Uranocene

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ImageFileL1 = Uranocene-2D-skeletal.png ImageFileR1 = Uranocene-2D-dimensions.png ImageFileL2 = Uranocene-3D-vdW.png ImageFileR2 = Uranocene-3D-balls.png ImageSize =
IUPACName = bis(η⁸-cyclooctatetraene)uranium
OtherNames = uranium cyclooctatetraenyl, U(COT)₂
Section1 = Chembox Identifiers
CASNo = 11079-26-8
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Section2 = Chembox Properties
Formula = C₁₆H₁₆U
MolarMass = 446.33 g/mol
Appearance = green crystals [cite journal | author = A. Streitwieser and U. Mueller-Westerhoff | title = Bis(cyclooctatetraenyl)uranium (uranocene). A new class of sandwich complexes that utilize atomic f orbitals | year = 1968 | journal = J. Am. Chem. Soc. | volume = 90 | issue = 26 | pages = 7364–7364 | doi = 10.1021/ja01028a044]
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Section3 = Chembox Hazards
MainHazards = ignites in air
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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. [cite journal | author = J. S. Hager, J. Zahardis, R. M. Pagni, R. N. Compton and J. Li | title = Raman under nitrogen. The high-resolution Raman spectroscopy of crystalline uranocene, thorocene, and ferrocene | year = 2004 | journal = The Journal of Chemical Physics | volume = 120 | issue = 6 | pages = 2708–2718 | doi =10.1063/1.1637586]

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 [ [http://www.radiochemistry.org/periodictable/la_series/A12.html Lanthanides & Actinides: Organoactinides ] ] . 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] ⁻. [cite journal | author = D. Seyferth | title = Uranocene. The First Member of a New Class of Organometallic Derivatives of the f Elements | year = 2004 | journal = Organometallics | volume = 23 | issue = 15 | pages = 3562–3583 | doi = 10.1021/om0400705]

References

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