σ-Bonded organometallic derivatives of yttrium(III) and thulium(III): An unusual ligand coupling reaction mediated by thulium(III)

The reaction between LnI3(THF)3.5 and 2 equiv. of {(Me3Si)2(Me2MeOSi)C}K (1) in THF at room temperature yields only the mono-substituted products {(Me3Si)2(Me2MeOSi)C}LnI2(THF)2 [Ln = Y (5), Tm (6)]; under more forcing conditions decomposition occurs. In contrast, the metathesis reaction between TmI3(THF)3.5 and 2 equiv. of the lithium iodide-containing salt {(Me3Si)2(Me2MeOSi)C}K(LiI)x yields the highly unusual separated ion pair complex [[{(Me3Si)2C(SiMe2)}2O]TmI2{Li(THF)3}2][[{(Me3Si)2C(SiMe2)}2O]TmI2] (8). The dianionic ligand in 8 is derived from the coupling of 2 equiv. of (Me3Si)2(Me2MeOSi)C−, accompanied by the formal elimination of Me2O. The structures of compounds 5, 6, and 8 have been determined by X-ray crystallography; compound 8 crystallizes as an unusual ion pair, the cation and anion of which differ only in the inclusion of 2 equiv. of Li(THF)3 in the former, bridged to thulium by iodide ions.