Synthesis and structural diversity of trivalent rare-earth metal diisopropylamide complexes

Abstract

A series of rare-earth metal diisopropylamide complexes has been obtained via salt metathesis employing LnCl₃(THF)_x and lithium (LDA) or sodium diisopropylamide (NDA) in n-hexane. Reactions with AM : Ln ratios ≥3 gave ate complexes (AM)Ln(NiPr₂)₄(THF)_n (n = 1, 2; Ln = Sc, Y, La, Lu; AM = Li, Na) in good yields. For smaller rare-earth metal centres such as scandium and lutetium, a Li : Ln ratio = 2.5 accomplished ate-free tris(amido) complexes Ln(NiPr₂)₃(THF). The chloro-bridged dimeric derivatives [Ln(NiPr₂)₂(μ-Cl)(THF)]₂ (Ln = Sc, Y, La, Lu) could be obtained in high yields for Li : Ln = 1.6–2. The product resulting from the Li : La = 1 : 1.6 reaction revealed a crystal structure containing two different molecules in the crystal lattice, [La(NiPr₂)₂(THF)(μ-Cl)]₂·La(NiPr₂)₃(THF)₂. Recrystallization of the chloro-bridged dimers led to the formation of the monomeric species Ln(NiPr₂)₂Cl(THF)₂ (Ln = Sc, Lu) and La(NiPr₂)₃(THF)₂. The reaction of YCl₃ and LDA with Li : Y = 2 in the absence of THF gave a bimetallic ate complex LiY(NiPr₂)₄ with a chain-like structure. For scandium, the equimolar reactions with LDA or NDA yielded crystals of tetrametallic mono(amido) species, {[Sc(NiPr₂)Cl₂(THF)]₂(LiCl)}₂ and [Sc(NiPr₂)Cl₂(THF)]₄, respectively. Depending on the Ln(III) size, AM, and presence of a donor solvent, ate complexes (AM)Ln(NiPr₂)₄(THF)_n show distinct dynamic behaviour as revealed by variable temperature NMR spectroscopy. The presence of weak Ln⋯CH(iPr) β-agostic interactions, as indicated by Ln–N–C angles <105°, is corroborated by DFT calculations and NBO analysis.