Metals biferrocene derivatives

Dong et al. have reported on crown ether-bound biferrocene, 21, in which the redox potentials are shifted by the capture of metal ions within the crown ether (55). For example, the electrochemical behavior observed for the biferrocene derivative with Ba2+ ion is fundamentally different, as new redox couples are observed for 9 with Ba2+ concentrations within the range 0 < [Ba2+] < 2 eq. The peak currents for the two new redox couples increase with concentrations of the Ba2+ ion until a full equivalent is added at this point, the original redox couples disappear and the new redox couples reach full development. 

The differences between biferrocenium and l,r-biferrocene[Fe(n)-Fe(in)] cations have been previously discussed [57]. It is sufficient to note here that the crystal structure of l,r-biferrocene[Fe(ii)-Fe(in)] picrate [61a] reveals a shorter Fe-Fe distance than that in the neutral compound [61b] (3.64 vs. 3.98 A) indicating increased interaction between the two metal centers in the cation. Possibly because a high yield synthesis of 1,1 -biferrocenylene is not available, and because the derivative chemistry of this compound is essentially undeveloped, no other relevant studies directed toward the preparation of molecular materials based on it have appeared in the literature. 

---