Rational Design of Silicon-Bridged Fluorenyl−Phenoxy Group 4 Metal Complexes as Catalysts for Producing High Molecular Weight Copolymers of Ethylene and 1-Hexene at Elevated Temperature

For producing high molecular weight copolymers of ethylene and 1-hexene, a series of silicon-bridged fluorenyl−phenoxy group 4 complexes R2Si(Flu)(3- t Bu-5-Me-2-C6H2O)MCl2 (4a: M = Ti; R = Me; Flu = fluoren-9-yl; 4b: M = Ti; R = Et; Flu = fluoren-9-yl; 4c: M = Ti; R = Me; Flu =2,7- t Bu2-fluoren-9-yl; 4d: M = Ti; R = Et; Flu =2,7- t Bu2-fluoren-9-yl; 8: M = Zr; R = Me; Flu =2,7- t Bu2-fluoren-9-yl; 9: M = Hf; R = Me; Flu =2,7- t Bu2-fluoren-9-yl) were prepared by two methods. One was a reaction of MCl4 (M = Ti, Zr, and Hf) with the dilithium salts generated by treating corresponding ligands 1a−d with n BuLi in the presence of Et3N in toluene and the other used MCl2(NR′2)2 (6a: M = Ti; R′ = Me, 6b: M = Zr; R′ = Et, 6c: M = Hf; R′ = Me) instead of MCl4 followed by successive chlorination with Me3SiCl. X-ray crystallographic study of 4d indicated that the cyclopentadienyl moiety of the fluorenyl ligand is bound to the titanium atom in a fashion between η3 and η5. The newly prepared titanium complexes 4a−d exhibited high catalytic activities for copolymerization of ethylene and 1-hexene in the presence of i Bu3Al/[Me2NHPh][B(C6F5)4] and afforded higher molecular weight copolymers than the parent tetramethyl-substituted cyclopentadienyl titanium complex Me2Si(η5-C5Me4)(3- t Bu-5-Me-2-C6H2O)TiCl2 (10). In particular, the active species generated from complex 4d was thermally stable and exhibited high polymerization activities even at 210 °C and produced high molecular weight copolymers with good 1-hexene content.