Synthesis and Structures of Cycloalkylidene‐Bridged Cyclopentadienyl Metallocene Catalysts: Effects of the Bridges of Ansa‐Metallocene Complexes on the Catalytic Activity for Ethylene Polymerization

A series of cycloalkylidene-bridged cyclopentadienyl metallocene complexes, [(CH 2 ) n C(C 5 H 4 ) 2 MCl 2 ] (M = Ti, n = 4 (4), 5 (5), 6 (6); M = Zr, n = 4 (7), 5 (8), 6 (9); M = Hf, n = 4 (10), 5 (11), 6 (12)), have been synthesized and applied to ethylene polymerization after activation with methyl aluminoxane (MAO). The cycloalkylidene-bridged titanocene catalysts exhibit much higher activities than the corresponding zirconocene and hafnocene analogues, and have the highest activities at higher temperatures. In comparison, the silacyclopentylidene-bridged metallocene complexes [(CH 2 ) 4 Si(C 5 H 4 ) 2 MCl 2 ] (M = Ti (13), Zr (14)) and isopropylene-bridged metallocene complexes [Me 2 C(C 5 H 4 ) 2 MCl 2 ] (M = Ti (15), Zr (16)) have also been synthesized and applied to ethylene polymerization. In both cases, the titanocene complexes show much higher activities than the corresponding zirconocene analogues, especially at a lower temperature. The molecular structures of complexes 4-9 have been determined by X-ray diffraction. The structure-activity relationships, especially the effects of the bridges of ansa-metallocene complexes, are discussed.