Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4.
One of the main industrial applications of organometallic chemistry is certainly the heterogeneous Ziegler-Natta olefin polymerization catalysis. This reaction produces polymer from a -olefin under mild conditions with high activity and selectivity. However, despite of its wide spread use, this reaction is still not very well understood. In particular, the structure of the active species involved in the reaction has not been clearly identified yet.
The actual catalytic system, used in the industrial process, is composed of TiCl4 supported on MgCl2. To improve the performances of the catalyst two Lewis bases have to been added. The first one, called Internal Lewis Base, is added first to the MgCl2 surface. The second one, called External Lewis Base, is added afterwards with the alkylating agent AlEt3. These two compounds have a dramatic impact on the catalyst activity, but their mode of action is not clearly determined at this time.
In the present work we depict an original approach to model the actual active active site of Zieger-Natta heterogeneous catalysis. Using DFT based calculations we investigate the effect of the environment on the mechanism of the polymerization of propylene, in order to determine the effects of the presence of Lewis Bases in the vicinity of the active site.