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Access to Ultra‐High‐Molecular Weight Poly(ethylene) and Activity Boost in the Presence of Cyclopentene With Group 4 Bis‐Amido Complexes
Author(s) -
Narayana Gurram Venkata,
Xu Guangjuan,
Wang Dongren,
Frey Wolfgang,
Buchmeiser Michael R.
Publication year - 2014
Publication title -
chempluschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.801
H-Index - 61
ISSN - 2192-6506
DOI - 10.1002/cplu.201300378
Subject(s) - chemistry , metallocene , tetrahydrofuran , ethylene , crystal structure , crystallography , cyclopentene , stereochemistry , medicinal chemistry , polymer chemistry , catalysis , polymerization , organic chemistry , polymer , solvent
Zr IV complexes of the type [Me 2 Si{(NR)(6‐{2‐(diethylboryl)phenyl}pyridyl‐2‐yl‐N)}ZrCl 2 ⋅thf] (R= t Bu ( 4 ), adamantyl ( 7 a ); thf=tetrahydrofuran), [Me 2 Si{(NAd)(6‐{2‐(diphenylboryl)phenyl}pyridyl‐2‐yl‐N)}ZrCl 2 ] (Ad=adamantyl ( 7 b )), the nonbridged half‐titanocene complexes of the type [(N‐{6‐(2‐diethylborylphenyl)pyrid‐2‐yl}‐NR)Cp′TiCl 2 ] (R=Me, Cp′=C 5 H 5 ( 12 ), Cp′=C 5 Me 5 ( 13 )), and the titanium(IV)‐based metallocene‐type complex [bis{N‐(6‐{2‐(diethylboryl)phenyl}pyrid‐2‐yl)NMe}TiCl 2 ] ( 14 ) have been synthesized. The structures of complexes 7 b , 12 , and 13 were determined by single‐crystal X‐ray diffraction analysis. In solution, complex 4 slowly rearranges to [Me 2 Si{(N‐ t Bu)(6‐{2‐(diethylboryl)phenyl}pyridyl‐2‐yl‐N)} 2 Zr] ( 4 a ), the structure of which was unambiguously confirmed by single‐crystal X‐ray crystallography. Similarly, reaction of HfCl 4 with Me 2 Si({RNLi}{6‐[2‐(diethylboryl)phenyl]pyridyl‐2‐ylNLi}) yielded the corresponding Hf IV complexes [Me 2 Si{(NR)(6‐{2‐(diethylboryl)phenyl}pyridyl‐2‐ylN)} 2 Hf] (R= t Bu ( 8 ) and Ad ( 9 )). Upon activation of these complexes with methylalumoxane (MAO), complexes 4 , 7 a, 7 b , and 12 – 14 showed activities up to 750 kg of polyethylene (PE)/mol cat. bar h in the homopolymerization of ethylene (E), producing mainly linear PE (high‐density PE, HDPE) with molecular weights in the range of 1 800 000< M n <4×10 6 g mol −1 . In the copolymerization of E with cyclopentene (CPE), the polymerization activities of complexes 4 , 7 a , and 7 b can be enhanced by a factor of 140 up to 7500 kg PE/mol cat. bar h, which produced PE‐ co ‐poly(CPE) containing 3.5 mol % of CPE. This dramatic increase in polymerization activity for E in the presence of CPE can be attributed to an involvement of CPE in the polymerization process rather than to solvent polarity.