Ytterbium(II) amides and crown ethers: addition versus amide substitution

New Yb(II) amides [Yb(NPh2)2(THF)4] (1) and Yb{NPh(SiMe3)}2(THF)x (x=1 or 3) (2) were obtained by the salt elimination method and the structure of the dimer [Yb{NPh(SiMe3)}{μ-NPh(SiMe3)}(THF)]2 (2a) was determined. Reactions of the amides 1, 2 and [Yb{N(SiMe3)2}2(THF)2] (3) with [18]crown-6 gave the crystalline structurally characterised molecular complex [Yb(NPh2)2([18]crown-6)] (4) in the case of the smaller NPh2− ligand and the salt [Yb{N(SiMe3)2}([18]crown-6)][Yb{N(SiMe3)2}3] (5) with the bulky bis(trimethylsilyl)amido ligand. Crystalline 4 has a “threaded” structure with the NPh2 groups on the opposite sides of the [18]crown-6 ligand and the N−Yb−N′ angle of 176.6°. An X-ray diffraction study of the related potassium amide [K([18]crown-6)(NPh2)] (6) reveals that the K ion coordinates to one of the Ph-rings rather than to the amido nitrogen atom. There is significant delocalisation of negative charge in the amido ligand of crystalline 6, unlike in 4.