Cyclopentadienylmagnesium bromide

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 ... 

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... 

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 ... 

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 . 

Substitution. Ai,Ai-Diorganohydroxylamine benzoates react with RMgX in the presence of CUCI2 to provide RNR R". Alkylation of cyclopentadienylmagnesium bromide with tertiary alkyl halides occurs when Cu(OTf)2 is present. ... 

Successive addition of bromine to oxepin and the action of cyclopentadienylmagnesium bromide, followed by the treatment with triethylamine was used for the synthesis (albeit in a low yield) of a higher vinylogous fulvalene (6) (Scheme 2) <84CB2006>. 

The chlorobenzonorbornadienes (643) and (644) react very slowly with PhMgBr + CuBr as shown. The stereospecificity is taken as evidence for an ion-pair, rather than a radical mechanism. (643) reacts with magnesium, giving (645) with remarkable stereoselectivity, and (645) can also be made by the stereospecific addition of benzyne to cyclopentadienylmagnesium bromide. Equilibration or selective destruction of the syn-isomer of (645) are justifiably discounted but no explanation of the stereospecificity is offered. Reaction of (645) with DjO occurs with >90% retention of configuration. ... 

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