Abstract
The green compound poly[(tetra-hydro-furan)-tris-[μ-η5:η5-1-(tri-methyl-sil-yl)cyclo-penta-dien-yl]caesium(I)ytterbium(II)], [CsYb(C8H13Si)3(C4H8O)] n or [(THF)Cs(μ-η5:η5-Cp')3YbII] n was synthesized by reduction of a red THF solution of (C5H4SiMe3)3YbIII with excess Cs metal and identified by X-ray diffraction. The compound crystallizes as a two-dimensional array of hexa-gons with alternating CsI and YbII ions at the vertices and cyclo-penta-dienyl groups bridging each edge. This, based off the six-electron cyclo-penta-dienyl rings occupying three coordination positions, gives a formally nine-coordinate tris-(cyclo-penta-dien-yl) coordination environment to Yb and the Cs is ten-coordinate due to the three cyclo-penta-dienyl rings and a coordinated mol-ecule of THF. The complex comprises layers of Cs3Yb3 hexa-gons with THF ligands and Me3Si groups in between the layers. The Yb-C metrical parameters are consistent with a 4f 14 YbII electron configuration.
Highlights
The new +2 oxidation states for the rare-earth metals Y, La, Ce, Pr, Gd, Tb, Ho, Er, and Lu were recently discovered by reduction of Cpx3Ln (Cpx = C5H4SiMe3, C5H3(SiMe3)2; Ln = rare-earth metal) using alkali metal reductants Li, Na, K, and KC8 (Fig. 1) (Hitchcock et al, 2008; MacDonald et al, 2013; Fieser et al, 2015; Evans, 2016; Palumbo et al, 2018)
It was thought that chelating agents were necessary to sequester the alkali metal to prevent interactions with cyclopentadienide ligands and subsequent ligand dissociation leading to product decomposition
This idea was challenged by examining reduction reactions of Cp030M (Cp00 = C5H3(SiMe3)2; M = La, Ce, U) with Li and Cs in the absence of chelating agents (Huh et al, 2018)
Summary
It was thought that chelating agents were necessary to sequester the alkali metal to prevent interactions with cyclopentadienide ligands and subsequent ligand dissociation leading to product decomposition This idea was challenged by examining reduction reactions of Cp030M (Cp00 = C5H3(SiMe3); M = La, Ce, U) with Li and Cs in the absence of chelating agents (Huh et al, 2018). The Cs reductions yielded polymeric complexes of general formula [Cp00M(-Cp00)2Cs(THF)2]n where the Cs cation has coordinated THF and cyclopentadienide ligands Attempts to extend this chemistry to smaller rare-earth metals by reduction of Cp03Ln (Cp0 = C5H4SiMe3; Ln = Y, Tb, Dy) showed evidence of LnII in solution; the reduction products were highly unstable and decomposed even at 238 K. Ranges for Cp0(centroid)Á Á ÁYbÁ Á ÁCp0(centroid) in Cp30Yb (Fieser et al, 2015), [K(crypt)][Cp30Yb] (Fieser et al, 2015), and [(THF)Cs(-5:5Cp0)3Yb]n
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