Uranocene

Uranocene U(C₈H₈)₂ is the most notable cyclooctatetraenide of the f elements and one of the first organouranium compounds to be synthesized. Uranocene is a member of the actinocenes, a group of metallocenes incorporating elements from the actinide series. It is the most studied bis[8]annulene-metal system.

Additional recommended knowledge

Daily Visual Balance Check

Better weighing performance in 6 easy steps

How to ensure accurate weighing results every day?

Synthesis

Uranocene was first prepared by the reaction of uranium tetrachloride and dipotassium cyclooctatetraene, viz.

2K + C₈H₈ → K₂(C₈H₈)

2K₂(C₈H₈) + UCl₄ → U(C₈H₈)₂ + 4KCl.^[2]

Physical and chemical properties

Uranocene is paramagnetic, pyrophoric, and stable to hydrolysis. The η⁸-cyclooctatetraenyl groups are planar, as expected for a ring containing 10 π-electrons, and are mutually parallel, forming a sandwich containing the uranium atom. In the solid state, the rings are eclipsed, conferring D_8h symmetry on the uranocene molecule. In solution the rings rotate with a low energy barrier.

Uranium-COT bond

The nature of the uranium-cyclooctatetraenyl bond is the subject of continuing research and debate ^[3]. UV-PES indicates the bonding in uranocene has contributions from 5f and 6d orbitals.

Analogous compounds

Some examples of analogous compounds of the form M(C₈H₈)₂ exist for M = (Nd, Tb, Pu, Pa, Np, Th, and Yb). Extensions include the air-stable derivative U(C₈H₄Ph₄)₂ and the cycloheptatrienyl species [U(C₇H₇)₂]⁻.^[4]

References

1. ^ A. Streitwieser and U. Mueller-Westerhoff (1968). "Bis(cyclooctatetraenyl)uranium (uranocene). A new class of sandwich complexes that utilize atomic f orbitals". J. Am. Chem. Soc. 90 (26): 7364-7364. doi:10.1021/ja01028a044.
2. ^ J. S. Hager, J. Zahardis, R. M. Pagni, R. N. Compton and J. Li (2004). "Raman under nitrogen. The high-resolution Raman spectroscopy of crystalline uranocene, thorocene, and ferrocene". The Journal of Chemical Physics 120 (6): 2708-2718. doi:10.1063/1.1637586.
3. ^ http://www.radiochemistry.org/periodictable/la_series/A12.html
4. ^ D. Seyferth (2004). "Uranocene. The First Member of a New Class of Organometallic Derivatives of the f Elements". Organometallics 23 (15): 3562-3583. doi:10.1021/om0400705.

Further reading

• The f elements, Nikolas Kaltsoyannis and Peter Scott. ISBN 0-19-850467-5
• Chemistry of the Elements, N. N. Greenwood and A. Earnshaw. ISBN 0-08-022057-6