Synthesis and characterization of bis(guanidinate)lanthanide diisopropylamido complexes: New highly active initiators for the polymerizations of ε-caprolactone and methyl methacrylate

Treatment of LnCl3 with [(SiMe3)2NC(NiPr)2]Li in 1:2 molar ratio afforded the soluble bis(guanidinate)lanthanide chlorides {[(SiMe3)2NC(NiPr)2]2Ln(μ-Cl)}2 (Ln=Y (1), Nd (2)). Amination of 1 and 2 with two equivalents of LiN(iPr)2 in a mixture solution of toluene and hexane gave [(SiMe3)2NC(NiPr)2]2LnN(iPr)2 (Ln=Y (3), Nd (4)) in good isolated yields. The single-crystal structural analyses of 2 and 3 revealed that the coordination geometries of lanthanide metals are best described as a distorted pseudo-octahedron and a pseudo-pyramid, respectively. Complexes 3 and 4 exhibited extremely high activity for the polymerizations of ε-caprolactone and methyl methacrylate (MMA).