The influence of metals, alkyne substituents, Cp substitution complex 3 reacted with one equivalent of water to yield the dimeric alkylidene-µ-oxo complex [(thi) 2 Ti(CPh=CHPh)] 2 (µ-and additional ligands on the stability of bridged and unbridged η 2 -alkyneϪtitanocene and Ϫzirconocene complexes O) (6). The reaction of the unbridged zirconocene compound (thi) 2 ZrCl 2 gave the alkyne complex (thi) 2 Zr(THF)(η 2 -Me 3 -has been investigated. The reduction of the complex [(η 5 -C 5 H 4 )ϪSiMe 2 Ϫ(η 5 -C 5 H 4 )]TiCl 2 with magnesium in the pre-SiC 2 SiMe 3 ) (7) which is stabilized by THF. At higher temperature THF was eliminated from the orange complex 7 form-sence of tolan (PhC 2 Ph) does not give the expected alkyneϪ titanocene complex [(η 5 -C 5 H 4 )ϪSiMe 2 Ϫ(η 5 -C 5 H 4 )]Ti(η 2 -ing the green complex (thi) 2 Zr(η 2 -Me 3 SiC 2 SiMe 3 ). This behaviour was investigated in detail using NMR spectroscopy PhC 2 Ph) but by coupling of two tolan molecules the corresponding titanacyclopentadiene [(η 5 -C 5 H 4 )ϪSiMe 2 Ϫ(η 5 -and compared to similar complexes such as Cp 2 Zr(η 2 -Me 3 -SiC 2 SiMe 3 ) (not stable without THF), (ebthi) 2 Zr(η 2 -Me 3 SiC 2 -C 5 H 4 )]TiC 4 Ph 4 (1) was obtained. In the analogous reaction with Me 3 SiC 2 SiMe 3 the stable η 2 -alkyne complex without SiMe 3 ) (ebthi = ethylenebistetrahydroindenyl; stable without THF) and Cp* 2 Zr(η 2 -Me 3 SiC 2 SiMe 3 ) (Cp* = pentamethyl-additional ligands [(η 5 -C 5 H 4 )ϪSiMe 2 Ϫ(η 5 -C 5 H 4 )]Ti(η 2 -Me 3 -SiC 2 SiMe 3 ) (2) was formed, due to the sterical influence of Cp, stable without THF). All complexes were characterized by spectroscopic methods. X-ray structural determinations the alkyne substituents. The compounds without additional ligands (thi) 2 Ti(η 2 -PhC 2 Ph) (3) and (thi) 2 Ti(η 2 -Me 3 SiC 2 -were conducted for the complexes 1, 3 and 7. Compound 3 is the first example of a structurally characterized tolanϪtita-SiMe 3 ) (5) were isolated from the unbridged titanocene complex (thi) 2 TiCl 2 (thi = tetrahydroindenyl). Two equivalents of nocene complex without additional ligands.