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)(η5-C5H3)Fe(CO)]2-(μ-CO)2 (2) with a hydrogenated double bond in one of the cyclopentadiene ligands, the diiron complex (Me2C)(Me2Si)[(η5-C5H3)Fe(CO)2]2 (3), and the desilylation product 4 were obtained. When the reaction was performed in refluxing xylene, the novel complex (Me2C)(η5-C5H3)-(η5:η1-C5H3)[(Me2Si)Fe(CO)2][Fe(CO)2] (5) with and Fe-Si bond, which should be accompanied by the cleavage of a C-Si bond in the ligand, was isolated in addition to the complees 2～4. When bis(cyclopentadienyl) ligands bridged with R2C (R2C=Me2C, (CH2)5C)AND Me2E(E=Si, Ge) groups were used instead of 1, the similar novel complexes (R2C)(η5-C5H3)(η5:η1-C5H3)[(Me2E)Fe(CO)2] (R2C=Me2C, E=Ge (7); R2C=(CH2)5C, E=Si(17), Ge (21)) with and Fe-E bond were obtained in addition to the diiron complexes (R2C)(Me2E)-[(η5-C5H3)Fe(CO)]2[Fe(CO)2](R2C=Me2C, E=Ge (8); R2C=(CH2)5C,E=Si (18), Ge (22)) and the desilylation or degermylation products. When a tert-butyl group was introduced into the cyclopentadienyl rings, or two phenyl groups were introduced at the bridging silicon atom instead of two methyl groups in 1, only the diiron complexes (Me2C)(Me2E)[η5-t-BuC5H2]Fe(CO)2]2 (E=Si(10), Ge (13)) and (Me2C)(Ph2Si)[(η5-C5H3)Fe(CO)2]2 (15) were obtained, in addition to the desilylatin or degermylation products. Whem a methylene bridge was used instead of an isopropylene bridge in 1 and 6, the partially hydrogenated complexes (Me2E)(η3-CHC5H6)(η5-C5H3)Fe(CO)3Fe(CO)2(E=Si(24),Ge (28)), the diiron complexes (CH2)(Me2E)[(η5-C5H3)Fe(CO)]2(μ-CO)2(E=Si (25), Ge (29)), and the desilylation or degermylation products were obtained. The molecular structures of 2, 3, 5, 7, 8, 10, 11t, 15, 17, 18, 21, 24, 25, 28, and 29 were determinde by X-ray diffraction.

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(CO3)2 were obtained from the reactions of carbon and sliicon 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) [(η5-C5H4)W(CO)3]2, a class of structurally novel comolexes (X) (η5-C5H3) [(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 dobuly 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 ditungstem 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 benn determinde by X-ray diffraction. The M-M distances in complexes 2 [3.4328(12)A], 8 [3.453(2)A], and 11 [3.403(2) A] 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.

The ansa-metallocene complexes Me2Ge(η5-C5Me4)2MCI2[M=Ti(1), Zr(2)], Me2Ge(η5-C5H3Bu-t)2ZrCl2(3) and Me2Ge(η5-C5H4)(η5-C5H3R)ZrCl2[R=Me(4), t-Bu (5)] were prepared by the reaction of the corresponding ligands with n-BuLi and MCl4 2THF, respectively. The molecular structures of 1 and 2 have benn determinde by the X-ray diffraction method. Complexe 2-5 in combination with MAO were studied as catalysts for ethylene polymerizatiion and all the germyl-bridged zirconocene catalysts show high activities at relative high temperatures. This indicates that the germyl-bridged zirconocene systems show thermally stable catalyst sysstems for polymerization of ethylene.

A series of doubly bridged dinuclear titanium and zirconium complexes (Me2C)(Me2E)(C5H3)2(Cp'MCI2)2 [E=Si,Cp'=C5H5, M=Ti (1), Zr (2); E=Ge, Cp'=C5H5, M=Ti (3), Zr (4); Cp'=C5Me4H, M=Zr, E=Si (5), Ge (6)] and (Me2SiOSiMe2)2(C5H3)2(Cp'MCI2)2[Cp'=C5H5, M=Ti (7), Zr (8); Cp=C5Me4H, M=Zr (9)] were synthesized by the reaction of the lithium compounds of the corresponding doubly bridged cyclopentadienyl ligands with CpTiCl3, CpZrCl3(THF)2 or C5Me4HZrCl3, respectively. These complexes were characterized by 1H-NMR, MS and elemental analysis. The crystal structure of 4 was determined by the X-ray diffraction. Their catalytic properties for ethylene polymerization were also studied in the presence of MAO.