New sandwich complexes of di- and trivalent ytterbium: Reduction of Yb(3+) by a bulky cyclooctatetraenyl dianion

The influence of bulky silyl-substituted cyclooctatetraenyl ligands on the formation and structure of ytterbium sandwich complexes has been investigated. Treatment of anhydrous YbCl3 with equimolar amounts of [K(DME)]2(COTTBS) (2, COTTBS = [C8H6(SiMe2tBu)2-1,4 ]2−) and KCp∗ (Cp∗ = pentamethylcyclopentadienyl) in DME solution (DME = 1,2-dimethoxyethane) afforded a mixture of neutral Cp∗Yb(COTTBS) (3, purple crystals) and anionic [K(DME)4][Yb(COTTBS)2] (4, royal blue crystals) which could be separated by selective extraction. In contrast, the closely related reaction of YbCl3 with equimolar amounts of K2(DME)2(COT‴) (5, COT‴ = [C8H5(SiMe3)3-1,3,6]2−) and KCp∗ resulted in spontaneous reduction of Yb3+ to the divalent oxidation state and formation of dark blue-green (DME)2K(μ-COT‴)YbCp∗ (6) as the sole reaction product. The compounds 3, 4, and 6 were structurally characterized by X-ray diffraction.