Six ferrocenes a crowd for benzene

Hexaferrocenylbenzene, a benzene ring almost impossibly substituted with six ferrocene groups, has been synthesized and characterized by K. Peter C. Vollhardt of the University of California, Berkeley, and his colleagues at the University of Southern Denmark and New Mexico Highlands University (Chem. Commun. 2006, 2572). Chemists have been after the supercrowded molecule (shown) for decades but had been stuck at tetraferrocenylbenzene. Vollhardt's group made a breakthrough recently when it figured out how to prepare a cyclopentadienyl "superligand" fully substituted with five ferrocene groups (C&EN, Feb. 20, page 9). Using similar chemistry, the researchers made the ferrocenylated benzene by reacting hexaiodobenzene with diferrocenylzinc, (C₅H₅FeC₅H₄)₂Zn. The difficulty in preparing the fully substituted benzene is apparent from the product mixture, which included 56% yield of pentaferrocenylbenzene and only 4% yield of hexaferrocenylbenzene. Hexaferrocenylbenzene is of interest for an endless number of potential uses, Vollhardt notes, including electronic and magnetic materials, catalysis, a molecular gear for nanoscale machinery, and as the core for "Ferris wheel" macromolecules.