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.
[2] It may be prepared in the manner common for other metallocenes, i.e., by reaction of manganese(II) chloride with sodium cyclopentadienide: 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] The ionic character of manganocene gives it an unusual pattern of reactivities compared to metallocenes of other transition metals in the same row.
[2] Manganocene polymerizes ethylene to high molecular weight linear polyethylene in the presence of methylaluminoxane or diethylaluminium chloride as cocatalysts.