Cyclopentadienides of ytterbium (III) and ytterbium (II)

Abstract The reaction of anhydrous ytterbium (III) chloride with sodium cyclopentadienide followed by crystallization from tetrahydrofuran (THF) gives the tetrahydrofuranate Yb(C 5 H 5 ) 3 · C 4 H 8 O (I), which can easily be converted into the ammoniate Yb(C 5 H 5 ) 3 · NH 3 (II) by treatment with the stoichiometric amount of ammonia. Ytterbium tricyclopentadienide free from any additional Lewis base can only be obtained by using Fischer's method consisting of reacting YbCl 3 with KC 5 H 5 in toluene. The emerald-green diamagnetic Yb(C 5 H 5 ) 2 (IV) was prepared by reducing Yb(C 5 H 5 ) 2 Cl with finely dispersed sodium metal. Infra-red, visible and ultra-violet absorption spectra and proton resonance spectra confirm the proposed formulations. All the available data strongly suggest the view that the bonding between the ytterbium and the C 5 H 5 − rings is essentially ionic in character in all the compounds described in this paper.