Isoselective Polymerization of rac-Lactide by Highly Active Sequential {ONNN} Magnesium Complexes.

The coordination chemistry and the activities in the ring-opening polymerization catalysis of racemic lactide 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) 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.