New bis(allyl)(diketiminato) and tris(allyl) lanthanide complexes and their reactivity in the polymerization of polar monomers

Article abstract of DOI:10.1021/om050309x

The reaction of LnCl₃(THF)_N (Ln = La, n = 4; Ln = Y, Sm, Nd, n = 3) with 3 equiv of allylMgCl in THF/1,4-dioxane followed by crystallization in 1,4-dioxane/toluene proceeds in very high yields to give the tris(η³-allyl) complexes [Laη³-C₃H ₅)₃(κ¹dioxane)]₂(μ-dioxane) and [Ln(η³-C₃H₅)₃(μ-dioxane) ]_infin; (Ln = Y, 1; Sm, 2; Nd). Improved one-pot syntheses for the tris(η³-allyl) lanthanum and neodymium compounds are reported. The crystal structures of 1 and 2 show that the compounds consist of distorted square-pyramidal lanthanide centers in linear polymer chains. The reaction of [η³-C₃H₅)₃(κ¹- dioxane)]₂(μ-dioxane) and [Ln(η³-C ₃H₅(μ-dioxane)]_infin; with the diketimine ligand 2-(2,6-diisopropylphenyl)amino-4-(2,6-diiso-propylphenyl)imino-2-pentene (BDI-H) in THF at 60°C generates cleanly the β-diketiminato complexes Ln(η³-C₃H₅)₂{κ ²-HC(Me-CNAr)₂} (Ar = 2,6-C₆H₃ ⁱPr₂; Ln = La, 3; Y, 4; Sm, 5; Nd, 6) with propene elimination. The crystal structure of 5 shows a distorted tetrahedral SmN ₂(allyl)₂ core, with the samarium atom positioned 1.438(4) A out of the C₃N₂ ligand plane. All complexes are highly effective single-component catalysts for the ring-opening polymerization of ε-caprolactone and rac-lactide. Polymer end group analysis shows that the polymerization process is initiated by allyl transfer to monomer.