Ethylene-bridged tetramethylcyclopentadienylamide titanium complexes: Ligand synthesis and olefin polymerization properties

The N-alkyl-2(2,3,4,5-tetramethylcyclopentadienyl)ethylamines C5Me4H(CH2)(2)NHR (R = i-Pr, t-Bu) were obtained from the reaction of 2,3,4,5-tetramethylcyclopent-2-enone with deprotonated imines LiCH2CH=NR followed by dehydration and reduction using LiAlH4. The parent compound with R = H was obtained via a similar procedure using deprotonated acetonitrile and derivatized to the R = Me species. The Ti(IV) complexes [C5Me4(CH2)(2)NR]TiCl2 (R = t-Bu, i-Pr, Me) were prepared and tested for catalytic propene homopolymerization using methylaluminoxane (MAO) cocatalyst. Surprisingly, the catalysts with R = i-Pr, t-Bu were found to be inactive, and only for R = Me was catalytic formation of atactic polypropene observed. This is in marked contrast with the analogous systems with ligands with a SiMe2-bridge that readily homopolymerize propane under similar conditions.