Synthesis and Structures of Ln(II) and Ln(III) Dialkyls Derived from LnI₂ (Ln = Nd, Tm, Yb)

Whereas the reactions between either NdI2 or TmI2 and 1 equiv of the dipotassium salt [{(Me3Si)2C(SiMe2)}2O]K2(OEt2) (2) yield only intractable mixtures of products, reactions between LnI2 and 1 equiv of {(Me3Si)(Me2MeOSi)C(SiMe2CH2)}2K2 (3) yield the lanthanide(III) compounds {(Me3Si)(Me2MeOSi)C(SiMe2CH2)}2Ln(OMe)(THF) [Ln = Tm (9), Nd (10)] via a ligand degradation reaction. In contrast, YbI2 reacts smoothly with either 2 or 3 to give the ytterbium(II) alkyls [{(Me3Si)2C(SiMe2)}2O]Yb(THF)2 (4) and {(Me3Si)(Me2MeOSi)C(SiMe2CH2)}2Yb(THF) (5), respectively, in excellent yields. Compounds 4 and 5 have been characterized by multielement (1H, 13C{1H}, 29Si, and 171Yb) NMR spectroscopy, and compounds 4, 5, 9, and 10 by elemental analyses and X-ray crystallography. Compounds 9 and 10 crystallize as structurally similar monomers with a distorted trigonal prismatic geometry about the Ln(III) ions; in 4 and 5 the Yb centers lie in a distorted trigonal bipyramidal geometry. Compound 5, although potentially diastereomeric, gives rise to a single set of NMR signals over the temperature range 20 to −80 °C, suggesting either the presence of only one diastereomer or that exchange between diastereomers is rapid on the NMR time scale.