Presenting a ferrocene Ferris wheel

By fusing ferrocene molecules together, a research team has prepared new iron-based macrocycles that resemble a Ferris wheel. Ferrocene linear chains and macrocycles have been made before, but they contained spacer groups separating the metallocene units, which don’t allow much interaction between the iron atoms. Michael S. Inkpen, Nicholas J. Long, and Tim Albrecht of Imperial College London and their colleagues have now made examples in which five to nine ferrocene units are fused by direct cyclopentadienyl C–C linkages. These redox-active ferrous/ferric nanorings have substantial charge delocalization and are more stable than previous ferrocene-based macromolecules, with the six-membered version representing an organometallic analog of benzene (Nat. Chem. 2016, DOI: 10.1038/nchem.2553). The researchers made the ferrocene rings via copper-mediated Ullmann coupling reactions of dilute solutions of iodinated ferrocene or linear ferrocene oligomers. The internal cavity of the molecules provides opportunities for host-guest chemistry, and the charge delocalization could lead to electronic and magnetic applications, the researchers say. The team is now investigating more efficient synthetic routes to the macrocycles and methods for derivatizing the rings and potentially linking them together to form large-scale arrays.