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Cyclopentadienylmolybdenum tricarbonyl dimer
IUPAC name
Other names cyclopentadienyl molybdenum

carbonyl dimer

CAS number 12091-64-4
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


Solubility in water insoluble
Crystal structure monoclinic
Dipole moment 0.112 D
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.

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


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 (dMoMo = 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.


  1. ^ Brian Mann (1997-01-06). "Fluxionality of Cp2Mo2(CO)6". University of Sheffield.  
  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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