Effects of the Linking of Cyclopentadienyl and Ketimide Ligands in Titanium Half‐Sandwich Olefin Polymerization Catalysts

• Published in: ChemCatChem 2017-08, Vol.9 (16), p.3160-3172
• Main Authors: Varga, Vojtech, Večeřa, Miloš, Gyepes, Róbert, Pinkas, Jiří, Horáček, Michal, Merna, Jan, Lamač, Martin
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts; Chemical industry; Copolymerization; cyclopentadienyl ligands; Ethylene; ligand effects; Polymerization; sandwich complexes; Titanium
• ISSN: 1867-3880; 1867-3899
• DOI: 10.1002/cctc.201700498

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=CtBu2)] (1; Cp=η5‐cyclopentadienyl) was used as a reference compound for comparison with the recently described complex [{η5‐C5H4CMe2CMe2C(tBu)=N‐κN}TiCl2] (2 a) and a new derivative that has a longer linker between Cp and the ketimide, [{η5‐C5H4CH2CH2CMe2C(tBu)=N‐κN}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. Unleashed activity: Effects of ketimide ligand distortion that result from its intramolecular tethering in Ti half‐sandwich complexes are investigated with respect to the olefin polymerization activity. The role of the cocatalyst on the catalytic performance is decisive. Huge differences between the studied complexes are found if Al‐based cocatalysts are used, whereas the activating system in which hydrosilane and B(C6F5)3 are used performs well for both types.