Cyclopentadienylmagnesium chloride

In the solid state cyclopentadienylmagnesium chloride exists as a dimer [CpMgCl (OEt2)]2 (202) (Figure 87). The dimeric structure is caused by two symmetrically... 

Monocyclopentadienylzirconium trichloride has been prepared from zirconium tetrachloride by reaction with cyclopentadienylmagnesium chloride in toluene/diethyl ether solution 240, 241). Both the chloride and bromide have been prepared from the corresponding tetrahalides and magnesium cyclopentadienide in xylene at 100°-110°C 451), or by continuous recirculation of cyclopentadiene vapor upward through a bed of zirconium trihalide (250°-300°C) resting on a glass sinter. The products were purified by sublimation. Yields were only about 15% compared to the 60-70% obtained from syntheses carried out in solution. The melting points and colors for the monocyclopentadienyl metal trihalides and for other cyclopentadienyl metal halide compounds are tabulated in Table I. 

The bis(77-cyclopentadienyl)zirconium dichloride has been synthesized by a variety of routes and a variety of authors. It can be recovered from reaction systems of zirconium tetrachloride and sodium cyclopentadienide in tetrahydrofuran or ethyleneglycol dimethyl ether 89, 194, 343, 471) or with lithium cyclopentadienide 472) in place of the sodium compound. The hafnium compound was prepared in a similar manner 343, 471). In general, the residue obtained upon evaporation of the solvent is extracted with chloroform and the product from the extraction is recrystallized from benzene. The dichloride was also prepared 451) by the continuous recirculation of cyclopentadiene vapor through a bed of ZrCl2 at 270°-350°C. Another route to the chloride is the reaction of zirconium tetrachloride with cyclopentadienylmagnesium chloride 559) in benzene yet another involves the reaction of zirconium tetrachloride and cyclopentadiene in ethylamine as the solvent at room temperature 367). 

The methods of preparation of ferrocene have been reviewed by Pauson and by Fischer. Ferrocene has been made by the reaction of ferric chloride with cyclopentadienylmagnesium bromide, by the direct thermal reaction of cyclopentadiene with iron metal, by the direct interaction of cyclopentadiene with iron carbonyl, by the reaction of ferrous chloride with cyclopentadiene in the presence of organic bases such as diethyl-amine, by the reaction of ferrous chloride with sodium cyclo-[lentadienide in liquid ammonia, and from cyclopentadiene and... 

Another convenient method of preparing this Jt-complex of iron is a two-step process in which the first step involves preparation of cyclopentadienyl Grignard reagent, such as 2,4-cyclopentadienylmagnesium bromide CsHsMgBr which may then be combined with ferric chloride to yield dicyclopen tadienyl iron ... 

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