Anilidopyridyl-Pyrrolide and Anilidopyridyl-Indolide Group 3 Metal Complexes: Highly Active Initiators for the Ring-Opening Polymerization of rac-Lactide

Three new group 3 metal complexes, bearing anilidopyridyl-pyrrolide (L1) and anilidopyridyl-indolide (L2) as dianionic tridentate ligands, with the general formula LMN- (SiHMe2)2 were synthesized (complex 1, M = Y, L = L1; complex 2, M = Sc, L = L1; complex 3, M = Y, L = L2). All complexes were fully characterized and tested as initiators for the ROPs of rac-lactide. The yttrium complexes 1 and 3 resulted in highly active catalysts (TOF up to 104 mollactide molY −1 h−1), whereas the scandium complex showed moderate activities. This class of catalysts allowed a good control of the macromolecular architecture of the polymer, namely, the nature of end groups, the molecular weights, and their distribution. Moreover, the obtained PLAs showed Pr values in the range of 0.57−0.84, depending on the nature of the initiator and solvent. Well-controlled and rapid ROPs of rac-lactide were obtained in the solvent-free polymerizations at 130 °C as well, suggesting that complexes 1−3 are stable at high temperature. Finally, in the presence of 2-propanol, complex 1 promoted the immortal ROP of rac-lactide, showing a remarkable TOF of 3.5 × 104 mollactide molY −1 h−1.