Heteroleptic Complexes of Lanthanum(III) and Neodymium(III) with Oxygen- or Nitrogen-Functionalized Tris(triorganosilyl)methyl Ligands

Abstract

Metathesis reactions between LaI3(THF)4 and either 2 equiv of [(Me3Si)2{Me2(Me2N)Si}C]K or 1 equiv of {(Me3Si)(Me2MeOSi)C(SiMe2CH2)}2K2 in THF yield the heteroleptic lanthanum dialkyls [(Me3Si)2{Me2(Me2N)Si}C]2LaI (3) and [{(Me3Si)(Me2MeOSi)C(SiMe2CH2)}2]LaI(THF) (5), respectively. In contrast, the reaction between LaI3(THF)4 and 2 equiv of [(Me3Si)2{Me2(MeO)Si}C]K in THF, under a variety of reaction conditions, gives a mixture of the mono- and disubstituted compounds [(Me3Si)2{Me2(MeO)Si}C]LaI2(THF) (7) and [(Me3Si)2{Me2(MeO)Si}C]2LaI(THF) (8), which cannot be separated by crystallization. The reaction between this mixture and 1 equiv of KN(SiMe3)2 yields the heteroleptic complex [(Me3Si)2{Me2(MeO)Si}C]LaI{N(SiMe3)2}(THF) (9). While exact analogues of 3, 5, 8, and 9 could not be isolated for neodymium, a metathesis reaction between NdI3(THF)3.5 and the lithium iodide containing potassium alkyl {(Me3Si)(Me2MeOSi)C(SiMe2CH2)}2K2·xLiI in THF yields the ate complex {(Me3Si)(Me2MeOSi)C(SiMe2CH2)}2Nd(μ-I)2Li(THF)2 (10). An unexpected ligand degradation is observed in the reaction between NdI3(THF)3.5 and 2 equiv of [(Me3Si)2{Me2(MeO)Si}C]K in THF: this reaction yields the methoxy-bridged dimer {[(Me3Si)2{Me2(MeO)Si}C]Nd(I)(THF)(μ-OMe)}2 (11), via Si−O cleavage of one of the ligands. Compounds 3, 5, and 8−11 have been characterized by elemental analyses and X-ray crystallography; the diamagnetic compounds 3, 5, 8, and 9 have additionally been characterized by NMR spectroscopy. The diastereomeric compound 5 gives a single set of resonances in its 1H and 13C{1H} NMR spectra, suggesting either a rapid dynamic equilibrium between the two possible diastereomers on the NMR time scale or the formation of a single diastereomer of this compound.