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

The reaction of LnCl(3)(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( eta(3) -allyl) complexes [La(eta(3)-C3H5)(3)(K-1-dioxane)](2)(mu-dioxane) and [Ln( eta(3) -C3H5)(3)(mu-dioxane)](infinity) (Ln = Y, 1; Sm, 2; Nd). Improved one-pot syntheses for the tris(eta(3)-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 [La(eta(3)-C3H5)(3)(K-1-dioxane)](2)(mu-dioxane) and [Ln(eta(3)- C3H5)(3)(mu-dioxane)](infinity) with the diketimine ligand 2-(2,6-diisopropylphenyl)amino-4-(2,6-diisopropylphenyl)imino-2-pentene (BDI-H) in THF at 60 degrees C generates cleanly the beta-diketiminato complexes Ln(eta(3)-C3H5)(2){kappa(2)-HC(MeCNAr)(2)] (Ar = 2,6-(C6H3Pr2)-Pr-i; Ln = La, 3; Y, 4; Sm, 5; Nd, 6) with propene elimination. The crystal structure of 5 shows a distorted tetrahedral SmN2(allyl)(2) core, with the samarium atom positioned 1.438(4) angstrom out of the C3N2 ligand plane. All complexes are highly effective single-component catalysts for the ring-opening polymerization of c-caprolactone and rac-lactide. Polymer end group analysis shows that the polymerization process is initiated by allyl transfer to monomer.