Highly selective ethylene trimerization catalyzed by half-sandwich indenyl titanium complexes with pendant arene groups and MAO

• A series of titanium complexes [Ind-(bridge)-Ar]TiCl3 have been synthesized.
• No intramolecular coordination could be observed by X-ray study.
• Some of the complexes were proved very active for ethylene trimerization.
• Temperature and the bridge have a dramatic influence on ethylene trimerization.

A series of half-sandwich indenyl titanium complexes [Ind-(bridge)-Ar]TiCl3 (C1–C9) bearing pendant arene group on indenyl ring have been synthesized and used for the catalytic ethylene trimerization to 1-hexene in the presence of MAO. The molecular structures of complexes C3 [Ind-C(cyclo-C5H10)-Ph]TiCl3 and C5 [Ind-C(cyclo-C5H10)-(p-MePh)]TiCl3 have been established by single-crystal X-ray diffraction study. No intramolecular coordination interaction between the arene moiety and the titanium center could be observed in the solid state of these complexes. At 0 °C and 0.8 MPa of ethylene pressure, upon activation with MAO, C3 possesses the highest activity of 1968 kg of 1-hexene/(mol-Ti h) and the overall selectivity of 95.9% by mass for 1-hexene, and is also more active than the corresponding cyclopentadienyl analog [Cp-C(cyclo-C5H10)-Ph]TiCl3 (C10) under the identical conditions. The substituents of various steric and electronic effects on the pendant arene group and the bridge unit between the indenyl and this arene group exert great influence on the activity and selectivity of these indenyl titanium complexes for ethylene trimerization to 1-hexene. Similar to cyclopentadienyl analogs, upon activation with MAO the resultant indenyl catalytic systems also show great sensitivity to the temperature. With the increase of the reaction temperature, both the activity and selectivity of 1-hexene declined.

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