Bis(imidazolin-2-iminato) Rare Earth Metal Complexes: Synthesis, Structural Characterization, and Catalytic Application

Reaction of anhydrous rare earth metal halides MCl3 with
2 equiv of 1,3-bis­(2,6-diisopropylphenyl)­imidazolin-2-imine (ImDippNH) and 2 equiv of trimethylsilylmethyl lithium (Me3SiCH2Li) in THF furnished the complexes [(ImDippN)2MCl­(THF)n] (M
= Sc, Y, Lu). The molecular structures of all three compounds were
established by single-crystal X-ray diffraction analyses. The coordination
spheres around the pentacoordinate metal atoms are best described
as trigonal bipyramids. Reaction of YbI2 with 2 equiv of
LiCH2SiMe3 and 2 equiv of the imino ligand ImDippNH in tetrahydrofuran did not result in a divalent complex,
but instead the Yb­(III) complex [(ImDippN)2YbI­(THF)2] was obtained and structurally characterized. Treatment of
[(ImDippN)2MCl­(THF)n] with 1 equiv of LiCH2SiMe3 resulted in the
formation of [(ImDippN)2M­(CH2SiMe3)­(THF)n]. The coordination arrangement
of these compounds in the solid state at the metal atoms is similar
to that found for the starting materials, although the introduction
of the neosilyl ligand induces a significantly greater distortion
from the ideal trigonal-bipyramidal geometry. [(ImDippN)2Y­(CH2SiMe3)­(THF)2] was used
as precatalyst in the intramolecular hydroamination/cyclization reaction
of various terminal aminoalkenes and of one aminoalkyne. The complex
showed high catalytic activity and selectivity. A comparison with
the previously reported dialkyl yttrium complex [(ImDippN)­Y­(CH2SiMe3)2(THF)3]
showed no clear tendency in terms of activity.