TERMINAL ALKYNES IN THE COORDINATION SPHERE OF TITANOCENE COMPLEXES -ELEMENTARY STEPS IN CATALYTIC DIMERIZATIONS AND OLIGOMERIZATIONS OF ALKYNES

The titanocene acetylene complex [CpTi(eta(2)-Me3SiC drop CSiMe3)] (1 4) reacts with 1-alkynes such as phenylacetylene (15a), 1-hexyne (15b) , 1-dodecyne (15c) and trimethylsilylacetylene (15d) by ligand exchang e and proton shift, to yield exclusively the 1-alkenyltitanocene acety lides [CpTi-2(CH=CHR) (C drop CR)] (21) (R=Ph (21a), CH3(CH2)(3) (21b ), CH3(CH2)(9) (21c), SiMe3 (21d)). The X-ray structure of 21a is pres ented. In reaction of acetylene HC drop CH (15e) with 14 other product s are formed. However, no intermediates, like [CpTi-2(eta(2)-RC drop CH)] (17), [CpTi-2(H)C drop CR] (17) or [Cp*Ti-2=C=CHR] (22) in react ions of 14 with 15 are detectable. On the other hand, a stable titanoc enehydride [CpTi-2(H)OCH3] (23) is obtained by oxidative addition of CH3OH with CpTi-2, generated from 14.