Syntheses and Structures of Homoleptic Lanthanide Complexes with Chelating o-Dimethylaminobenzyl Ligands:  Key Precursors in Lanthanide Chemistry

Reaction of o-Me2N-C6H4CH2K with YCl3 in THF yielded (o-Me2N-C6H4CH2)3Y (5-Y) in the form of light yellow crystalline plates (59% yield). The crystal structure shows three bidendate benzyl ligands bound to Y, which has a prismatic coordination sphere. The La analogue (5-La) was prepared similarly (41% crystalline 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-Me3Si-C6H4CH2)3La from o-Me3Si-C6H4CH2K and LaCl3 unexpectedly gave [(o-Me3Si-C6H4CH2)4La-][Li+·(THF)4] (32% crystalline yield), the source of the Li+ ion being impure o-Me3Si-C6H4CH2K. Crystal structure determination revealed the (o-Me3Si-C6H4CH2)4La- ion in which La has a distorted tetrahedral coordination sphere. The complexes (o-Me2N-C6H4CH2)3Y and (o-Me2N-C6H4CH2)3La show extraordinary thermal stability, but also sufficient reactivity in deprotonation of 9-t-BuN(H)SiMe2-fluorene. The product, (9-t-BuNSiMe2-fluorenyl)(...