title: Niobium- and tantalum-based ethylene polymerisation catalysts bearing methylene- or dimethyleneoxa-bridged calixarene ligands.
abstract: Treatment of p-tert-butylcalix[6]areneH(6) (H(6)tBu-L) or p-tert-butylcalix[8]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-butylhexahomotrioxacalix[3]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-butylcalix[4]arene}(2)] (M=Nb (8), Ta (9)) and [(MCl(2))p-tert-butylcalix[4]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.
authors.affiliation: Wolfson Materials and Catalysis Centre, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich, NR4 7TJ, UK. carl.redshaw@uea.ac.uk
authors.forename: Carl
authors.initials: C
authors.lastname: Redshaw
authors.forename: Michael
authors.initials: M
authors.lastname: Rowan
authors.forename: Damien M
authors.initials: DM
authors.lastname: Homden
authors.forename: Mark R J
authors.initials: MR
authors.lastname: Elsegood
authors.forename: Takehiko
authors.initials: T
authors.lastname: Yamato
authors.forename: Carol
authors.initials: C
authors.lastname: Pérez-Casas
mesh_terms: D047250:Calixarenes / Q000737:chemistry*; D002384:Catalysis; D003432:Cross-Linking Reagents / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006859:Hydrogen / Q000737:chemistry; D008024:Ligands; D008745:Methylation; D008958:Models, Molecular; D015394:Molecular Structure; D009556:Niobium / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D020959:Polyethylene / Q000138:chemical synthesis / Q000737:chemistry*; D013635:Tantalum / Q000737:chemistry*
chemical_list: D003432:Cross-Linking Reagents; D008024:Ligands; D009556:Niobium; D047250:Calixarenes; D013635:Tantalum; D006859:Hydrogen; D020959:Polyethylene; D010100:Oxygen