Bis(benzene)chromium
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| Bis(benzene)chromium | |
|---|---|
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| General | |
| Systematic name | Bis(benzene)chromium |
| Other names | di(benzene)chromium |
| Molecular formula | C12H12Cr |
| Molar mass | 208.22 g/mol |
| Appearance | brown-black crystals |
| CAS number | 1271-54-1 |
| Properties | |
| Density and phase | ? g/cm³, ? |
| Solubility in water | insoluble |
| Other solvents | slightly: benzene, THF |
| Melting point | 284-285 °C |
| Boiling point | sublimes:160 °C in vacuo. |
| Structure | |
| Coordination geometry |
pseudooctahedral |
| Crystal structure | ? |
| Dipole moment | 0 D |
| Hazards | |
| MSDS | External MSDS |
| Main hazards | flammable |
| Flash point | 180 °F |
| R/S statement | R: 11 S: 16-33 |
| RTECS number | GB5850000 |
| Supplementary data page | |
| Structure and properties |
n, εr, etc. |
| Thermodynamic data |
Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Related compounds | Ferrocene chromocene |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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Bis(benzene)chromium is the chemical compound with the formula Cr(η6-C6H6)2. It is sometimes called dibenzenechromium.
Contents |
[edit] Preparation
The compound played an important historic role in the development of sandwich compounds. 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.[1][2] The product of the reaction was yellow [Cr(C6H6)2]+, which was then reduced to the neutral complex. Slightly 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
In retrospect, compounds closely related to [Cr(C6H6)2]+ had been prepared many years before by Franz Hein, by the reaction of phenylmagnesium bromide and CrCl3.[3] Hein's reaction affords cationic sandwich complexes containing bi- and terphenyl, which baffled chemists until the breakthrough by Fischer and Hafner,[4] 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]+.[5][6]. Illustrating the rapid pace of this research, the same issue of Chem. Ber. also describes the Mo(0) complex.[7]
[edit] Reactions
The compound reacts with carboxylic acids to give chromium(II) carboxylates, such as chromium(II) acetate, which have interesting structures. Oxidation affords [Cr(C6H6)2]+.
The compound finds limited use in organic synthesis.[8]
[edit] References
- ^ King, R. B. Organometallic Syntheses. Volume 1 Transition-Metal Compounds; Academic Press: New York, 1965. ISBN 0-444-42607-8
- ^ Elschenbroich, C.; Salzer, A. ”Organometallics : A Concise Introduction” (2nd Ed) (1992) Wiley-VCH: Weinheim. ISBN 3-527-28165-7
- ^ Seyferth, D. "Bis(benzene)chromium. 1. Franz Hein at the University of Leipzig and Harold Zeiss and Minoru Tsutsui at Yale" Organometallics 2002, volume 21, pages 1520-1530. DOI: 10.1021/om0201056
- ^ Seyferth, D. "Bis(benzene)chromium. 2. Its Discovery by E. O. Fischer and W. Hafner and Subsequent Work by the Research Groups of E. O. Fischer, H. H. Zeiss, F. Hein, C. Elschenbroich, and Others" Organometallics 2002, volume 21, pages 2800-2820. DOI: 10.1021/om020362a
- ^ Fischer, E. O; Seus, D. "Zur Frage der Struktur der Chrom-phenyl-Verbindungen. Über Aromatenkomplexe von Metallen VI" Chemische Berichte 1956, band 89, p 1809-1815
- ^ Hein, F. "Zur Frage der Struktur der Chrom-phenyl-Verbindungen. Bemerkungen zur Abhandlung von E. O. Fischer und D. Seus" Chemische Berichte 1956, band 89, p 1816-1821,
- ^ Fischer, E. O.; Stahl, H.-O. "Di-benzol-molybdän (O). Über Aromatenkomplexe von Metallen V" Chemische Berichte, 1956, volume 89, pages 1805-1808
- ^ Herndon, J. W. "Dibenzenechromium" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.
