Isoselective Polymerization of <i>rac</i>‐Lactide by Highly Active Sequential {ONNN} Magnesium Complexes
Tomer Rosen, Jitendrasingh Rajpurohit, S. Lipstman, Vincenzo Venditto, Moshe Kol
Abstract
Abstract The coordination chemistry and the activities in the ring‐opening polymerization catalysis of racemic lactide (LA) of magnesium complexes of a series of {ONNN}‐type sequential monoanionic ligands are described. All ligands include pyridyl and substituted‐phenolate as peripheral groups. The ligands bearing either chiral or meso ‐bipyrrolidine cores led to single diastereomeric complexes, whereas the ligands bearing a diaminoethane core led to diastereomer mixtures. All {ONNN}Mg‐X complexes [X=Cl, HMDS (hexamethyldisilazide)] led to highly active and isoselective catalysts. The complexes bearing the chiral bipyrrolidine core exhibited the highest activities (full consumption of 5000 equiv. of rac ‐LA at RT within 5 min) and highest isoselectivities ( P m =0.91), as well as a living character. The complexes of the meso ‐bipyrrolidine based ligands were almost as active and slightly less stereoselective, while those of the diaminoethane based ligands exhibited reduced activities and isoselectivities.