Cyclopentadienyl-metal compounds synthesis from cyclopentadiene

Syntheses of cyclopentadienyl metal compounds from cyclopentadiene are carried out under widely varying conditions depending on the properties of the metallic reactants. These reactions may be carried out in the vapor phase at temperatures as high as 600° C or they may be carried out in the liquid phase in the presence of a solvent at 25° C. The cyclopentadienyl metal compounds produced are isolated either by sublimation, if the reaction has been run in the vapor phase, or by crystallization, if the compound has been formed in solution. If the compound is to be used as an intermediate in a subsequent synthesis, then it is not usually isolated in pure form, but is used in solution in a suitable solvent of high dielectric constant or as a slurry in a hydrocarbon solvent. 

Synthesis of cyclopentadienyl metal compounds from basic metal salts derived from a base and a neutral or acidic metal salt is limited primarily to cyclopentadiene and in a few instances methylcyclopentadiene (37). The use of other substituted cyclopentadienes has not been reported and it is probable that only the very strongest bases would be effective in promoting their reaction. 

In a first approximation supra-Cp metal complexes can be prepared the same way as normal or other Cp-metal and organo-metal bonds in general. The methods used most often (see Appendix) are the metathesis reaction [Eq. (1)] followed in number by oxidative additions (Eq. (2)] and metallation/deprotonation reactions [Eq. (3)]. The latter is especially important for the cyclpentadienyl alkali metal compounds. A useful variation of reaction (3) is the formation of CpTl in an acid/base reaction from cyclopentadiene and thallium ethoxide [Eq. (3b)]. This represents a convenient route to cyclopentadienylthallium compounds, which are also valued (in place of Cp alkalis) as mild Cp-transfer reagents for the synthesis of difficultly isolable cyclopentadienyl derivatives (77). 

Synthesis of cyclopentadienyl compounds of metals from cyclopentadiene depends on the strongly acidic properties of cyclopentadiene. This acidity may be attributed to the ready formation of the highly resonance-stabilized cyclopentadienide anion, CsHs , in which there are six delocalized ir electrons. This method is limited primarily to the active metals of Groups lA and IIA and to their strongly basic compounds. The compounds produced are principally the ionically bonded metal cyclopentadienides. 

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