Tetraferrocenyl[5]cumulene, (Fc)2C=C=C=C=C=C(Fc)2:: Synthesis, electrochemistry, and reactivity, including nickel(0)-promoted [3]ferrocenophane formation and [2+2] cycloaddition with fullerene C60

Tetraferrocenyl[5]cumulene (Fc)(2)C=C=C=C=C=C(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)(2)C=C=C=C=C=C(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 alkynes, and (iv) [2+2] cycloaddition with C-60 and C-70, yielding the first cumulene derivatives of fullerenes. MS, UV-vis IR, Raman, NMR, cyclic voltammetry, controlled potential coulometry, Mossbauer spectroscopy, and X-ray single-crystal structure analysis have been performed to characterize the new compounds.