New heteroscorpionate lanthanide complexes for ring-opening polymerisation of (epsilon)-caprolactone and rac-lactide

Yttrium and lanthanum amido-complexes with bis(pyrazol-1-yl) acetates in their coordination spheres were studied as the catalysts in epsilon-caprolactone and lactide ring-opening polymerisation. A high molecular mass poly(epsilon-caprolactone) (PCL) was obtained in almost quantitative yield under mild conditions. rac-Lactide polymerisations were less efficient and required quite harsh experimental conditions to obtain atactic PLA samples with moderate yields. The average chain-length of PCL was dependent upon the choice of the metal centre and the presence of substituents on the pyrazole rings of the ancillary ligand. The ground-state geometries of the complexes and the first stages of epsilon-caprolactone polymerisation were computationally modelled by means of DFT calculations. (C) 2015 Institute of Chemistry, Slovak Academy of Sciences