Regioselektive Reaktionen der fremdligandfreien Titanocen-Alkin-Komplexe Cp2Ti(RC2SiMe3)(R=Me3Si, Ph, t-Bu, n-Bu)

Article abstract of DOI:10.1016/0022-328X(95)98949-Z

Depending of different substituents in the reaction of Cp2TiCl2 with magnesium and the alkynylsilanes RC<*>CSiMe3 (R=SiMe3, Ph, t-Bu, n-BU, n-Pr, Me) in tetrahydrofuran, titanacyclopropenes (R=SiMe3, Ph, t-Bu 1, n-Bu 2), symmetrical substituted titanacyclopentadienes (R=Me 5) or in a competition reaction both types of complexes (R=n-Pr 3 and 4) were obtained.The compound Cp2Ti(t-BuC2SiMe3) 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.Cp2Ti(Me3SiC2SiMe3) and Cp2Ti(PhC2SiMe3) to investigate the influence of different substituents (t-Bu, SiMe3<, 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 β-SiMe3-substituted products, which rearrange in some cases into the thermodynamically more stable α-SiMe3-substituted products.Keywords: Alkyne; Cyclopentadienyl; Early transition metals; Trimethylsilyl; Titanium; X-ray diffraction