Premium
Titanium and Zirconium Complexes with Non‐Salicylaldimine‐Type Imine–Phenoxy Chelate Ligands: Syntheses, Structures, and Ethylene‐Polymerization Behavior
Author(s) -
Suzuki Yasuhiko,
Tanaka Hidetsugu,
Oshiki Toshiyuki,
Takai Kazuhiko,
Fujita Terunori
Publication year - 2006
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.200600256
Subject(s) - methylaluminoxane , imine , denticity , chemistry , polymerization , adduct , ligand (biochemistry) , ethylene , chelation , zirconium , medicinal chemistry , stereochemistry , metallocene , crystallography , polymer chemistry , crystal structure , catalysis , inorganic chemistry , organic chemistry , biochemistry , receptor , polymer
New Ti and Zr complexes that bear imine–phenoxy chelate ligands, [{2,4‐di‐ t Bu‐6‐(RCH=N)‐C 6 H 4 O} 2 MCl 2 ] ( 1 : M=Ti, R=Ph; 2 : M=Ti, R=C 6 F 5 ; 3 : M=Zr, R=Ph; 4 : M=Zr, R=C 6 F 5 ), were synthesized and investigated as precatalysts for ethylene polymerization. 1 H NMR spectroscopy suggests that these complexes exist as mixtures of structural isomers. X‐ray crystallographic analysis of the adduct 1 ⋅HCl reveals that it exists as a zwitterionic complex in which H and Cl are situated in close proximity to one of the imine nitrogen atoms and the central metal, respectively. The X‐ray molecular structure also indicates that one imine phenoxy group with the syn CN configuration functions as a bidentate ligand, whereas the other, of the anti CN form, acts as a monodentate phenoxy ligand. Although Zr complexes 3 and 4 with methylaluminoxane (MAO) or [Ph 3 C] + [B(C 6 F 5 ) 4 ] − /Al i Bu 3 displayed moderate activity, the Ti congeners 1 and 2 , in association with an appropriate activator, catalyzed ethylene polymerization with high efficiency. Upon activation with MAO at 25 °C, 2 displayed a very high activity of 19900 (kg PE) (mol Ti) −1 h −1 , which is comparable to that for [Cp 2 TiCl 2 ] and [Cp 2 ZrCl 2 ], although increasing the polymerization temperature did result in a marked decrease in activity. Complex 2 contains a C 6 F 5 group on the imine nitrogen atom and mediated nonliving‐type polymerization, unlike the corresponding salicylaldimine‐type complex. Conversely, with [Ph 3 C] + [B(C 6 F 5 ) 4 ] − /Al i Bu 3 activation, 1 exhibited enhanced activity as the temperature was increased (25–75 °C) and maintained very high activity for 60 min at 75 °C (18740 (kg PE) (mol Ti) −1 h −1 ). 1 H NMR spectroscopic studies of the reaction suggest that this thermally robust catalyst system generates an amine–phenoxy complex as the catalytically active species. The combinations 1 /[Ph 3 C] + [B(C 6 F 5 ) 4 ] − /Al i Bu 3 and 2 /MAO also worked as high‐activity catalysts for the copolymerization of ethylene and propylene.