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(C₅H₅)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 ...

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 s(C₅H₅)₂sup>+ dimerizes, forming a binuclear complex with an Os-Os bond. In contrast, the decamethylosmocenium cation 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