New highly active Fe(II) pyridylamido catalysts for the ring opening polymerization and copolymerization of cyclic esters

Two Fe(II) complexes bearing chelating monoanionic [N,N]− pyridylamido ligands with bulky 2,6-dialkylphenyl substituents at both the amido and the ortho-pyridine moieties were synthesized and characterized. Single crystal X-ray diffraction analysis confirmed the formation of heteroleptic mononuclear [N,N]FeIIN(SiMe3)2 three-coordinated complexes. The two complexes were tested as catalysts for the Ring Opening Polymerization (ROP) of l-lactide (L-LA) and ε-caprolactone (CL) in the presence of 1 equiv. of alcohol co-initiator, resulting in high activity under both mild conditions (in solution at room temperature and low monomer/catalyst ratio) and more industrially relevant conditions (higher temperature and high monomer/catalyst ratio). The high activity and living character of the Fe(II) catalysts allowed the synthesis of stereo-multiblock polylactides by one-pot sequential addition of l-LA, d-LA and rac-LA at room temperature and in short reaction times, as well as the synthesis of di-block PCL-b-PLLA and three-block PLLA-b-PCL-b-PLLA copolymers by a similar approach.