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Niobium- and tantalum-based ethylene polymerisation catalysts bearing methylene- or dimethyleneoxa-bridged calixarene ligands
Authors:Redshaw Carl  Rowan Michael  Homden Damien M  Elsegood Mark R J  Yamato Takehiko  Pérez-Casas Carol
Institution:Wolfson Materials and Catalysis Centre, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich, NR4 7TJ, UK. carl.redshaw@uea.ac.uk
Abstract:Treatment of p-tert-butylcalix6]areneH(6) (H(6)tBu-L) or p-tert-butylcalix8]areneH(8) (H(8)tBu-L(1)) with MCl(5)] (M=Nb, Ta) in refluxing toluene or dichloromethane affords, after work-up, the complexes {M(NCMe)Cl(2)}(2)(tBu-L)] (M=Nb (1), Ta (2)) and (MCl(2))(2)(tBu-L(1)H(2))] (M=Nb (4), Ta (5)), respectively. Complex 1, as well as {Nb(2)(mu-O)(2)(mu-Cl)(tBu-LH)}(2)] (3), is also available from NbOCl(3)] and H(6)tBu-L. Reaction of MOCl(3)] (M=Nb, Ta) with Li(3)(tBu-L(2)) in diethyl ether, where H(3)tBu-L(2) is p-tert-butylhexahomotrioxacalix3]areneH(3), affords, after work-up, the trimeric complexes {M(tBu-L(2))(mu-O)}(3)] (M=Nb (6), Ta (7)). The behaviour of 1 to 7 (not 3), as well as the known complexes {(MCl)p-tert-butylcalix4]arene}(2)] (M=Nb (8), Ta (9)) and (MCl(2))p-tert-butylcalix4]arene(OMe)] (M=Nb (10), Ta (11)), as pro-catalysts for the polymerisation of ethylene has been investigated. In the presence of dimethyl (or diethyl)aluminium chloride, methylaluminoxane or trimethylaluminium, these niobium and tantalum procatalysts are all active (<35 g mmol(-1) h(-1) bar(-1)), for the polymerisation of ethylene affording high-molecular-weight linear polyethylene. The dimethyleneoxa-bridged systems (derived from 6 and 7) are more active (84 and 46 g mmol(-1) h(-1) bar(-1), respectively) than the methylene-bridged systems. The molecular structures of 1-6 and 10 (acetonitrile solvate) are reported.
Keywords:calixarenes  ethylene  niobium  polymerization  tantalum
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