in which cyclopentadiene is directly reacted with solid magnesium at 500-600 °C. Under water- and oxygen-free conditions, freshly distilled monomeric cyclopentadiene is directed through a tube furnace by an inert carrier gas (such as helium, argon, or nitrogen) and passed over magnesium turnings or powder. Magnesocene deposits on cooler surfaces past the exit end of the furnace. The product of this process is typically a white, fluffy mass of fine microcrystals, but large, colorless single crystals can be obtained by adjusting temperature and flow rate. If solid magnesocene is not needed, the receiving flask can instead be filled with solvent and the product collected in solution, which Barber noted as much safer to handle than the pure solid. Mg + 2C5H6 ->[500-600 ^oC] Mg(C5H5)2 + H2 This procedure is capable of producing a gram of product every two minutes under ideal conditions, and that with a vertical setup (in which cyclopentadiene is directed downwards and the product collected below) nearly pure product can be obtained at >80% yield (by cyclopentadiene). A horizontal setup was shown to be possible but at the expense of product purity, due to gas flow restriction by product accumulation. Liquid-phase methods Magnesocene can be produced from magnesium turnings in THF at mild conditions with cyclopentadienyltitanium trichloride (CpTiCl3) acting as a catalyst. Maslennikov et al. later showed similar catalytic activity with Cp2TiCl2, TiCl3, TiCl4, and VCl3. The mechanism, as shown by electron spin resonance, proceeds through a Cp2TiH2MgCl intermediate. Magnesocene formation from elemental magnesium has not been observed in THF without a catalyst present. Attempts to substitute THF with diethyl ether, diglyme, or benzene resulted only in polymerization of cyclopentadiene. The syntheses of magnesocene and its derivatives have also been carried out in hydrocarbon solvents, such as heptane, from Cp and (nBu)(sBu)Mg. Metallation of cyclopentadiene can also be accomplished by Mg-Al alkyl complexes with a final magnesocene yield of 85%. Reactivity & potential applications Magnesocene serves as an intermediate in the preparation of transition metal metallocenes: MgCp2 + MCl2 -> MCp2 + MgCl2 Magnesocene also undergoes ligand exchange reactions with MgX2 (X = halide) to form CpMgX half-sandwich compounds in THF: MgCp2 + MgX2 <=> 2 CpMgX The resulting half-sandwich halides can serve as starting materials for synthesizing substituted cyclopentadienes from organic halides. Because of its high reactivity, magnesocene is an attractive target for semiconductor research as a starting material for chemical vapor deposition and doping applications.