Osmocene is an
organoosmium compound found as a white solid. It is a
metallocene
A metallocene is a compound typically consisting of two cyclopentadienyl anions (, abbreviated Cp) bound to a metal center (M) in the oxidation state II, with the resulting general formula Closely related to the metallocenes are the metallocene d ...
with the formula Os(C
5H
5)
2.
Synthesis
Osmocene is commercially available. It may be prepared by the reaction of
osmium tetroxide
Osmium tetroxide (also osmium(VIII) oxide) is the chemical compound with the formula OsO4. The compound is noteworthy for its many uses, despite its toxicity and the rarity of osmium. It also has a number of unusual properties, one being that the ...
with
hydrobromic acid
Hydrobromic acid is a strong acid formed by dissolving the diatomic molecule hydrogen bromide (HBr) in water. "Constant boiling" hydrobromic acid is an aqueous solution that distills at and contains 47.6% HBr by mass, which is 8.77 mol/L. ...
followed by
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
and
cyclopentadiene.
It was first synthesized by
Ernst Otto Fischer
Ernst Otto Fischer (; 10 November 1918 – 23 July 2007) was a German chemist who won the Nobel Prize for pioneering work in the area of organometallic chemistry.
Early life
He was born in Solln, a borough of Munich. His parents were Karl T. Fi ...
and Heinrich Grumbert via the reaction of
osmium(IV) chloride with excess
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 p ...
in
dimethoxyethane
Dimethoxyethane, also known as glyme, monoglyme, dimethyl glycol, ethylene glycol dimethyl ether, dimethyl cellosolve, and DME, is a colorless, aprotic, and liquid ether that is used as a solvent, especially in batteries. Dimethoxyethane is mi ...
, where osmium(II) chloride is presumed to be an intermediate formed ''in situ''. Alternatively,
cyclopentadienyl magnesium bromide
Cyclopentadienyl magnesium bromide is a chemical compound with the molecular formula . The molecule consists of a magnesium atom bonded to a bromine atom and a cyclopentadienyl group, a ring of five carbons each with one hydrogen atom.
The compou ...
could be reacted with osmium(IV) chloride, though this has worse yields.
Properties
Osmocene is a white solid. The molecular structure features an osmium ion sandwiched between two
cyclopentadienyl rings. It is isomorphous to the lighter homologue
ruthenocene
Ruthenocene is an organoruthenium compound with the formula (C5H5)2Ru. This pale yellow, volatile solid is classified as a sandwich compound and more specifically, as a metallocene.
Structure and bonding
Ruthenocene consists of a ruthenium ion s ...
, both crystallizing in an eclipsed conformation. This is in contrast to
ferrocene, which crystallizes with its rings staggered.
Compared to ferrocene and ruthenocene, osmocene is less reactive towards electrophilic aromatic substitution but has the greatest tendency towards
adduct
An adduct (from the Latin ''adductus'', "drawn toward" alternatively, a contraction of "addition product") is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all co ...
formation with
Lewis acids.
The osmocenium cation
5H5)2">s(C5H5)2sup>+ dimerizes, forming a binuclear complex with an Os-Os bond. In contrast, the decamethylosmocenium cation
5(CH3)5)2">s(C5(CH3)5)2sup>+ is stable as the monomer.
Uses
In 2009, Horst Kunkely and Arnd Vogler reported the possibility of
photocatalytic water splitting
Photocatalytic water splitting is an artificial photosynthesis process using photocatalysis for the dissociation of water (H2O) into hydrogen () and oxygen (). Only light energy (photons), water, and a catalyst(s) are needed, since this is what ...
with osmocene as a catalyst.
References
{{Osmium compounds
Metallocenes
Organoosmium compounds