Ferrocene Fe(C5H5)2 is the prototypical metallocene, a type of organometallic chemical compound, consisting of two cyclopentadienyl rings bound on opposite sides of a central iron atom and forming an organometallic sandwich compound.
It was first made unintentionally from the reaction of cyclopentadiene and iron powder in the 1950's, originally designed to couple the diene. Instead a lightly orange powder was obtained. The structure was confirmed by NMR. Led to an explosion of interest in d-block metal carbon bonds and brought about development and the now flourishing study of organometallic chemistry.