Unprecedented reaction of bridged bis(guanidinate) lanthanide complexes: sterically induced deprotonation

Abstract

Reaction of LnCl₃ with a lithium salt of bridged bis(guanidinate) bearing a rigid naphthalene linker [Li₂{LH₂}₂Li₂] (LH₂ = 1,8-C₁₀H₆{NC(NⁱPr)(NHⁱPr)}₂) (1), which was synthesized by the reaction of 1,8-diaminonaphthalene with 2 equiv. of ⁿBuLi, followed by treatment with 2 equiv. of N,N′-diisopropylcarbodiimide, yielded the chlorides [LnCl{LH₂}] (Ln = Yb (2), Y (3)) in good yields. Metathesis reaction of 2 and 3 with NaN(SiMe₃)₂ did not afford the corresponding amide complexes, but the deprotonation products of [Ln{LH}]₂ (LH = 1,8-C₁₀H₆{NC(NⁱPr)(NHⁱPr)}{NC(NⁱPr)₂}; Ln = Yb (4), Y (5)) were isolated instead. The LH in 4 and 5 both act as a bridging ligand binding to two metals in a μ–η¹:η²:η² fashion, and the re-arrangement of LH occurred during the reaction. The size of the amido group was found to have a great influence on the outcome of the metathesis reaction. Reaction of 2 with bulky NaNH(C₆H₃ⁱPr₂-2,6) afforded 4 as the only product, whereas the same reaction with less bulky LiNH(C₆H₄Cl-4) and LiNH(C₆H₄CH₃-4) led to the corresponding amides, [Yb{LH₂}(NHC₆H₄Cl-4)]₂ (6) and [Yb{LH₂}(NHC₆H₄CH₃-4)]₂ (7), respectively. The re-arrangement of ligands was also observed in both cases. A possible pathway for the deprotonation of LH₂ was discussed. Molecular structures of 1–7 were determined by X-ray single crystal analysis.