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)nC(C5H4)2MCl2] (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 [(CH2)4Si(C5H4)2MCl2] (M = Ti (13), Zr (14)) and isopropylene‐bridged metallocene complexes [Me2C(C5H4)2MCl2] (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. Much higher catalytic activities for ethylene polymerization are displayed by cycloalkylidene‐bridged titanocenes than by their zirconocene and hafnocene analogues (structures shown); titanocene activities are also the highest at higher temperatures. The structure–activity relationships of these metallocenes, and especially the effects of the bridges of ansa‐metallocene complexes, are discussed.