DESACTIVATION OF CATALYSTS IN THE POLYMER IZATION OF ACETYLENE BY BIS(TRIMETHYLSILYL)ACETYLENE COMPLEXES OF TITANOCENE OR ZIRCONOCENE

Unexpected inactive byproducts were observed in the catalytic polymeri zation of acetylene using metallocene alkyne complexes Cp2M(L)(eta(2)- Me3SiC2SiMe3), 1: M = Ti, without L; 2: M = Zr, L = thf. The reaction of 1 was investigated in detail by NMR to give quantitatively at -20 d egrees C the titanacyclopentadiene Cp2Ti-CH=CH-C(SiMe3)=C(SiMe3) (3). Around 0 degrees C 3 starts to rearrange to yield the dihydroindenyl c omplex 4 via coupling of one Cp-ligand with the titanacyclopentadiene. In the reaction of 2 under analogous conditions a zirconacyclopentadi ene Cp2Zr-CH=CH-C(SiMe3)=C(SiMe3) (5) and the dimeric complex [Cp2Zr(C (SiMe3)=CH(SiMe3)](2)[mu-sigma(1,2)-C=C] (6) were observed. Whereas 5 decomposes to a mixture of unidentified paramagnetic species, 6 was is olated and investigated by NMR spectroscopy and X-ray analysis. In the reaction of rac-(ebthi)Zr(eta(2)-Me3SiC2SiMe3) (ebthi = ethylenbistet rahydroindenyl) with 2-ethynyl-pyridine the complex rac(ebthi>ZrC(SiMe 3)=CH(SiMe3)](sigma-C=CPy) 7 was obtained, which was investigated by a n X-ray analysis.