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

Abstract

The influence of bulky silyl-substituted cyclooctatetraenyl ligands on the formation and structure of ytterbium sandwich complexes has been investigated. Treatment of anhydrous YbCl 3 with equimolar amounts of [K(DME)] 2(COT TBS) ( 2, COT TBS = [C 8H 6(SiMe 2 t Bu) 2-1,4 ] 2−) and KCp ∗ (Cp ∗ = pentamethylcyclopentadienyl) in DME solution (DME = 1,2-dimethoxyethane) afforded a mixture of neutral Cp ∗Yb(COT TBS) ( 3, purple crystals) and anionic [K(DME) 4][Yb(COT TBS) 2] ( 4, royal blue crystals) which could be separated by selective extraction. In contrast, the closely related reaction of YbCl 3 with equimolar amounts of K 2(DME) 2(COT‴) ( 5, COT‴ = [C 8H 5(SiMe 3) 3-1,3,6] 2−) and KCp ∗ resulted in spontaneous reduction of Yb 3+ 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.