THE ZIEGLER-NATTA OLEFIN INSERTION REACTION FOR CATIONIC METALS

The catalytic Ziegler-Natta polymerization reaction has been studied f or a set of metal cations, in order to identify the role of the positi ve charge on this process. Geometry optimizations have been performed for the reactant metal-methyl systems, the pi-coordinated olefin syste ms, the transition states for the olefin insertion and finally for the product metal-propyl systems. All valence electrons are correlated. T he cations selected for this study are the transition metals Zr+ and T i+, the non-transition metals Be+, Mg+, Al+ and finally also Si+. The transition metal cations are found to have very low barriers for the i nsertion. but the lowest barrier is actually found for Be+. The result s are discussed in terms of the ionization energies and the accessibil ity to valence p and d orbitals. Comparisons are made to previous theo retical work on cationic model systems.