Dimanganese decacarbonyl

Synthesis

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

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 (293 pm), 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. 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)₁₀ proceeds with scission of the Mn-Mn bond.

Mn₂(CO)₁₀ + Br₂ → 2[Mn(CO)₅Br]

Safety

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