Rare-Earth Amidate Complexes. Easily Accessed Initiators For ε-Caprolactone Ring-Opening Polymerization

The direct synthesis of yttrium amidate complexes using the simple reaction of amide proligands and Y(N(SiMe3)2)3 results in the high-yielding preparation and isolation of crystalline, monomeric materials. The complex, tris(N-2′,6′-diisopropylphenyl(naphthyl)amidate)yttrium mono(tetrahydrofuran) (4), was structurally determined to be a 7-coordinate C1 symmetric structure, maintaining one bound tetrahydrofuran molecule. Compound 4 (C12H17[NCO]C10H7)3Y(C4H8O) crystallized in the monoclinic space group P2(1)/c with a = 13.7820(11) Å, b = 33.598(3) Å, c = 16.0575(12) Å, α = 90°, β = 98.762(3)°, γ = 90°, Z = 4. Solution phase NMR spectroscopic characterization of this same complex showed a highly symmetric species, consistent with a fluxional coordination environment for these compounds. Preliminary studies into the initiation of ε-caprolactone ring-opening polymerization using these complexes indicate high activity, producing high molecular weight polymer.