Bis(benzene)chromium

Dibenzenechromium, Chromdibenzol

Brown to black, air-sensitive crystals

Crystalline

1.519 g · cm -3

284-285 ° C

About 150 ° C ( high vacuum )

Soluble in benzene, sparingly soluble in diethyl ether

Risk

Template: Infobox chemical / molecular formula search available

Bis (benzene ) chromium ( exactly: bis ( η6 - benzene) chromium (0)) or dibenzenechromium is the organometallic compound with the formula Cr ( C6H6 ) 2

Bis ( benzene) chromium is a brown to black, crystalline solid. It is sensitive to oxygen and must therefore be handled under protective gas.

The chromium atom is formed by two parallel benzene molecules each six -coordinate ( η6 ). It is the prototype of a bis (arene ) metal complex, and played an important role in the development of the sandwich complexes in organometallic chemistry. The structure is very similar to the sandwich structure of the metallocenes ( chromocene ).

History

Bis ( benzene) chromium was first produced in 1955 by Ernst Otto Fischer and Walter Hafner. The method used is therefore also known as " Fischer- Hafner method". EO Fischer won in 1973 with Geoffrey Wilkinson awarded the Nobel Prize in Chemistry for his work on the chemistry of sandwich compounds ( elucidation of the structure of ferrocene and the synthesis of bis ( benzene) chromium ). A sample of bis ( benzene) chromium part of the inventory of the Deutsches Museum Bonn.

Production and representation

The synthesis of bis ( benzene) chromium requires oxygen - free working methods (see Schlenk technique). In the first synthesis carried out, the present ( also referred to as Friedel-Crafts reductive method) as the Fischer- Hafner method known reaction that chromium ( III) chloride, aluminum and benzene in the presence of aluminum chloride. The thus prepared air-stable cation is reduced in a further step with the sodium bis ( benzene) chromium.

Properties

Physical Properties

Bis (benzene ) chromium ( 18 valence electrons ) has no unpaired electrons and accordingly no magnetic moment. The cation ( valence 17 ) has an unpaired electron and having a magnetic moment of 1.77 Bohr magnetons.

As shown in the illustrated solid -state structure of bis ( benzene) chromium in the crystal before in a eklikptischen conformation.

Chemical Properties

Bis ( benzene) chromium reacts with carboxylic acids to chromium (II) -carboxylates, such as chromium (II ) acetate with a Cr / Cr - quadruple bond.

The oxidation of bis ( benzene) chromium, for example, by oxygen, leading to the green -colored cation [ Cr ( C6H6) 2] . By carbonylation of the half-sandwich complex η6 ​​- benzene ( tricarbonyl ) chromium is formed.

Use

Bis ( benzene) chromium is used in the organic synthesis as a catalyst for the dehydrogenation.