Syntheses and Structures of Homoleptic Lanthanide Complexes with Chelating o-Dimethylaminobenzyl Ligands: Key Precursors in Lanthanide Chemistry.
Reaction of o-Me2NC6H4CH2K with YCl3 in THF yielded (o-Me2NC6H4CH2)3Y (5-Y) as light yellow cryst. plates (59% yield). The crystal structure shows three bidentate benzyl ligands bound to Y, which has a prismatic coordination sphere. The La analog (5-La) was prepd. similarly (41% cryst. yield) and is isostructural to 5-Y, but shows more extensive multihapto bonding of the benzyl ligand to the larger metal (short aryl-La interactions). Attempted synthesis of (o-Me3SiC6H4CH2)3La from o-Me3SiC6H4CH2K and LaCl3 unexpectedly gave [Li(THF)4]+[(o-Me3SiC6H4CH2)4La]- (32% cryst. yield), the source of the Li+ ion being impure o-Me3SiC6H4CH2K. Crystal structure detn. revealed the (o-Me3SiC6H4CH2)4La- ion in which La has a distorted tetrahedral coordination sphere. The complexes (o-Me2NC6H4CH2)3Y and (o-Me2NC6H4CH2)3La show extraordinary thermal stability, but also sufficient reactivity in deprotonation of 9-t-BuN(H)SiMe2fluorene. The product, (h3-9-t-BuNSiMe2fluorenyl)(o-Me2Nbenzyl)Y(THF) (7; 85% cryst. yield), shows a monomeric crystal structure with allylic coordination of the fluorenyl ring and bidentate coordination of the benzyl ligand. This complex was successfully hydrogenated with mol. H2 (10 bar) to yield the dimer [(9-t-BuNSiMe2fluoren-9-yl)YH(THF)2]2 (8; 84% cryst. yield), in which the fluorenyl part of the ligand is bound to Y only in h1-fashion.
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