Biferrocene

Biferrocene is the organometallic compound with the formula [(C5H5)Fe(C5H4)]2. 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 [(C5H5)Fe(C5H4)]2+ attracted attention as a prototypical mixed-valence compound.

A related compound is biferrocenylene, [Fe(C5H4)2]2 wherein all cyclopentadienyl rings are coupled. Formally, biferrocene is derived from one fulvalene ligand, and biferrocenylene is derived from two.

Reactions
Biferrocene can easily be converted into a mixed-valence complex, which is called biferrocenium. This [Fe(II)-Fe(III)] cation is a class II type (0.707 > α > 0) mixed-valence complex according to the Robin-Day classification.

Derivatives
Aminophosphine ligands with biferroceno substituents have been prepared as catalysts for asymmetric allylic substitution and asymmetric hydrogenation of alkenes.

Related compounds

 * Bis(fulvalene)diiron