A THEORETICAL INVESTIGATION OF THE FUNDAMENTAL STEPS IN ZIEGLER-NATTACATALYSIS - A COMPARISON OF DENSITY-FUNCTIONAL, HARTREE-FOCK, AND 2ND-ORDER MOLLER-PLESSET PERTURBATION THEORIES

Local (LDF) and nonlocal (NLDF) density functional, Hartree-Fock (HF), and second-order Moller-Plesset perturbation (MP2) theories were used to study the fundamental reaction steps of Ziegler-Natta catalysis in the model TiCl2CH3+ system. This comprised a detailed theoretical cha racterization of the ethylene binding and insertion reactions: TiCl2CH 3+ + C2H4 --> TiCl2CH3(C2H4)(+) and TiCl2CH3(C2H4)(+) --> TiCl2(C3H7). The geometries of all species in the two reactions were fully optimi zed at all levels of theory, and the energy changes for the two reacti ons were calculated at all levels of theory. The basis set superpositi on error associated with the ethylene binding reaction was assessed by the counterpoise method at all levels of theory. The results show tha t the extended theories (NLDF and MP2) predict geometries and energeti cs that are substantially different from their respective pared theori es (LDF and HF). This is due primarily to ways in which nonbonded inte ractions are handled by each of these methods. The overall agreements between the calculated geometries and energetics predicted by NLDF and MP2 theories are good.