Nickelocene is usually prepared by reaction an alkali metal cyclopentadienide, prepared from an alkali metal and cyclopentadiene with an anhydrous nickel(II) salt, figure 1. Cyclopentadiene is unstable at room temperature, rapidly undergoing a Diels-Alder reaction with its self to produce the dimer, dicyclopentadiene. Dicyclopentadiene is used as a source of cyclopentadiene by heating it in a distillation apparatus, which causes it to undergo a retro Diels-Alder reaction to form cyclopentadiene. Cyclopentadiene can also be deprotonated by potassium hydroxide in dimethylsulfoxide. The nickel salt still has to be dissolved in an ethereal solvent, 1,2-dimethoxyethane being the best. Diethyl ether also works, but the yields suffer, this would be the most OTC procedure since the only reagent that is hard to find is dicyclopentadiene. The synthesis described involves the use of sodium to form the cyclopentadienide ion and tetrahydrofuran as a solvent.
Attachment: Synthetic Scheme.pdf (28kB)