REGIOSELECTIVE REACTIONS OF FOREIGN-LIGAND-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) with magnesium and the alkynylsilanes RC = CSiMe(3) (R = SiMe(3), Ph, (t)Bu, (n)Bu, Pr-n, Me) in tetrahydrofuran, titanacyclopropenes (R = SiMe(3), Ph, (t)Bu 1, (n)Bu 2), symmetrical substituted titanacyclopentadienes (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 substituted alkyne without further ligands and was characterized by X-ray crystal 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 investigate the influence of different substituents ((t)Bu, SiMe(3), Ph) upon alkyne complexation. The chemo- and regio-selectivities of the obtained alkyne complexes was studied in reactions with alkynes, alcohols, carbon dioxide and acetone. The reaction course depends mostly on steric restrictions, being in the first step kinetically favored at the Si-substituted C-atom of the alkyne and giving beta-SiMe(3)-substituted products, which rearrange in some cases into the thermodynamically more stable alpha-SiMe(3)-substituted products.