Bis(benzene)chromium
Encyclopedia
Bischromium is the organometallic compound with the formula
Cr(η6
-C6H6)2. It is sometimes called dibenzenechromium. The compound played an important role in the development of sandwich compounds in organometallic chemistry
and is the prototypical complex containg two arene
ligand
s.
s. It was first prepared by Hafner and Fischer by the reaction of CrCl3
, aluminium, and benzene, in the presence of AlCl3
. This so-called reductive Friedel-Crafts method was pioneered by E.O. Fischer
and his students. The product of the reaction was yellow [Cr(C6H6)2]+, which was then reduced to the neutral complex. Idealized equations for the synthesis are:
Compounds closely related to [Cr(C6H6)2]+ had been prepared many years before Fischer's work by Franz Hein
by the reaction of phenylmagnesium bromide
and CrCl3. Hein's reaction affords cationic sandwich complexes containing bi
- and terphenyl
, which baffled chemists until the breakthrough by Fischer and Hafner, and thus Hein had unknowingly discovered sandwich complexes a half century ahead of the work on ferrocene
. Fischer and Seus soon prepared Hein's [Cr(C6H5-C6H5)2]+. Illustrating the rapid pace of this research, the same issue of Chem. Ber.
also describes the Mo(0) complex.
, which have interesting structures. Oxidation affords [Cr(C6H6)2]+. Carbonylation gives (benzene)chromium tricarbonyl
.
The compound finds limited use in organic synthesis
.
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
Cr(η6
Hapticity
The term hapticity is used to describe how a group of contiguous atoms of a ligand are coordinated to a central atom. Hapticity of a ligand is indicated by the Greek character 'eta', η. A superscripted number following the η denotes the number of contiguous atoms of the ligand that are bound to...
-C6H6)2. It is sometimes called dibenzenechromium. The compound played an important role in the development of sandwich compounds 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...
and is the prototypical complex containg two arene
Arene
Arene or Arênê or Arène may refer to:*an aromatic hydrocarbon*Arene , a genus of marine snails in the family Areneidae*Arene , the wife of Aphareus and mother of Idas and Lynceus in Greek mythology...
ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
s.
Preparation
The substance is air sensitive and its synthesis requires air-free techniqueAir-free technique
Air-free techniques refer to a range of manipulations in the chemistry laboratory for the handling of compounds that are air-sensitive. These techniques prevent the compounds from reacting with components of air, usually water and oxygen; less commonly carbon dioxide and nitrogen...
s. It was first prepared by Hafner and Fischer by the reaction of CrCl3
Chromium(III) chloride
Chromium chloride is a violet coloured solid with the formula CrCl3. The most common form of CrCl3 sold commercially is a dark green hexahydrate with the formula [CrCl24]Cl.2H2O. Two other hydrates are known, pale green [CrCl5]Cl2.H2O and violet [Cr6]Cl3...
, aluminium, and benzene, in the presence of AlCl3
Aluminium chloride
Aluminium chloride is the main compound of aluminium and chlorine. It is white, but samples are often contaminated with iron trichloride, giving it a yellow colour. The solid has a low melting and boiling point. It is mainly produced and consumed in the production of aluminium metal, but large...
. This so-called reductive Friedel-Crafts method was pioneered by E.O. 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:...
and his students. The product of the reaction was yellow [Cr(C6H6)2]+, which was then reduced to the neutral complex. Idealized equations for the synthesis are:
- CrCl3 + 2/3 Al + 1/3 AlCl3 + 2 C6H6 → [Cr(C6H6)2]AlCl4 + 2/3 AlCl3
- [Cr(C6H6)2]AlCl4 + 1/2 Na2S2O4 → [Cr(C6H6)2] + NaAlCl4 + SO2
Compounds closely related to [Cr(C6H6)2]+ had been prepared many years before Fischer's work by Franz Hein
Franz Hein
Franz Hein was a German scientist. One of his notable contributions is in the discovery of π- complexes of chromium.-History:...
by the reaction of phenylmagnesium bromide
Phenylmagnesium bromide
Phenylmagnesium bromide, with the simplified formula , is a magnesium-containing organometallic compound. It is so commonly used that it is commercially available as a solution in diethyl ether or tetrahydrofuran . Phenylmagnesium bromide is a Grignard reagent...
and CrCl3. Hein's reaction affords cationic sandwich complexes containing bi
Biphenyl
Biphenyl is an organic compound that forms colorless crystals. It has a distinctively pleasant smell. Biphenyl is an aromatic hydrocarbon with a molecular formula 2...
- and terphenyl
Terphenyl
Terphenyls are a group of closely related aromatic hydrocarbons. Also known as diphenylbenzenes or triphenyls, they consist of a central benzene ring substituted with two phenyl groups. The three isomers are ortho-terphenyl, meta-terphenyl, and para-terphenyl. Commercial grade terphenyl is...
, which baffled chemists until the breakthrough by Fischer and Hafner, and thus Hein had unknowingly discovered sandwich complexes a half century ahead of the work on 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...
. Fischer and Seus soon prepared Hein's [Cr(C6H5-C6H5)2]+. Illustrating the rapid pace of this research, the same issue of Chem. Ber.
Chemische Berichte
Until 1998, Chemische Berichte was a German-language scientific journal featuring chemistry of all disciplines...
also describes the Mo(0) complex.
Reactions
The compound reacts with carboxylic acids to give chromium(II) carboxylates, such as chromium(II) acetateChromium(II) acetate
Chromium acetate hydrate, also known as chromous acetate, is the coordination compound with the formula Cr242. This formula is commonly abbreviated Cr242. This red-coloured compound features a quadruple bond...
, which have interesting structures. Oxidation affords [Cr(C6H6)2]+. Carbonylation gives (benzene)chromium tricarbonyl
(Benzene)chromium tricarbonyl
chromium tricarbonyl is an organometallic compound with the formula Cr3. This yellow crystalline solid compound is soluble in common nonpolar organic solvents...
.
The compound finds limited use in organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
.