5-Methoxy-Substituted Zirconium Bis-indenyl ansa-Complexes: Synthesis, Structure, and Catalytic Activity in the Polymerization and Copolymerization of Alkenes

A number of 2-methyl-4-aryl-5-methoxy-6-alkylindenes and C2-symmetric Me2Si-bridged ansa-zirconocenes based on them were synthesized. Zirconocenes were obtained by means of highly effective and scalable racemo-selective synthetic approach based on the use of a Zr tert-butyl amide complex. The structure of μ-(bis-[η5-6-tert-butyl-5-methoxy-2-methyl-4-tert-butylphenyl-1H-inden-1-yl]dimethylsilanediyl)dichlorozirconium(IV) (14) has been established with X-ray analysis. The introduction of a methoxy group into the indenyl fragment of zirconocene significantly improved its catalytic performance (i.e., its activity, stereoselectivity, molecular mass potential, and thermal stability) in the polymerization and copolymerization of propylene in comparison with the benchmark Spaleck-zirconocene. The role of the methoxy group is proposed to stabilize the cationic catalytic intermediates, which was confirmed using DFT calculations.