Cyclopentadienide salts preparation

The ionic nature of the cyclopentadienide salts has been confirmed in a variety of ways. When they were first prepared it was noted that it was possible to prepare other metal salts from potassium cyclopentadienide by double decomposition [1]. The ionic character was demonstrated by conductivity measurements in liquid ammonia,[10], and from spectra [11]. 

Introduction of electron-withdrawing groups attached to the cyclo-pentadiene ring greatly increases the stability and lowers the reactivity of the related cyclopentadienide anions, presumably because of enhanced delocalisation of the negative charge. An example of such an unreactive cyclopentadienide salt was first prepared in 1912 by the condensation of nitromalonaldehyde with hexane-2,5-dione in the presence of alkali [34] ... 

A variant on this method dispenses with the need of first preparing a cyclopentadienide salt. Cyclopentadiene and toluene-p-sulphonazide react together in the presence of an amine such as diethylamine to give diazocyclopentadiene [59]. Phenylated diazocyclopentadienes have also been prepared in this way, [52,53,57,60], the yields being notably better than those obtained by the original method. 

As previously mentioned, the first cyclopentadienide salt to be prepared was the potassium salt, obtained by the action of potassium on cyclopentadiene dissolved in benzene under an atmosphere of nitrogen [1]. It separated out as a yellow precipitate, insoluble in benzene. Since then many other salts have been made including a... 

Alkali metal cyclopentadienide salts are important reagents in organometallic chemistry, having been used to prepare innumerable cyclopentadienyl complexes. Potassium cyclopentadienide, KCp, is usually made by deprotonation of cyclo-pentadiene with potassium metal either in organic solvents such as THF and benzene or in liquid ammonia, or by deprotonation with KH" or KOH. The analogous sodium compound, NaCp, was reported by the groups of Fischer and... 

Scheme 13. One-pot preparation of pentakis(methylthio)cyclopentadienide as the sodium salt. The yield is 51% (61).

Silyl cyclopentadienes1,2 3 have been formed through the interaction of a cyclopentadienide prepared in situ with an appropriate silicon halide however, purification of the desired product required filtration, removal of solvent, and vacuum distillation at elevated temperatures. The synthesis of the silicon compounds, C5H5(SiH3) and C5H4(CH3)(SiH3), described here utilizes a low-temperature reaction between liquid bromosilane and the salt K[RC5H4] (where R = H, CH3), in a 1 2 mole ratio, respectively.4 5... 

Cyclopentadienyl complexes, as previously discussed, are exceptionally numerous and have been the subject of extensive study. Several routes are available for introducing this ligand into a metal complex. One approach is to react a metal compound with the cyclopentadienide ion, C5H5. This ion can be purchased as the sodium salt in solution it can also be prepared by the following two-step process. 

A general method for the preparation of all / e ta/za/Uocyclopentadienyl compounds is the reaction of sodium cyclopentadienide with a metal halide or complex halide in tetrahydrofuran, ethylene glycol dimethyl ether, di-methylformamide or similar solvent. A solution of the sodium salt is obtained by treating dispersed sodium with the hydrocarbon in tetrahydrofuran ... 

Indene and fluorene (benzo- and dibenzo-cyclopentadiene) also have acidic methylene groups and can be converted into metal indenides and fluorenides respectively. A tetramethylammonium salt of fluorene has also been prepared [47]. It is an orange compound which remains unchanged when kept under nitrogen, and decomposes to give fluorene and 9-methylfluorene when heated in ether. Annelation reduces the acidity of the cyclopentadiene ring, however [48]. This infers reduced stabilisation of the cyclopentadienide anion relative to the... 

Calicene itself has not been described,but a number of substituted derivatives are known. Methods for their preparation include reactions of cyclopentadienide ions with cyclopropeirtum salts or with 3,3-dihalogenocyclopropenes, e.g. [257-259] ... 

Alkyl- or aryl-cycloheptatrienes are formed readily by the reaction of tropylium salts with Grignard regents or with organo-lithium derivatives [3,16,19,83]. For example by using vinyl magnesium chloride, vinylcycloheptatriene and hence vinyltropylium salts have been prepared [32]. With lithium cyclopentadienide cyclopenta-dienylcycloheptatriene is formed and not an ionic tropylium cyclopentadienide [19,35] ... 

Thallium(I).- All the chemistry here concerns cyclo-pentadienyl ligands. Thallium salts of the substituted species T1 (t -C5H4X) [X = C(0)Ph,224 pph2 ] have been prepared from the sodium cyclopentadienide and TlOEt. The former has been used in the synthesis of various transition metal species e.g. 

In general, reactions between alkali metal cyclopentadienides and metal salts are carried out at the reflux temperature of the chosen solvent for a period of several hours. However, longer periods of reflux are required for the reaction of certain metal salts. Thus, the preparation of ruthenocene requires several days of refluxing in 1,2-dimethoxyethane to complete the reaction between RUCI3 and NaCp (59). 

Displacement of carbon monoxide from metal carbonyls by alkali metal cyclopentadienides is a convenient method for preparing the alkali metal salts of the mixed cyclopentadienyl metal carbonyls. This reaction of carbonyls of Group VIB transition metals is represented by the equation... 

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