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.

The catalytic hydrogenation of the indenyl complex(Me2SiSiMe2)[η5-Ind)Fe(CO)]2(μ-CO)2(2) in CH2Cl2 afforded the tetrahyroindenyl complex (Me2SiSiMe2)[(η5-IndH4)Fe(CO)]2(μ-CO)2 (3), existing as a mixture of cis and trans isomers (3c and 3t), which were separated by column chromatography. When the two isomers were heated in xylene, respectively, the cis substrate 3c rearranged to the trans product [Me2Si(η5-IndH4)Fe(CO)2]2 (4c). This indicates that the rearrangement reaction is stereospecific, which is consistent with the result observed in the rearrangement of complex(Me2SiSiMe2)[η5-t-BuC5H3)Fe(CO)]2(μ-CO)2(5). By analogy with the mechanism porposed based on detailed investigation of 5, the pathway for formation of 4 is described. Molecular structures of 3c, 3t, 4t, and 4c were determinde by X-ray diffraction.

The binuclear ruthenium complex (Me2-SiSiMe2)[(η5-C5H4)Ru(CO)]2(μ-CO)2(3) was obtained in poor yield by reaction of Ru3(CO)12 with C5H5Me2-SiSiMe2C5H5 in boiling heptane. A thermal rearrange-ment reaction of 3 in heptane afforded the complex [(Me2Si)(η5-C5H4)Ru(CO)2]2 (4), which was evidently formed via a metathesis between Si-Si and Ru-Ru bonds in 3. Molecular structures of 3 and 4 have been determined by X-ray diffraction.