REGIOSELECTIVE REACTIONS OF FOREIGN-LIGAN D-FREE TITANOCENE-ALKYNE COMPLEXES CP(2)TI(RC(2)SIME(3)) (R=ME(3)SI, PH, (T)BU, (N)BU)

Depending on different substituents in the reaction of Cp(2)TiCl(2) wi th magnesium and the alkynylsilanes RC = CSiMe(3) (R = SiMe(3), Ph, (t )Bu, (n)Bu, Pr-n, Me) in tetrahydrofuran, titanacyclopropenes (R = SiM e(3), Ph, (t)Bu 1, (n)Bu 2), symmetrical substituted titanacyclopentad ienes (R = Me 5) or in a competition reaction both types of complexes (R = Pr-n 3 and 4) were obtained. The compound Cp(2)Ti((t)BuC(2)SiMe(3 )) 1 is the first example of a titanocene complex with an alkyl substi tuted alkyne without further ligands and was characterized by X-ray cr ystal structure analysis. The structural and spectroscopical data of 1 were compared with those of other well known complexes of that type, e.g. Cp(2)Ti(Me(3)SiC(2)SiMe(3)) and Cp(2)Ti(PhC(2)SiMe(2)) to investi gate the influence of different substituents ((t)Bu, SiMe(3), Ph) upon alkyne complexation. The chemo- and regio-selectivities of the obtain ed alkyne complexes was studied in reactions with alkynes, alcohols, c arbon dioxide and acetone. The reaction course depends mostly on steri c restrictions, being in the first step kinetically favored at the Si- substituted C-atom of the alkyne and giving beta-SiMe(3)-substituted p roducts, which rearrange in some cases into the thermodynamically more stable alpha-SiMe(3)-substituted products.