Ab initio molecular dynamics study of metallocene catalysed ethylene polymerization .3. Bis- versus mono-cyclopentadienyl metallocenes

Ab initio molecular dynamics simulations of a catalytic reaction are presented. Ethylene insertion is observed to proceed in a SiHg-bridged di(cyclopentadienyl)methylzirconocene cation as well as in the corresponding titanocene cation. The entire reaction path starting from the pi coordinated ethylene-metallocene complex up to and including propyl formation takes place in about 150 fs for the zirconocene and 500 fs for the titanocene. For both a Zr and a Ti based monocyclopentadienyl metallocene no insertion was observed, which is indicative of a barrier to insertion. In accordance with this, stepwise variation of the relevant C-C distance along the reaction path as set prior to the dynamics simulation did reveal insertion. These data are in qualitative agreement with results obtained from static simulations on similar species.