Syntheses of methylene-bridged ansa-zirconocene complexes and copolymerization studies of ethylene and norbornene

Abstract Methylene-bridged ansa -metallocene complexes bearing substituents on the cyclopentadienyl (Cp) and fluorenyl (Flu) moieties, namely methylene[9-(2,7-di- tert -butyl)fluorenyl(2-(1,3-dimethylcyclopentadienyl))]zirconium dichloride ( 1a ) and its analogue, methylene[(9-(2,7-di- tert -butyl)fluorenyl(2-(1-methyl-3-phenyl)cyclopentadienyl))]zirconium dichloride ( 2a ), have been prepared from (2,7-di- tert -butyl)-9-prop-2-ynyl-9H-fluorene ( 2 ). This procedure includes the use of 3-bromo-1-propyne which affords the methylene bridging unit by way of an intermolecular Pauson–Khand reaction in which norbornadiene and a pendant alkyne cyclize to form a ring that later becomes a substituted cyclopentadienyl group. Ethylene–norbornene (E–N) copolymerization was then carried out using these new complexes ( 1a and 1b ) in the presence of methylaluminoxane (MAO) as a cocatalyst; these activities can be compared to that of isopropylene[9-fluorenyl-cyclopentadienyl]zirconium dichloride ( 3a ). The activity of catalyst 1a was comparable to that of 3a but much higher than that of 2a . In addition, 1a shows higher norbornene insertion performance, and gives an E–N copolymer with a higher glass transition temperature ( T g ) than 2a under identical conditions; both 1a and 2a give a lower T g polymer than 3a does.