Uranocene

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Uranocene
IUPAC name bis(η8-cyclooctatetraenyl)uranium(IV)
Other names uranium cyclooctatetraenyl, U(COT)2
Identifiers
CAS number 11079-26-8
Properties
Molecular formula C16H16U
Molar mass 446.33 g/mol
Appearance green crystals[1]
Hazards
Main hazards ignites in air
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

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.

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 D8h 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. 
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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



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