Organouranium chemistry - AbsoluteAstronomy.com

Organouranium chemistry is the science exploring the properties, structure and reactivity of organouranium compounds, which are organometallic compounds containing a carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

to uranium

Uranium

Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

chemical bond

Chemical bond

A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...

. The field is of some importance to the nuclear industry and of theoretical interest in organometallic chemistry

Organometallic chemistry

Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...

.

The development of organouranium compounds started in World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

when the Manhattan Project

Manhattan Project

The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army...

required volatile uranium compounds for ²³⁵U/²³⁸U isotope

Isotope

Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

separation. For example Henry Gilman

Henry Gilman

Henry Gilman 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....

attempted to synthesize compounds like tetramethyluranium and others worked on uranium metal carbonyl

Metal carbonyl

Metal carbonyls are coordination complexes of transition metals with carbon monoxide ligands. These complexes may be homoleptic, that is containing only CO ligands, such as nickel carbonyl , but more commonly metal carbonyls contain a mix of ligands, such as Re3Cl...

s but none of the efforts met success due to organouranium instability. After the discovery of ferrocene

Ferrocene

Ferrocene is an organometallic compound with the formula Fe2. It is the prototypical metallocene, a type of organometallic chemical compound consisting of two cyclopentadienyl rings bound on opposite sides of a central metal atom. Such organometallic compounds are also known as sandwich compounds...

in 1951, Todd Reynolds and Geoffrey Wilkinson

Geoffrey Wilkinson

Sir Geoffrey Wilkinson FRS was a Nobel laureate English chemist who pioneered inorganic chemistry and homogeneous transition metal catalysis.-Biography:...

in 1956 synthesized the uranium metallocene

Metallocene

A metallocene is a compound typically consisting of two cyclopentadienyl anions bound to a metal center in the oxidation state II, with the resulting general formula 2M. Closely related to the metallocenes are the metallocene derivatives, e.g. titanocene dichloride, vanadocene dichloride...

Cp₃UCl from sodium

Sodium

Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

cyclopentadienide

Cyclopentadiene

Cyclopentadiene is an organic compound with the formula C5H6. This colorless liquid has a strong and unpleasant odor. At room temperature, this cyclic diene dimerizes over the course of hours to give dicyclopentadiene via a Diels–Alder reaction...

and uranium tetrachloride

Uranium tetrachloride

Uranium tetrachloride is compound of uranium in oxidation state +4. It was used in the electromagnetic isotope separation process of uranium enrichment. It is one of the main starting materials for organouranium chemistry.- Synthesis :...

as a stable but extremely air-sensitive compound. In it the U-Cl bond is an ionic bond

Ionic bond

An ionic bond is a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions. Ionic bonds are formed between a cation, which is usually a metal, and an anion, which is usually a nonmetal. Pure ionic bonding cannot exist: all ionic compounds have some...

and the uranium bonds with the three cyclopentadienyl

Cyclopentadienyl complex

A cyclopentadienyl complex is a metal complex with one or more cyclopentadienyl groups . Based on the type of bonding between the metals and the cyclopentadienyl]] moieties, cyclopentadienyl complexes are classified into the following three categories: a) π-complexes, b) σ-complexes, and c) ionic...

ligands are covalent of the type found in sandwich compound

Sandwich compound

In organometallic chemistry, a sandwich compound is a chemical compound featuring a metal bound by haptic covalent bonds to two arene ligands. The arenes have the formula CnHn, substituted derivatives and heterocyclic derivatives...

s with involvement of the uranium 5f atomic orbital

Atomic orbital

An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus...

s.

Ernst Otto Fischer

Ernst Otto Fischer

Ernst Otto Fischer was a German chemist who won the Nobel Prize for pioneering work in the area of organometallic chemistry.-Early life:...

in 1962 discovered tetracyclopentadienyluranium Cp₄U by reaction of NaCp 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

Sandwich compound

with uranium in a tetrahedral molecular geometry

Tetrahedral molecular geometry

In a tetrahedral molecular geometry a central atom is located at the center with four substituents that are located at the corners of a tetrahedron. The bond angles are cos−1 ≈ 109.5° when all four substituents are the same, as in CH4. This molecular geometry is common throughout the first...

. 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

Andrew Streitwieser

Andrew Streitwieser is an American chemist known for his contributions to physical organic chemistry.Streitwieser was born in 1927 in Buffalo, New York and he grew up in New York City. He attended Columbia College and then Columbia University where he earned a PhD in the research group of William...

prepared the stable but pyrophoric compound uranocene

Uranocene

Uranocene U2 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...

(COT)₂U which has an atom of uranium sandwiched between two Cyclooctatetraenide dianions(D_8h molecular symmetry

Molecular symmetry

Molecular symmetry in chemistry describes the symmetry present in molecules and the classification of molecules according to their symmetry. Molecular symmetry is a fundamental concept in chemistry, as it can predict or explain many of a molecule's chemical properties, such as its dipole moment...

). The uranium f orbitals interact substantially with the aromatic

Aromaticity

In organic chemistry, Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August...

rings just as the d-orbitals in ferrocene

Ferrocene

interact with the Cp ligands. Uranocene differs from ferrocene because its HOMO

Homo

Homo may refer to:*the Greek prefix ὅμο-, meaning "the same"*the Latin for man, human being*Homo, the taxonomical genus including modern humans...

and LUMO

Lumo

Lumo is a 2007 documentary film about twenty-year-old Lumo Sinai, a woman who fell victim to "Africa's First World War." While returning home one day, Lumo and another woman were gang-raped by a group of soldiers fighting for control of the Democratic Republic of the Congo during the 1994 Rwandan...

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

Uranium borohydride U4 is a volatile uranium complex with borohydride. This green-coloured compound is polymeric in the solid but evaporates to a tetrahedral monomer.-Preparation:...

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 reagent

Organolithium reagent

An organolithium reagent is an organometallic compound with a direct bond between a carbon and a lithium atom. As the electropositive nature of lithium puts most of the charge density of the bond on the carbon atom, effectively creating a carbanion, organolithium compounds are extremely powerful...

s 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

Pentalene is a polycyclic hydrocarbon composed of two fused cyclopentadiene rings. It has chemical formula C8H6. It is antiaromatic, because it has 4n pi electrons. For this reason it dimerizes even at temperatures as low as -100°C....

ligands instead of COT ligands.

See also