Cyclopentadienylmolybdenum tricarbonyl dimer
IUPAC name	bis(tricarbonyl[η5-cyclopentadienyl] molybdenum)(Mo—Mo)
Other names	cyclopentadienyl molybdenum carbonyl dimer Bis(tricarbonylcyclopentadienylmolybdenum)
Identifiers
CAS number	12091-64-4
Properties
Molecular formula	Mo2(η-C5H5)2(CO)6
Molar mass	489.96 g/mol
Appearance	dark red crystalline solid
Melting point	222 °C
Boiling point	dec.
Solubility in water	insoluble
Structure
Crystal structure	monoclinic
Dipole moment	0.112 D
Hazards
R-phrases	20/21/22
S-phrases	36
Related compounds
Related compounds	(η-C5H5)2Mo2(CO)4
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Cyclopentadienylmolybdenum tricarbonyl dimer is the chemical compound with the formula Cp₂Mo₂(CO)₆, where Cp is C₅H₅. This a dark red crystalline solid is air stable in solid form, but decomposes in solution when exposed to air. It is one of the most important and most accessible organomolybdenum compounds, although it has no practical uses.

[edit] Structure and synthesis

The molecule exists in two rotamers, gauche and anti.^[1] The six CO ligands are terminal and the Mo-Mo bond distance is 3.2325 Å.^[2] The compound is prepared by treatment of Mo(CO)₆ in hot dicyclopentadiene. A high-yield route to the dimer involves a two-step, one-pot synthesis.^[3] In the first step Mo(CO)₆ is converted in hot CH₃CN to the air-sensitive Mo(CO)₃(CH₃CN)₃.

Mo(CO)₆ + 3 CH₃CN → Mo(CO)₃(CH₃CN)₃ + 3 CO

2 Mo(CO)₃(CH₃CN)₃ + 2 C₅H₆ → (C₅H₅)₂Mo₂(CO)₆ + H₂ + 6 CH₃CN

[edit] Reactions

Thermolysis of this compound in hot solution of diglyme (bis(2-methoxyethyl)ether) results in decarbonylation, giving the tetracarbonyl, which has a formal triple bond between the Mo centers (d_MoMo = 2.448 Å):^[4]

(C₅H₅)₂Mo₂(CO)₆ → (C₅H₅)₂Mo₂(CO)₄ + 2 CO

The resulting cyclopentadienylmolybdenum dicarbonyl dimer in turn binds a variety of substrates across the metal-metal triple bond.

[edit] References

1. ^ Brian Mann (1997-01-06). "Fluxionality of Cp₂Mo₂(CO)₆". University of Sheffield. http://brian-mann.staff.shef.ac.uk/Cp2Mo2CO6.html. 
2. ^ R. D. Adams, D. M. Collins, and F. A. Cotton (1974). "Molecular Structures and Barriers to Internal Rotation in Bis(η5 -cyclopentadienyl)hexacarbonylditungsten and Its Molybdenum Analog". Inorg. Chem. 13: 1086–1090. doi:10.1021/ic50135a015. 
3. ^ M. David Curtis, Michael S. Hay (1990). "Cyclopentadienyl Metal Carbonyl Dimers of Molybdenum and Tungsten". Inorganic Syntheses (New York: J. Wiley & Sons) 28: 150–152. doi:10.1002/9780470132593.ch40. ISBN 9780471526193. 
4. ^ Cotton, F. A.; Walton, R. A. “Multiple Bonds Between Metal Atoms” Oxford (Oxford): 1993, p 564ff. ISBN 0-19-855649-7.

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