Uranocene
Uranocene is an organouranium chemical compound composed of a uranium atom sandwiched between two cyclooctatetraenide (COT) rings. Its chemical formula is U(C8H8)2, often abbreviated as U(COT)2. It belongs to a broader class of metallocenes, specifically actinocenes when the central metal is an actinide element.
Uranocene was first synthesized in 1968 by Andrew Streitwieser and Ulrich Müller-Westerhoff at the University of California, Berkeley. Its discovery provided significant insight into the bonding nature of actinide complexes and fueled the development of organoactinide chemistry.
The molecule has a sandwich structure with the uranium atom located between two planar, parallel COT rings. The uranium atom is formally in the +4 oxidation state. The COT rings are dianions (C8H82-), each carrying a -2 charge, which balances the +4 charge of the uranium ion. The uranium-COT bond is primarily covalent, involving significant f-orbital contributions from the uranium atom.
Uranocene is air-sensitive, reacting readily with oxygen. It is a dark green solid that is soluble in organic solvents. Its stability is attributed to the aromatic character of the cyclooctatetraenide ligands and the effective shielding of the uranium atom.
Uranocene has been studied extensively using various spectroscopic techniques, including X-ray diffraction, NMR spectroscopy, and electronic spectroscopy. These studies have provided valuable information about its structure, bonding, and electronic properties.
Analogues of uranocene have been synthesized with different substituents on the COT rings. These modifications can influence the electronic and steric properties of the complex. Other actinocenes, such as thorocene (Th(COT)2), have also been prepared.
Uranocene's significance lies in its role as a foundational compound in organoactinide chemistry and its contribution to understanding the bonding capabilities of the actinide elements.