Dimanganese decacarbonyl

Dimanganese decacarbonyl is the chemical compound with the formula Mn₂(CO)₁₀. This metal carbonyl is an important reagent in the organometallic chemistry of manganese.^[1]

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Synthesis

The compound was first prepared in low yield by the reduction of manganese iodide with magnesium under CO.^[2] A more efficient preparation entails reduction of anhydrous MnCl₂ with sodium benzophenone ketyl under 200 atmospheres of CO.^[3] The availability of inexpensive Methylcyclopentadienyl manganese tricarbonyl ("MMT") has led to a low pressure route to Mn₂(CO)₁₀.^[4]

Structure

Mn₂(CO)₁₀ has no bridging CO ligands: it can be described (CO)₅Mn-Mn(CO)₅. There are two kinds of CO ligands; one CO on each Mn is coaxial with the Mn-Mn bond, and four on each manganese that are perpendicular to it (equatorial). In the stable rotamer, the two Mn(CO)₅ subunits are staggered. The overall molecule thus belongs to the point group D_4d, which is an uncommon symmetry.

Reactions

Mn₂(CO)₁₀ is air stable as a crystalline solid, but solutions require Schlenk techniques. It finds limited use in organic synthesis.^[5] Characteristic reactions:

• Reduction of Mn₂(CO)₁₀ gives the manganese pentacarbonyl anion, which can be isolated as a salt:

Mn₂(CO)₁₀ + 2 Na → 2 Na[Mn(CO)₅]

The anion is a versatile nucleophile. Protonation gives the hydride [HMn(CO)₅], and methylation gives [(CH₃)Mn(CO)₅].

• Halogenation of Mn₂(CO)₁₀proceeds with scission of the Mn-Mn bonds.

Mn₂(CO)₁₀ + Br₂ → 2[Mn(CO)₅Br]

Safety

Mn₂(CO)₁₀ is a volatile source of a metal and a source of CO.

References

1. ^ Elschenbroich, C. ”Organometallics” (2006) Wiley-VCH: Weinheim. ISBN 978-3-29390-6
2. ^ Brimm, E. O.; Lynch, M. A.; Sesny, W. J. "Preparation and Properties of Manganese Carbonyl" Journal of the American Chemical Society 1954, volume 76, page 3831 - 3835.
3. ^ King, R. B. Organometallic Syntheses. Volume 1 Transition-Metal Compounds; Academic Press: New York, 1965. ISBN 0-444-42607-8
4. ^ King, R. B.; Stokes, J. C.; Korenowski, T. F. "A Convenient Synthesis of Dimanganese Decarbonyl from Inexpensive Starting Materials at Atmospheric Pressure" Journal of Organometallic Chemistry 1968, volume 11, Pages 641-643.
5. ^ Pauson, P. L. “Decacarbonyldimanganese” in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.