Neutral “Cp-Free” Silyl-Lanthanide(II) Complexes: Synthesis, Structure, and Bonding Analysis

Complexes featuring lanthanide silicon
bonds represent a research area still in its infancy. Herein, we report
a series of Cp-free lanthanide (+II) complexes bearing σ-bonded
silyl ligands. By reactions of LnI2 (Ln = Yb, Eu, Sm) either
with a 1,4-oligosilanyl dianion [K-Si­(SiMe3)2SiMe2­SiMe2Si­(SiMe3)2-K)] (1) or with 2 (Me3Si)3SiK (3) the corresponding neutral metallacyclopentasilanes
({Me2Si­(Me3Si)2Si}2)­Ln·(THF)4 (Ln = Yb (2a), Eu (2b), Sm (2c)), or the disilylated complexes ({Me3Si}3Si)2Ln·(THF)3 (Ln = Yb (4a), Eu (4b), Sm (4c)), were selectively
obtained. Complexes 2b, 2c, 4b, and 4c represent the first examples of structurally
characterized Cp-free Eu and Sm complexes with silyl ligands. In both
series, a linear correlation was observed between the Ln–Si
bond lengths and the covalent radii of the corresponding lanthanide
metals. Density functional theory calculations were also carried out
for complexes 2a–c and 4a–c to elucidate the bonding situation between
the Ln­(+II) centers and Si.