Imino phenoxide complexes of group 4 metals: synthesis, structural characterization and polymerization studies

A complete library of new alkoxides containing group 4 metals and the imino phenol ligand were synthesized in high yields and purity. These compounds showed catalytic activity towards the polymerization of L-lactide (L-LA), rac-lactide (rac-LA), epsilon-caprolactone (CL), delta-valerolactone (VL), rac-beta-butyrolactone (rac-BL), ethylene and propylene. The zirconium catalysts were found to yield better polymerization results in comparison to the titanium and hafnium analogues. The number average molecular weight (M-n) values of the polymers are very high for LA and CL with controlled molecular weight distributions (MWDs). Analyses of MALDI-TOF and H-1 NMR spectra of low M-n oligomers reveal that the ligand initiates the ring-opening polymerization (ROP). For ethylene and propylene polymerization, we have achieved moderate to good activity using MAO as a co-catalyst.