A New Class of Mono- and Tetra-nuclear Titanatranes: Synthesis, Structure, and Ethylene Polymerization Studies. Role of Single-Sited Active Species?

Mono- and tetranuclear titanatranes bearing the C3-symmetric aminotriol ligand N(CH2CHPhOH)3 were synthesized. The structure of the tetratitanium compound was determined by single-crystal X-ray crystallography. The new titanatrane derivative included four aminotriols ligated to four titanium atoms, forming a tetranuclear unit with μ2-O and μ3-O bridges. The mono- and tetranuclear titanatranes were capable of polymerizing ethylene with a turnover frequency of up to 375 kg of PE/((mol of catalyst) h bar). The polymers obtained had Tm ≈ 133 °C, indicative of linear polyethylene, and were further characterized by NMR. The ethylene polymerization activities of mono- and tetranuclear titanium catalysts were related by a factor of 4, indicating possibly the formation of a common single-site active species.