Cyclopentadienides, reaction with pyridinium

Tetrakis-cyclopentadienyl cerium (CeCp4) has been reported to be formed by the reaction of bis(pyridinium) hexachlorocerate with sodium cyclopentadienide [17]. Similarly indenyl and fluorenyl derivatives were prepared. Later work showed the same reactants in tetrahydrofurane to yield, Ce(Cp3), tricyclopentadienyl cerium complex instead of Ce(Cp4) [18]. 

The reaction of the l-(diaminocyclopropenyliumyl)pyridinium dication 30 with two equivalents of potassium pentakis(methoxycarbonyl)cyclopentadienide (31) also afforded the ionic salt 32 of 1 2 composition, whose structure was determined by X-ray crystallography. On the other hand, the reaction of 30 with the lithium salt of the 7,7,8,8-tetracyanoquinodimethane adical anion 33 resulted in covalent bond formation giving the substituted bis(cyclo-propenylium) dication 34. °... 

The synthesis of tetrakis- (or tetra-) cyclopentadienyl cerium was reported first by reaction of bis(pyridinium)hexachlorocerate and sodium cyclopentadienide (Kalsotra et al. 1971) the same reaction has been extended to other Ji-ligands such as indenyls and fluorenyls. However, in 1983 it was reported that the reaction of sodium cyclopentadienide with bis(pyridinium)hexachlorocerate in THF yields tricyclopentadienyl cerium(III) instead of tetrakiscyclopentadienyl cerium(IV) (Deacon et al. 1983). 

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