Tetraferrocenyl[5]cumulene, (Fc)₂CCCCCC(Fc)₂: Synthesis, Electrochemistry, and Reactivity, Including Nickel(0)-Promoted [3]Ferrocenophane Formation and [2+2] Cycloaddition with Fullerene C₆₀

Abstract

Tetraferrocenyl[5]cumulene (Fc)2CCCCCC(Fc)2 (Fc = ferrocenyl) is synthesized from 1,1-diferrocenyl-1-methoxypropyne by formal dimerization of diferrocenylethenylidenecarbene generated in situ by deprotonation and elimination of methoxide. The cumulene is an air-stable compound of blue color with an electron-rich cumulene moiety, as indicated by various spectroscopic methods. In contrast to other (shorter) ferrocenyl cumulenes which show no reactivity due to steric hindrance, (Fc)2CCCCCC(Fc)2 is a quite reactive compound, as exemplified by (i) transition metal complex formation with Rh(I), (ii) [3]ferrocenophane generation by Ni(0)-promoted intramolecular electrophilic aromatic substitution, and (iii) [2+2] cycloaddition with olefins and alkynes, and (iv) [2+2] cycloaddition with C60 and C70, yielding the first cumulene derivatives of fullerenes. MS, UV−vis, IR, Raman, NMR, cyclic voltammetry, controlled potential coulometry, Mössbauer spectroscopy, and X-ray single-crystal structure analysis have been performed to characterize the new compounds.