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

The synthesis of C-2 symmetric enantiomerically pure open Ca and Sr metallocenes, [(eta(5)-pdl*)(2)Ca(thf)] (1) and [(eta(5)-pdl*)(2)Sr(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.