Organouranium chemistry is the science exploring the properties, structure and reactivity of organouranium compounds, which are organometallic compounds containing a carbon to uranium chemical bond. The field is of some importance to the nuclear industry and of theoretical interest in

organometallic chemistry Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...

History

The development of organouranium compounds started in World War II when the Manhattan Project required volatile uranium compounds for ²³⁵U/²³⁸U isotope separation. For example,

Henry Gilman Henry Gilman (May 9, 1893 – November 7, 1986) was an American organic chemist known as the father of organometallic chemistry, the field within which his most notable work was done. He discovered the Gilman reagent, which bears his name. Earl ...

attempted to synthesize compounds like tetramethyluranium, and others worked on uranium metal carbonyls, but none of the efforts met success due to organouranium instability. After the discovery of

ferrocene Ferrocene is an organometallic compound with the formula . The molecule is a complex consisting of two cyclopentadienyl rings bound to a central iron atom. It is an orange solid with a camphor-like odor, that sublimes above room temperature, a ...

in 1951, Todd Reynolds and Geoffrey Wilkinson in 1956 synthesized the uranium metallocene Cp₃UCl from

sodium cyclopentadienide Sodium cyclopentadienide is an organosodium compound with the formula C5H5Na. The compound is often abbreviated as NaCp, where Cp− is the cyclopentadienide anion. Sodium cyclopentadienide is a colorless solid, although samples often are pi ...

and uranium tetrachloride as a stable but extremely air-sensitive compound. In it, the U-Cl bond is an ionic bond, while the bonds with the three

cyclopentadienyl Cyclopentadienyl can refer to *Cyclopentadienyl anion, or cyclopentadienide, **Cyclopentadienyl ligand *Cyclopentadienyl radical, • *Cyclopentadienyl cation, See also *Pentadienyl In organic chemistry, pentadienyl refers to the organic radic ...

ligands are covalent of the type found in sandwich compounds with involvement of the uranium 5f atomic orbitals. Ernst Otto Fischer in 1962 discovered tetracyclopentadienyluranium Cp₄U by reaction of KCp with UCl₄ (6% yield) as a compound stable in air as a solid but not in solution. A zero molecular dipole moment and IR spectroscopy revealed that it was also a sandwich compound with uranium in a tetrahedral molecular geometry. In 1970, Fischer added Cp₃U to the list of known organouranium compounds by reduction of Cp₄U with elemental uranium. In 1968, the group of Andrew Streitwieser prepared the stable but pyrophoric compound uranocene (COT)₂U, which has an atom of uranium sandwiched between two cyclooctatetraenide anions (D_8h

molecular symmetry Molecular symmetry in chemistry describes the symmetry present in molecules and the classification of these molecules according to their symmetry. Molecular symmetry is a fundamental concept in chemistry, as it can be used to predict or explain m ...

). The uranium f orbitals interact substantially with the aromatic rings just as the d-orbitals in

interact with the Cp ligands. Uranocene differs from ferrocene because its HOMO and LUMO are centered on the metal and not on the rings and all reactions thus involve the metal often resulting in ligand - metal cleavage. Uranocenes show ease of reduction of U(IV) compounds to U(III) compounds; otherwise they are fairly unreactive. A close relative that does have sufficient reactivity, obtained by reaction of uranocene with

uranium borohydride Uranium borohydride is the inorganic compound with the empirical formula uranium, U(BH4)4. Two polymeric forms are known, as well as a monomeric derivative that exists in the gas phase. Because the polymers convert to the gaseous form at mild temp ...

is the half-sandwich compound (COT)U(BH₄)₂ discovered in 1983 by the group of M.J. Ephritikhine. Compounds of this type react in many different ways, for instance alkylation at uranium with organolithium reagents or conversion to hybrid sandwich compounds. Other organouranium compounds are inverted uranocenes with a COT ligand in between two uranium atoms or uranium sandwich compounds with

pentalenide Pentalene is a polycyclic hydrocarbon composed of two fused cyclopentadiene rings. It has chemical formula . It is antiaromatic, because it has 4''n'' π electrons where ''n'' is any integer. For this reason it dimerizes even at temperatures as ...

ligands instead of COT ligands.

References

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