Theoretical investigations on Ziegler-Natta catalysis: Coordination of the electron donors to titanium modified MgCl 2 support

Abstract

Theoretical ab initio methods have been used to study the formation of the support-catalyst complex and the coordination of electron donors to this complex. A Mg 4Cl 8TiCl 4 cluster was used to model the catalyst surface. Determination of the coordination geometry of the supported catalyst indicated that the TiCl 4 catalyst coordinates octahedrally to the surface of the support, leaving one coordination site of the titanium empty. This vacant coordination site is in a stereospecific position. The coordination of different electron donors (alcohols, ketones, esters and their model compounds) through their oxygen atom to the Mg 4Cl 8TiCl 4 cluster was also studied. On the basis of the interaction energies, released in the coordination of the donors, the alcohol donors bind more strongly to the support than the ketones and esters. The extra stability of the alcohols can be explained by hydrogen bonding. The coordination geometries of the electron donors studied can be estimated rather reliably even with small model compounds.