Gerard H. J. van Doremaele

AB INITIO MOLECULAR DYNAMICS STUDY OF METALLOCENE CATALYSED ETHYLENE POLYMERIZATION. III. BIS- VERSUS MONO-CYCLOPENTADIENYL METALLOCENES

Ab initio molecular dynamics simulations of a catalytic reaction are presented. Ethylene insertion is observed to proceed in a SiH2-bridged di-(cyclopentadienyl)methylzirconocene cation as well as in the corresponding titanocene cation. The entire reaction path starting from the π 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.

Ab initio molecular dynamics study of metallocene-catalysed ethylene polymerisation: temperature effects

Abstract The feasibility of using ab initio molecular dynamics simulations to study chemical reactions is illustrated by further studies on ethylene insertion into a bridged bis (cyclopentadienyl) methylzirconocene. Previous observation that the insertion is extremely fast, suggesting the absence of an energetic barrier, is further supported by results obtained from simulations at various temperatures. In view of the short time span (170 fs) for insertion, coupling to an external heat bath cannot be justified. Therefore, a microcanonical molecular dynamics simulation starting at T = 0 K was performed. This simulation also revealed extremely fast ethylene insertion, which was accompanied by a temperature rise of a few hundred kelvin.