Effects of the Linking of Cyclopentadienyl and Ketimide Ligands in Titanium Half-Sandwich Olefin Polymerization Catalysts
Abstract
The role of the ketimide ligand geometry in Ti half-sandwich complexes and the consequent effects in olefin polymerization catalysis (ethylene, styrene, 1-hexene polymerization, and ethylene/1-hexene copolymerization) were investigated under various conditions. [CpTiCl2(N=CtBu(2))] (1; Cp = eta(5)-cyclopentadienyl) was used as a reference compound for comparison with the recently described complex [{eta(5)-C5H4CMe2CMe2C(tBu)=N-kN}TiCl2] (2a) and a new derivative that has a longer linker between Cp and the ketimide, [{eta(5)-C5H4CH2CH2CMe2C(tBu)=N-kN}TiCl2] (9). The presence of a distorted intramolecularly tethered ketimide moiety reduces the polymerization activity significantly in systems that contain Al-based cocatalysts (methylaluminoxane, triisobutylaluminum).
However, in Al-free systems both types of compounds provided active polymerization catalysts. Notably, the recently reported activation system Et3SiH/B(C6F5)(3) was for the first time demonstrated to activate Ti complexes for ethylene and 1-hexene (co)polymerization catalysis by hydride transfer.