Manganocene

Manganocene or bis(cyclopentadienyl)manganese(II) is an organomanganese compound with the formula [Mn(C5H5)2]n. It is a thermochromic solid that degrades rapidly in air. Although the compound is of little utility, it is often discussed as an example of a metallocene with ionic character.[2]

Manganocene
Names
Other names
Bis(cyclopentadienyl)manganese
Identifiers
3D model (JSmol)
ECHA InfoCard 100.149.777
Properties
C10H10Mn
Molar mass 185.128 g·mol−1
Appearance amber solid < 159 °C, pink > 159 °C
Melting point 175 °C (347 °F; 448 K)
Boiling point 245 °C (473 °F; 518 K)
Hazards[1]
GHS pictograms
GHS Signal word Danger
H228, H315, H319, H335
P210, P261, P305+351+338
NFPA 704 (fire diamond)
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g. hydrogen peroxideSpecial hazards (white): no code
2
2
3
Flash point 52 °C (126 °F; 325 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Synthesis and structure

It may be prepared in the manner common for other metallocenes, i.e., by reaction of manganese(II) chloride with sodium cyclopentadienide:

MnCl2 + 2 CpNa → Cp2Mn + 2 NaCl

In the solid state below 159 °C, manganocene adopts a polymeric structure with every manganese atom coordinated by three cyclopentadienyl ligands, two of which are bridging ligands. Above 159 °C, the solid changes color from amber to pink and the polymer converts to the structure of a normal sandwich complex, i.e., the molecule Mn(η5-C5H5)2.[2]

Reactions

The ionic character of manganocene gives it an unusual pattern of reactivities compared to metallocenes of other transition metals in the same row. It is kinetically labile, being readily hydrolysed by water or hydrochloric acid, and readily forms adducts with two- or four-electron Lewis bases.[2]

Manganocene polymerizes ethylene to high molecular weight linear polyethylene in the presence of methylaluminoxane or diethylaluminium chloride as cocatalysts. It does not polymerize propylene.[2]

References
  1. "Bis(cyclopentadienyl)manganese". American Elements. Retrieved October 31, 2019.
  2. Layfield, Richard A. (2008). "Manganese(II): the black sheep of the organometallic family". Chem. Soc. Rev. 37: 1098–1107. doi:10.1039/B708850G.
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