Preparation of enantiomerically pure open calcocene and strontocene complexes and their application in ring opening polymerizations of rac-lactide

Abstract

The synthesis of C₂ symmetric enantiomerically pure open Ca and Sr metallocenes, [(η⁵-pdl*)₂Ca(thf)] (1) and [(η⁵-pdl*)₂Sr(thf)₂] (2) (pdl* = dimethylnopadienyl) is described and these complexes were fully characterized. The solid state structures confirm that the pdl* ligands coordinate exclusively with the less sterically demanding site to the Ca and Sr atoms. These complexes are active catalysts for the controlled ring opening polymerization (ROP) of rac-lactide to give heterotactically enriched polylactides (PL) with narrow polydispersities (PDI = 1.29–1.31) and without adding further activators.