What molecule am I?
Ever since the discovery of ferrocene in the 1940s, hundreds of “sandwich” compounds, in which a metal atom is “sandwiched” between two arene rings, have been synthesized. In 1968, Andrew Streitweiser, Jr.,* and Ulrich Mueller-Westerhoff at the University of California, Berkeley, advanced the field by preparing uranocene, an actinide metal sandwiched between two cyclic polyolefins.
In contrast to ferrocene with its cyclopentadienide (Cp) rings, the coordinating molecule in uranocene is the dianion of cyclooctatetraene (COT). Streitweiser and Mueller-Westerhoff treated COT with elemental potassium to make the dianion and then added uranium tetrachloride at 0 ºC to produce uranocene, a green crystalline solid. COT has a folded structure; but its dianion is planar, making it a suitable “bread” for the sandwich.
Uranocene is stable to water, acids, bases, and moderate heating—but it ignites spontaneously in air. In ferrocene, the Cp rings’ six π electrons interact with the 3d orbitals in iron. In uranocene, uranium’s 6d orbitals similarly combine with the COT’s 10 π electrons; but uranium 5f orbitals are also involved, contributing to the molecule’s stability.
In 2004, Ditmar Seyferth at MIT wrote a comprehensive review of organometallic compounds that contain f-orbital elements.
Learn more about this molecule from CAS, the most authoritative and comprehensive source for chemical information.