Highly selective trimerization of ethylene with half-sandwich cyclopentadienyl and indenyl titanium complexes bearing pendant thienyl group

• A series of titanium complexes [Cp(Ind)-(bridge)-thienyl]TiCl3 have been synthesized.
• No intramolecular coordination could be observed by X-ray study.
• The substitutents at the 5-position of the thienyl group can increase the trimerization activity.
• Indenyl complexes are more active and more tolerant of temperature than Cp complexes.

A series of half-sandwich titanium complexes bearing thienyl group [Cp(Ind)-bridge-thienyl]TiCl3 (CS1–CS10) have been synthesized and show high selective ethylene trimerizaion to 1-hexene. The molecular structure of CS8 [Ind-C(cyclo-C5H10)-(5-Me-thienyl)]TiCl3 was confirmed by X-ray. No intramolecular coordination interaction between the sulfur atom on the thienyl group and the titanium center could be observed in the solid state of these complexes. After activated with MAO, the complexes can effectively catalyze ethylene trimerization. For [Cp-bridge-thienyl]TiCl3/MAO system, the best productivity is obtained at 30 °C; increasing the bulk of the substituent on the 5-position of the thienyl can improve the productivity for 1-hexene. CS6 [Cp-C(cyclo-C5H10)-(5-SiMe3-thienyl)]TiCl3 upon with MAO can make a productivity of 553 kg/(mol Ti-h) and 1-hexene selectivity of 86% at 30 °C, 0.5 MPa ethylene pressure. For [Ind-bridge-thienyl] TiCl3/MAO system, catalysts have more active and more tolerant of temperature comparing to corresponding Cp complexes. For example, CS8 can make the productivity of 697 kg/(mol Ti-h) and 1-hexene selectivity of 95% at 80 °C, 0.5 MPa ethylene.

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