with up to four formyl functionalities have been synthesized by selective one- or two-fold ortho-lithiation of 1,1′-di(1,3-dioxan-2-yl)ferrocene followed by the reaction with dimethylformamide. Subsequent deprotection afforded tri- and tetraformyl-ferrocene in good yields. Wittig reactions convert the aldehydes to tri- and tetravinyl-ferrocene. The structures of three formyl-ferrocenes in the solid-state have been determined by single crystal X-ray diffraction. In two of the structures the ferrocene moieties form 1D chains by parallel displaced π-interactions with Cp⋯Cp distances as short as 3.21 Å. Electrochemical measurements (CV) demonstrated an irreversible behavior of the electron-poor multi-formyl ferrocenes. Reducing the measurement temperature down to −40 °C and the usage of [NnBu4][B(C6F5)4] prevents side reactions and hence reversible redox-processes could be obtained. It was found that the number of formyl functionalities correlates with the ferrocenyl's redox potential in a strictly linear fashion.

Graphical abstractFerrocenes with up to four formyl functionalities have been synthesized in good yields. As revealed by X-ray crystallography the C5H3-rings in two examples show strong π interactions with C5H3⋯C5H3 distances as short as 3.21 Å. Electrochemical measurements (CV) demonstrated that the number of formyl functionalities correlates with the ferrocenyl's redox potential in a strictly linear fashion.Figure optionsDownload full-size imageDownload as PowerPoint slide