Cyclopentadienylmagnesium

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 ... 

The substituted cyclopentadienylmagnesium compounds 62a and 62b have been prepared from the corresponding fulvenes (equation 8) and were structurahy characterized in the solid state by X-ray crystallography . The structures are, as expected, (tj -bonded cyclopentadienyl groups) for bis(cyclopentadienyl)magnesium compounds. 

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

A cyclopentadienylmagnesium bromide containing a heteroatom-functionalized substituent at the cyclopentadienyl group has also been structurally characterized. When l-[2-(dimethylamino)ethyl]-2,3,4,5-tetramethylcyclopentadienylmagnesium bromide is recrystallized from dichloromethane, dimeric [(Mc2N(CH2)2)Me4C5MgBr]2 (206) (Figure 88) is obtained. Its X-ray crystal-structure determination reveals a structure in the solid state... 

Like 215, cyclopentadienylmagnesium ethoxide exists in the solid state as tetrameric [CpMgOEt]4 (216) with a heterocubane structure (Figure. In 216 the cyclopenta-dienyl groups are /j -bonded to the magnesium atoms. 

In a similar way Cp(Me)Mg(OEt2) is capable of deprotonating iV,Ai -bis(2,4,6-tri-methylphenyl)(ierr-butyl)amidine to form the corresponding cyclopentadienylmagnesium amidinate complex (226) (equation 17). An X-ray crystal-structure determination of 226, of which the structure is shown schematically (equation 17), showed that this compound also exists as a monomer in the solid state. Like in 225 the cyclopentadienyl group is /7 -bonded to magnesium while the amidinate anion is Ai,A -chelate bonded with almost equal Mg—N bond distances [Mg-N 2.090(2) and 2.097(2) A]. Furthermore, an additional... 

The only data omitted in this analysis are those for vinyl- (determined in THF) and cyclopentadienylmagnesium bromide. Including the data point for cyclopentadienyl in the analysis worsens the correlation. This may be caused by a difference in carbon bonding to the magnesium for cyclopentadienide compared to the other carbon-magnesium bonds. This bonding will be mentioned in a later section on magnesium sandwich compounds. 

Ruthenocene has been prepared in 20% yields by reaction of cyclopentadienylmagnesium bromide with ruthenium(III) acetyl-acetonate.8 More recently,4 the compound has been made in 43-52% yield by treatment of sodium cyclopentadienide with ruthenium trichloride in tetrahydrofuran or 1,2-dimethoxyethane. 

The discovery of ferrocene was one of those fortuitous accidents that was wholly unforeseeable —the kind of discovery which, over and over again, has changed the course of science, Pauson was trying to synthesize fulvalene, 1, by first coupling two molecules of cyclopentadienylmagnesium bromide with FeCl3 and then dehydrogenating the product ... 

Cyclopentadienylmagnesium hydride (CpMgH). The hydride is prepared by reaction of cyclopentadicne in THF with magnesium hydride it exists as the dimer (1) in this solvent. 

Mono-n-cyclopentadienylmagnesium compounds have so far only been isolated in the form of adducts with oxygen or nitrogen bases. The bis-(tetrahydrofuran) complexes of cyclopentadienyl(phenyl)- and -(methyl)-magnesium have been synthesized by Whitesides and co-workers (96) according to Eq. (4). 

Several years later, Grignard and Courtot (111) found that cyclopentadiene reacted with ethylmagnesium bromide, liberated ethane, and formed a new Grignard reagent, cyclopentadienylmagnesium bromide. 

Cyclopentadienylmagnesium bromide has been known since 1914 117) and potassium cyclopentadienide since 1901 (260). Considering that many attempts had been made to prepare organoiron compounds in this manner, it is surprising that ferrocene was not reported considerably earlier. 

Purification can be achieved by resublimation (subl. 100°C, 1 bar). Under similar conditions, methylcyclopentadiene yields a mixture of dicyclopentadienylmagnesium and bis(methylcyclopentadienyl)magnesium. With catalytic amounts of cyclo-pentadienyltitanium trichloride this reaction can be performed at 0°C within 48 h. Dicyclopentadienylmagnesium can also be prepared by sublimation [250°C, 10 torr (10" bar)] of cyclopentadienylmagnesium bromide . 

Cyclopentadienylmagnesium-halide reagents in THF react with benzyne to give only products of 2 -H 3 cycloadditions ... 

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