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 (L-1) and anilidopyridyl-indolide (L-2) as dianionic tridentate ligands, with the general formula LMN(SiHMe2)(2) were synthesized (complex 1, M = Y, L = L-1; complex 2, M = Sc, L = L-1; complex 3, M = Y, L = L-2). 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 10(4) mol(lactide) mol(gamma)(-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 P-r 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 degrees 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 TOP of 3.5 X 10(4) mol(lactide) mol(gamma)(-1) h(-1). RI Pellecchia, Claudio/G-6300-2011