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 [(μ-L)Zr(O(i)Pr)3]2 1-3 [L = (C1)BTP-H (1), (TCl)BTP-H (2), (pent)BTP-H (3)] and tetrasubstituted Zr(IV), Hf(IV) complexes ZrL4 4-6 [L = (C1)BTP-H (4), (TCl)BTP-H (5), (pent)BTP-H (6)] and HfL4 7-9 [L = (C1)BTP-H (7), (TCl)BTP-H (8), (pent)BTP-H (9)] were prepared by the reaction of Zr(O(i)Pr)4·((i)PrOH) and Hf(O(t)Bu)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 = (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 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.
Department of Chemistry, Indian Institute of Technology Madras, Chennai-600 036, Tamil Nadu, India. dchakraborty@iitm.ac.in.
Sreenath
S
Pappuru
Eswara Rao
ER
Chokkapu
Debashis
D
Chakraborty
Venkatachalam
V
Ramkumar
D002384:Catalysis; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004146:Dioxanes / Q000737:chemistry*; D004852:Epoxy Compounds / Q000737:chemistry*; D005030:Ethylenes / Q000737:chemistry*; D008024:Ligands; D008280:Magnetics; D008670:Metals / Q000737:chemistry; D008968:Molecular Conformation; D010757:Phosphorous Acids / Q000737:chemistry; D058105:Polymerization; D014230:Triazoles / Q000737:chemistry*
D056831:Coordination Complexes; D004146:Dioxanes; D004852:Epoxy Compounds; D005030:Ethylenes; D008024:Ligands; D008670:Metals; D010757:Phosphorous Acids; D014230:Triazoles; C570063:phosphonic acid; C012771:benzotriazole; C036216:ethylene; C091880:dilactide