Tricyclopentadienyl complexes Synthesis

The base-free compounds of CpjLn type are known for all metals of the being considered block including radioactive promethium (Table III.3.). The cyclopentadienyl complexes of trivalent Sc, Y, La, Ce, Pr, Nd, Sm and Gd prepared in 1954 by Wilkinson and Birmingham in the reaction of anhydrous metal chlorides with CpNa were the first REM organoderivatives [119]. Later this method has been modified and applied to Eu, Tb, Dy, Ho, Er, Tm, Yb and Lu [88, 91, 120, 121]. Up to now it remains to be the main way to the tricyclopentadienyl REM complexes. Besides CpNa, cyclopentadienides or substituted cyclopentadienides of lithium and potassium are used in these reactions [31,95, 100,101, 111, 116]  

The reactions are carried out in the THE medium with the rigorous exclusion of contacts with air and water. The products are isolated as the tetrahydrofuranates. However, a coordinatively bonded solvent is easily removed on heating or sublimation of a complex in vacuum. The yield of the products as a rule is 60-80%. There are no differences between the conditions of Cp3Ln preparation when dicyclopentadienyl chlorides Cp2 LnCl are used as the initial REM derivatives [112]. 

Solvent-free complexes are obtained when the reactions of LnCl3 with CpK proceed in benzene or ether medium [11]. 

To prepare heteroleptic tricyclopentadienides the displacement of chlorine in LnCl3 by cyclopentadienyl rings with different substituents are carried out in a stepwise manner. This way has been employed specifically to synthesize a series of complexes with cyclopentadienyl rings bonded by an etiher group -CH2CH2OCH2CH2- [98]. These reactions can be conducted without isolation of intermediate monochloride  

Another way to the heteroleptic tricyclopentadienyl derivatives is the oxidation of metallocene (Me5C5)2Ln(II) with cyclopentadiene [37]  

---

The discovery of ferrocene and of the other sandwich complexes initiated a new field of organometallic chemistry, the chemistry of the w-complexes. Wilkinson and Birmingham (1954) prepared the first organometallic w-complexes of the rare earths, the tricyclopentadienyl complexes of Sc, Y, La, Ce, Pr, Nd, Sm and Gd. It was not until 14 years later with the synthesis of triphenyl scandium (Hart and Saran, 1968) that the first a-bonded aryl-rare-earth compound was made. 

---