Ring-opening polymerization of ?-caprolactone and ?-valerolactone using new Sm(III) ?-halo-bis(trimethylsilyl)amido complexes

New Sm(III) μ-halo-bis(trimethylsilyl)amido complexes [Sm(μ-X) {N(SiMe3)2}2(THF)]2 (X = Cl, Br) were synthesized and their crystal structures were analyzed. These complexes were used as catalysts for the homopolymerization of ε-caprolactone and δ-valerolactone and found to initiate ring-opening polymerization (ROP) of these monomers in high conversion over a short period, giving homopolymers with a moderate polydispersity index (∼ 2.0). The effect of temperature and the catalyst amount on the molecular weight distribution was also studied. Mechanistic studies were conducted using 1 : 1 and 1 : 6 molar ratios of μ-halo-bis-(trimethylsilyl)amido complexes and ε-caprolactone by 1H-NMR and 13C-NMR spectroscopic techniques and revealed the presence of more than one initiating species.