Group IV complexes containing the benzotriazole phenoxide ligand as catalysts for the ring-opening polymerization of lactides, epoxides and as precatalysts for the polymerization of ethylene

A series of Ti(IV), Zr(IV) and Hf(IV) benzotriazole phenoxide (BTP) complexes were synthesized and characterized by various spectroscopic techniques, elemental analysis and X-ray crystallography. The monosubstituted Zr(IV) BTP complexes [(mu-L) Zr((OPr)-Pr-i)(3)](2) 1-3 [L = (BTP)-B-C1-H (1), (BTP)-B-TCl-H (2), (BTP)-B-pent-H (3)] and tetrasubstituted Zr(IV), Hf(IV) complexes ZrL4 4-6 [L = (BTP)-B-C1-H (4), (BTP)-B-TCl-H (5), (BTP)-B-pent-H (6)] and HfL4 7-9 [L = (BTP)-B-C1-H (7), (BTP)-B-TCl-H (8), (BTP)-B-pent-H (9)] were prepared by the reaction of Zr(OiPr)(4)center dot((PrOH)-Pr-i) and Hf ((OBu)-Bu-t) 4 in toluene with the respective ligands in different stoichiometric proportions. The reaction between BTP and TiCl4 and ZrCl4 and HfCl4 in a 2 : 1 stoichiometric reaction resulted in the formation of disubstituted group IV chloride complexes L2MCl2 10-12 [L = (BTP)-B-C1-H, M = Ti, Zr and Hf]. The molecular structures of complexes 1, 4, 7, 10, 11, and 12 were determined by single-crystal X-ray studies. The X-ray structure of 1 reveals a dimeric Zr(IV) complex containing a Zr2O2 core bridged through the oxygen atoms of the phenoxide groups. Each Zr atom is distorted from an octahedral symmetry. These complexes were found to be active towards the ring-opening polymerization (ROP) of L-lactide (L-LA) and rac-lactide (rac-LA). Complex 1 produced highly heterotactic poly(lactic acid) (PLA) from rac-LA under melt conditions with narrow molecular weight distributions (MWDs) and well controlled number average molecular weights (M-n). Additionally, epoxide polymerizations using rac-cyclohexene oxide (CHO), rac-propylene oxide (PO), and rac-styrene oxide (SO) were also carried out with these complexes. The yield and molecular weight of the polymer was found to increase with the extension of reaction time. Compounds 1-12 were activated by methylaluminoxane (MAO) and show good activity for ethylene polymerization and produced high molecular weight polyethylene.