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((SiMe2Bu)-Bu-t)(2)-1,4](2-)) and KCp* (Cp* = pentamethylcy-clopentadienyl) 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 K-2(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)(2)K(mu-COT''') YbCp* (6) as the sole reaction product. The compounds 3, 4, and 6 were structurally characterized by Xray diffraction. (c) 2010 Elsevier B.V. All rights reserved.