PREPARATION AND REGIOSELECTIVE REACTIONS OF THE PHOSPHINE-FREE ZIRCONECENE-ALKYNE COMPLEX CP(2)ZR(THF)((T)BUC(2)SIME(3))

The reaction of Cp(2)ZrCl(2) with magnesium and (t)BuC(2)SiMe(3) in tetrahydrofuran yields the first zirconocene complex with an alkyl substituted alkyne without additional phosphine ligands Cp(2)Zr(THF)((t)BuC(2)SiMe(3)) 1. That complex is stable at room temperature and was characterized by its IR and NMR spectra. The spectroscopical data of 1 were compared with those of the well known complex of that type Cp(2)Zr(THF)(Me(3)SiC(2)SiMe(3)) 2 to study the influence of different sterical and electronical influences of the substituents ((t)Bu and SiMe(3)) upon alkyne complexation. The chemo- and regio-selectivity of complex 1 was studied in a hydrogen transfer reaction and in reactions with carbon dioxide and acetone. The results show mostly a kinetically favored reaction at the Si-substituted C-atom of the complexed alkyne, giving the beta-SiMe(3)-product, which rearranges into the thermodynamically more stable alpha-SiMe(3)-substituted products. In contrast to titanocene in the case of zirconocene complexes coupling reactions of RC=CSiMe(3) (R = SiMe(3), (t)Bu) could be realized.