Synthesis of the First Rare Earth Metal Bis(alkyl)s Bearing an Indenyl Functionalized N-Heterocyclic Carbene

Treatment of indenyl-modified imidazolium bromide [C9H7CH2CH2(NCHCHN(C6H2Me3-2,4,6)CH)Br] ((IndH-NHC-H)Br) with rare earth metal tetra(alkyl) lithium (Ln(CH2SiMe3)4Li(THF)4) or with
(trimethylsilylmethyl)lithium (LiCH2SiMe3) and rare earth metal tris(alkyl)s (Ln(CH2SiMe3)3(THF)2)
sequentially afforded the first NHC-stabilized monomeric rare earth metal bis(alkyl) complexes (Ind-NHC)Ln(CH2SiMe3)2 (1, Ln = Y; 2, Ln = Lu; 3, Ln = Sc) via double-deprotonation reactions. Complexes
1−3 are THF-free isostructural monomers. The monoanionic Ind-NHC species bond to the central metal
ion in a η5:κ1 constrained geometry configuration (CGC) mode, which combine with the two cis-located
alkyl moieties to form a tetrahedron ligand core, leading to the chirality of the complexes. Under the
presence of activators AlEt3 and [Ph3C][B(C6F5)4], complex 2 showed catalytic activity toward the
polymerization of isoprene to afford 3,4-regulated polyisoprene (91%).