Syntheses and Structures of Homoleptic Lanthanide Complexes with Chelatingo-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)(o-Me2N-benzyl)Y·(THF) (7; 85% crystalline 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 molecular H2 (10 bar) to yield the dimer (9-t-BuNSiMe2-fluorenyl)YH·(THF)22 (8; 84% crystalline yield), in which the fluorenyl part of the ligand is bound to Y only in η1-fashion.