Preparation and properties of some bis(cyclopentadienyl)ytterbium( II ) complexes and the X-ray crystal and molecular structures of [Yb(η-C ₅ H ₄ SiMe ₃ ) ₂ (thf) ₂ ]

Reduction of [{Yb(η-C5H4SiMe3)2Cl}2] by Na–Hg in tetrahydrofuran (thf) yields the purple, diamagnetic, toluene-soluble YbII title complex, from which similarly highly reactive, but thermally stable, YbII complexes [Yb(η-C5H4SiMe3)2(tmeda)](tmeda = Me2NCH2CH2NMe2) and Yb(η-C5H4SiMe3)2 are obtained, or [{Yb(η-C5H4-SiMe3)2I}2] from oxidation by I2; X-ray analysis of the title compound to R= 0·077 shows a roughly tetrahedral disposition of valencies around Yb, with Yb–Oav= 2·41 Å and Yb–C(η)av= 2·75 Å.