THEORETICAL INVESTIGATIONS ON ZIEGLER-NATTA CATALYSIS - COORDINATION OF THE ELECTRON-DONORS TO TITANIUM-MODIFIED MGCL2 SUPPORT

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 Mg4Cl8TiCl4 cluster was used to model the catalyst surface. Determination of the coordination geometry of the supported c atalyst indicated that the TiCl4 catalyst coordinates octahedrally to the surface of the support, leaving one coordination site of the titan ium empty. This vacant coordination site is in a stereospecific positi on. The coordination of different electron donors (alcohols, ketones, esters and their model compounds) through their oxygen atom to the Mg4 Cl8TiCl4 cluster was also studied. On the basis of the interaction ene rgies, released in the coordination of the donors, the alcohol donors bind more strongly to the support than the ketones and esters. The ext ra stability of the alcohols can be explained by hydrogen bonding. The coordination geometries of the electron donors studied can be estimat ed rather reliably even with small model compounds.