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

摘要

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 (μ-L)Zr(O~iPr)_3_21-3 L = ~(C1)BTP-H (1), ~(TCl)BTP-H (2), ~(pent)BTP-H (3) and tetrasubstituted Zr(iv), Hf(iv) complexes ZrL_44-6 L = ~(C1)BTP-H (4), ~(TCl)BTP-H (5), ~(pent)BTP-H (6) and HfL47-9 L = ~(C1)BTP-H (7), ~(TCl)BTP-H (8), ~(pent)BTP-H (9) were prepared by the reaction of Zr(O~iPr)_4·(~iPrOH) and Hf(O~tBu)_4 in toluene with the respective ligands in different stoichiometric proportions. The reaction between BTP and TiCl_4 and ZrCl_4 and HfCl_4 in a 2:1 stoichiometric reaction resulted in the formation of disubstituted group IV chloride complexes L_2MCl_210-12 L = ~(C1)BTP-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 Zr_2O_2 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.