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, [(CH2)(n)(C5H4)(2)MCl2] (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 silacyclopentylidenebridged metallocene complexes [(CH2)(4)Si(C5H4)(2)MCl2] (M = Ti (13), Zr (14)) and isopropylene-bridged metallocene complexes [Me2C(C5H4)(2)MCl2] (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.