The (C5H5 - n Me n )2Zr[η2-C2(SiMe3)2] (n = 2−5; 1,3-dimethyl, 1,2,3-trimethyl) (2C−F) complexes were prepared by the reduction of corresponding zirconocene dichlorides with magnesium in THF in the presence of bis(trimethylsilyl)acetylene (BTMSA). All of them are stable in the absence of THF. Crystal structures of (C5HMe4)2Zr[η2-C2(SiMe3)2] (2E) and (C5Me5)2Zr[η2-C2(SiMe3)2] (2F) and of the analogous titanium complexes are isomorphous. The red shift of the ν(C⋮C) vibration and the downfield shift of 13C δ(C⋮C) indicate that BTMSA in 2C−F is more strongly coordinated than in analogous titanocene complexes. The nonisolated complex (C5H4Me)2Zr[η2-C2(SiMe3)2](THF) (2 B·THF) rearranges after the loss of THF to give the dimer [(η5-C5H4Me)(η1-C(SiMe3)CH(SiMe3)Zr(μ-η1:η5-C5H3Me)]2 (3B).

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