Biferrocene
Biferrocene is the organometallic compound with the formula [(CH)Fe(CH)]. It is the product of the formal dehydrocoupling of ferrocene, analogous the relationship between biphenyl and benzene. It is an orange, air-stable solid that is soluble in nonpolar organic solvents. Biferrocene can be prepared by the Ullmann coupling of iodoferrocene. Its one-electron oxidized derivative [(CH)Fe(CH)] attracted attention as a prototypical mixed-valence compound. A related compound is biferrocenylene, [Fe(CH)] wherein all cyclopentadienyl rings are coupled. Formally, biferrocene is derived from one fulvalene ligand, and biferrocenylene is derived from two.