Novel zirconium-iron multinuclear complex catalysts for olefin polymerizations

Novel zirconium-iron dinuclear complexes, [FcSiMe₂(R¹R²Cp)ZrCl₂Cp] (Fc; Ferrocenyl, R¹ =R² =H; 2a, R¹ =Me, R² =H; 2b, R¹ =R² =Me; 2c, R¹ =Ph, R² =H; 2d), [FcSiMe₂Cp{ZrCl₂(Me₅Cp)}] (3a), hafnium-iron dinuclear complex, [FcSiMe₂Cp{HfCl₂(Me₅Cp)}] (3b) and zirconium-iron trinuclear complex, [ZrCl₂(FcSiMe₂Cp)₂] (4), were synthesized and complexes 2d and 4 were characterized by an X-ray diffraction method. Olefin polymerizations were conducted by using these multimetallic zirconocene catalysts with the coexistence of methylaluminoxane or tetrakis(pentafluorophenyl)borates. The maximum catalytic activities of complexes 2, 3 and 4 were observed at low temperatures (15-45 °C) in ethylene polymerization, contrary to the conventional zirconocene catalyst ([ZrCl₂Cp₂]), showing the maximum activity at between 70-80 °C. A detailed investigation of ethylene polymerization and NMR measurements of the active species suggested that the interesting behavior of these complexes arose from an electronic cooperative effect between the zirconium and iron atoms. It was also revealed that complexes 2 were highly reactive toward propylene or diene in the copolymerization of ethylene and propylene or terpolymerization of ethylene, propylene and diene.