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

Guide to balance cleaning: 8 simple steps

Daily Visual Balance Check

What is the Correct Way to Check Repeatability in Balances?

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