series of cycloalkylidenebridged 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 silacyclopentylidenebridged 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.

The indenyl iron compound (

When the doubly bridged bis(cyclopentadiene) ligand (Me2C)(Me2Si)(C5H4)2 (1) reacted with Fe(CO)5 in refluxing toluene, the unusual product [(C5H6)(Me2C)(Me2Si)(

Dimolybdenum complexes (X)(Y)[(η5-C5H3)Mo(CO)3]2 [Y ) Me2Si, X ) Me2C, (CH2)5C, CH2; Y ) Ph2Si, X) Me2C] and desilylation products (X)[(η5-C5H4)Mo(CO)3]2 were obtained from the reactions of carbon and silicon doubly bridged biscyclopentadiene ligands (X)(Y)(C5H4)2 with Mo(CO)6 in refluxing xylene. When these ligands reacted with W(CO)6, under similar conditions, in addition to ditungsten complexes (X)(Y)[(η5-C5H3)W(CO)3]2 [X ) Me2C; Y ) Me2Si, Ph2Si] and desilylation products (X)[(è5-C5H4)W(CO)3]2, a class of structurally novel complexes (X)(η5-C5H3)(η5,η1-5H3)[(Y)W(CO)3][W(CO)3] [for X ) Me2C, (CH2)5C; Y ) Me2-Si] with a W-Si bond were also isolated. The reactions of carbon and germanium doubly bridged biscyclopentadiene ligands (X)(Me2Ge)(C5H4)2 [X ) Me2C, (CH2)5C] with Mo(CO)6 or W(CO)6 gave similar novel complexes (X)(η5-C5H3)(η5,η1-C5H3)[(Me2Ge)M(CO)3][M(CO)3] [X ) Me2C, (CH2)5C; M ) Mo, W] with a M-Ge bond. The reactions also produced degermylation products. However, the corresponding dimolybdenum or ditungsten complexes were not isolated in these cases. The molecular structures of 2, 6, 8, 10, 11, 13, 14, 15, 19, 21, 22, 25t, and 26t have been determined by X-ray diffraction. The M-M distances in complexes 2 [3.4328 (12) Å], 8 [3.453 (2) Å], and 11 [3.403 (2) Å] are conspicuously elongated and are in fact the longest ever reported among the biscyclopentadienyl dimolybdenum or ditungsten complexes. The factors affecting the structures of dimolybdenum or ditungsten complexes are discussed.