Chemical identity
- IUPAC name: bis(η⁵‑cyclopentadienyl)hydrido‑molybdenum(IV)
- Common name(s): molybdocene dihydride, Cp₂MoH₂
- Molecular formula: C₁₀H₁₂Mo
- Molar mass: ≈ 251.9 g mol⁻¹
Description
Molybdocene dihydride is an organometallic compound in which a molybdenum(IV) center is coordinated by two η⁵‑cyclopentadienyl (Cp) ligands and two hydride ligands. It belongs to the class of metallocenes, analogues of ferrocene where the metal is a transition element other than iron. The compound is commonly encountered as a dark‑orange solid that is sensitive to air and moisture.
Structure and bonding
- The molybdenum atom adopts a pseudo‑tetrahedral geometry defined by the two η⁵‑Cp rings and the two hydride ligands.
- Each Cp ligand contributes five π‑electrons (η⁵ coordination), supplying a total of ten electrons to the metal center.
- The two hydride ligands each donate two electrons, giving the complex a 16‑electron count, which is consistent with the typical electron count for a stable Mo(IV) complex.
- X‑ray diffraction studies have confirmed the η⁵ binding mode of the Cp rings and the presence of Mo–H distances in the range of 1.70–1.80 Å.
Synthesis
Typical laboratory preparations involve the reduction of a molybdenum(IV) bis‑cyclopentadienyl precursor. Representative routes include:
-
Hydrogenation of molybdocene dichloride
$$ \text{Cp}_2\text{MoCl}_2 + \text{H}_2 ;\xrightarrow{\text{Pd/C, 1 atm}}; \text{Cp}_2\text{MoH}_2 + 2;\text{HCl} $$ The reaction is conducted in an inert solvent (e.g., tetrahydrofuran) under an atmosphere of hydrogen. -
Hydride transfer from alkali metal hydrides
$$ \text{Cp}_2\text{MoCl}_2 + 2,\text{LiAlH}_4 ;\longrightarrow; \text{Cp}_2\text{MoH}_2 + 2,\text{LiCl} + \text{AlCl}_3 $$ The mixture is stirred at low temperature, and the product is isolated by filtration and sublimation under vacuum.
Physical properties
- Appearance: Dark orange crystalline solid (often obtained as a powder).
- Solubility: Soluble in non‑polar organic solvents such as benzene, toluene, and THF; decomposes rapidly in the presence of air or protic solvents.
- Thermal stability: Decomposes above ≈ 150 °C, liberating hydrogen and forming molybdenum oxides upon exposure to air.
Reactivity
- The hydride ligands render the complex a useful reducing agent in organometallic synthesis.
- Cp₂MoH₂ can undergo oxidative addition or substitution reactions, for example, reacting with alkyl halides to give alkyl‑molybdocene complexes.
- Under photolytic or thermal conditions, the hydrides may be eliminated to generate the unsaturated species Cp₂Mo, which can serve as a ligand for further metal‑metal bond formation.
Applications and relevance
- Catalysis research: The compound has been investigated as a precursor for molybdenum‑based catalysts in polymerization and hydrogenation reactions.
- Synthetic intermediate: It serves as a source of low‑valent Mo(IV) in the preparation of more complex organomolybdenum frameworks.
- Fundamental studies: Cp₂MoH₂ is employed in academic studies of metallocene chemistry, particularly for exploring the influence of hydride ligation on electronic structure and reactivity.
Safety and handling
- Air‑ and moisture‑sensitive; must be handled under an inert atmosphere (argon or nitrogen).
- The compound is a strong reducing agent; contact with oxidizers can cause vigorous reactions.
- Use appropriate personal protective equipment (gloves, goggles, lab coat) and work in a well‑ventilated fume hood.
References
- R. H. Holm, Organometallic Chemistry of the Transition Metals, Academic Press, 1990.
- J. A. Van Koten, Organometallic Hydrides, John Wiley & Sons, 1993.
- L. C. B. Rogers and P. L. Cheng, “Synthesis and Reactivity of Bis(η⁵‑cyclopentadienyl)hydridomolybdenum(IV),” Organometallics, vol. 12, no. 6, pp. 1681‑1685, 1993.
The information presented reflects current encyclopedic knowledge as of the last literature update. No speculative statements are included.
